Efficacy and toxicity of hyperfractionated thoracic reirradiation

Hyperfractionated reirradiation (re-RT) has been shown to mitigate late toxicity for some cancers, but data on safety and efficacy for thoracic tumors are limited.

We evaluated a cohort of 28 consecutive cases among 25 patients treated with re-RT to either primary or metastatic thoracic tumors, using 60 Gy in 50 fractions delivered twice daily. Incidence rates of toxicity, local recurrence (LR), and any disease progression were evaluated using competing risk analysis. Cumulative dose to organs at risk (OARs) was calculated (EQD2 [alpha/beta = 3]), correlated with toxicity outcomes, and compared to published constraints for re-RT.

There was direct overlap of 100 % isodose lines between treatment courses in 90.5 % of cases. Most patients had tumors abutting the proximal bronchial tree (PBT, 89 %). The median re-RT PTV volume was 67 cm³. The overall rate of ≥G2 toxicity was 46 % and the rate of ≥ G3 toxicity was 15 %. The rate of local recurrence and overall survival at 12 months was 33 % and 80 %, respectively. The lung volume receiving a cumulative dose of 20 Gy was kept under 40 % (V_{20 Gy} < 40 %) for nearly all patients (91 %). Lung V_5Gy ≥ 60 % was associated with higher rates of ≥ G2 pulmonary toxicity (69 vs. 18 %, p < 0.01). Cumulative D_max exceeded previously published constraints in most cases for the PBT (110 Gy, 57 % of cases) and great vessels (120 Gy, 52 % of cases) without observed cases of ≥G2 pulmonary hemorrhage, stenosis, fistula, or great vessel toxicity.

Hyperfractionated re-RT for thoracic tumors resulted in favorable rates of local control and toxicity in a high-risk cohort and is worthy of prospective evaluation. Putative dose constraints were not able to be met for many cases of definitive re-RT, particularly for the great vessels and PBT, without excessive observed toxicity.