Radiation exposure of breast tissue in lymphoma radiotherapy: a systematic review of breast dose metrics published since 2000.

Background and purpose: We present a systematic review of breast dose metrics reported in lymphoma patients receiving radiotherapy and provide reporting recommendations for breast dose in future publications.

Methods and materials: Studies reporting breast doses in lymphoma radiotherapy published between January 2000 and May 2023 were included. Frequency of reporting factors likely to affect breast dose were calculated. Doses for the most frequently reported metrics (mean breast dose (MBD) (Gy, percentage of prescription), V5Gy and V10Gy (%)) were calculated across articles and compared for target volume approaches, radiotherapy techniques, and inclusion of the axilla.

Results: Thirty-four distinct breast dose metrics were found across 57 articles. MBD was the most commonly reported. Axilla irradiation significantly increased MBD, V5Gy and V10Gy, yet 21 articles reported breast doses for a mixed cohort with respect to axillary irradiation. Forty-eight of 57 articles did not report the breast contouring guidelines used. Among articles reporting MBD for proton or butterfly-volumetric modulated arc therapy (VMAT), there was no significant reduction in breast radiation dose for protons compared to butterfly-VMAT.

Interpretation: A wide variety of breast dose metrics are reported in the literature, making it challenging to pool breast tissue exposure data in lymphoma radiotherapy. Factors shown in individual studies to affect breast dose should be reported more systematically to enable large scale analysis. Reporting the presence/absence of axillary irradiation is crucial, due to the significant effect on breast dose. We provide reporting recommendations for breast dose metrics to improve research into radiotherapy-induced breast cancer.