ESTRO 2022 - Abstract Book

S552

Abstract book

ESTRO 2022

Conclusion We have successfully translated OE-MRI onto an MRL for the first time. OE-MRI measurements in normal tissue (NC) and tumour are consistent between the MRSim and the MRL at 1.5 T. This novel technique facilitates introduction of hypoxia adapted radiotherapy on the MRL.

OC-0624 An objective measure of response on WBMRI in mHSPC treated with ADT, EBRT, and Radium-223

V. GIACOMETTI 1 , A.C. Grey 2 , A. McCann 3 , K.M. Prise 1 , A.R. Hounsell 4,1 , C.K. McGarry 4,1 , J.M. O’Sullivan 5,1

1 Queen's University Belfast, Patrick G. Johnston Centre for Cancer Research, Belfast, United Kingdom; 2 Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Department of Imaging Services, Belfast, United Kingdom; 3 Belfast Health and Social Care Trust, Radiological Sciences and Imaging Regional Medical Physics Service, Belfast, United Kingdom; 4 Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Department of Radiotherapy Physics, Belfast, United Kingdom; 5 Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Department of Clinical Oncology, Belfast, United Kingdom Purpose or Objective Bone is the most common site of metastasis in advanced prostate cancer. Assessment of response to therapy in bone metastases remains challenging [1]. Magnetic resonance (MRI) plays an important role in bone metastasis detection and response assessment. However, an objective measure of response remains elusive. The aim of this study was to generate an objective method to assess MRI response in the vertebrae of patients with metastatic hormone sensitive prostate cancer (mHSPC), before/after radiation therapy and Radium-223 and to correlate changes with clinical outcomes, including survival. Materials and Methods Whole body MRI (WBMRI) images from 25 patients from the neo-adjuvant Androgen Deprivation Therapy pelvic Radiotherapy and RADium-223 clinical trial (ADRRAD) [2] were imported into the Varian Eclipse (v13.5) (Varian Medical Systems, Palo Alto) treatment planning system. Patients received androgen deprivation therapy (ADT), and 6 cycles of Docetaxel prior to external beam radiotherapy (EBRT) (74Gy/37 fractions to prostate and pelvic nodes), and 6 cycles of Radium-223 (55kBq/kg). Three sets of WBMRI were acquired: (MRI1) baseline scan performed at most 28 days before commencing EBRT, (MRI2) performed at 2 months post completion of Radium-223 and (MRI3) performed 6 months post completion of Radium- 223. MRI response was assessed by a radiologist based on post baseline MRI images. Vertebrae outside the EBRT field were semi-automatically contoured in the sagittal T1 sequences of the three sets of WBMRI, and the MRI intensity was measured. To compare the differences in intensity across MRI1, MR2 and MRI3, spinal cord was chosen as a reference tissue to normalise the measurements. The correlation between MRI intensity and clinical outcomes was investigated by performing Mann-Whitney-Wilcoxon and Student’s t-test in R (v4.1.0) (statistical significance set at p=0.05). Survival curves were generated and discrimination measures for survival outcome were investigated for MRI1. Results Using a discrimination measure of 1.8 on the MRI1 normalised spine intensity, MRI1 was found to be a reliable quantitative indicator (p=0.021) correlating with overall survival (Figure 1). ∆ MRI(3-1) and ∆ MRI(3-2) were found to be reliable quantitative indicators (p<0.05) for distinguishing responder and non-responder patients (as defined by best response annotated independently by a radiologist) (Figure 2). No significant differences were found between patient response vs MRI1 and ∆ MRI(2-1).