ESTRO 2023 - Abstract Book

S70

Saturday 13 May

ESTRO 2023

was estimated in a subset of 102 patients included in a previously-published randomized controlled trial testing stem cell sparing RT(1). Next, for each endpoint D func,PG , dose to other organs and clinical factors were used to develop multivariable NTCP models in 663 patients. Finally, these models were validated in the remaining 350 patients. Results Dose to contralateral PG (sub)structures was significantly associated with patient-rated daytime, eating-related and physician-rated grade ≥ 2 xerostomia. No associations with patient-rated general, activity-related and nighttime xerostomia were found.The estimations of r were smaller than 3.6 for most xerostomia endpoints (Table 1), demonstrating that D mean,PG underestimates the contribution of dose to the SCR region to the risk of xerostomia. The most-frequently additional risk factors identified in multivariable modeling were pretreatment xerostomia and D mean oral cavity (Table 1). The models showed moderate-to-good discrimination and calibration after internal and external validation (Table 2).

Conclusion We developed a new dose metric to account for the larger contribution of dose to the stem cell rich region to the risk of xerostomia. This new dose metric was subsequently used to develop novel multivariable models that can be used for the routine implementation of stem cell sparing RT. (1) Steenbakkers, RJHM et al. Parotid Gland Stem Cell Sparing Radiation Therapy for Patients with Head and Neck cancer: A Double-Blind Randomized Controlled Trial. Int. J. Radiat. Oncol. 112, 306-316 (2022). OC-0110 Head and neck adenoid cystic carcinoma treated with raster scanning carbon ion radiotherapy at CNAO B. Vischioni 1 , M. Bonora 2 , S. Ronchi 1 , R. Ingargiola 2 , A.M. Camarda 2 , S. Molinelli 3 , S. Imparato 4 , F. Fiorino 5 , T. Rancati 6 , M. Ciocca 3 , E. Orlandi 2 1 CNAO National Center for Oncological Hadrontherapy, Radiation Oncology Department, Pavia, Italy; 2 CNAO National Center for Oncological Hadrontherapy, Radiation Oncology Department , Pavia, Italy; 3 CNAO National Center for Oncological Hadrontherapy, Medical Physics Department, Pavia, Italy; 4 CNAO National Center for Oncological Hadrontherapy, Radiology Department, Pavia, Italy; 5 Universita' Milano Bicocca, Statistical Department, Milano, Italy; 6 Fondazione IRCCS Istituto Nazionale dei Tumori, Prostate Cancer Program, Milano, Italy Purpose or Objective 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). Materials and Methods 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 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