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Robust Lymph Nodes Proton Scanning Irradiation for Locally Advanced Breast Cancer
E682
International Journal of Radiation Oncology Biology Physics
hypofractionated regimens, which may ultimately redefine the standard of care for this select patient population. Author Disclosure: C. Geady: None. B.M. Keller: None. M.E. Ruschin: None. E. Hahn: None. N. Makhani: None. S. Bosnic: None. D. Vesprini: None. H. Soliman: None. J. Lee: None. C. McCann: None.
Purpose/Objective(s): There is a multi-institutional trial investigating the potential benefit of reducing the heart dose using proton therapy in comparison to photon radiation therapy for women with breast cancer, specifically when internal mammary lymph nodes (IMN) are irradiated. This study evaluated planning techniques for scanning proton beam therapy to generate robust coverage for breast and nodal irradiation. Materials/Methods: Two left-sided breast cancer patients were included: 1 postmastectomy chest wall (CW) and 1 postlumpectomy intact breast (WB). Clinical target volumes (CTVs) included CW/WB and supraclavicular, axillary, and IMN. Both conventional and robust optimizations were used for treatment planning. For each optimization, 3 plans were calculated: a single en-face field (1F), 2 fields with single field optimization (2F SFO), and the same 2 fields with multiple field optimization (2F MFO). For conventional optimization (Con Opt), proton-specific PTVs were designed to account for both range and setup uncertainties. For robust optimization (Rob Opt), plans were created based on CTVs, and PTVs were not used. The prescription was 50.4 Gy (RBE). For all plans, 95% of the total CTVs’ volumes received at least 50.4 Gy. Robustness was evaluated for 12 scenarios, which were combinations of 6 isotropic setup errors of 5 mm and +/- 3.5% range uncertainty. For WB/CW, the average values of nominal dose (ND) and the range of uncertainty doses (UD) are reported for D95% and V95%. For IMN, because of its small volume, D99% and V95% are reported. Heart mean dose and ipsilateral lung V20Gy are also reported. Results: The volumes for CW/WB and IMN were 513 mL and 4 mL. Small variations were shown for the uncertainty doses of CW/WB coverage: D95%Z50.5 Gy (49.3-50.8 Gy); V95%Z100% (98.2-100%). The coverage for IMN can be subject to large uncertainties for conventional optimization. The minimum dose for D99 was maintained above 45 Gy for 2F SFO plans, whereas it was below 45 Gy for 1F and 2F MFO plans. Robust optimization effectively reduced uncertainties for IMN coverage for all three types of plans (Table). The average heart mean doses were 0.5 Gy for both conventional and robust optimized plans. Ipsi-lateral lung V20Gy was 17.5% for conventional optimized plans and 14% for robust optimized plans. Conclusion: Dose coverage for large volume structures, in this case WB/ CW, was robust for all evaluated plans and scenarios. Dose coverage for small volume structures located at a heterogeneous interface, in this case IMN nodes, can be subject to large uncertainties for conventional optimization, with 2F SFO being the most robust configuration. Robust optimization effectively reduced uncertainties for IMN coverage and allowed the safe use of MFO, meanwhile maintaining similar OAR doses.
3670 A VMAT Quality Assurance Technique Based on EPID in Cine Mode for Large Field Gynecological Cancer Radiation Therapy Q. Wu,1 O. Craciusnescu,1 B. Liang,2 K. Light,3 I. Vergalasova,3 B. Liu,2 and F. Zhou2; 1Duke University, Durham, NC, 2Beihang University, Beijing, China, 3Duke University Medical Center, Durham, NC Purpose/Objective(s): Radiation therapy (RT) for gynecological cancers is challenging because gross tumors and electively treated lymph nodes included in the target volume are usually large and their shapes are concave. Intensity modulated RT has been used in the practice with excellent dose coverages to target and sparing of nearby critical organs, at the cost of large number of fields (>10) and extended treatment time. Recently, the volumetric modulated arc therapy (VMAT) technique has been developed to provide equivalent dose distributions with only 2-3 arcs and much shorter treatment time. The field size used is typically larger than 3030 cm2 and exceeds the maximum dimension allowed by the commercial quality assurance (QA) systems. The purpose of this study is to develop an EPIDbased QA technique that can handle a large VMAT field. Materials/Methods: The VMAT plan is delivered on a medical linear accelerator with MV imager operated in Cine mode. The acquired images are converted to portal dose after calibration and 2D profile correction. The gantry and MU index information encoded in the header of each image are used to extract a subarc from the original arc and the corresponding portal dose is calculated. By stacking up all these frames, a 3D matrix can be constructed with the third axis representing gantry angle. Subsequently 3D g-analysis can be performed between the predicted and measured matrices. The EPID has a resolution of 0.80.8 mm2. Depending on the version of MV imager, field size up to 4030 or 4040 cm2 can be verified. An integrated PD analysis without gantry angle information was compared. Measurements were performed for 38 arcs from 13 patient plans. Photon energies of 6X, 10X, and 15X were used in the plan depending on the patient geometry. Results: In the PD analysis, criteria of 3% in dose difference, 3 mm in distance to agreement, and 5% in threshold were chosen, resulting in (98.61.2)% for the pass rate of g>1.0. In comparison, our 3D analysis has the pass rate of (95.53.9)%, with the additional criteria of 3 in gantry angle to agreement. By projecting the 3D matrix along each main axis, our analysis can be reduced to 3 2D analyses, with one mimicking the PD analysis when the 3D matrix collapses along the gantry angle, with a result of (97.13.6)%. Results on other 2 planes are (98.91.1)% and (98.51.4)%, respectively. Additional criteria can be chosen to diagnose potential treatment abnormalities. Conclusion: We have developed an EPID-based QA technique for VMAT and demonstrated that it can be used in the RT of gynecological cancers with large field sizes that cannot be verified fully by the commercial systems. The 3D g-analysis provides rich information on the treatment delivery, especially along the gantry angle rotation that distinguishes VMAT from IMRT. It has a sub-mm resolution and an efficient operation process that is less prone to setup errors. Author Disclosure: Q. Wu: None. O. Craciusnescu: None. B. Liang: None. K. Light: None. I. Vergalasova: None. B. Liu: None. F. Zhou: None.
3671 Robust Lymph Nodes Proton Scanning Irradiation for Locally Advanced Breast Cancer J. Yu,1 K.M. Langen,1 M.P. Mehta,2 E.M. Nichols,1 and S.J. Feigenberg3; 1 University of Maryland School of Medicine, Baltimore, MD, 2Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 3University of Maryland Medical Center, Baltimore, MD
Abstract 3671; Table 1. 2F SFO
IMN D99%, Gy Con Rob IMN V95%, % Con Rob
Opt Opt Opt Opt
1F
2F MFO
ND
UD
ND
UD
ND
UD
50.1 50.5 100 100
45.2 -50.2 45.9 -50.6 84 -100 96 - 100
49.6 50.7 100 100
40.9 -50.2 48.9 -51.6 68.3 -100 96 - 100
50.0 50.6 100 100
43.8 -49.9 47.6 -50.5 59.9 - 100 98 - 100
Author Disclosure: J. Yu: None. K.M. Langen: None. M.P. Mehta: None. E.M. Nichols: None. S.J. Feigenberg: None.
3672 Cardiac Toxicity From Proton Radiation Therapy of Left-Sided Breast Cancer: LET and RBE Considerations D. Giantsoudi,1 N. Depauw,1 H. Paganetti,2 and S. MacDonald2; 1 Massachusetts General Hospital, Harvard Medical School, Boston, MA, 2 Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Increased risk of coronary heart disease has been correlated with mean cardiac radiation doses as low as 2.0 Gy(RBE). Proton postmastectomy radiation therapy (PMRT) for left-sided breast cancer can significantly decrease the cardiac irradiation doses. Currently constant proton relative biological effectiveness (RBE) is assumed without
International Journal of Radiation Oncology Biology Physics
hypofractionated regimens, which may ultimately redefine the standard of care for this select patient population. Author Disclosure: C. Geady: None. B.M. Keller: None. M.E. Ruschin: None. E. Hahn: None. N. Makhani: None. S. Bosnic: None. D. Vesprini: None. H. Soliman: None. J. Lee: None. C. McCann: None.
Purpose/Objective(s): There is a multi-institutional trial investigating the potential benefit of reducing the heart dose using proton therapy in comparison to photon radiation therapy for women with breast cancer, specifically when internal mammary lymph nodes (IMN) are irradiated. This study evaluated planning techniques for scanning proton beam therapy to generate robust coverage for breast and nodal irradiation. Materials/Methods: Two left-sided breast cancer patients were included: 1 postmastectomy chest wall (CW) and 1 postlumpectomy intact breast (WB). Clinical target volumes (CTVs) included CW/WB and supraclavicular, axillary, and IMN. Both conventional and robust optimizations were used for treatment planning. For each optimization, 3 plans were calculated: a single en-face field (1F), 2 fields with single field optimization (2F SFO), and the same 2 fields with multiple field optimization (2F MFO). For conventional optimization (Con Opt), proton-specific PTVs were designed to account for both range and setup uncertainties. For robust optimization (Rob Opt), plans were created based on CTVs, and PTVs were not used. The prescription was 50.4 Gy (RBE). For all plans, 95% of the total CTVs’ volumes received at least 50.4 Gy. Robustness was evaluated for 12 scenarios, which were combinations of 6 isotropic setup errors of 5 mm and +/- 3.5% range uncertainty. For WB/CW, the average values of nominal dose (ND) and the range of uncertainty doses (UD) are reported for D95% and V95%. For IMN, because of its small volume, D99% and V95% are reported. Heart mean dose and ipsilateral lung V20Gy are also reported. Results: The volumes for CW/WB and IMN were 513 mL and 4 mL. Small variations were shown for the uncertainty doses of CW/WB coverage: D95%Z50.5 Gy (49.3-50.8 Gy); V95%Z100% (98.2-100%). The coverage for IMN can be subject to large uncertainties for conventional optimization. The minimum dose for D99 was maintained above 45 Gy for 2F SFO plans, whereas it was below 45 Gy for 1F and 2F MFO plans. Robust optimization effectively reduced uncertainties for IMN coverage for all three types of plans (Table). The average heart mean doses were 0.5 Gy for both conventional and robust optimized plans. Ipsi-lateral lung V20Gy was 17.5% for conventional optimized plans and 14% for robust optimized plans. Conclusion: Dose coverage for large volume structures, in this case WB/ CW, was robust for all evaluated plans and scenarios. Dose coverage for small volume structures located at a heterogeneous interface, in this case IMN nodes, can be subject to large uncertainties for conventional optimization, with 2F SFO being the most robust configuration. Robust optimization effectively reduced uncertainties for IMN coverage and allowed the safe use of MFO, meanwhile maintaining similar OAR doses.
3670 A VMAT Quality Assurance Technique Based on EPID in Cine Mode for Large Field Gynecological Cancer Radiation Therapy Q. Wu,1 O. Craciusnescu,1 B. Liang,2 K. Light,3 I. Vergalasova,3 B. Liu,2 and F. Zhou2; 1Duke University, Durham, NC, 2Beihang University, Beijing, China, 3Duke University Medical Center, Durham, NC Purpose/Objective(s): Radiation therapy (RT) for gynecological cancers is challenging because gross tumors and electively treated lymph nodes included in the target volume are usually large and their shapes are concave. Intensity modulated RT has been used in the practice with excellent dose coverages to target and sparing of nearby critical organs, at the cost of large number of fields (>10) and extended treatment time. Recently, the volumetric modulated arc therapy (VMAT) technique has been developed to provide equivalent dose distributions with only 2-3 arcs and much shorter treatment time. The field size used is typically larger than 3030 cm2 and exceeds the maximum dimension allowed by the commercial quality assurance (QA) systems. The purpose of this study is to develop an EPIDbased QA technique that can handle a large VMAT field. Materials/Methods: The VMAT plan is delivered on a medical linear accelerator with MV imager operated in Cine mode. The acquired images are converted to portal dose after calibration and 2D profile correction. The gantry and MU index information encoded in the header of each image are used to extract a subarc from the original arc and the corresponding portal dose is calculated. By stacking up all these frames, a 3D matrix can be constructed with the third axis representing gantry angle. Subsequently 3D g-analysis can be performed between the predicted and measured matrices. The EPID has a resolution of 0.80.8 mm2. Depending on the version of MV imager, field size up to 4030 or 4040 cm2 can be verified. An integrated PD analysis without gantry angle information was compared. Measurements were performed for 38 arcs from 13 patient plans. Photon energies of 6X, 10X, and 15X were used in the plan depending on the patient geometry. Results: In the PD analysis, criteria of 3% in dose difference, 3 mm in distance to agreement, and 5% in threshold were chosen, resulting in (98.61.2)% for the pass rate of g>1.0. In comparison, our 3D analysis has the pass rate of (95.53.9)%, with the additional criteria of 3 in gantry angle to agreement. By projecting the 3D matrix along each main axis, our analysis can be reduced to 3 2D analyses, with one mimicking the PD analysis when the 3D matrix collapses along the gantry angle, with a result of (97.13.6)%. Results on other 2 planes are (98.91.1)% and (98.51.4)%, respectively. Additional criteria can be chosen to diagnose potential treatment abnormalities. Conclusion: We have developed an EPID-based QA technique for VMAT and demonstrated that it can be used in the RT of gynecological cancers with large field sizes that cannot be verified fully by the commercial systems. The 3D g-analysis provides rich information on the treatment delivery, especially along the gantry angle rotation that distinguishes VMAT from IMRT. It has a sub-mm resolution and an efficient operation process that is less prone to setup errors. Author Disclosure: Q. Wu: None. O. Craciusnescu: None. B. Liang: None. K. Light: None. I. Vergalasova: None. B. Liu: None. F. Zhou: None.
3671 Robust Lymph Nodes Proton Scanning Irradiation for Locally Advanced Breast Cancer J. Yu,1 K.M. Langen,1 M.P. Mehta,2 E.M. Nichols,1 and S.J. Feigenberg3; 1 University of Maryland School of Medicine, Baltimore, MD, 2Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 3University of Maryland Medical Center, Baltimore, MD
Abstract 3671; Table 1. 2F SFO
IMN D99%, Gy Con Rob IMN V95%, % Con Rob
Opt Opt Opt Opt
1F
2F MFO
ND
UD
ND
UD
ND
UD
50.1 50.5 100 100
45.2 -50.2 45.9 -50.6 84 -100 96 - 100
49.6 50.7 100 100
40.9 -50.2 48.9 -51.6 68.3 -100 96 - 100
50.0 50.6 100 100
43.8 -49.9 47.6 -50.5 59.9 - 100 98 - 100
Author Disclosure: J. Yu: None. K.M. Langen: None. M.P. Mehta: None. E.M. Nichols: None. S.J. Feigenberg: None.
3672 Cardiac Toxicity From Proton Radiation Therapy of Left-Sided Breast Cancer: LET and RBE Considerations D. Giantsoudi,1 N. Depauw,1 H. Paganetti,2 and S. MacDonald2; 1 Massachusetts General Hospital, Harvard Medical School, Boston, MA, 2 Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Increased risk of coronary heart disease has been correlated with mean cardiac radiation doses as low as 2.0 Gy(RBE). Proton postmastectomy radiation therapy (PMRT) for left-sided breast cancer can significantly decrease the cardiac irradiation doses. Currently constant proton relative biological effectiveness (RBE) is assumed without