ESTRO 2022 - Abstract Book

S428

Abstract book

ESTRO 2022

into account patient performance status and smoking history, sarcopenia defined as low LM3A remained a significant prognostic factor deteriorating OS (HR 1.64, CI 1.07-2.52, p= 0.023) . Upon completion of therapy, 33% of previously non- sarcopenic patients were classified as sarcopenic based on follow-up CT imaging. 97% of patients with pre-treatment sarcopenia remained sarcopenic. Median weight decreased by 5.6%, whereas median L3MA decreased by less than 1% over the course of therapy. Neither posttherapeutic sarcopenia nor the onset of sarcopenia during/after therapy significantly affected OS. Conclusion Pretherapeutic sarcopenia defined as a low skeletal muscle mass is a significant prognostic factor in elderly HNSCC patients undergoing (chemo-)radiation. Skeletal muscle indices seem to be independent prognosticators of therapy beyond patient weight loss and could allow for tailored supportive interventions to improve oncologic outcomes.

MO-0478 Is proton therapy a risk factor for radiation ulcers in oropharyngeal carcinoma?

H. Langendijk 1 , A. van den Hoek 1 , T. Meijer 1 , E. Oldehinkel 1 , H. Verbeek 2 , J. Free 1 , S. Both 1 , D. Scandura 3 , R. Steenbakkers 1

1 University Medical Center Groningen, Radiation Oncology, Groningen, The Netherlands; 2 University Medical Center Groningen, radiation Oncology, Groningen, The Netherlands; 3 University Medical center Groningen, Radiation Oncology, Groningen, The Netherlands Purpose or Objective In 2018, we started to treat oropharyngeal cancer (OPC) patients with intensity modulated proton therapy (IMPT). Some of these patients developed radiation ulcers in the high dose area raising questions regarding RBE effects. Therefore, the main aim was to evaluate if IMPT increased the risk of radiation ulcers compared to modern photon techniques (IMRT and VMAT) and to identify risk factors for radiation ulcers. Patients had to meet the following eligibility criteria: histologically proven OPC; treated with definitive radiotherapy (RT) either or not combined with concurrent chemotherapy or cetuximab; curative intent; use of IMRT or VMAT (photons) or IMPT to a total dose of 70 Gy or 70 GY RBE (constant RBE 1.1), respectively and included in our prospective data registration program. For the selection of OPC patients for IMPT, the model-based approach was used. The primary endpoint was the cumulative incidence of radiation ulcers grade ³ 1 at 1 year after start of RT (ULCER 1-year ). Univariate and multivariable analyses were performed using the Cox proportional hazard model. Results From 2007 to 2020, 498 patients met the eligibility criteria. Before Jan 2018, 371 OPC patients were treated with photons. From Jan 2018 to Dec 2020, 81 patients were treated with IMPT and 46 patients with photons. In univariate analysis, ULCER 1-year was 10.5% after photons and 10.8% after IMPT (p=0.478). Most ulcers 47 (87%) were scored as grade 1 (no complaints) or grade 2 (conservative treatment), while 7 patients (13%) progressed into grade ³ 3 (requiring surgery, life-threatening or death). Median time to first occurrence was similar between both groups: 5.0 months (IQR: 3.6 to 7.2) after photons and 5.8 months (IQR: 4.4-10.1) after IMPT. No difference was noted regarding recovery which was 4.1 months (IQR: 2.5-6.9) and 4.6 months (IQR: 2.4-7.8) after photons and IMPT, respectively. Multivariable analysis identified 4 risk factors, including T-stage, ulcerative/exophytic growth pattern, smoking during treatment and ACE-27 comorbidity score (Table 1). When IMPT was forced into this multivariable model, IMPT was again not associated with an increased risk of the cumulative risk of radiation ulcer (P=0.546). Based on the multivariable analysis, 3 risk groups were defined (Table 1), which was a strong predictor for the risk of ULCER 1-year (Figure 1) Materials and Methods This was a retrospective analysis of prospectively collected data.