Abstract book - ESTRO meets Asia

S79 ESTRO meets Asia 2018

Purpose or Objective Radiation treatment to the left breast is associated with increased cardiac morbidity and mortality. This study aims to evaluate the reduction of cardiac radiation dose with voluntary inspiration breath-hold (VIBH) technique compared to free breathing (FB) in patients with left- sided breast cancer. It also aims to identify predictors of patients who are associated with more benefit with VIBH. Material and Methods Twenty-six patients with left-sided breast cancer (22 post-breast conservative surgery (BCT) and 4 post- mastectomy(M)) underwent VIBH and FB planning computed tomography scans, and the 2 plans were compared. Cardiac shields were used in the post- BCT plans if necessary, provided that clinical treatment volume coverage was not compromised, while chest wall coverage took priority in post-M plans. The single- isocenter conformal fields in the field treatment plans were generated with the Eclipse Treatment Planning System (Varian Medical Systems) for both FB and DIBH images. The prescribed dose was 40Gy in 15 fractions for the whole breast or the chest wall. Dose volume histogram parameters for heart, lung and optimized planning target volume (OPTV) were compared between VIBH and FB. The impact of VIBH was compared in post- BCS and post-M patients using Wilcoxon signed rank test. Results Dose conformity and PTV coverage were similar with VIBH and FB. When compared with FB, VIBH resulted in a significant reduction of mean cardiac dose from 3.18+/- 1.51 to 1.61+/-0.63Gy (p<0.0001). The relative heart volume irradiated with 20Gy-40Gy was consistently reduced. 71% patients had an absolute reduction of mean heart dose by 1Gy with VIBH. VIBH decreased the mean heart dose by 2.62Gy (3.88 vs. 1.26Gy; p=0.03) in post-M group, and 1.38Gy (3.06 vs. 1.68Gy; p<0.0001) in post-BCT group. Differences between FB and VIBH-derived lung V18Gy (19.67 vs. 20.69Gy, p=0.83) were non-significant. On multivariate analysis, age, body weight and use of chemotherapy were not associated with differences in mean heart dose. Conclusion VIBH demonstrated significant reduction of cardiac doses without compromising the target volume coverage. Differences in lung doses were non-significant. Although VIBH provides a better treatment outcome with lower cardiac dose compared with FB, VIBH is more time consuming and requires patient's cooperation. In centres where VIBH availability is limited, VIBH is more preferably used in post-M patients than post-BCT patients as cardiac shields are more readily applicable in post-BCT patients. PO-196 Evaluation of Target volume coverage by Conventional vs RTOG contouring based plans in breast cancer P. Verma 1 , K. Sahni 1 , M. Rastogi 1 , S.S. Nanda 1 , R. Khurana 1 , R. Hadi 1 , S. Sapru 1 , A.K. Gandhi 1 , S. Farzana 1 , A. Shrivastava 1 , S.P. Mishra 1 , A. Bharti 1 , N. Agarwal 1 , A.P. Singh 1 , S. Das 1 , S. Manna 1 1 Ram Manohar Lohia Institute of Medical Sciences, Radiation Oncology, Lucknow U.P, India Purpose or Objective Irradiation in breast cancer has undergone spectral changes from conventional two-dimensional anatomical landmarks based planning to soft tissue/vessel based radiation therapy oncology group (RTOG) contouring guideline based planning. Bony landmarks used for conventional field boundaries have often little anatomical correlation with the draining lymphatics. Therefore, an evident need exists to optimize plans based on existing delineation guidelines. In this study, we have evaluated the differences in dosimetric parameters to the organs at risks (OARs) and target volumes in patients treated with

conventional plans vis-à-vis RTOG contour guided target volum- based treatment plans. Material and Methods 30 patients of histopathologically proven infiltrating ductal carcinoma breast, with performance status ≥80, age 18-80 years including both mastectomy and breast conservation surgery (BCS) with indication for post- operative RT, were enrolled in this prospective observational cohort study with approval from institutional ethics committee. Patients were treated conventional treatment plans with 50 Gray in 25 fractions with additional 10 Gray in 5 fraction boost in BCS patients. Further, RTOG consensus guidelines were used to contour the breast/chest wall, level I, II and III axillary nodes, supraclavicular fossa (SCF) and internal mammary node (IMN). OARs contoured included heart, ipsilateral (I/L) and contralateral (C/L) lungs, C/L breast, esophagus and spinal cord. Dose volume histograms (DVHs) for these contours were generated from conventional treatment plans. Further new treatment plans were generated based on RTOG target volumes intended to cover > 90% PTV by 90% of isodose line. DVH parameters of the 2 set of plans were compared using paired t test. A p value of < 0.05 was considered statistically significant. Results Patient characteristics have been enunciated in table 1. The mean volume of breast/chest wall PTV covered by 90% isodose line (V90) was better with RTOG plan as compared to conventional plan (93.39 ± 3.51 vs 90.39 ± 4.21, p=0.001). Similarly mean V90 for total axilla (97.44 ± 2.92 vs 90.39 ± 9.17, p=0.0001) and combined PTV (92.60 ± 3.53 vs 88.81 ± 4.54,p=0.0001) was better with RTOG plan. As for OARs, conventional vs RTOG Dmean for heart was 2.56 ± 1.31 vs 2.60 ±1.42 (Gy) (p=0.63) and V5Gy for heart was 7.08 ± 5.83 vs 7.38 ± 6 (%) (p=0.15) respectively. For conventional Vs RTOG plans I/L lung V20Gy 28.77 ± 6.31 vs 28.94 ± 5.21(%) (p=0.71) and V5Gy for C/L breast was 0.48 ± 1.22 vs 0.54 ± 1.25 (p=0.47) respectively.

Conclusion Our study showed RTOG guideline-based target volumes had inferior coverage with conventional plans. On the contrary 3D-CRT plans directed at RTOG contours provide statistically significant better coverage for target volumes with non-significant increase in dose to the OARs.