Re-irradiation for locoregionally recurrent tumors of the thorax: a single-institution, retrospective study.

<bold>Background: </bold>Re-irradiation (re-RT) of the thorax is challenging due to the impact of prior therapies on normal tissues, and there are few reports of definitive re-RT. The treatment toxicities and efficacy of re-RT are not well known. The aim of the present study was to assess the safety and efficacy of definitive re-RT of the thorax.<bold>Methods: </bold>Patients who were treated with thoracic re-RT between March 2007 and December 2014 were retrospectively analyzed. Primary and re-irradiation plans were required to have an overlap of dose distributions for the 80 % isodose level. All doses were recalculated to an equivalent dose of 2 Gy per fraction (EQD2). When possible, analysis of dose accumulation was carried out using the medical image merge (MIM) (®) software program (version 6.5, MIM Software Inc., Cleveland, OH). Administration dosages for organs at risk were defined.<bold>Results: </bold>Fourteen (67 %) and seven (33 %) patients with non-small cell carcinoma (NSCLC) and small cell carcinoma (SCLC), respectively, were identified. The patients' median age was 72 (range 53-85) years. Fifteen patients (71 %) had "proximal" tumors, defined as tumors at the distal 2 cm of the trachea, carina, and main bronchi. The median interval from initial RT to re-RT was 26.8 (range 11.4-92.3) months. Re-RT was delivered by X-ray beam and proton beam therapy in 20 (95 %) patients and 1 (5 %) patient, respectively. The median radiation dose of re-RT was 60 (range 54-87.5) Gy10 and 50 (range 50.0-87.5) Gy10 for patients with NSCLC and SCLC, respectively. Grade 3 acute radiation pneumonitis occurred in only one patient. There were no other serious complications. The median follow-up time was 22.1 (range 2.3-56.4) months. The median local progression-free survival time (LPFS) and overall survival time (OS) were 12.9 (95 % confidence interval (CI): 8.9-27.9) months and 31.4 (95 % CI: 16.9-45.9) months, respectively. Patients receiving ≥ 60 Gy10 at re-RT had longer LPFS (p = 0.04).<bold>Conclusions: </bold>Good safety with longer OS than in previous reports was demonstrated. Re-RT seems to be a promising treatment option. Further study to define the risk-benefit ratios is necessary. [ABSTRACT FROM AUTHOR]