ESTRO 2024 - Abstract Book

S3604

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Ten left-sided patients with breast cancer and lymph node irradiation (including IMN) scanned in deep inspiration breath hold (DIBH) were retrospectively selected to represent a challenging cohort with respect to dose planning. A total of 40 plans were generated. Conventional plan (CONV) and hybrid plans with three different arc geometries denoted H arc1 , H arc2 and H arc3 (Fig.1) were generated for each patient in the Varian Eclipse planning system. The hybrid plans were compared to the conventional plan in terms of dose indices for both lungs, contralateral breast, heart, CTV breast and CTV nodal .

Results:

Coverage criteria V 95% ≥ 98% for CTV breast and V 90% ≥ 98% for CTV nodal were satisfied in all four plans (Table1).

H arc3 and H arc2 resulted in reduced V 35Gy and D mean to ipsilateral lung i.e., V 35Gy (2,35 ±0,73% and 6,68±2,31% respectively) and D mean (13,03±1,34Gy and 13,72 ±1,13Gy respectively) compared to CONV (V 17Gy ; 17,35 ±5,02% and D mean ; 15,13±2,31Gy). However, H arc3 also lead to increase in V 5Gy to all OARs and increase in D mean to the heart and contralateral OARs. For heart, H arc2 achieved reduced V 35Gy (0,12±0,22Gy vs 1,59±2,07Gy), comparable D mean (3,24±1,47Gy vs 3,56±2,07Gy) and comparable V 17Gy (5,10±4,98% vs 6,04±6,11%) to CONV. For contralateral breast and lung, V5 Gy and D mean was increased in H arc3 plans and while comparable to CONV in H arc1 and H arc2 plans. Conformity and homogeneity indices (CI and HI) were improved with H arc2 (0,55±0,08 and 0,08±0,01 respectively)