Re-irradiation of adenoid cystic carcinoma: analysis and evaluation of outcome in 52 consecutive patients treated with raster-scanned carbon ion therapy.

Background: Treatment of local relapse in adenoid cystic carcinoma (ACC) following prior radiation remains a challenge: without the possibility of surgical salvage patients face the choice between palliative chemotherapy and re-irradiation. Chemotherapy yields response rates around 30% and application of tumouricidal doses is difficult due to proximity of critical structures. Carbon ion therapy (C12) is a promising method to minimize side-effects and maximize re-treatment dose in this indication. We describe our initial results for re-irradiation in heavily pre-treated ACC patients.

Methods: Patients treated with carbon ion therapy between 04/2010 and 05/2013 (N=52pts, median age: 54 a) were retrospectively evaluated regarding toxicity (NCI CTC v.4), tumour response (RECIST) and control rates. 48pts (92.3%) received carbon ions only, 4pts received IMRT plus C12.

Results: 4pts were treated following R1-resection, 43pts for inoperable local relapse. Most common tumour sites were paranasal sinus (36.5%), parotid (19.2%), and base of skull (17.3%). Pts received a median dose of 51GyE C12/63Gy BED and cumulative dose of 128Gy BED [67-182Gy] after a median RT-interval of 61months. Median target volume was 93ml [9-618ml]. No higher-grade (>°II) acute reactions were observed, 7pts showed blood-brain-barrier changes (°I/II: 8pts; °III: 2pts), 1 pt corneal ulceration, xerophthalmia 7pts, °IV bleeding 1 pt, tissue necrosis 2pts, otherwise no significant late reactions. Objective response rate (CR/PR) was 56.6%. With a median follow-up of 14months [1-39months] local control and distant control at 1a are 70.3% and 72.6% respectively. Of the 18pts with local relapse, 13pts have recurred in-field, 1 pt at the field edge, 3pts out of field, and one in the dose gradient.

Conclusion: Despite high applied doses, C12 re-irradiation shows moderate side-effects, response rates even in these heavily pre-treated patients are encouraging and present a good alternative to palliative chemotherapy. Though most local recurrences occur within the high-dose area, further dose escalation should be viewed with caution.