KEY POINTS
- This secondary RadComp analysis included 1,160 patients receiving comprehensive breast or chest-wall and regional nodal irradiation: 586 were treated with protons and 574 with photons.
- Mean whole-heart dose was substantially lower with protons at 0.89 Gy(RBE) versus 2.99 Gy with photons (p<0.001). Mean doses to the left ventricle, left atrium, and left anterior descending artery were also significantly reduced.
- Mean left anterior descending artery dose was 0.98 Gy(RBE) with protons versus 4.53 Gy with photons, while the volume receiving at least 5 Gy was 2.09% versus 32.08%, respectively.
- Protons did not reduce every cardiac dose metric. Whole-heart D0.03cm³ was higher with protons (44.66 vs 27.37 Gy[RBE]), as was maximum heart dose (47.29 vs 30.84 Gy[RBE]), reflecting high-dose regions near the chest wall.
- Median PROMIS fatigue increased from 49 at baseline to 55 at treatment completion, then returned to 49 at six months. The change was statistically significant but small and transient.
- Shortness-of-breath scores remained broadly stable: 88% reported grade 0–1 severity at baseline and 86% at six months. Grade ≥3 symptoms were uncommon across all evaluated measures, occurring in no more than 5.5% of participants.
- No whole-heart or cardiac-substructure dose metric was significantly associated with fatigue, shortness of breath, chest pain, chest tightness, or angina during the first six months, including analyses stratified by treatment modality or laterality.
CLINICAL TAKEAWAY
Protons clearly reduced average cardiac exposure, especially to left-sided structures, but this did not produce a measurable early patient-reported benefit. Six-month symptoms are neither sufficiently specific nor sufficiently late to answer RadComp’s central question of whether protons reduce major cardiovascular events.
SOURCE
International Journal of Radiation Oncology, Biology, Physics