ESTRO 2024 - Abstract Book

S4979

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2024

Purpose/Objective:

In recent years, there has been significant progress in the treatment of advanced cancer, particularly in the context of metastases-directed stereotactic body radiotherapy (SBRT) [1-5]. This approach is commonly employed for patients with oligometastatic disease, aiming to achieve durable control of local metastases or provide palliation of symptoms. Additionally, emerging evidence supports the idea that SBRT can activate both local and systemic immunostimulatory responses in patients with metastatic melanoma (MM), which can have a synergistic effect when combined with immune checkpoint inhibitors, as indicated by the recent consensus from the EORTC–ESTRO OligoCare consortium [6-8]. However, challenges persist in optimisation of this combined treatment approach, including determining the optimal number and selection of lesions for irradiation. While 18 F-FDG PET/CT biomarkers have shown promise in predicting responses to immunotherapy, their application within the context of SBRT remains relatively unexplored [9, 10]. Response assessment techniques such as PERCIST/RECIST only look at a subset of lesions. However, by harnessing all the valuable information embedded in 18 F-FDG PET/CT scans, there may be potential to identify oligoprogression earlier in treatment planning. This study explores the use of quantitative imaging biomarkers, which offer a non-invasive and comprehensive evaluation of tumour burden, providing valuable insights into lesional heterogeneity. Automated segmentation and machine learning techniques to track regions of interest (ROI) suspicious of cancer across baseline (BL) and follow-up (FU) 18 F FDG PET/CT images may assist in identifying patients with MM who are most likely to benefit from targeted radiotherapy. Based on the promising results of a prospective nonrandomised clinical trial, in which patients with MM were treated with systemic immunotherapy plus radiation therapy to 1 to 2 disease sites with the goal of achieving an abscopal response [11], we aimed to evaluate the proportion of patients treated with immunotherapy who have oligoprogressive disease as defined as 1 to 2 new or increasing ROIs who may be potential candidates for targeted radiotherapy.

Material/Methods:

102 patients with MM treated with immunotherapy between 2013 and 2022 were evaluated under IRB approval (RGS3289). A total of 204 18 F-FDG PET/CT scans were retrospectively collected from pre-immunotherapy at baseline and first follow-up time points for imaging analysis. TRAQinform IQ software technology (AIQ Solutions) was used to identify, track, and compare FDG-positive ROI over time. The technology then classified each ROI as new, increasing, stable, decreasing, or disappeared based on changes in total lesion glycolysis (TLG). The software output was reviewed by experts in Nuclear Medicine to evaluate the accuracy of ROI generation. Imaging features were extracted using machine-learning technology and an assessment of heterogeneity of disease response was made across the two timepoints.

Results:

The patient population included 69 males and 33 females, average age 64 (range 23-87). Patients received standard of-care treatment between BL and FU including pembrolizumab (n= 60), ipilimumab (n= 6), nivolumab (n= 11) and ipilimumab + nivolumab (n= 24). Of 102 patients, 501 ROI were identified at BL, and 615 were identified at FU. 45/102 patients demonstrated heterogeneous response, defined as having both new/increasing ROI and decreasing/disappeared ROI (Figure 1). A total of 6 patients had no ROI detected at either timepoint. Individual ROI level analysis showed 62/102 patients had ≥ 1 increasing/new ROI, of which 33/62 had between 1 to 2 ROI and would have been potential candidates for targeted radiation therapy. The remaining 29/62 patients had ≥ 2 new/increasing