ESTRO 2025 - Abstract Book

S1442

Clinical - Lung

ESTRO 2025

4491

Poster Discussion High Dose to Perfused but not Ventilated Lung is Associated with Clinical Toxicity

Neil D Wallace 1 , Nicholas Hardcastle 2,3,4 , Mathias Bressel 5,3 , Lachlan McIntosh 2 , Nicholas Bucknell 1,6 , Michael Hofman 7,3 , Tomas Kron 2,3 , Jason Callahan 7,8 , David Ball 1,3 , Michael MacManus 1,3 , Nikki Plumridge 1,3 , Mark Shaw 1,3 , Daniel Steinfort 9,10 , Lisa Selbie 11 , Shankar Siva 1,3 1 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 2 Department of Physical Science, Peter MacCallum Cancer Centre, Melbourne, Australia. 3 Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia. 4 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia. 5 Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Melbourne, Australia. 6 Department of Radiation Oncology, Sir Charles Gairdner Hospital, Perth, Australia. 7 Department of Nuclear Medicine, Peter MacCallum Cancer Centre, Melbourne, Australia. 8 Department of Nuclear Medicine, Melbourne Theranostic Innovation Centre, Melbourne, Australia. 9 Department of Respiratory Medicine, Royal Melbourne Hospital, Melbourne, Australia. 10 School of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, Australia. 11 Department of Clinical Research, Peter, Melbourne, Australia Purpose/Objective: 68 Gallium Ventilation/Perfusion (V/Q) PET/CT is a high-resolution imaging modality which permits quantitative evaluation of functioning lung. The purpose of this study was to seek associations between dosimetry to functional lung and clinical toxicity in those undergoing definitive radiotherapy for locally-advanced non-small-cell lung cancer (NSCLC). Material/Methods: We conducted a prospective non-randomized observational clinical trial for 67 patients undergoing RT +/- chemotherapy for locally-advanced NSCLC (Universal Trial Number U1111-1138-4421). Patients underwent V/Q PET/CT before RT, mid-treatment and at 3- and 12-months after treatment. Clinical toxicity was evaluated at 3 monthly intervals for 12 months after RT. We have previously reported the serial changes in lung ventilation and perfusion after RT, and associations between volumes of functional lung and clinical toxicity (1). For this exploratory analysis, regions of ventilated and perfused lung at pre-specified thresholds (activity greater than 5%, 30% and 70% of maximum standardized uptake value) (2) were segmented on the RT planning scan. Independent samples t-test was used to test for associations between mean lung dose, V20Gy, and V54Gy to each of these segments of functional lung and the incidence of pneumonitis. To validate our results, we performed the same tests according to the functional lung volumes described by Lucia et al in their study utilizing 68 Gallium V/Q PET/CT for functional lung preservation after SBRT (3). Results: Of 67 enrolled patients (23 (34%) female, mean age 68), 63 were evaluable. Grade ≥2 pneumonitis occurred in 20/63 (32%). An association was observed between V54 Gy of perfused lung at the 30% threshold – median V54 Gy was 12.9% (IQR 8.7-14.8%) in those who developed grade ≥2 pneumonitis and 6.3% (IQR 3.7-8.5%) in those who did not, p=0.003. A similar association was observed between grade ≥2 pneumonitis and V54 Gy to perfused lung at the 50% (p=0.008), 70% (p=0.012), and 90% (p=0.030) thresholds defined by Lucia et al (3). No associations were observed between grade ≥2 pneumonitis and V54 Gy to anatomical lung or ventilated lung at any threshold. No associations were seen between MLD or V20 Gy to anatomical, ventilated or perfused lung at any threshold and grade ≥2 pneumonitis.

Conclusion: The volume of well-perfused lung receiving near-prescription dose during radical lung radiotherapy may be predictive for clinical toxicity. This finding warrants further investigation.

Keywords: Functional Lung Imaging