Radiation Doses to the Breast and Predicted Breast Cancer Risk Among Patients Treated for Hodgkin Lymphoma With Modern Radiation Therapy.

Purpose: To contrast breast radiation exposure from chest radiation therapy (RT) between 2006 and 2021 with those given between 1965 and 1997, and to compare breast cancer (BC) risk 25 years after treatment predicted using 2 models.

Methods And Materials: Radiation dose distributions to the breast from 101 chest RTs given from 2006 until 2021 for Hodgkin lymphoma (HL) or other lymphoma in 1 German and 2 Dutch hospitals were compared with doses received by 505 Dutch patients with HL treated from 1965 until 1997 and sampled into a nested case-control study, weighted to represent a cohort of patients with HL. Dose-volume histograms, mean dose, and doses to 10 breast segments were evaluated. Absolute BC risks 25 years after historic and recent treatments were estimated for low- and high-risk profiles (HL stage III versus I at age 24 in 2010, treatment-induced menopause at age 24 years versus none, first live birth at age 20 years versus nulliparous, BC family history no versus yes, no HL relapse, nonsmoking at HL diagnosis, exposed to anthracyclines and cardiotoxic RT).

Results: The average mean breast dose decreased from 21.4 Gy for historic to 3.0 Gy for recent treatments. The breast volume receiving ≥ 20 Gy (V) decreased from 48.7% to 2.2%, and the lowest dose to the highest exposed 20% of breast volume (D) from 39.0 Gy to 2.8 Gy. Most metrics decreased from 2006 to 2021. Using quadrant-specific doses, median absolute BC risk 25 years after treatment decreased from 21.0% to 6.9% for historic versus recent treatments for a high-risk patient and from 3.1% to 0.9% for a low-risk patient, respectively. Using mean dose, median absolute BC risks decreased from 20.3% to 6.0% and from 3.1% to 0.9% for the high- and low-risk patients, respectively.

Conclusions: Modern RT treatments expose the breast to lower radiation doses and irradiated volumes than those used before 2000. BC risk predictions using the mean breast dose were slightly lower than predictions using quadrant-specific doses.