ESTRO 2023 - Abstract Book

S116

Saturday 13 May

ESTRO 2023

Stereotactic body radiotherapy (SBRT) is a guideline-recommended treatment option for patients with medically inoperable early stage lung cancer and pulmonary oligometastases. In case of ultra-central tumor location - defined as tumor contact (PTV) with proximal bronchial tree (PBT), trachea or esophagus - SBRT is associated with an increased risk of severe toxicity. Therefore, the role of SBRT for ultra-central lung tumors remains controversial. The aim of this study was to perform a detailed dosimetric analysis of PBT subsegments to evaluate safety of SBRT in ultra-central lung tumors. Materials and Methods Fifty-seven ultra-central lung tumor patients treated with SBRT at our institution from 2014 to 2021 were included. Ultra central lung tumors were defined as tumor (PTV) abutting or involving trachea, PBT or esophagus. Descriptive analysis, Cox regression, Kaplan-Meier method and log-rank test were employed to analyze overall survival (OS), local control (LC) and progression-free survival (PFS). Bayesian inference was employed to build a dose-response model for toxicity. While the prior was based on meta-analysis of previous literature, the likelihood was computed based on a binomial distribution taking into account the number of observed patients without toxicity. Results Twenty-seven (47.4%) of the irradiated lesions were primary lung tumors and 30 (52.6%) metastases.The most common primary tumor was non-small cell lung cancer (NSCLC) with 37 (64.9%) cases, of which 12 patients had primary non metastatic NSCLC, and 25 patients had locally recurrent or oligometastatic NSCLC. Colorectal cancer, small-cell lung cancer, head-and-neck cancer, metastatic melanoma and sarcoma combined accounted for twenty oligometastatic patients (35.1%). Patients were treated with risk-adapted SBRT of median 45.0 Gy (30.0-60.0 Gy) respectively 55.2 Gy (33-88 Gy, EQD2, α / β = 10 Gy) in 8 or 10 fractions. The most commonly prescribed dose was 48 Gy in 8 fractions (n=30, 53.0%). The median prescription isodose to the PTV was 65.0% (65.0-85.0%). The median planning target volume was 30.0 cm3 (6.0 199.0 cm3). After a median follow-up of 2.2 years (0.6-9.3 y), the one-year and two-year LC rates were 85.2% and 77.1%, respectively. The median OS was 3.4 years (0.6-9.3 y), OS at 2 years was 71.3%. The median PFS was 1.0 year (0.2-5.7y). Grade ≥ 3 radiation pneumonitis was observed in two patients (3.5%), while no bronchial stenosis, hemorrhage or fistula was observed. The median D0.02cc to PBT was 84.4 Gy (EQD2, α / β = 3 Gy: 43.9-159.3 Gy). The dose-response model predicted a toxicity limited to 4.9% (0 - 11.4%) when delivering 100 Gy (EQD2, α / β = 3 Gy) to any location of the PBT (D0.2cc) (Figure 1b).

Conclusion This study reports a detailed dosimetric analysis of PBT subsegments after SBRT for ultra-central lung tumors. A dose threshold of 100Gy EQD2 to the PBT and its sub-segments is expected to result in low rates of severe bronchial toxicity, while maintaining high rates of local tumor control. PD-0155 Health-related quality of life in the randomised ARTFORCE PET-Boost trial in locally-advanced NSCLC S. Cooke 1 , J. Belderbos 1 , B. Reymen 2 , M. Lambrecht 3,4 , G. Fredberg Persson 5,6,7 , C. Faivre-Finn 8 , E. Dieleman 9 , J. van Diessen 1 , J. Sonke 1 , D. De Ruysscher 10 1 Netherlands Cancer Institute (NKI-AVL), Radiation Oncology, Amsterdam, The Netherlands; 2 MAASTRO Clinic, GROW – School for Oncology and Developmental Biology, Maastricht University Medical Center, Radiation Oncology, Maastricht, The Netherlands; 3 KU Leuven – University of Leuven, Department of Oncology, Experimental Radiation Oncology, Leuven, Belgium; 4 University Hospitals Leuven, Radiotherapy-Oncology, Gasthuisberg, Belgium; 5 Copenhagen University Hospital - Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 6 Copenhagen University Hospital – Herlev and Gentofte, Department of Oncology, Copenhagen, Denmark; 7 University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark; 8 University of Manchester, The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom; 9 Amsterdam University Medical Centers location AMC, Radiation Oncology, Amsterdam, The Netherlands; 10 MAASTRO Clinic, GROW – School for Oncology and Developmental Biology, Maastricht University Medical Center, Radiation Oncology , Maastricht, The Netherlands Purpose or Objective In patients with locally advanced non-small cell lung cancer (LA-NSCLC), the ARTFORCE PET-Boost trial (clinicaltrials.gov: NCT01024829) showed that two isotoxic, personalised, dose-escalation strategies resulted in excellent 1-year freedom from local failure rates of >90% at 1-year, as compared to the historic rate of 70%. However, dose-escalation comes at an increased risk of adverse events. In this study we assessed the impact of these two dose-escalation strategies on health related quality of life (HRQoL).