Prone to good outcomes.

This large single-institution series of 5-fraction accelerated partial breast irradiation (APBI) describes outcomes for patients treated mainly using prone positioning as opposed to supine positioning used in most of the EBRT APBI trials. Over 300 patients with mostly invasive, T1 breast cancer were treated prone using opposed tangent fields from 2010 to 2019. They used a 1.5 cm PTV margin from the lumpectomy cavity excluding 6 mm from the skin surface. This was prescribed 30 Gy in 5 fractions covering 95% of the target. Of note, two-thirds of patients were treated on consecutive days. The ipsilateral breast constraints were V50% < 60% and V100% < 35%. The average actual ipsilateral V50% was 41% and the average V100% was 20.3%. Both metrics, on average, were slightly lower with prone versus supine positioning. At 5 years median follow-up, the IBTR rate was 2.1% with most of those occurring outside the original quadrant. The rate of acute grade 1-2 skin toxicity was 35% with no grade 3 toxicity. | Shah, Pract Radiat Oncol 2021