KEY POINTS
- This single-institution prospective registry analysis included 176 women with unilateral, non-inflammatory breast cancer treated with conventionally fractionated postmastectomy radiotherapy: 93 with intensity-modulated proton therapy and 83 with photon radiotherapy.
- All patients received 50 Gy(RBE) in 25 fractions to the chest wall and regional lymphatics. Intensity-modulated proton therapy plans explicitly treated the superficial 3-mm skin structure as an organ at risk while maintaining skin and target coverage.
- Acute Common Terminology Criteria for Adverse Events grade ≥2 dermatitis occurred in 47% with intensity-modulated proton therapy versus 48% with photons (p=0.91). Grade 3 dermatitis occurred in 3% versus 7%, respectively (p=0.22), with no grade 4–5 events.
- Target coverage was equivalent, with median clinical target volume V95% of 97.3% for intensity-modulated proton therapy and 97.4% for photons (p=0.81). Photon plans had slightly higher skin D0.01cc, D1cc, and D10cc, although all differences were below 3%.
- Patient-reported skin outcomes were generally similar. At 12 months, skin color change was reported less frequently after intensity-modulated proton therapy than photons (6% vs 26%; p=0.04), although response rates differed between groups.
CLINICAL TAKEAWAY
Explicit skin contouring and dose optimization can prevent the excess acute dermatitis historically associated with breast proton therapy while preserving target coverage. These findings support skin-constrained intensity-modulated proton therapy planning for postmastectomy radiotherapy but remain hypothesis-generating because the comparison was nonrandomized, single-institutional, and limited to conventional fractionation.
SOURCE
International Journal of Radiation Oncology, Biology, Physics