ESTRO 2025 - Abstract Book

S578

Clinical - Breast

ESTRO 2025

Conclusion: These prospective data confirm that retropectoral IIBR does not delay the initiation of adjuvant treatments, and the rate of reconstruction failure remains low after PMRT with Tomotherapy. Keywords: Implant breast reconstruction, breast Tomotherapy

References: a Kaidar-Person O, Radiother Oncol. 2019 Aug;137:159-166. doi: 10.1016/j.radonc.2019.04.010

3477

Digital Poster DOSIMETRIC COMPARISON OF ESTRO VS. RTOG TARGET DELINEATION FOR BREAST CANCER: IMPLICATIONS ON ORGANS AT RISK. SAUMYARANJAN MISHRA 1 , TAPAS KUMAR DASH 2 , SULAGNA MOHANTY 2 , CHINMAYA BEHERA 2 , SHYAM SINGH BISHT 3 1 RADIATION ONCOLOGY, SADGURU CANCER HOSPITAL, CUTTACK, India. 2 RADIATION ONCOLOGY, ACHARYA HARIHAR POST GRADUATE INSTITUTE OF CANCER, CUTTACK, India. 3 RADIATION ONCOLOGY, MEDANTA, THE MEDICITY, GURGAON, India Purpose/Objective: Regional nodal irradiation (RNI) is gaining momentum as breast surgeries become more conservative. Due to the convex shape of the thoracic wall, target delineation plays a crucial role in radiation dose to organs at risk (OAR). We intend to analyze the doses to OAR and target coverage based on target delineation according to the two most commonly used guidelines: ESTRO and RTOG. Material/Methods: This is an observational prospective comparative study. Twenty breast cancer patients were included, of whom 15 were post-modified radical mastectomy, and 5 had breast conservation surgery. Each patient had two plans made by delineating according to both RTOG and ESTRO contouring guidelines. All patients were planned with the IMRT technique However, treatment was carried out following the institutional standard protocol. Differences in dose volume relationships of organs at risk (heart, lungs, contralateral breast) were analyzed between the two plans. Results: There was a significant difference in PTV volumes for both primary and nodal PTVs, with ESTRO PTV volumes being significantly smaller compared to RTOG PTVs. The mean PTV volumes for chest wall irradiation are 766 cc versus 1020.5 cc (p-value 0.002) as per ESTRO versus RTOG contouring guidelines. For whole breast irradiation, the mean PTV volumes are 1285 cc versus 1428 cc (p-value 0.04) according to ESTRO versus RTOG contouring. Our study has shown significant dose reductions in the ESTRO plan compared to the RTOG plan in the ipsilateral lung (V5, V20, Dmean), heart (V10, Dmean), spinal cord (Dmax),. In heart all the substructures ( LAD, left circumflex artery, atria, ventricles) are getting significantly lesser dose in ESTRO contouring. However, there was no significant dose reduction in the contralateral lung and contralateral breast . The CTV nodal coverage was significantly improved with ESTRO guidelines compared to RTOG. This improvement is probably due to the smaller volume of the ESTRO target. There was no difference in target coverage of the chest wall or breast PTV. Conclusion: Target delineation based on ESTRO guidelines results in better nodal coverage with a reduced dose to the ipsilateral lung, heart, spinal cord, and esophagus compared to RTOG guideline-based contouring. This reduction is primarily due to the smaller target volume in the ESTRO guidelines. This will have evident clinical implications in reducing clinical toxicity. However, the implications of the reduced volume are uncertain in locally advanced disease with a high nodal burden, warranting further clinical studies in such cases. Keywords: RTOG, ESTRO CONTOURING