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A Study on Conventional IMRT and RapidArc Treatment Planning Techniques for Head and Neck Cancers
I. J. Radiation Oncology d Biology d Physics
S836
Volume 78, Number 3, Supplement, 2010
Materials/Methods: Ten SBRT cases were investigated retrospectively for various tumor sites, including lung, liver, spine, kidney and prostate with fraction doses ranging from 6 to 15 Gy. Single-arc (full-arc or partial arc) and/or two-arc VMAT plans were generated on CMS Monaco TPS (Version 2.03.01, CMS Inc., MO) using biologically based optimization with Monte Carlo dose calculation. HT plans were created on TomoTherapy Hi?ART planning station (Version 3.2.3.2, TomoTherapy Inc., WI) using a jaw size of 2.5 cm. DCAT plans were generated on BrainLAB radiotherapy treatment planning software (BrainSCAN, Version 5.31, Germany). Fixed field IMRT/conformal plans were developed on CMS XiO TPS (Version 4.4, CMS Inc., MO). Metrics used to evaluate the dosimetric plan quality include target coverage, heterogeneity index (HI), target mean/maximum/minimum doses, DVHs and patient mean dose. Evaluation of dose delivery efficiency and accuracy were performed using a cylindrical diode array detector system ArcCHECK (Sun Nuclear Corp., FL). Results: Both VMAT and HT are capable of providing more uniform target dose and better normal structure sparing compared to fixed field and DCAT plans. For lung SBRT, the PTV coverages are 95.9, 97 and 98.3% with HIs of 1.09, 1.08 and 1.13 respectively for the VMAT, HT and DCAT plans. For liver SBRT, the HI for HT plan is the lowest (1.04) compared to VMAT (1.06) and XiO (1.24). The target coverage of VMAT (99.6%) is slightly higher than the HT plan (97%). VMAT offers more efficient dose delivery than HT. Compared to HT treatment durations of 25, 17.9 and 7 min for the lung, liver and prostate cases, a reduction of 74%, 66% and 17% treatment times is measured for the VMAT plans. The estimated treatment time of DCAT for spine is reduced by 24.7% compared to VMAT plan, while for lung, liver and kidney cases, the treatment times of DCAT are comparable or shorter. The total MUs are 1594, 6100 and 857 for the VMAT, HT and DCAT plans for the lung SBRT; 2368, 5985 and 2921 MUs for prostate and 2864, 15360 and 1464 MUs for liver for the VMAT, HT and XiO plans respectively. Plan delivery accuracy for all the modalities was comparable with average passing rates greater than 95%. Conclusions: Single-arc VMAT improved target uniformity and normal tissue sparing compared to CMS XiO fixed field and BrainLAB DCAT plans for SBRT. In comparison to HT, VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans. Author Disclosure: X. Qi, None; A. Hu, None; W. Dzingle, None; K. Stuhr, None; H. Rice, None; Q. Diot, None; F. Newman, None.
3414
A Validating Study of ABAS: An Atlas-based Auto-Segmentation Program for Delineation of Target Volumes in Breast and Anorectal Cancer
L. Anders, F. Stieler, K. Siebenlist, J. Schaefer, F. Wenz, F. Lohr Department of Radiation Oncology of the University Medical Center Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany Purpose/Objective(s): Rising numbers of patients in the field of radiation therapy require an optimization of the efficiency and automatism of the work process. One approach is the computer-assisted segmentation with atlas-based segmentation programs (ABAS) of clinical target volumes (CTV) and organs at risk (OAR), which automatically generate an estimate of CTV and OAR. We tested and evaluated the quality of those delineated volumes in context of treatment planning for breast and anorectal cancer. Materials/Methods: The algorithm used (Electa Software, St. Louis, MO) is based on the principle that an atlas with defined CTV serves as a template case to delineate automatically target volumes of sample patient cases. Automatic delineation results are compared with CTV‘s of breast and anorectal cancer, which are contoured manually according to guidelines of the Radio Therapy Oncology Group (RTOG). Results are quantified by analyzing the Dice Similarity Index (DSC), the logit Dice transformation (logitDSC) and Percent Overlap (PO). Dice Indices . 0.84 and logDSC . 0.750 are defined to be acceptable. Furthermore this study introduces an additional feature of the software, Staple, which is designed to improve the delineation outcome. Results: ABAS produced good results for the CTV of the breast and the rectum. However, delineations of the inguinal lymphatic flow were dissatisfying. Average DSC for CTV of the breast were between 0.86 and 0.9056 (Range [0,1]), of the average logit(DSC) between 0.7944 and 0.9889 (Range [-inf,inf]) and of the average PO between 75.5% and 82.89%. For anorectal cancer average DSC lied in between 0.7917 and 0.8467, average logit(DSC) in between 0.6083 and 0.7667 and average PO in between 68% and 73.67%. Conclusions: Generally ABAS produced satisfactory and time-saving results for the clinical target volumes of breast and anorectal cancer. In addition the introduction of Staple succeeded in enhancing the contouring outcome. Small target volumes with inaccurate definition of boundary layers are yet to be delineated manually. Author Disclosure: L. Anders, None; F. Stieler, None; K. Siebenlist, None; J. Schaefer, None; F. Wenz, None; F. Lohr, None.
3415
A Study on Conventional IMRTand RapidArc Treatment Planning Techniques for Head and Neck Cancers
S. Kumar1,2, P. Sriram1, K. Saranya1, N. Bhuvaneswari1, N. Vivekanandan1 1
Cancer Institute, Chennai, India, 2Cancer Institute, Chennai, India
Purpose/Objective(s): To evaluate the performance of volumetric arc modulation with Rapid Arc against conventional IMRT for head and neck cancers. Materials/Methods: Five patients treated with IMRT for advanced tumors of naso-, oro-, hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning has been done by means of a simultaneously integrated boost technique. A total dose of 70 Gy has been delivered to the boost volume (PTVboost) and 57.7 Gy to the elective PTV (PTVelective) in 35 equal treatment fractions. PTVboost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes whereas the PTVelective consisted of elective nodal regions. Planning has been done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam has been equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360 degree gantry rotation and double arc consists of 2 co-planar arcs of 360 degree in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45 degree to cover entire tumor which
Proceedings of the 52nd Annual ASTRO Meeting reduces tongue and groove effect during gantry rotation. All plans were generated with 6MV X-rays for CLINAC 2100 linear accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm. Results: Double arc plans show superior dose homogeneity in PTV compared to single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in Double arc technique by 4.5% when compared to IMRT (9 Field) and Single arc techniques. For healthy tissue no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V15Gy (5.81% for Single arc and 4.69% for double arc) and V20Gy (7.55% for Single arc and 5.89% for double arc) dose levels when compared to 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200 cGy per fraction was 474 ± 80 MU and 447 ± 45 MU for double arc and single arc as against 948 ± 162 MU for 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc plans shows a reduction in the parotid mean dose when compared with single Arc and IMRT plans. Conclusions: Rapid Arc using double arc proved a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The inconvenience with IMRT observed was higher monitor units and longer treatment time. Author Disclosure: S. Kumar, None; P. Sriram, None; K. Saranya, None; N. Bhuvaneswari, None; N. Vivekanandan, None.
3416
Hypofractionated Stereotactic Radiotherapy for Brain Metastases: A Dosimetric and Treatment Efficiency Comparison between Volumetric Modulated Arc Therapy and Intensity Modulated Radiotherapy
Y. Ma, J. Yu, M. Li, Y. Yin, L. Kong, X. Sun, X. Lin, Y. Yang Department of Radiation Oncology, Shandong Tumor Hospital and Institute, Jinan, China Purpose/Objective(s): A treatment planning comparison study was performed to evaluate the dosimetric characteristic and treatment efficiency of volumetric modulated arc therapy (VMAT) with step-and-shoot intensity modulated radiotherapy (IMRT) for the hypofractionated stereotactic radiotherapy (HFSRT) in patients with oligo brain metastases. Materials/Methods: CT datasets of 10 patients with two to four brain metastases were selected for the comparison. Three plans were generated for each case: step-and-shoot IMRT, single (RA1) and double (RA2) arcs with RapidArc technique (RA, Varian Medical System). The prescribed dose was 50Gy in 10 fractions and all plans were normalized to the mean dose to the PTV. For PTV, plans aim to achieve at least 95% of PTV was encompassed by the prescription dose. Dosimetric parameters including target coverage, conformity index (CI), homogeneity index (HI), maximum dose to critical structures and the volume of the healthy tissue receiving low dose were analyzed from dose-volume histogram. Additionally, we compared the monitor units and the pure beamon time to evaluate the treatment efficiency. Results: The plans generated using three techniques were acceptable clinically. The Paddick CI was 0.868 (IMRT), 0.863(RA1) and 0.895 (RA2), the HI was 7.7 (IMRT), 7.5 (RA1) and 6.5(RA2), respectively. The target conformity and homogeneity were improved slightly with RA2 compared to IMRT and RA1.Compared with IMRT, the maximum dose in RA2 plans to the brainstem, left and right optic nerves, left and right lens was reduced by 1.6Gy, 6Gy, 3Gy, 1.5Gy, 1.3Gy, respectively. The percentage of healthy tissue volume receiving 5Gy was larger with RA1 (56.7%) and RA2 (57.1%) than with IMRT (52.9%), while the percentage of volume receiving 15Gy and 20Gy were smaller with RA1 (27.1%, 18.7%) and RA2 (25%, 16.3%) than with IMRT (28.8%, 19.1%). No significantly difference was observed between RA1 and RA2. The number of MU per fraction was 1944 ± 374 (IMRT), 1199 ± 173 (RA1) and 1387 ± 186 (RA2), respectively. The pure beam-on time needed per fraction was 6.5 ± 1.2min (IMRT), 1.25 min (RA1) and 2.5 min (RA2), respectively. Conclusions: RA, single or double arcs, is a feasible technique with highly conformal dose distribution for the HFSRT in patients with oligo brain metastases. Compared with IMRT, RA1 provides similar plan quality, while RA2 provide additional improvement in sparing of OARs with slightly better PTV coverage. The treatment efficiency, using less monitor units and shorter delivery time, is the most obvious advantage. Author Disclosure: Y. Ma, None; J. Yu, None; M. Li, None; Y. Yin, None; L. Kong, None; X. Sun, None; X. Lin, None; Y. Yang, None.
3417
A Comparison of Treatment Planning Techniques for Lung Stereotactic Body Radiation Therapy
M. Michaletz-Lorenz, C. G. Robinson, D. A. Low, C. Bloch, R. J. Bertrand, A. P. Apte, D. F. Mullen, S. A. Fergus, S. M. Goddu Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): To evaluate stereotactic body radiation therapy (SBRT) treatment planning techniques for early stage nonsmall cell lung carcinoma (NSCLC) patients, using fixed beam conformal radiotherapy (FBCRT), helical tomotherapy (HT), and next generation of axial tomotherapy (AT) on a research platform. Materials/Methods: CT images and structures from 7 clinical patients previously planned and treated by FBCRT, with maximum planning target volume (PTV) dimensions from 3.0 cm-3.9 cm, were retrospectively planned with HT and AT. Prescription dose was 54 Gy in 3 fractions with 95% PTV coverage using 6 MV photons. Dosimetric constraints were largely per RTOG 0236. FBCRT was planned using 8-12 non-coplanar beams with multileaf collimation (120-MLC) on Philips Pinnacle3 RTP System. HT and AT were planned on TomoTherapy Hi-Art Planning Station using constant couch speed (HT) or fixed couch (AT), a fixed jaw setting of 1.0 cm (HT) or 5.0 cm (AT), and intensity modulating MLCs. Directional blocking was applied to avoid beamlet entry to the heart and contralateral lung. Several methods were explored with AT to best obtain PTV homogeneity and conformality, leading to an optimized pseudo-PTV with S/I extensions of 3-6 mm (original PTV was used for DVH and isodose evaluation). Of the 7 patients, 2 were excluded from AT due to tumor length exceeding axial planning software specifications. Results: The value of each result is listed in the following technique sequence: FBCRT, HT, AT. Values are reported as means ± SD. High dose PTV conformality (VRx/Vptv) was 1.17 ± .11, 1.03 ± .02, 1.23 ± .10; low dose conformality R50% (V50%Rx/ Vptv) was 5.83 ± 1.53, 4.91 ± .60. 7.06 ± .77; total lung-ITV mean dose was 4.03 ± 1.07 Gy, 3.31 ± .95 Gy; 4.44 ± 1.27 Gy
S837
S836
Volume 78, Number 3, Supplement, 2010
Materials/Methods: Ten SBRT cases were investigated retrospectively for various tumor sites, including lung, liver, spine, kidney and prostate with fraction doses ranging from 6 to 15 Gy. Single-arc (full-arc or partial arc) and/or two-arc VMAT plans were generated on CMS Monaco TPS (Version 2.03.01, CMS Inc., MO) using biologically based optimization with Monte Carlo dose calculation. HT plans were created on TomoTherapy Hi?ART planning station (Version 3.2.3.2, TomoTherapy Inc., WI) using a jaw size of 2.5 cm. DCAT plans were generated on BrainLAB radiotherapy treatment planning software (BrainSCAN, Version 5.31, Germany). Fixed field IMRT/conformal plans were developed on CMS XiO TPS (Version 4.4, CMS Inc., MO). Metrics used to evaluate the dosimetric plan quality include target coverage, heterogeneity index (HI), target mean/maximum/minimum doses, DVHs and patient mean dose. Evaluation of dose delivery efficiency and accuracy were performed using a cylindrical diode array detector system ArcCHECK (Sun Nuclear Corp., FL). Results: Both VMAT and HT are capable of providing more uniform target dose and better normal structure sparing compared to fixed field and DCAT plans. For lung SBRT, the PTV coverages are 95.9, 97 and 98.3% with HIs of 1.09, 1.08 and 1.13 respectively for the VMAT, HT and DCAT plans. For liver SBRT, the HI for HT plan is the lowest (1.04) compared to VMAT (1.06) and XiO (1.24). The target coverage of VMAT (99.6%) is slightly higher than the HT plan (97%). VMAT offers more efficient dose delivery than HT. Compared to HT treatment durations of 25, 17.9 and 7 min for the lung, liver and prostate cases, a reduction of 74%, 66% and 17% treatment times is measured for the VMAT plans. The estimated treatment time of DCAT for spine is reduced by 24.7% compared to VMAT plan, while for lung, liver and kidney cases, the treatment times of DCAT are comparable or shorter. The total MUs are 1594, 6100 and 857 for the VMAT, HT and DCAT plans for the lung SBRT; 2368, 5985 and 2921 MUs for prostate and 2864, 15360 and 1464 MUs for liver for the VMAT, HT and XiO plans respectively. Plan delivery accuracy for all the modalities was comparable with average passing rates greater than 95%. Conclusions: Single-arc VMAT improved target uniformity and normal tissue sparing compared to CMS XiO fixed field and BrainLAB DCAT plans for SBRT. In comparison to HT, VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans. Author Disclosure: X. Qi, None; A. Hu, None; W. Dzingle, None; K. Stuhr, None; H. Rice, None; Q. Diot, None; F. Newman, None.
3414
A Validating Study of ABAS: An Atlas-based Auto-Segmentation Program for Delineation of Target Volumes in Breast and Anorectal Cancer
L. Anders, F. Stieler, K. Siebenlist, J. Schaefer, F. Wenz, F. Lohr Department of Radiation Oncology of the University Medical Center Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany Purpose/Objective(s): Rising numbers of patients in the field of radiation therapy require an optimization of the efficiency and automatism of the work process. One approach is the computer-assisted segmentation with atlas-based segmentation programs (ABAS) of clinical target volumes (CTV) and organs at risk (OAR), which automatically generate an estimate of CTV and OAR. We tested and evaluated the quality of those delineated volumes in context of treatment planning for breast and anorectal cancer. Materials/Methods: The algorithm used (Electa Software, St. Louis, MO) is based on the principle that an atlas with defined CTV serves as a template case to delineate automatically target volumes of sample patient cases. Automatic delineation results are compared with CTV‘s of breast and anorectal cancer, which are contoured manually according to guidelines of the Radio Therapy Oncology Group (RTOG). Results are quantified by analyzing the Dice Similarity Index (DSC), the logit Dice transformation (logitDSC) and Percent Overlap (PO). Dice Indices . 0.84 and logDSC . 0.750 are defined to be acceptable. Furthermore this study introduces an additional feature of the software, Staple, which is designed to improve the delineation outcome. Results: ABAS produced good results for the CTV of the breast and the rectum. However, delineations of the inguinal lymphatic flow were dissatisfying. Average DSC for CTV of the breast were between 0.86 and 0.9056 (Range [0,1]), of the average logit(DSC) between 0.7944 and 0.9889 (Range [-inf,inf]) and of the average PO between 75.5% and 82.89%. For anorectal cancer average DSC lied in between 0.7917 and 0.8467, average logit(DSC) in between 0.6083 and 0.7667 and average PO in between 68% and 73.67%. Conclusions: Generally ABAS produced satisfactory and time-saving results for the clinical target volumes of breast and anorectal cancer. In addition the introduction of Staple succeeded in enhancing the contouring outcome. Small target volumes with inaccurate definition of boundary layers are yet to be delineated manually. Author Disclosure: L. Anders, None; F. Stieler, None; K. Siebenlist, None; J. Schaefer, None; F. Wenz, None; F. Lohr, None.
3415
A Study on Conventional IMRTand RapidArc Treatment Planning Techniques for Head and Neck Cancers
S. Kumar1,2, P. Sriram1, K. Saranya1, N. Bhuvaneswari1, N. Vivekanandan1 1
Cancer Institute, Chennai, India, 2Cancer Institute, Chennai, India
Purpose/Objective(s): To evaluate the performance of volumetric arc modulation with Rapid Arc against conventional IMRT for head and neck cancers. Materials/Methods: Five patients treated with IMRT for advanced tumors of naso-, oro-, hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning has been done by means of a simultaneously integrated boost technique. A total dose of 70 Gy has been delivered to the boost volume (PTVboost) and 57.7 Gy to the elective PTV (PTVelective) in 35 equal treatment fractions. PTVboost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes whereas the PTVelective consisted of elective nodal regions. Planning has been done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam has been equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360 degree gantry rotation and double arc consists of 2 co-planar arcs of 360 degree in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45 degree to cover entire tumor which
Proceedings of the 52nd Annual ASTRO Meeting reduces tongue and groove effect during gantry rotation. All plans were generated with 6MV X-rays for CLINAC 2100 linear accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm. Results: Double arc plans show superior dose homogeneity in PTV compared to single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in Double arc technique by 4.5% when compared to IMRT (9 Field) and Single arc techniques. For healthy tissue no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V15Gy (5.81% for Single arc and 4.69% for double arc) and V20Gy (7.55% for Single arc and 5.89% for double arc) dose levels when compared to 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200 cGy per fraction was 474 ± 80 MU and 447 ± 45 MU for double arc and single arc as against 948 ± 162 MU for 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc plans shows a reduction in the parotid mean dose when compared with single Arc and IMRT plans. Conclusions: Rapid Arc using double arc proved a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The inconvenience with IMRT observed was higher monitor units and longer treatment time. Author Disclosure: S. Kumar, None; P. Sriram, None; K. Saranya, None; N. Bhuvaneswari, None; N. Vivekanandan, None.
3416
Hypofractionated Stereotactic Radiotherapy for Brain Metastases: A Dosimetric and Treatment Efficiency Comparison between Volumetric Modulated Arc Therapy and Intensity Modulated Radiotherapy
Y. Ma, J. Yu, M. Li, Y. Yin, L. Kong, X. Sun, X. Lin, Y. Yang Department of Radiation Oncology, Shandong Tumor Hospital and Institute, Jinan, China Purpose/Objective(s): A treatment planning comparison study was performed to evaluate the dosimetric characteristic and treatment efficiency of volumetric modulated arc therapy (VMAT) with step-and-shoot intensity modulated radiotherapy (IMRT) for the hypofractionated stereotactic radiotherapy (HFSRT) in patients with oligo brain metastases. Materials/Methods: CT datasets of 10 patients with two to four brain metastases were selected for the comparison. Three plans were generated for each case: step-and-shoot IMRT, single (RA1) and double (RA2) arcs with RapidArc technique (RA, Varian Medical System). The prescribed dose was 50Gy in 10 fractions and all plans were normalized to the mean dose to the PTV. For PTV, plans aim to achieve at least 95% of PTV was encompassed by the prescription dose. Dosimetric parameters including target coverage, conformity index (CI), homogeneity index (HI), maximum dose to critical structures and the volume of the healthy tissue receiving low dose were analyzed from dose-volume histogram. Additionally, we compared the monitor units and the pure beamon time to evaluate the treatment efficiency. Results: The plans generated using three techniques were acceptable clinically. The Paddick CI was 0.868 (IMRT), 0.863(RA1) and 0.895 (RA2), the HI was 7.7 (IMRT), 7.5 (RA1) and 6.5(RA2), respectively. The target conformity and homogeneity were improved slightly with RA2 compared to IMRT and RA1.Compared with IMRT, the maximum dose in RA2 plans to the brainstem, left and right optic nerves, left and right lens was reduced by 1.6Gy, 6Gy, 3Gy, 1.5Gy, 1.3Gy, respectively. The percentage of healthy tissue volume receiving 5Gy was larger with RA1 (56.7%) and RA2 (57.1%) than with IMRT (52.9%), while the percentage of volume receiving 15Gy and 20Gy were smaller with RA1 (27.1%, 18.7%) and RA2 (25%, 16.3%) than with IMRT (28.8%, 19.1%). No significantly difference was observed between RA1 and RA2. The number of MU per fraction was 1944 ± 374 (IMRT), 1199 ± 173 (RA1) and 1387 ± 186 (RA2), respectively. The pure beam-on time needed per fraction was 6.5 ± 1.2min (IMRT), 1.25 min (RA1) and 2.5 min (RA2), respectively. Conclusions: RA, single or double arcs, is a feasible technique with highly conformal dose distribution for the HFSRT in patients with oligo brain metastases. Compared with IMRT, RA1 provides similar plan quality, while RA2 provide additional improvement in sparing of OARs with slightly better PTV coverage. The treatment efficiency, using less monitor units and shorter delivery time, is the most obvious advantage. Author Disclosure: Y. Ma, None; J. Yu, None; M. Li, None; Y. Yin, None; L. Kong, None; X. Sun, None; X. Lin, None; Y. Yang, None.
3417
A Comparison of Treatment Planning Techniques for Lung Stereotactic Body Radiation Therapy
M. Michaletz-Lorenz, C. G. Robinson, D. A. Low, C. Bloch, R. J. Bertrand, A. P. Apte, D. F. Mullen, S. A. Fergus, S. M. Goddu Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): To evaluate stereotactic body radiation therapy (SBRT) treatment planning techniques for early stage nonsmall cell lung carcinoma (NSCLC) patients, using fixed beam conformal radiotherapy (FBCRT), helical tomotherapy (HT), and next generation of axial tomotherapy (AT) on a research platform. Materials/Methods: CT images and structures from 7 clinical patients previously planned and treated by FBCRT, with maximum planning target volume (PTV) dimensions from 3.0 cm-3.9 cm, were retrospectively planned with HT and AT. Prescription dose was 54 Gy in 3 fractions with 95% PTV coverage using 6 MV photons. Dosimetric constraints were largely per RTOG 0236. FBCRT was planned using 8-12 non-coplanar beams with multileaf collimation (120-MLC) on Philips Pinnacle3 RTP System. HT and AT were planned on TomoTherapy Hi-Art Planning Station using constant couch speed (HT) or fixed couch (AT), a fixed jaw setting of 1.0 cm (HT) or 5.0 cm (AT), and intensity modulating MLCs. Directional blocking was applied to avoid beamlet entry to the heart and contralateral lung. Several methods were explored with AT to best obtain PTV homogeneity and conformality, leading to an optimized pseudo-PTV with S/I extensions of 3-6 mm (original PTV was used for DVH and isodose evaluation). Of the 7 patients, 2 were excluded from AT due to tumor length exceeding axial planning software specifications. Results: The value of each result is listed in the following technique sequence: FBCRT, HT, AT. Values are reported as means ± SD. High dose PTV conformality (VRx/Vptv) was 1.17 ± .11, 1.03 ± .02, 1.23 ± .10; low dose conformality R50% (V50%Rx/ Vptv) was 5.83 ± 1.53, 4.91 ± .60. 7.06 ± .77; total lung-ITV mean dose was 4.03 ± 1.07 Gy, 3.31 ± .95 Gy; 4.44 ± 1.27 Gy
S837