ESTRO 38 Abstract book

S1115 ESTRO 38

also hold utility in defining targetable boost regions. The aim of this study was to evaluate the feasibility of defining a deliverable simultaneous integrated boost (SIB) to a dominant intraprostatic lesion (DIL) in the context of intensity modulated radiotherapy using automated thresholding of 18 F-fluorocholine PET within a radiotherapy treatment planning system. Material and Methods Five prostate cases were selected. All patients had high risk prostate cancer and were on androgen deprivation therapy. DILs were defined automatically by 60%, 70% and 80% of maximum prostatic uptake of 18F-fluorocholine on PET-CT using the RayStation 7 Treatment Planning System. A comparison of prostate gross tumour volumes (GTV), planning target volumes (PTV) and SUVmetrics between DIL and prostate gland was undertaken. PTVprostate was defined on MRI/CT as whole prostate GTV plus 5mm, (posterior margin 3mm). PTV DIL was defined as GTV plus 3mm. Median values for PTVs with ranges are reported. Results Median SUVmax of prostate gland was 8.5 (range 4.9 - 18.1). All patients had Gleason 9 disease. Median prostate GTV was 44.6 cm 3 (range 21.0 – 73.4 cm 3 ). Median GTV for DIL defined by 60% SUVmax was 9.2 cm 3 (range 2.6 – 24.9 cm 3 ) accounting for 16% of the prostatic GTV (range 6 - 33.9%). Median GTV for DIL defined by 70% SUVmax was 4.4 cm3 , 8.2% of prostatic GTV (range 2.9 - 17.2). Median DIL defined by 80% SUVmax was 1.5 cm3, 2.7% of prostatic GTV (range 0.4 – 5.9%). Region of Interest Median volume cm 3 (range) Median % volume prostate PTV (range) PTV prostate (manual) 83.2 (45.6 - 124.6) - 60% SUVmax (automated PTV) 13 (8.6 - 46.2) 18.9 (8.5 - 37) 70% SUVmax (automated PTV) 7.9 (4.7 - 31.1) 10.3 (5.4 - 24.9) 80% SUVmax (automated PTV) 3.8 (1.2 - 15.6) 4.5 (2.6 - 16) Conclusion DIL defined using automated thresholding of 60% and 70% of SUVmax was technically feasible using readily available treatment planning software. 60% of SUVmax defined a suitable boost volume with DILs <50% of the total prostate volume. The impact of this metric on organ-at-risk constraints in the context of dose escalation is being studied in a larger cohort. Ongoing work is examining how these PET-derived boost volumes compare with MR lesions and how PET-MRI may have utility in this context. EP-2032 Automated Bone Scan Index (aBSI) as an Imaging Biomarker in Castration Sensitive Prostate Cancer A. Alshehri 1,2 , J. O'Sullivan 2,3 , K. Prise 2 , S. Jain 2,3 , P. Turner 3 , C. Campfield 1 , S. Biggart 1 , C. Chatzigiannis 1 , A. Cole 2,3 1 Northern Ireland Cancer Centre- Belfast Health and Social Care Trust, Nuclear Medicine Department, Belfast, United Kingdom ; 2 Centre for Cancer Research and Cell Biology- Queen’s University Belfast, Cancer Research and Cell Biology, Belfast, United Kingdom ; 3 Northern Ireland Cancer Centre- Belfast Health and Social Care Trust, Oncology, Belfast, United Kingdom Purpose or Objective There is an unmet need for monitoring response to prostate cancer therapeutics in the management of bony metastases. A number of modalities including whole body MRI, PSMA-PET, CT scanning and Isotope Bone Scans (IBS) are used dependent on resources and centre preference.

Material and Methods Thirty-four patients with stage III to IVb HNSCC (UICC 7th edition) undergoing definitive RCT (total dose 70 Gy, 3 cycles of cisplatin administered over 7 weeks) were included in this study. Patients were prospectively imaged with 18 F-FDG PET/CT at baseline and with serial FMISO PET and serial 3 Tesla mpMRI for T1w-, T2w-TSE, dynamic contrast enhanced (DCE) perfusion measurements (k trans , v e ) and diffusion weighted measurements (DWI) including apparent diffusion coefficient (ADC) maps in weeks 0, 2 and 5. Gross tumour volumes for tumour (GTV-T) and normal tissue (NT) were contoured. For MRI and FMISO PET analysis, mean values and SUVmax were obtained within GTV-T and NT. Patients were identified as responders or non-responders during follow-up. SUVmax FMISO PET and mean values for mpMRI parameters at weeks 0, 2, and 5 were compared between responders and non-responders with the t-test at a significance level of p≤0.05. Results 20 patients met inclusion criteria for image analysis by presenting a complete set of serial FMISO PET data and serial 3T MRI data. Mean follow-up time was 9.5 months. 11 patients were diagnosed with local recurrence. For GTV-T, responders showed less tumour hypoxia on FMISO PET than non-responders for weeks 0 and 2 (SUVmax=2.15±0.39 vs. 2.48±1.28 and 1.95±0.39 vs. 2.05±0.39, p>0.05). Baseline tumour volume was larger for non-responders than for responders (54.4±57.5ml vs. 31.0±15.1ml, p>0.05) and decreased at week 5 to 25.3±36.3 ml vs. 13.6±9.4 ml, p>0.05. On mpMRI, tumour apparent diffusion coefficient ADC increased over time for both responders and non-responders from week 0 to 5. The increase was higher for responders than non-responders (51.1% vs. 5.7%, p=0.094). The volume transfer constant ktrans increased from week 0 to 5 for both responders and non-responders. The increase was higher for non- responders than responders (27.4% vs. 11.3%, p>0.05) and differed in pattern, as for non-responders the increase in ktrans reached a maximum at week 2 and then dropped, while for responders a steady increase in ktrans was found until week 5 (non-responders vs. responders (week 2 to 5: -0.107min -1 vs.+0.021min -1 ). Interstitial space volume fraction ve was increased between week 0 and 5 by 37.8% for responders vs. 27.1% for non-responders, p>0.05. Conclusion Tumour volume and FMISO-PET-derived tumour hypoxia were higher among patients with local relapse as compared to locally controlled patients (p>0.05). DCE parameters ktrans and ve and DW parameter ADC differed between relapsing and non-relapsing patients, however without reaching statistical significance in this cohort. Further studies are ongoing. EP-2031 18F-Choline-PET-CT to guide simultaneous integrated boost in prostate cancer R. Pearson 1 , R. Samuel 2 , H. McCallum 3 , J. Frew 3 , E. Howell 4 , R. Maxwell 4 1 Newcastle University, Northern Institute for Cancer Research, Newcastle upon Tyne, United Kingdom ; 2 Leeds Cancer Centre, Dept of Clinical Oncology, Leeds, United Kingdom ; 3 Newcastle upon Tyne Hospitals NHS Foundation Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom ; 4 Newcastle University, Centre for In Vivo Imaging, Newcastle upon Tyne, United Kingdom Purpose or Objective 18 F-fluorocholine positron emission tomography (PET-CT) has an established role in detecting recurrent prostatic carcinoma but is not routinely used to guide radiotherapy delineation in the UK. Radiotherapy dose escalation to a boost volume has potential to improve tumour control and is the focus of current research protocols using MRI. A suitable boost volume may be defined as <50% of the total prostate volume on MRI, however quantitative PET may