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).