Session Item

To report outcome of head and neck adenoid cystic carcinoma (ACC) patients (pts) treated with carbon ion RT (CIRT) at the National Center for Oncological Hadrontherapy (CNAO).

Between 2013 and 2020, 184 ACC pts (Males/Females 89/95) were treated with active CIRT. Pts median age was 54 yrs (range 20 – 87). Tumour site was minor salivary gland in 112 (61%) and major salivary gland in 72 (39%) pts. Majority of pts were naïve (71%), 53 pts (29%) were recurrent never irradiated. Definitive and postoperative RT were performed in 68 and 116 pts (63%), respectively, among these latter 85 pts (73%) had surgical positive margins (R1), and 31 (27%) macroscopical residual disease (R2). Overall, before starting CIRT 153 pts (81%) had macroscopical gross tumor volume (GTV) detected at the simulation MRI. Prescribed total dose was 65.6-68.8 Gy(RBE) in 16 fractions (4.1-4.3 Gy(RBE)/fr, 4 fr/week). Local relapse free survival (LRFS), progression free survival (PFS), overall survival (OS), and distant metastasis free survival (DMFS) were estimated by the Kaplan–Meier method and compared using the Log-rank test. Toxicity was evaluated according to the CTCAE v.4.0.

Results: With a median follow-up of 45 months (range: 7-90), 5 yrs- LRFS, OS, PFS and DMFS were 52.2%, 64.6%, 35.5% and 63%, respectively. At univariate analysis prognostic factors for both LRFS and OS were tumor site (p <0.0001 and 0.054 respectively), stage (p <0.0001 and 0.0005 respectively), and surgery before CIRT (p=0.042 and 0.042). Performance status (p<0.0001), age (p=0.006) and GTV (p<0.0001) were additional prognostic factors for OS. Interestingly, worse OS was reported for pts with any GTV at preCIRT MRI compared to macroscopically resected pts (p=0.008), with shorter OS in pts after debulking surgery and unresected pts (43% and 54% 5 yrs OS) compared to R1 postoperative pts with macroscopic disease at pre CIRT MRI (78% OS) and pts with microscopic disease (93%, p=0.014). At multivariate analysis prognostic factors for OS were large GTV volume (0cc, vs <50cc, vs >50cc, p=0.006), site (higher risk for sub-lingual glands vs others, p=0.02), stage (IV vs <IV, p=0.03) and age (risk factor, p=0.006), for LPFS stage (IV vs <IV, p=0.003) and site (higher risk for sub-lingual glands & paranasal sinuses p<0.00001). At the end of CIRT no toxicity >G3 was reported. Interestingly, higher acute toxicity was reported for the patients with tumor located at the minor salivary glands (p=0.03) and with flap reconstruction after surgery (p=0.04). Late maximum toxicity reported during follow up was G0 in 11%, G1 in 23%, G2 in 48%, G3 in 15%, G4 in 2% and G5 in 1% of the pts.

CNAO data for ACC are in line with other CIRT facilities. A multidisciplinary effort is required for better selecting pts for CIRT. Our results point out that CIRT might be offered as an alternative curative option to surgery in locally advanced cases deemed to be R2.