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Impact of collimator leaf width and treatment technique on stereotactic radiosurgery and radiotherapy plans for intra- and extracranial lesions

Impact of collimator leaf width and treatment technique on stereotactic radiosurgery and... Background: This study evaluated the dosimetric impact of various treatment techniques as well as collimator leaf width (2.5 vs 5 mm) for three groups of tumors – spine tumors, brain tumors abutting the brainstem, and liver tumors. These lesions often present challenges in maximizing dose to target volumes without exceeding critical organ tolerance. Specifically, this study evaluated the dosimetric benefits of various techniques and collimator leaf sizes as a function of lesion size and shape. Methods: Fifteen cases (5 for each site) were studied retrospectively. All lesions either abutted or were an integral part of critical structures (brainstem, liver or spinal cord). For brain and liver lesions, treatment plans using a 3D-conformal static technique (3D), dynamic conformal arcs (DARC) or intensity modulation (IMRT) were designed with a conventional linear accelerator with standard 5 mm leaf width multi-leaf collimator, and a linear accelerator dedicated for radiosurgery and hypofractionated therapy with a 2.5 mm leaf width collimator. For the concave spine lesions, intensity modulation was required to provide adequate conformality; hence, only IMRT plans were evaluated using either the standard or small leaf-width collimators. A total of 70 treatment plans were generated and each plan was individually optimized according to the technique employed. The Generalized Estimating Equation (GEE) was used to separate the impact of treatment technique from the MLC system on plan outcome, and t-tests were performed to evaluate statistical differences in target coverage and organ sparing between plans. Results: The lesions ranged in size from 2.6 to 12.5 cc, 17.5 to 153 cc, and 20.9 to 87.7 cc for the brain, liver, and spine groups, respectively. As a group, brain lesions were smaller than spine and liver lesions. While brain and liver lesions were primarily ellipsoidal, spine lesions were more complex in shape, as they were all concave. Therefore, the brain and the liver groups were compared for volume effect, and the liver and spine groups were compared for shape. For the brain and liver groups, both the radiosurgery MLC and the IMRT technique contributed to the dose sparing of organs-at-risk(OARs), as dose in the high-dose regions of these OARs was reduced up Page 1 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 to 15%, compared to the non-IMRT techniques employing a 5 mm leaf-width collimator. Also, the dose reduction contributed by the fine leaf-width MLC decreased, as dose savings at all levels diminished from 4 – 11% for the brain group to 1 – 5% for the liver group, as the target structures decreased in volume. The fine leaf-width collimator significantly improved spinal cord sparing, with dose reductions of 14 – 19% in high to middle dose regions, compared to the 5 mm leaf width collimator. Conclusion: The fine leaf-width MLC in combination with the IMRT technique can yield dosimetric benefits in radiosurgery and hypofractionated radiotherapy. Treatment of small lesions in cases involving complex target/OAR geometry will especially benefit from use of a fine leaf-width MLC and the use of IMRT. Varian 2100Clinac system (Varian Medical Systems, Palo Background Stereotactic intracranial radiosurgery (SRS) and extracra- Alto, CA), which served as the baseline for comparison. nial body radiosurgery and radiotherapy (SBRT) are char- The Novalis Tx radiosurgery system became commercially acterized by ablative, high dose irradiation of target available in early 2008, and was equipped with a newly structures. Complex targets, such as spine metastases, designed micro-mulitleaf collimator (HD120 MLC) sys- brain lesions abutting the brain stem, and liver lesions tem, replacing the standard Millennium MLC system. In present challenges in maximizing the dose to the target contrast to previous micro-MLC systems [2,21-24], the volume while not exceeding the critical organ tolerances Novalis Tx radiosurgery MLC is within the gantry housing, [1-20]. This study evaluates the benefits of a dedicated instead of being an add-on tertiary system [2,21-24]. The radiosurgery system with a fine leaf-width collimator for mounting of an add-on tertiary MLC not only prolongs these different groups of patients. More specifically, this the treatment procedure, but also reduces the clearance study evaluates the dosimetric benefits of this system as a between the gantry and couch, therefore limiting the free- function of target size and shape complexity. dom to select certain beam angles. The Novalis Tx HD120 MLC has 32 leaf pairs in the center, each a with leaf width of 2.5 mm (projected at the isocenter) and 14 leaf pairs on Materials and methods Patient Data each side (a total of 28) with a leaf width of 5 mm; thus, This retrospective study included 15 cases (5 each for the total number of leaves is 120. Our initial measure- brain, liver and spine sites) treated with SRS/SBRT at our ments also showed a sharper penumbra. The HD120 MLC institution. As shown in Additional file 1, these lesions leaf side penumbra was 2.5 mm vs. 2.8 mm with the ranged in size from 2.6 – 12.5 cc, 17.5 – 153.1 cc, and 20.9 standard MLC, and the HD120 MLC leaf end penumbra – 87.7 cc for the brain, liver, and spine groups, respec- was 2.8 mm vs. 3.6 mm with the standard MLC[25]. For tively. The volumes selected were intended to represent conformal static treatment (3D) and dynamic conformal the ranges of the target volumes typically encountered for arc treatment (DARC) treatments, the maximum dose rate these sites. The selected cases all involved lesions next to with the Novalis Tx system is 1000 MU/min versus 600 or within critical structures, i.e., lesions next to the brain- MU/min with the Clinac system, allowing faster radiation stem for the brain group, lesions within the liver for the delivery. liver group, and tumors near/abutting the spinal cord for the spine group. The brain and liver lesions were mostly For each case, the normal structures and OARs were con- ellipsoidal, with brain lesions having smaller volumes. toured by a physician with expertise in SRS/SBRT. The tar- The spine lesions were more complex in shape, as they get volumes were contoured by the same physician. For were all concave; volumes were similar to the liver lesions. the brain lesions, the planning target volume (PTV) was Therefore, the brain and the liver groups were compared generated by expanding the contrast-enhancing T1- for volume effect and the liver and the spine groups were weighted MRI volume by 1-mm, except at the junctions of compared for shape effect. Figure 1 displays the rendering the tumor and brainstem where no expansion was added. of the target volumes and critical structures in 3D space The liver lesions were treated with deep inhale breath- for these three sites. hold technique and cone-beam CT (CBCT) guidance, and the PTV was obtained by expanding the lesion volume by Treatment planning 5 mm right-left and anterior-posterior and 7 mm supe- Treatment plans were designed with the Novalis Tx radio- rior-inferior. The PTV expansion for spine lesions was also surgery system (BrainLab AG, Munich, Germany and Var- non-uniform, usually 3 mm except at the lesion and cord ian Medical Systems, Palo Alto, CA) versus the standard interface, where 0 – 1 mm expansion was used. Page 2 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 E Figure 1 xamples of lesions and adjacent critical structures/organs for the brain (a), the liver(b), and the spine (c) groups Examples of lesions and adjacent critical structures/organs for the brain (a), the liver(b), and the spine (c) groups. The 3D rendering of the geometrical relationships is shown in (d) for the brain case (left), liver case (middle) and spine case (right). Treatment plans were generated using three techniques: adequate conformality. Hence, only IMRT plans were gen- 3D, DARC, and IMRT. For the brain and liver lesions, erated for the spine lesions, again using both the standard plans using all three techniques were designed. For each MLC and HD120 MLC. Typically, the 3D plans used 6–12 lesion and planning technique, plans were generated beams, DARC plans used 4 – 7 arcs and IMRT plans used using both the standard MLC and the HD120 MLC. All 4–12 static beams. The multiple arcs for the brain lesions the spine lesions exhibited concave shapes, and the 3D were mainly designed to take advantage of different couch and the DARC techniques could not provide clinically angles and those for the liver lesions utilized different Page 3 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 beam weightings through different sections of anatomy. MLC and the standard MLC on dosimetric parameters for Each plan was individually optimized according to the IMRT. treatment techniques selected. Beam angles (non-copla- nar or coplanar) were chosen to minimize doses to the Results critical structures and to achieve high dose fall-off around PTV coverage the target at the same time. For IMRT planning, planning For each case, the PTV coverage was essentially equivalent objectives included dose uniformity to the PTV and dose among different plans. Additional file 2 lists the dosimet- constraints for the OARs as well as dose falloff at the target ric indices for all cases. The small standard deviations for boundary. For each plan, 90% of the prescription dose all plans indicate consistency in applying the treatment covered at least 97% of the PTV. techniques to achieve the optimal dose coverage; i.e., the prescription isodose covered at least 97% of the target vol- In summary, a total of 70 treatment plans were designed ume and the dose heterogeneity inside the target was kept and each plan was individually optimized according to at about 10%. For each individual case, the D was min the technique employed. For the purpose of the dosimet- within 2% and D was within 2.5% among different max ric analysis in this study, the prescription dose was set to plans. Using the 3D treatment technique with standard a nominal 12.5 Gy in a single fraction for the brain MLC as baseline, Figure 2 displays the percentage differ- lesions, three 12-Gy fractions totaling 36 Gy for the liver ence between plans using other treatment techniques and lesions, and 18 Gy in a single fraction for the spine the HD120 MLC system and the baseline plans. lesions, respectively. Compared to the standard MLC system, the HD120 MLC Dosimetric evaluation parameters and statistical analysis improved the dose homogeneity for the brain group, with Each treatment plan was evaluated with respect to target larger D (p < 0.01) and smaller D (p < 0.01). In con- min max coverage criteria and OAR sparing criteria. For targets, the trast, the HD120 MLC had no significant impact on D , min mean PTV doses, as well as the minimum and maximum D , or D values for either the liver group or the spine max mean doses to the PTVs, were compared. The maximum dose group. The use of intensity modulation also significantly (D ) was defined as the maximum dose value that cov- reduced the D values for the liver group (p <0.01). max max ers 1% of the target volume (i.e. D ) and the minimum Although statistically significant, all the above differences dose (D ) was defined as the minimum dose value that were quite small (< 2%) and may likely have little clinical min covers 99% of the target volume (i.e. D ). The dosimetric significance. metrics for the OARs were D , D , D and D for the max mean 5 1 OAR dose sparing brainstem; D , D and D for the liver; and D , mean 10 30 max D and D for the spine cases, respectively. Again, using the 3D treatment technique with the stand- mean 10 ard MLC as the baseline, Figure 3 displays the percentage We generalized the shape into two basic categories: the difference between the baseline and plans using other round/ellipsoidal shapes which are representative of all treatment techniques and/or the HD120 MLC system the targets in the brain and the liver group, and the con- cave shapes which are representative of all the spine cases, For the brain group, the HD120 MLC and the use of inten- as shown in figure 1. We also generalized the volumes sity modulation contributed jointly to dose sparing of the into two major categories, the small volume sizes which brainstem, as a positive interaction of these two factors are generally seen in the intracranial group and the large was detected with GEE (p = 0.003). First, the intensity volume sizes which are generally seen in the extracranial modulation technique showed significant sparing for the group, as shown in Additional file 1. brainstem, compared to other treatment techniques (Additional file 3). Specifically, IMRT produced the great- Both the treatment technique and the MLC system can est dose reduction in the high-dose region, as reflected by impact the dosimetric outcome for the brain and the liver the D and D doses. The reduction in D was about 10% 1 5 1 groups. Therefore, the Generalized Estimating Equation and 9%, and in D was about 18% and 14%, when 3D and technique (GEE) [26,27] was used to separate their indi- DARC techniques, respectively, were replaced by the IMRT vidual influences and to analyze their interactions for technique. Secondly, for the IMRT technique the HD120 dosimetry outcomes. The analysis started by testing for MLC also reduced all brainstem doses (p = 0.04) relative the two-factor interaction, followed either by testing for to the standard MLC. The improved field shaping with the the individual factor effect if no interaction was detected HD120 MLC also helped to reduce the D dose for all at critical value of 0.05, or by conducting the pair-wise techniques by 3 – 9% (p = 0.003). Third, the HD120 MLC group comparison if the interaction was significant at the combined with IMRT jointly benefited dose reduction in 0.05 level. For the spine lesions, a paired-t test was per- the middle dose range, reflected by the D dose, (p = formed to evaluate the difference between the HD120 0.001). As a result, the mean dose to the brainstem was Page 4 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 Dosimetric Indices For PTVs (brain) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Dosimetric Indices For PTVs (liver) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Dosimetric Indices For PTVs (spine) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Standard MLC HD120 MLC Th p Figure 2 lan e pe s, the rcen 3D tagtreatment technique with standard MLC e difference of PTV coverage between plans using other treatment techniques and MLC systems and the baseline The percentage difference of PTV coverage between plans using other treatment techniques and MLC sys- tems and the baseline plans, the 3D treatment technique with standard MLC. Page 5 of 10 (page number not for citation purposes) Dose Ratio Dose Ratio Dose Ratio Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 Dosimetric Indices For Brainstem D1 D5 D10 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 Dosimetric Indices For Liver D10 D30 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.10 1.05 1.00 0.95 0.90 0.85 0.80 Dosimetric Indices For Spine D1 D10 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.05 0.95 0.9 0.85 0.8 0.75 0.7 Standard MLC HD120 MLC The p Figure 3 lan percentage d s, the 3D treatment technique with standard MLC ifference of OAR sparing between plans using other treatment techniques and MLC systems and the baseline The percentage difference of OAR sparing between plans using other treatment techniques and MLC systems and the baseline plans, the 3D treatment technique with standard MLC. Page 6 of 10 (page number not for citation purposes) Dose Ratio Dose Ratio Dose Ratio Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 reduced by 35%, between the best (IMRT with the HD120 ment planning techniques, yielding dose indices that var- MLC) and the worst (3D with standard MLC) plans. ied less than 2.5% for the same lesion. Similarly, the HD120 MLC and the IMRT techniques con- The results from this study suggested that the degree of tributed jointly to the dose sparing for the liver group improved organ sparing varied with target size and shape. (Additional file 4). The HD120 MLC reduced doses at The targets in the brain and liver groups are similar in both D and D , as well as the mean dose (p < 0.01). The shape (round or ellipsoidal) differed substantially in vol- 10 30 dose reduction (at all levels) attributable to the HD120 ume (small vs. large). The lesions in the brain were several MLC was between 3 – 5% with the 3D and DARC tech- times smaller than those in the liver, and the volume of niques and between 1 – 2% with the IMRT technique. the brainstem was also several times smaller than that of When comparing treatment techniques, IMRT plans were the liver itself. The HD120 MLC yields a better match of significantly better than either 3D or DARC plans. The the beam aperture to the target projection; however, its IMRT technique improved the dose sparing at all levels, as benefits become less noticeable as the target/OAR the D , D and D indices were reduced by over 12% becomes larger. Therefore, the dose reduction contributed 10 30 mean over the 3D/DARC techniques. by the HD120 MLC decreased, from 4 – 11% to 1 – 5%, as target sizes increased between the brain and liver For the spine group, using the HD120 MLC substantially groups. On the other hand, the targets in the liver and improved cord sparing (p < 0.01) as the ability to map the spine groups were of roughly the same size but fell into dose to the concave-shaped target improved (Additional different shape groups (round vs. concave, respectively). file 5). Figure 4 displays dose distribution for a spine case. The concave lesion shape presented a challenge for con- As shown, the dose fall off is much steeper at the target- ventional techniques to provide adequate target coverage cord junction for the smaller leaves. The overall dose and optimal organ sparing. Clinically, all spine SBRT reduction was 14%, 19% and 29% for the D , D and lesions in our institution are planned with IMRT, owing to 1 10 D dose indices, respectively. the ability to manipulate the intensity at virtually the mean voxel level using this technique. Since spinal cords were Effect of target shape and volume size always adjacent to the target volume, the ability to manip- The effect of target volume was compared with the brain ulate the radiation beam with greater precision via the and the liver group. As stated earlier, the targets were in high-definition MLC leaves helped reduce the doses the general round or ellipsoidal for both the brain and liver cord received. Therefore, in contrast to the moderate ben- lesions, and the most significant differences between efit for liver lesions, the HD120 MLC significantly these two groups were the target and OAR volumes. The improved cord sparing for the spine group, realizing a lesions in the brain were several times smaller than those 14%–19% dose reduction in D and D , respectively. 1 10 in the liver, and the size of the brainstem was also several times smaller than the liver. The dose reduction (combin- Conclusion ing all levels) contributed by the HD120 MLC decreased, The finer HD120 MLC in combination with IMRS pro- from 4 – 11% to 1 – 5%, as target sizes increased from the vides significant dosimetric benefits for SRS/SBRT. Spar- brain group to the liver group. ing of the OARs is dependent on the lesion and critical organ size and shape complexity. Small lesions (such as The effect of target shape was compared with the spine brain lesions treated with SRS) and complex target/OAR and the liver group. While the target volumes were similar geometry (such as the spine lesions encountered in SBRT) for the liver and the spine groups, the target shapes were will benefit most from the finer-leaf collimator and treat- much more complex in the spine group (concave vs. ment planning capabilities provided by a dedicated radi- round or ellipsoidal for the liver). In contrast to the mod- osurgery system, compared to larger and more rounded or erate contribution for liver lesions, the HD120 MLC sig- regularly shaped target volumes. Prospective clinical trials nificantly improved cord sparing for the spine group. By with comprehensive data collection should be conducted using the 120HD MLC, the dose to the cord was reduced to determine whether these dosimetric advantages trans- on average by 19% to 14% at high to middle dose levels late into clinically significant benefits. (D to D , respectively) for the spine plans. 1 10 Competing interests Discussion The authors declare that they have no competing interests. This study was designed to provide similar target coverage for all plans. The prescription dose was set to the isodose Authors' contributions line at the periphery of the PTV that covered at least 97% All authors read and approved the final manuscript. of the target for all plans. Using this strategy, the DVH to the target volumes was very similar using different treat- Page 7 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 (a) (b) E Figure 4 xample dose distribution of a spine case, IMRT plans with (a) standard MLC system and (b) with HD120 MLC system Example dose distribution of a spine case, IMRT plans with (a) standard MLC system and (b) with HD120 MLC system. The black circles indicate the regions where dose fall off being significantly different between the two plans. Page 8 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 conformal arcs and intensity-modulated radiosurgery. Med QJW, ZW, FFY and JPK designed the study and the analy- Phys 2005, 32:405-411. sis, generated the treatment plans, performed the analysis 3. Perks JR, El-Hamri K, Blackburn TP, Plowman PN: Comparison of drafted and revised the manuscript. radiosurgery planning modalities for acoustic neuroma with regard to conformity and mean target dose. Stereotact Funct Neurosurg 2005, 83:165-171. ML participated in the study design, statistically analysis 4. Perks JR, St George EJ, El Hamri K, Blackburn P, Plowman PN: Ster- eotactic radiosurgery XVI: Isodosimetric comparison of and revised the manuscript. photon stereotactic radiosurgery techniques (gamma knife vs. micromultileaf collimator linear accelerator) for acoustic JM and ZC participated in the study design and revised the neuroma – and potential clinical importance. Int J Radiat Oncol Biol Phys 2003, 57:1450-1459. manuscript. 5. Dvorak P, Georg D, Bogner J, Kroupa B, Dieckmann K, Potter R: Impact of IMRT and leaf width on stereotactic body radio- CH participated in the study design, provided technique therapy of liver and lung lesions. Int J Radiat Oncol Biol Phys 2005, 61:1572-1581. assistance and revised the manuscript. 6. Flickinger JC, Loeffler JS, Larson DA: Stereotactic radiosurgery for intracranial malignancies. Oncology (Williston Park) 1994, 8:81-86. Additional material 7. Larson DA, Flickinger JC, Loeffler JS: The radiobiology of radio- surgery. Int J Radiat Oncol Biol Phys 1993, 25:557-561. 8. Solberg TD, Boedeker KL, Fogg R, Selch MT, DeSalles AA: Dynamic Additional file 1 arc radiosurgery field shaping: a comparison with static field Table S1. Target volumes for the brain, the liver and the spine groups. conformal and noncoplanar circular arcs. Int J Radiat Oncol Biol Phys 2001, 49:1481-1491. Click here for file 9. Benedict SH, Cardinale RM, Wu Q, Zwicker RD, Broaddus WC, [http://www.biomedcentral.com/content/supplementary/1748- Mohan R: Intensity-modulated stereotactic radiosurgery 717X-4-3-S1.doc] using dynamic micro-multileaf collimation. Int J Radiat Oncol Biol Phys 2001, 50:751-758. 10. Cardinale RM, Benedict SH, Wu Q, Zwicker RD, Gaballa HE, Mohan Additional file 2 R: A comparison of three stereotactic radiotherapy tech- Table S2. Dosimetrical Indices for PTVs of the brain, liver and spine niques; ARCS vs. noncoplanar fixed fields vs. intensity mod- groups. ulation. Int J Radiat Oncol Biol Phys 1998, 42:431-436. Click here for file 11. Yin FF, Ryu S, Ajlouni M, Zhu J, Yan H, Guan H, Faber K, Rock J, [http://www.biomedcentral.com/content/supplementary/1748- Abdalhak M, Rogers L, et al.: A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors. Med Phys 2002, 717X-4-3-S2.doc] 29:2815-2822. 12. Nelson JW, Yoo DS, Sampson JH, Isaacs RE, Larrier NA, Marks LB, Additional file 3 Yin FF, Wu QJ, Wang Z, Kirkpatrick JP: Stereotactic Body Radio- Table S3. Dosimetrical indices for the five braincases. therapy for Lesions of The Spine and Paraspinal Regions. Int J Radiat Oncol Biol Phys 2008. Click here for file 13. Chang BK, Timmerman RD: Stereotactic body radiation ther- [http://www.biomedcentral.com/content/supplementary/1748- apy: a comprehensive review. Am J Clin Oncol 2007, 30:637-644. 717X-4-3-S3.doc] 14. Chang EL, Shiu AS, Mendel E, Mathews LA, Mahajan A, Allen PK, Weinberg JS, Brown BW, Wang XS, Woo SY, et al.: Phase I/II study Additional file 4 of stereotactic body radiotherapy for spinal metastasis and its pattern of failure. J Neurosurg Spine 2007, 7:151-160. Table S4. Dosimetrical indices for the five liver cases. 15. Timmerman RD, Kavanagh BD, Cho LC, Papiez L, Xing L: Stereotac- Click here for file tic body radiation therapy in multiple organ sites. J Clin Oncol [http://www.biomedcentral.com/content/supplementary/1748- 2007, 25:947-952. 717X-4-3-S4.doc] 16. Kavanagh BD, McGarry RC, Timmerman RD: Extracranial radio- surgery (stereotactic body radiation therapy) for oligome- tastases. Semin Radiat Oncol 2006, 16:77-84. Additional file 5 17. Timmerman RD, Forster KM, Chinsoo Cho L: Extracranial stere- Table S5. Dosimetrical indices and statistical comparisons for the five otactic radiation delivery. Semin Radiat Oncol 2005, 15:202-207. spine cases. 18. Ryu S, Jin R, Jin JY, Chen Q, Rock J, Anderson J, Movsas B: Pain con- Click here for file trol by image-guided radiosurgery for solitary spinal metas- tasis. J Pain Symptom Manage 2008, 35:292-298. [http://www.biomedcentral.com/content/supplementary/1748- 19. Jin JY, Chen Q, Jin R, Rock J, Anderson J, Li S, Movsas B, Ryu S: Tech- 717X-4-3-S5.doc] nical and clinical experience with spine radiosurgery: a new technology for management of localized spine metastases. Technol Cancer Res Treat 2007, 6:127-133. 20. Ryu S, Jin JY, Jin R, Rock J, Ajlouni M, Movsas B, Rosenblum M, Kim JH: Partial volume tolerance of the spinal cord and complica- Acknowledgements tions of single-dose radiosurgery. Cancer 2007, 109:628-636. 21. Huq MS, Das IJ, Steinberg T, Galvin JM: A dosimetric comparison The authors wish to thank the Engineers and Physicists of Varian Medical of various multileaf collimators. Phys Med Biol 2002, Systems and BrainLAB for their technical assistance. 47:N159-170. 22. Fiveash JB, Murshed H, Duan J, Hyatt M, Caranto J, Bonner JA, Popple References RA: Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck 1. Monk JE, Perks JR, Doughty D, Plowman PN: Comparison of a neoplasms with intensity modulated radiation therapy. Med micro-multileaf collimator with a 5-mm-leaf-width collima- Phys 2002, 29:1116-1119. tor for intracranial stereotactic radiotherapy. Int J Radiat Oncol 23. Georg D, Dieckmann K, Bogner J, Zehetmayer M, Potter R: Impact Biol Phys 2003, 57:1443-1449. of a micromultileaf collimator on stereotactic radiotherapy 2. Jin JY, Yin FF, Ryu S, Ajlouni M, Kim JH: Dosimetric study using dif- of uveal melanoma. Int J Radiat Oncol Biol Phys 2003, 55:881-891. ferent leaf-width MLCs for treatment planning of dynamic Page 9 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 24. Kubo HD, Wilder RB, Pappas CT: Impact of collimator leaf width on stereotactic radiosurgery and 3D conformal radiotherapy treatment plans. Int J Radiat Oncol Biol Phys 1999, 44:937-945. 25. Chang Z, Wang Z, Wu QJ, Yan H, Bowsher J, Zhang J, Yin FF: Dosi- metric Characteristics of Novalis Tx System with High Def- inition Multi-leaf Collimator. Med Phys 2008 in press. 26. Zeger SL, Liang KY: Longitudinal data analysis for discrete and continuous outcomes. Biometrics 1986, 42:121-130. 27. Zeger SL, Liang KY, Albert PS: Models for longitudinal data: a generalized estimating equation approach. Biometrics 1988, 44:1049-1060. 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Impact of collimator leaf width and treatment technique on stereotactic radiosurgery and radiotherapy plans for intra- and extracranial lesions

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Springer Journals
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Copyright © 2009 by Wu et al; licensee BioMed Central Ltd.
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Medicine & Public Health; Oncology; Radiotherapy
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1748-717X
DOI
10.1186/1748-717X-4-3
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19159471
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Abstract

Background: This study evaluated the dosimetric impact of various treatment techniques as well as collimator leaf width (2.5 vs 5 mm) for three groups of tumors – spine tumors, brain tumors abutting the brainstem, and liver tumors. These lesions often present challenges in maximizing dose to target volumes without exceeding critical organ tolerance. Specifically, this study evaluated the dosimetric benefits of various techniques and collimator leaf sizes as a function of lesion size and shape. Methods: Fifteen cases (5 for each site) were studied retrospectively. All lesions either abutted or were an integral part of critical structures (brainstem, liver or spinal cord). For brain and liver lesions, treatment plans using a 3D-conformal static technique (3D), dynamic conformal arcs (DARC) or intensity modulation (IMRT) were designed with a conventional linear accelerator with standard 5 mm leaf width multi-leaf collimator, and a linear accelerator dedicated for radiosurgery and hypofractionated therapy with a 2.5 mm leaf width collimator. For the concave spine lesions, intensity modulation was required to provide adequate conformality; hence, only IMRT plans were evaluated using either the standard or small leaf-width collimators. A total of 70 treatment plans were generated and each plan was individually optimized according to the technique employed. The Generalized Estimating Equation (GEE) was used to separate the impact of treatment technique from the MLC system on plan outcome, and t-tests were performed to evaluate statistical differences in target coverage and organ sparing between plans. Results: The lesions ranged in size from 2.6 to 12.5 cc, 17.5 to 153 cc, and 20.9 to 87.7 cc for the brain, liver, and spine groups, respectively. As a group, brain lesions were smaller than spine and liver lesions. While brain and liver lesions were primarily ellipsoidal, spine lesions were more complex in shape, as they were all concave. Therefore, the brain and the liver groups were compared for volume effect, and the liver and spine groups were compared for shape. For the brain and liver groups, both the radiosurgery MLC and the IMRT technique contributed to the dose sparing of organs-at-risk(OARs), as dose in the high-dose regions of these OARs was reduced up Page 1 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 to 15%, compared to the non-IMRT techniques employing a 5 mm leaf-width collimator. Also, the dose reduction contributed by the fine leaf-width MLC decreased, as dose savings at all levels diminished from 4 – 11% for the brain group to 1 – 5% for the liver group, as the target structures decreased in volume. The fine leaf-width collimator significantly improved spinal cord sparing, with dose reductions of 14 – 19% in high to middle dose regions, compared to the 5 mm leaf width collimator. Conclusion: The fine leaf-width MLC in combination with the IMRT technique can yield dosimetric benefits in radiosurgery and hypofractionated radiotherapy. Treatment of small lesions in cases involving complex target/OAR geometry will especially benefit from use of a fine leaf-width MLC and the use of IMRT. Varian 2100Clinac system (Varian Medical Systems, Palo Background Stereotactic intracranial radiosurgery (SRS) and extracra- Alto, CA), which served as the baseline for comparison. nial body radiosurgery and radiotherapy (SBRT) are char- The Novalis Tx radiosurgery system became commercially acterized by ablative, high dose irradiation of target available in early 2008, and was equipped with a newly structures. Complex targets, such as spine metastases, designed micro-mulitleaf collimator (HD120 MLC) sys- brain lesions abutting the brain stem, and liver lesions tem, replacing the standard Millennium MLC system. In present challenges in maximizing the dose to the target contrast to previous micro-MLC systems [2,21-24], the volume while not exceeding the critical organ tolerances Novalis Tx radiosurgery MLC is within the gantry housing, [1-20]. This study evaluates the benefits of a dedicated instead of being an add-on tertiary system [2,21-24]. The radiosurgery system with a fine leaf-width collimator for mounting of an add-on tertiary MLC not only prolongs these different groups of patients. More specifically, this the treatment procedure, but also reduces the clearance study evaluates the dosimetric benefits of this system as a between the gantry and couch, therefore limiting the free- function of target size and shape complexity. dom to select certain beam angles. The Novalis Tx HD120 MLC has 32 leaf pairs in the center, each a with leaf width of 2.5 mm (projected at the isocenter) and 14 leaf pairs on Materials and methods Patient Data each side (a total of 28) with a leaf width of 5 mm; thus, This retrospective study included 15 cases (5 each for the total number of leaves is 120. Our initial measure- brain, liver and spine sites) treated with SRS/SBRT at our ments also showed a sharper penumbra. The HD120 MLC institution. As shown in Additional file 1, these lesions leaf side penumbra was 2.5 mm vs. 2.8 mm with the ranged in size from 2.6 – 12.5 cc, 17.5 – 153.1 cc, and 20.9 standard MLC, and the HD120 MLC leaf end penumbra – 87.7 cc for the brain, liver, and spine groups, respec- was 2.8 mm vs. 3.6 mm with the standard MLC[25]. For tively. The volumes selected were intended to represent conformal static treatment (3D) and dynamic conformal the ranges of the target volumes typically encountered for arc treatment (DARC) treatments, the maximum dose rate these sites. The selected cases all involved lesions next to with the Novalis Tx system is 1000 MU/min versus 600 or within critical structures, i.e., lesions next to the brain- MU/min with the Clinac system, allowing faster radiation stem for the brain group, lesions within the liver for the delivery. liver group, and tumors near/abutting the spinal cord for the spine group. The brain and liver lesions were mostly For each case, the normal structures and OARs were con- ellipsoidal, with brain lesions having smaller volumes. toured by a physician with expertise in SRS/SBRT. The tar- The spine lesions were more complex in shape, as they get volumes were contoured by the same physician. For were all concave; volumes were similar to the liver lesions. the brain lesions, the planning target volume (PTV) was Therefore, the brain and the liver groups were compared generated by expanding the contrast-enhancing T1- for volume effect and the liver and the spine groups were weighted MRI volume by 1-mm, except at the junctions of compared for shape effect. Figure 1 displays the rendering the tumor and brainstem where no expansion was added. of the target volumes and critical structures in 3D space The liver lesions were treated with deep inhale breath- for these three sites. hold technique and cone-beam CT (CBCT) guidance, and the PTV was obtained by expanding the lesion volume by Treatment planning 5 mm right-left and anterior-posterior and 7 mm supe- Treatment plans were designed with the Novalis Tx radio- rior-inferior. The PTV expansion for spine lesions was also surgery system (BrainLab AG, Munich, Germany and Var- non-uniform, usually 3 mm except at the lesion and cord ian Medical Systems, Palo Alto, CA) versus the standard interface, where 0 – 1 mm expansion was used. Page 2 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 E Figure 1 xamples of lesions and adjacent critical structures/organs for the brain (a), the liver(b), and the spine (c) groups Examples of lesions and adjacent critical structures/organs for the brain (a), the liver(b), and the spine (c) groups. The 3D rendering of the geometrical relationships is shown in (d) for the brain case (left), liver case (middle) and spine case (right). Treatment plans were generated using three techniques: adequate conformality. Hence, only IMRT plans were gen- 3D, DARC, and IMRT. For the brain and liver lesions, erated for the spine lesions, again using both the standard plans using all three techniques were designed. For each MLC and HD120 MLC. Typically, the 3D plans used 6–12 lesion and planning technique, plans were generated beams, DARC plans used 4 – 7 arcs and IMRT plans used using both the standard MLC and the HD120 MLC. All 4–12 static beams. The multiple arcs for the brain lesions the spine lesions exhibited concave shapes, and the 3D were mainly designed to take advantage of different couch and the DARC techniques could not provide clinically angles and those for the liver lesions utilized different Page 3 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 beam weightings through different sections of anatomy. MLC and the standard MLC on dosimetric parameters for Each plan was individually optimized according to the IMRT. treatment techniques selected. Beam angles (non-copla- nar or coplanar) were chosen to minimize doses to the Results critical structures and to achieve high dose fall-off around PTV coverage the target at the same time. For IMRT planning, planning For each case, the PTV coverage was essentially equivalent objectives included dose uniformity to the PTV and dose among different plans. Additional file 2 lists the dosimet- constraints for the OARs as well as dose falloff at the target ric indices for all cases. The small standard deviations for boundary. For each plan, 90% of the prescription dose all plans indicate consistency in applying the treatment covered at least 97% of the PTV. techniques to achieve the optimal dose coverage; i.e., the prescription isodose covered at least 97% of the target vol- In summary, a total of 70 treatment plans were designed ume and the dose heterogeneity inside the target was kept and each plan was individually optimized according to at about 10%. For each individual case, the D was min the technique employed. For the purpose of the dosimet- within 2% and D was within 2.5% among different max ric analysis in this study, the prescription dose was set to plans. Using the 3D treatment technique with standard a nominal 12.5 Gy in a single fraction for the brain MLC as baseline, Figure 2 displays the percentage differ- lesions, three 12-Gy fractions totaling 36 Gy for the liver ence between plans using other treatment techniques and lesions, and 18 Gy in a single fraction for the spine the HD120 MLC system and the baseline plans. lesions, respectively. Compared to the standard MLC system, the HD120 MLC Dosimetric evaluation parameters and statistical analysis improved the dose homogeneity for the brain group, with Each treatment plan was evaluated with respect to target larger D (p < 0.01) and smaller D (p < 0.01). In con- min max coverage criteria and OAR sparing criteria. For targets, the trast, the HD120 MLC had no significant impact on D , min mean PTV doses, as well as the minimum and maximum D , or D values for either the liver group or the spine max mean doses to the PTVs, were compared. The maximum dose group. The use of intensity modulation also significantly (D ) was defined as the maximum dose value that cov- reduced the D values for the liver group (p <0.01). max max ers 1% of the target volume (i.e. D ) and the minimum Although statistically significant, all the above differences dose (D ) was defined as the minimum dose value that were quite small (< 2%) and may likely have little clinical min covers 99% of the target volume (i.e. D ). The dosimetric significance. metrics for the OARs were D , D , D and D for the max mean 5 1 OAR dose sparing brainstem; D , D and D for the liver; and D , mean 10 30 max D and D for the spine cases, respectively. Again, using the 3D treatment technique with the stand- mean 10 ard MLC as the baseline, Figure 3 displays the percentage We generalized the shape into two basic categories: the difference between the baseline and plans using other round/ellipsoidal shapes which are representative of all treatment techniques and/or the HD120 MLC system the targets in the brain and the liver group, and the con- cave shapes which are representative of all the spine cases, For the brain group, the HD120 MLC and the use of inten- as shown in figure 1. We also generalized the volumes sity modulation contributed jointly to dose sparing of the into two major categories, the small volume sizes which brainstem, as a positive interaction of these two factors are generally seen in the intracranial group and the large was detected with GEE (p = 0.003). First, the intensity volume sizes which are generally seen in the extracranial modulation technique showed significant sparing for the group, as shown in Additional file 1. brainstem, compared to other treatment techniques (Additional file 3). Specifically, IMRT produced the great- Both the treatment technique and the MLC system can est dose reduction in the high-dose region, as reflected by impact the dosimetric outcome for the brain and the liver the D and D doses. The reduction in D was about 10% 1 5 1 groups. Therefore, the Generalized Estimating Equation and 9%, and in D was about 18% and 14%, when 3D and technique (GEE) [26,27] was used to separate their indi- DARC techniques, respectively, were replaced by the IMRT vidual influences and to analyze their interactions for technique. Secondly, for the IMRT technique the HD120 dosimetry outcomes. The analysis started by testing for MLC also reduced all brainstem doses (p = 0.04) relative the two-factor interaction, followed either by testing for to the standard MLC. The improved field shaping with the the individual factor effect if no interaction was detected HD120 MLC also helped to reduce the D dose for all at critical value of 0.05, or by conducting the pair-wise techniques by 3 – 9% (p = 0.003). Third, the HD120 MLC group comparison if the interaction was significant at the combined with IMRT jointly benefited dose reduction in 0.05 level. For the spine lesions, a paired-t test was per- the middle dose range, reflected by the D dose, (p = formed to evaluate the difference between the HD120 0.001). As a result, the mean dose to the brainstem was Page 4 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 Dosimetric Indices For PTVs (brain) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Dosimetric Indices For PTVs (liver) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Dosimetric Indices For PTVs (spine) Dmin Dmax Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.02 1.00 0.98 Standard MLC HD120 MLC Th p Figure 2 lan e pe s, the rcen 3D tagtreatment technique with standard MLC e difference of PTV coverage between plans using other treatment techniques and MLC systems and the baseline The percentage difference of PTV coverage between plans using other treatment techniques and MLC sys- tems and the baseline plans, the 3D treatment technique with standard MLC. Page 5 of 10 (page number not for citation purposes) Dose Ratio Dose Ratio Dose Ratio Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 Dosimetric Indices For Brainstem D1 D5 D10 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 Dosimetric Indices For Liver D10 D30 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.10 1.05 1.00 0.95 0.90 0.85 0.80 Dosimetric Indices For Spine D1 D10 Dmean 3D DARC IMRS 3D DARC IMRS 3D DARC IMRS 1.05 0.95 0.9 0.85 0.8 0.75 0.7 Standard MLC HD120 MLC The p Figure 3 lan percentage d s, the 3D treatment technique with standard MLC ifference of OAR sparing between plans using other treatment techniques and MLC systems and the baseline The percentage difference of OAR sparing between plans using other treatment techniques and MLC systems and the baseline plans, the 3D treatment technique with standard MLC. Page 6 of 10 (page number not for citation purposes) Dose Ratio Dose Ratio Dose Ratio Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 reduced by 35%, between the best (IMRT with the HD120 ment planning techniques, yielding dose indices that var- MLC) and the worst (3D with standard MLC) plans. ied less than 2.5% for the same lesion. Similarly, the HD120 MLC and the IMRT techniques con- The results from this study suggested that the degree of tributed jointly to the dose sparing for the liver group improved organ sparing varied with target size and shape. (Additional file 4). The HD120 MLC reduced doses at The targets in the brain and liver groups are similar in both D and D , as well as the mean dose (p < 0.01). The shape (round or ellipsoidal) differed substantially in vol- 10 30 dose reduction (at all levels) attributable to the HD120 ume (small vs. large). The lesions in the brain were several MLC was between 3 – 5% with the 3D and DARC tech- times smaller than those in the liver, and the volume of niques and between 1 – 2% with the IMRT technique. the brainstem was also several times smaller than that of When comparing treatment techniques, IMRT plans were the liver itself. The HD120 MLC yields a better match of significantly better than either 3D or DARC plans. The the beam aperture to the target projection; however, its IMRT technique improved the dose sparing at all levels, as benefits become less noticeable as the target/OAR the D , D and D indices were reduced by over 12% becomes larger. Therefore, the dose reduction contributed 10 30 mean over the 3D/DARC techniques. by the HD120 MLC decreased, from 4 – 11% to 1 – 5%, as target sizes increased between the brain and liver For the spine group, using the HD120 MLC substantially groups. On the other hand, the targets in the liver and improved cord sparing (p < 0.01) as the ability to map the spine groups were of roughly the same size but fell into dose to the concave-shaped target improved (Additional different shape groups (round vs. concave, respectively). file 5). Figure 4 displays dose distribution for a spine case. The concave lesion shape presented a challenge for con- As shown, the dose fall off is much steeper at the target- ventional techniques to provide adequate target coverage cord junction for the smaller leaves. The overall dose and optimal organ sparing. Clinically, all spine SBRT reduction was 14%, 19% and 29% for the D , D and lesions in our institution are planned with IMRT, owing to 1 10 D dose indices, respectively. the ability to manipulate the intensity at virtually the mean voxel level using this technique. Since spinal cords were Effect of target shape and volume size always adjacent to the target volume, the ability to manip- The effect of target volume was compared with the brain ulate the radiation beam with greater precision via the and the liver group. As stated earlier, the targets were in high-definition MLC leaves helped reduce the doses the general round or ellipsoidal for both the brain and liver cord received. Therefore, in contrast to the moderate ben- lesions, and the most significant differences between efit for liver lesions, the HD120 MLC significantly these two groups were the target and OAR volumes. The improved cord sparing for the spine group, realizing a lesions in the brain were several times smaller than those 14%–19% dose reduction in D and D , respectively. 1 10 in the liver, and the size of the brainstem was also several times smaller than the liver. The dose reduction (combin- Conclusion ing all levels) contributed by the HD120 MLC decreased, The finer HD120 MLC in combination with IMRS pro- from 4 – 11% to 1 – 5%, as target sizes increased from the vides significant dosimetric benefits for SRS/SBRT. Spar- brain group to the liver group. ing of the OARs is dependent on the lesion and critical organ size and shape complexity. Small lesions (such as The effect of target shape was compared with the spine brain lesions treated with SRS) and complex target/OAR and the liver group. While the target volumes were similar geometry (such as the spine lesions encountered in SBRT) for the liver and the spine groups, the target shapes were will benefit most from the finer-leaf collimator and treat- much more complex in the spine group (concave vs. ment planning capabilities provided by a dedicated radi- round or ellipsoidal for the liver). In contrast to the mod- osurgery system, compared to larger and more rounded or erate contribution for liver lesions, the HD120 MLC sig- regularly shaped target volumes. Prospective clinical trials nificantly improved cord sparing for the spine group. By with comprehensive data collection should be conducted using the 120HD MLC, the dose to the cord was reduced to determine whether these dosimetric advantages trans- on average by 19% to 14% at high to middle dose levels late into clinically significant benefits. (D to D , respectively) for the spine plans. 1 10 Competing interests Discussion The authors declare that they have no competing interests. This study was designed to provide similar target coverage for all plans. The prescription dose was set to the isodose Authors' contributions line at the periphery of the PTV that covered at least 97% All authors read and approved the final manuscript. of the target for all plans. Using this strategy, the DVH to the target volumes was very similar using different treat- Page 7 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 (a) (b) E Figure 4 xample dose distribution of a spine case, IMRT plans with (a) standard MLC system and (b) with HD120 MLC system Example dose distribution of a spine case, IMRT plans with (a) standard MLC system and (b) with HD120 MLC system. The black circles indicate the regions where dose fall off being significantly different between the two plans. Page 8 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 conformal arcs and intensity-modulated radiosurgery. Med QJW, ZW, FFY and JPK designed the study and the analy- Phys 2005, 32:405-411. sis, generated the treatment plans, performed the analysis 3. Perks JR, El-Hamri K, Blackburn TP, Plowman PN: Comparison of drafted and revised the manuscript. radiosurgery planning modalities for acoustic neuroma with regard to conformity and mean target dose. Stereotact Funct Neurosurg 2005, 83:165-171. ML participated in the study design, statistically analysis 4. Perks JR, St George EJ, El Hamri K, Blackburn P, Plowman PN: Ster- eotactic radiosurgery XVI: Isodosimetric comparison of and revised the manuscript. photon stereotactic radiosurgery techniques (gamma knife vs. micromultileaf collimator linear accelerator) for acoustic JM and ZC participated in the study design and revised the neuroma – and potential clinical importance. Int J Radiat Oncol Biol Phys 2003, 57:1450-1459. manuscript. 5. Dvorak P, Georg D, Bogner J, Kroupa B, Dieckmann K, Potter R: Impact of IMRT and leaf width on stereotactic body radio- CH participated in the study design, provided technique therapy of liver and lung lesions. Int J Radiat Oncol Biol Phys 2005, 61:1572-1581. assistance and revised the manuscript. 6. Flickinger JC, Loeffler JS, Larson DA: Stereotactic radiosurgery for intracranial malignancies. Oncology (Williston Park) 1994, 8:81-86. Additional material 7. Larson DA, Flickinger JC, Loeffler JS: The radiobiology of radio- surgery. Int J Radiat Oncol Biol Phys 1993, 25:557-561. 8. Solberg TD, Boedeker KL, Fogg R, Selch MT, DeSalles AA: Dynamic Additional file 1 arc radiosurgery field shaping: a comparison with static field Table S1. Target volumes for the brain, the liver and the spine groups. conformal and noncoplanar circular arcs. Int J Radiat Oncol Biol Phys 2001, 49:1481-1491. Click here for file 9. Benedict SH, Cardinale RM, Wu Q, Zwicker RD, Broaddus WC, [http://www.biomedcentral.com/content/supplementary/1748- Mohan R: Intensity-modulated stereotactic radiosurgery 717X-4-3-S1.doc] using dynamic micro-multileaf collimation. Int J Radiat Oncol Biol Phys 2001, 50:751-758. 10. Cardinale RM, Benedict SH, Wu Q, Zwicker RD, Gaballa HE, Mohan Additional file 2 R: A comparison of three stereotactic radiotherapy tech- Table S2. Dosimetrical Indices for PTVs of the brain, liver and spine niques; ARCS vs. noncoplanar fixed fields vs. intensity mod- groups. ulation. Int J Radiat Oncol Biol Phys 1998, 42:431-436. Click here for file 11. Yin FF, Ryu S, Ajlouni M, Zhu J, Yan H, Guan H, Faber K, Rock J, [http://www.biomedcentral.com/content/supplementary/1748- Abdalhak M, Rogers L, et al.: A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors. Med Phys 2002, 717X-4-3-S2.doc] 29:2815-2822. 12. Nelson JW, Yoo DS, Sampson JH, Isaacs RE, Larrier NA, Marks LB, Additional file 3 Yin FF, Wu QJ, Wang Z, Kirkpatrick JP: Stereotactic Body Radio- Table S3. Dosimetrical indices for the five braincases. therapy for Lesions of The Spine and Paraspinal Regions. Int J Radiat Oncol Biol Phys 2008. Click here for file 13. Chang BK, Timmerman RD: Stereotactic body radiation ther- [http://www.biomedcentral.com/content/supplementary/1748- apy: a comprehensive review. Am J Clin Oncol 2007, 30:637-644. 717X-4-3-S3.doc] 14. Chang EL, Shiu AS, Mendel E, Mathews LA, Mahajan A, Allen PK, Weinberg JS, Brown BW, Wang XS, Woo SY, et al.: Phase I/II study Additional file 4 of stereotactic body radiotherapy for spinal metastasis and its pattern of failure. J Neurosurg Spine 2007, 7:151-160. Table S4. Dosimetrical indices for the five liver cases. 15. Timmerman RD, Kavanagh BD, Cho LC, Papiez L, Xing L: Stereotac- Click here for file tic body radiation therapy in multiple organ sites. J Clin Oncol [http://www.biomedcentral.com/content/supplementary/1748- 2007, 25:947-952. 717X-4-3-S4.doc] 16. Kavanagh BD, McGarry RC, Timmerman RD: Extracranial radio- surgery (stereotactic body radiation therapy) for oligome- tastases. Semin Radiat Oncol 2006, 16:77-84. Additional file 5 17. Timmerman RD, Forster KM, Chinsoo Cho L: Extracranial stere- Table S5. Dosimetrical indices and statistical comparisons for the five otactic radiation delivery. Semin Radiat Oncol 2005, 15:202-207. spine cases. 18. Ryu S, Jin R, Jin JY, Chen Q, Rock J, Anderson J, Movsas B: Pain con- Click here for file trol by image-guided radiosurgery for solitary spinal metas- tasis. J Pain Symptom Manage 2008, 35:292-298. [http://www.biomedcentral.com/content/supplementary/1748- 19. Jin JY, Chen Q, Jin R, Rock J, Anderson J, Li S, Movsas B, Ryu S: Tech- 717X-4-3-S5.doc] nical and clinical experience with spine radiosurgery: a new technology for management of localized spine metastases. Technol Cancer Res Treat 2007, 6:127-133. 20. Ryu S, Jin JY, Jin R, Rock J, Ajlouni M, Movsas B, Rosenblum M, Kim JH: Partial volume tolerance of the spinal cord and complica- Acknowledgements tions of single-dose radiosurgery. Cancer 2007, 109:628-636. 21. Huq MS, Das IJ, Steinberg T, Galvin JM: A dosimetric comparison The authors wish to thank the Engineers and Physicists of Varian Medical of various multileaf collimators. Phys Med Biol 2002, Systems and BrainLAB for their technical assistance. 47:N159-170. 22. Fiveash JB, Murshed H, Duan J, Hyatt M, Caranto J, Bonner JA, Popple References RA: Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck 1. Monk JE, Perks JR, Doughty D, Plowman PN: Comparison of a neoplasms with intensity modulated radiation therapy. Med micro-multileaf collimator with a 5-mm-leaf-width collima- Phys 2002, 29:1116-1119. tor for intracranial stereotactic radiotherapy. Int J Radiat Oncol 23. Georg D, Dieckmann K, Bogner J, Zehetmayer M, Potter R: Impact Biol Phys 2003, 57:1443-1449. of a micromultileaf collimator on stereotactic radiotherapy 2. Jin JY, Yin FF, Ryu S, Ajlouni M, Kim JH: Dosimetric study using dif- of uveal melanoma. Int J Radiat Oncol Biol Phys 2003, 55:881-891. ferent leaf-width MLCs for treatment planning of dynamic Page 9 of 10 (page number not for citation purposes) Radiation Oncology 2009, 4:3 http://www.ro-journal.com/content/4/1/3 24. Kubo HD, Wilder RB, Pappas CT: Impact of collimator leaf width on stereotactic radiosurgery and 3D conformal radiotherapy treatment plans. Int J Radiat Oncol Biol Phys 1999, 44:937-945. 25. Chang Z, Wang Z, Wu QJ, Yan H, Bowsher J, Zhang J, Yin FF: Dosi- metric Characteristics of Novalis Tx System with High Def- inition Multi-leaf Collimator. Med Phys 2008 in press. 26. Zeger SL, Liang KY: Longitudinal data analysis for discrete and continuous outcomes. Biometrics 1986, 42:121-130. 27. Zeger SL, Liang KY, Albert PS: Models for longitudinal data: a generalized estimating equation approach. Biometrics 1988, 44:1049-1060. 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Radiation OncologySpringer Journals

Published: Jan 21, 2009

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