Prone to toxicity.

Top Line: Anyone who treats breast cancer can tell you the biggest predictor of radiation skin toxicity–large breasts.

The Study: The good news is these patients are easy to identify. The better news is there is a planning technique that can help. This Canadian phase 3 trial randomized 357 women with large breasts (read: a bra band ≥40 inches and/or ≥D cup) to supine versus prone whole-breast radiation. Let’s pause for a moment and touch on why prone. It produces a target with considerably less separation between medial and lateral breast tissue allowing for more homogeneous dosing (i.e., less hot spots in the usual suspects of axilla or inframammary fold). The primary outcome of moist desquamation was significantly more common after supine (40%) versus prone (27%) treatment. The impact of positioning was again demonstrated in multivariable analysis with supine positioning having double to odds (OR, 1.99) of producing moist desquamation, along with other predictable factors such as bra size (OR 2.56), use of a boost (OR 2.71), and, once again, conventional fractionation (OR 2.85). Note: 50Gy/25 was used until 2016 and 42.5Gy/16 thereafter.

TBL: Women with large breasts have less toxicity with prone positioning (and hypofractionation) when receiving whole breast radiation. | Vesprini, JAMA Oncol 2022