ESTRO 2021 Abstract Book

S1327

ESTRO 2021

Purpose or Objective Postmastectomy radiotherapy (PMRT) with TomoHelical TM (TH) or TomoDirect TM (TD) allows a uniform target coverage. In this study, we compare locoregional treatment plans using TD and TH in the setting of hypofractionated PMRT and immediate breast reconstruction. Materials and Methods The TD-treatment plans of breast cancer patients treated between May 2016 and August 2019 were retrospectively selected. All the TD plans were re-planned on TH with the same prescription dose (40.05 Gy/15 fractions) and according to our dose/volume constraints. Data about the 2 treatment plans were collected with a focus on PTV coverage and all the organ at risk (OARs) constraints. Results Fifty patients for a total number of 100 treatment plans (50 with TD and 50 re-calculated with TH) were analyzed. All the median value in the TD PTV CHEST WALL plans fulfilled the predefined planning objectives, even though TH emerged as best for target coverage with statistically significant difference for V90%, D 0.03 cm3, V107% and Dmax (Table 1). Overall TD reached the best statistically sparing of the OARs with the main differences with TH for the low doses of the ipsilateral (V16Gy, V8Gy, V4Gy) and contralateral lung (V4Gy) and Dmax of the contralateral breast (Figure1). All the other dose values for TH were higher than TD, but they fulfilled the recommended/acceptable predefined planning objectives. Table 1. Comparison of PTV dosimetry for TomoDirect TM (TD) and TomoHelical TM (TH)

Figure 1. Median dose-volume histogram of chest wall planning target volume (a), supraclavivular planning target volume (b) and organ at risks by type of TomoTherapy: TomoHelical TM (solid lines) versus TomoDirect TM (dotted lines).