Session Item

Dose conformality and homogeneity is commonly obtained in breast field-in-field (FIF) 3D-CRT but large and pendulous breasts can be challenging due to large inframammary fold and lateral displacement. This affects the risk of toxicity and organs at risk (OARs) doses. This study aimed to evaluate the geometric and dosimetric effects of a radiation bra during radiotherapy for large and pendulous breasts.

Between October 2021 and September 2022, 8 breast cancer patients underwent 2 CTs (without (NB) and with bra (WB)) to evaluate the impact of radiation bras. According to the patient’s chest and cup , a suitable bra was selected. Using FIF 3D-CRT, 6 of them were planned with the FAST-forward (FFW) schedule and 2 with the 42.4 Gy/16 fractions hypo-fractionated scheme. Measured parameters included the nipple-to-pectoral muscle distance (NPD), the maximum mediolateral thickness (MLT) along tangential fields, target coverage, its conformity (CI), and homogeneity indexes (HI). The evaluated OARs were the ipsilateral lung and the heart. The setup reproducibility has been evaluated through a daily pre-treatment CBCT.

The bra sizes ranged from 4 to 10 with optimal patient compliance. The bra provided a decrease in the median NPD (NB 8.0 cm; WB 7.3 cm) with a similar median MLT (NB 25.3 cm; WB 25 cm). While the target coverage was maintained (V95%: NB 98.9%; WB 99.4%), the median volume of the 105% and 107% isodoses NB and WB was 13.0 cm³ and 0.2 cm³, and 0.5 cm³ and 0.0 cm³, respectively. This led to a 0.6 median CI value for both NB and WB and a slight HI improvement (NB 0.09; WB 0.07). Although not clinically significant, a slight increase in lung doses was registered in WB plans. Heart doses did not registered any relevant variation. WB plans were successfully delivered with a daily pre-treatment CBCT correction. Only 1 patient registered a significant weight loss undermining the bra effectiveness. Having an acceptable NB plan, the delivery was terminated with it. A second CBCT was needed to verify the bra setup that was corrected in 23 out of 46 fractions. The final x, y, and z translational corrections registered a median value of -0.2, 0.5, and -0.2 cm, respectively. No acute toxicities have been registered.

The bra implementation was associated with improved geometric and dosimetric planning parameters: higher and properly positioned breasts guaranteed reduced hot spots. In particular, it could offer the FFW schedule to patients whose breast volume would not permit a sufficient dose homogeneity. A higher number of patients will allow the definition of the best cut-off parameters in the choice to use the bra and confirm its dosimetric impact. Nowadays, daily imaging is mandatory but higher expertise in repositioning could avoid the need of a second CBCT. The clinical follow-up will give a critical feedback on the opportunity to reduce toxicities thanks to a more homogeneous dose distribution.