ESTRO 2024 - Abstract Book

S688

Clinical - Breast

ESTRO 2024

of the breast skin, D 10cc , as well as the volume receiving 48 GyRBE, V 48 , were compared between the planned dose and the Monte Carlo (MC) recomputed dose. The L 10cc , MC-computed dose-averaged LET values received by 10cc of the skin volume, as well as the R 10cc , RBE3 (α/β = 3) received by 10 cc of the skin volume, were also gathered. The correlation between dermatitis and skin dosimetry was evaluated, disregarding the original prescription.

Results:

Of 50 patients, there were 18 grade 1, 29 grade 2, and 1 grade 3 dermatitis. Two patients did not complete RT. Box plots of the dosimetric analysis are provided in Figure 1. On average, planned skin D 10cc was 47.6 +/-0.5, 49.1 +/-0.8, and 48.9 GyRBE for Grades 1, 2, and 3, respectively. MC-recomputed D 10cc were, on average, exactly 1 GyRBE hotter. Average L 10cc values were 3.2 +/-1.3, 2.7 +/-0.9, and 2.4 keV/um for Grades 1, 2, and 3, respectively. R 10cc were 50.8 +/-1.4, 52.3 +/-1.6, and 52.1 GyRBE for Grades 1, 2, and 3, respectively. While these preliminary results are based on a limited sample, none of those dosimetric metrics showed an obvious correlation to dermatitis grade. However, a clear correlation was discovered regarding the amount of skin receiving 48 GyRBE. Planned V 48 were 5.7 +/-10.2, 19.6 +/-8.2, and 106 cc for Grades 1, 2, and 3, respectively. The correlation seems less evident in MC-computed V 48 due to the greater statistical noise.

Figure 1: Box plots of dosimetric quantities as a function of dermatitis Grade.

Conclusion:

Breast skin dermatitis is a common side effect of radiation therapy for breast cancer. Among a prospective cohort of patients receiving proton therapy for breast cancer, controlling the amount of skin receiving 48 GyRBE, regardless of the initial prescription dose, may be beneficial in limiting the extent of dermatitis. This is in contrast with photon breast radiotherapy, where a correlation was found based on skin D 10cc as well as V 52.5Gy (Liang et al., 2018).

Keywords: skin dose; proton therapy; dermatitis

References:

Liang, X., Li, Z., Zheng, D., Bradley, J. A., Rutenberg, M., & Mendenhall, N. P. (2018). A comprehensive dosimetric study of monte carlo and pencil ‐ beam algorithms on intensity ‐ modulated proton therapy for breast cancer. Journal of Applied Clinical Medical Physics, 20(1), 128-136. https://doi.org/10.1002/acm2.12497