ESTRO 2023 - Abstract Book

S1182

Digital Posters

ESTRO 2023

started ADT, 6 patients had stable PSA if compared to baseline and continued observation. Adverse events were recorded in 2 patients, one patient reported G2 GI and G1 GU toxicity, and G1 GU toxicity was reported in another case. Conclusion Promising results after SSRT for macroscopic prostate bed relapse were confirmed, with more than half of patients experienging BR. Reported toxicity was mild. Early report from this study reassure about feasibility of SSRT approach in this particular setting.

PO-1460 MR Delta Radiomics during Radiotherapy to Prostate Cancer: Does Dose per Fraction Matter?

M. Swinton 1 , R. Portner 2 , L. Brooks 3 , J. Zhong 4 , C. Eccles 5 , G. Price 6 , A. Hudson 1 , R. Bristow 7 , A. McWilliam 7 , A. Choudhury 1 , P. Hoskin 1 1 Christie Hospital, Clinical Oncology, Manchester, United Kingdom; 2 Rosemere Cancer Centre, Clinical Oncology, Preston, United Kingdom; 3 University of Manchester, Medicine, Manchester, United Kingdom; 4 University of Leeds, Radiology, Leeds, United Kingdom; 5 Christie Hospital, Radiotherapy, Manchester, United Kingdom; 6 University of Manchester, Cancer Digital Sciences and Machine Learning, Manchester, United Kingdom; 7 University of Manchester, Cancer Sciences, Manchester, United Kingdom Purpose or Objective Developing imaging biomarkers in prostate cancer (PCa) that associate with response to radiotherapy (RT) or Androgen Deprivation Therapy (ADT) may identify patients for radiation boost or additional adjuvant therapy. MR images acquired during prostate RT on an MR Linac allows analysis of dynamic changes in image features during treatment. We aimed to characterise changes in prostate radiomic features before and after ADT and during RT in PCa patients receiving either hypofractionated (60 Gy in 20# over 4 weeks) or stereotactic ablative radiotherapy (SABR – 36.25Gy in 5# over 2 weeks). Materials and Methods This is a retrospective radiomic analysis of 20 men receiving RT to their prostate on an MR Linac after neoadjuvant ADT. T2-weighted images acquired on a 1.5T Elekta Unity MR Linac were analysed on each treatment day R0-R4 for those receiving 5#. For 20#, imaging was acquired from Day 1 (R0) and at the end of each week of treatment (R1-R4). Regions of Interest of dominant intraprostatic lesion (DIL) and whole prostate (WP) were outlined on R0 and a co-registration method used to copy contours to R1-R4. A diagnostic MRI acquired prior to ADT (D0) was also analysed. MR images across treatment for each patient were normalised to the first fraction. First order radiomic features for WP and DIL extracted following the imaging standardisation biomarker initiative guidelines. Mean and median intensity, kurtosis, uniformity and entropy were extracted, and Mann-Whitney U testing assessed differences between fractionations Results 8 men received 20# and 12 men received 5# RT. Mean Intensity in both WP and DIL reduced between D0 and R0 (Fig. 1). Mean Intensity in WP was greater than DIL at D0 (p=0.04) and R0 (p<0.01) but converged during RT with no difference at R3 (p=0.13) or R4 (p=0.32). An increase in mean intensity from R0 to R1 followed by a reduction by R5 was seen in both DIL and WP (Fig. 1). Mean intensity curves for both WP and DIL did not differ for 20# and 5# regimens (Fig. 2). Compared to WP, DIL had lower entropy and higher uniformity at D0 with differences reducing at later time points (R0-R4). Kurtosis showed no difference between WP and DIL at D0 but separated with higher values in WP than DIL after ADT and RT.