KEY POINTS
- This prospective single-institution phase 2 trial sub-analysis included 148 patients with early-stage breast cancer treated with breast-conserving surgery followed by single-fraction stereotactic partial breast irradiation.
- Treatment was delivered with GammaPod to 17.5 Gy in 1 fraction, prescribed to 95% of the planning target volume; the nominal dose was 18.4 Gy.
- Median follow-up was 29.9 months; 18 patients (12.1%) developed fat necrosis, including 6 patients (4.1%) with symptomatic fat necrosis.
- Cumulative fat necrosis incidence at 6, 12, 18, and 24 months was 1.4%, 6.8%, 9.5%, and 11.3%, respectively; symptomatic rates were 0.7%, 2.7%, 3.4%, and 4.6%.
- In multivariable analysis, age ≥60 years predicted overall fat necrosis — odds ratio 5.87, 95% confidence interval 1.41–24.4, p = 0.01 — and V19.3 ≥5 cc was also significant — odds ratio 5.28, p = 0.01; V19.3% was the only significant predictor of symptomatic fat necrosis.
CLINICAL TAKEAWAY
Single-fraction GammaPod partial breast irradiation was associated with a relatively low rate of fat necrosis in this selected early breast cancer cohort. The practical planning message is to control high-dose subvolumes, especially the volume receiving at least 105% of the prescription dose. The evidence is useful trial-level toxicity data, but it remains single-institution, non-randomized, and limited by non-standardized fat necrosis grading.
SOURCE
International Journal of Radiation Oncology, Biology, Physics