3766 - Proton Therapy for Head/Neck Adenoid Cystic Carcinoma (ACC)

I. Youssef¹, D. Kallini¹, N. Mohamed², J. J. Yoon³, K. Zakeri¹, A. Shamseddine¹, Y. Yu¹, L. Chen¹, D. Gelblum¹, S. McBride¹, N. Riaz¹, E. Sherman⁴, R. J. Wong⁵, M. Cohen⁵, I. Ganly⁵, L. Dunn², L. Michel⁴, A. Ho², and N. Y. Lee¹; ¹Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, ²Memorial Sloan Kettering Cancer Center, New York, NY, ³New York Cancer & Blood Specialists, Queens, NY, ⁴Department of Medical Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, ⁵Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): The standard of care for head/neck ACC is surgery and postoperative radiation. Definitive radiation is reserved for those with unresectable disease. Given the advantage of proton beam to tailor its dose around the tumor while sparing critical tissues, we sought to report our proton experience in the treatment of head/neck ACC. Materials/

Methods: This is a review of all head/neck ACC patients treated with proton therapy at our center from 11/12 to12/23. Included cohorts were upfront and re-irradiation cases, definitive versus adjuvant, M0 and M1 diseases. Locoregional control (LRC) and overall survival (OS) rates were estimated using the Kaplan-Meier method.
Results: Out of the 128 patients, 109 had upfront radiation, while 19 received re-irradiation. In the upfront radiation cohort, 78 patients received protons after resection, with the following T and N stages: T1(30%), T2(19%), T3(14%), T4(37%); N0(86%), N1(8%), N2(5%), N3(1%). Of the 31 patients who received definitive proton therapy, the T and N stages were: T2(6.5%), T3(6.5%) T4(87%), N0(84%), N1(10%), N2(6%). 4% versus 39% had M1 disease in the adjuvant versus definitive group (P<.001). Adjuvant versus definitive disease site breakdown: sinonasal (18 versus 19), parotid (22 versus 1), submandibular (17 versus 0), hard palate (11 versus 4), other (10 versus 7). There was less base of skull involvement in the adjuvant versus definitive group, 17% versus 61%, p<.001. Median proton dose for the adjuvant group was 66CGE (range: 59.40-76.22) and for the definitive was 70CGE (range: 14.8-76.3). 51% (N=56) received chemotherapy, the majority concurrent with cisplatin. With a median follow-up of 45 months for living patients, the 2- and 4- year LRC for adjuvant versus definitive patients were 96% and 91% versus 90% and 82%, respectively. The 2-and 4-year OS for patients receiving upfront proton therapy adjuvantly versus definitively were 92% and 90% versus 87% and 54%, respectively. 19 patients received re-irradiation [median dose 60CGE (range 14.8-70.07CGE]: 13 definitive radiation without surgery versus 6 after salvage surgery. 7 patients received Quad shot regimen (median dose 44.4CGE). In the definitive group, the rT-stages were rT3 (8%) and rT4 (92%) while 67% had rT3 disease and none had rT4 disease in the adjuvant group. 74% had BOS involvement. In the definitive, unresected group, 70% had metastatic disease, versus 50% in the adjuvant group. With a median follow-up of 44 months for all living patients, the 2 and 4-year LRC for all re-irradiated patients were 93% and 62% respectively. Of the re-irradiated patients with BOS involvement, 2-year LRC was 100% and only 3 patients had recurred at last follow-up.
Conclusion: The use of proton therapy for ACC appears favorable. High LRC was observed for patients who had definitive head/neck ACC with base of skull involvement, and even for those patients who received prior head/neck radiation.