Defining radio-recurrent intra-prostatic target volumes using PSMA-targeted PET/CT and multi-parametric MRI.

Our purpose was to evaluate intra-prostatic cancer volumes for salvage radiotherapy in men with recurrent prostate cancer confined to the prostate post-primary radiotherapy using mpMRI and 18F-DCFPyL PET/CT (PET).

Men with biochemical failure post-primary radiotherapy were enrolled in a multi-centre trial investigating mpMRI and PET. All men with isolated intra-prostatic recurrence are included in this secondary analysis. The intra-prostatic gross tumour volume (GTV) was manually delineated on mpMRI and was also delineated on PET using three methods: 1. manually, 2. using a 30% threshold of maximum intra-prostatic standard uptake value (SUVmax), and 3. using a 67% threshold of this SUVmax. Clinical target volumes (CTV) including expansions on each GTV were generated. Conformity indices were performed between the mpMRI CTV and each PET CTV. Correlation with biopsy and clinical outcomes were performed.

Of the 36 men included, 30 (83%) had disease in two quadrants or less using the combination of mpMRI and PET. Mean target volume (union of CTV on mpMRI and CTV manually delineated on PET) was 12.2 cc (49% of prostate gland volume). 12/36 (33%) men had a biopsy. Per-patient sensitivity was 91% for mpMRI and 82% for PET.

mpMRI and PET provide complementary information for delineation of intra-prostatic recurrent disease. Union of CTV on mpMRI and PET is often less than 50% of the prostate, suggesting this imaging could help define a target for focal salvage therapy.

Clinical and translational radiation oncology. 2021 Nov 14*** epublish ***

Wei Liu, Hatim Fakir, Gurpreet Randhawa, Ryan Alfano, Mark Corkum, Zahra Kassam, Irina Rachinsky, Hans T Chung, Peter Chung, Andrew Loblaw, Gerard Morton, Tracy Sexton, Anil Kapoor, Aaron Ward, Katherine Zukotynski, Louise Emmett, Glenn Bauman

Department of Oncology, Division of Radiation Oncology, London Health Sciences Centre and Western University, London, Canada., Department of Oncology and Department of Medical Biophysics, London Health Sciences Centre and Western University, London, Canada., Faculty of Engineering, University of Waterloo, Waterloo, Canada., Department of Radiation Oncology, Windsor Regional Cancer Centre, Windsor Regional Hospital, Windsor, Canada., Division of Radiation Oncology, The Ottawa Hospital Cancer Centre and the University of Ottawa, Ottawa, Canada., Department of Medical Imaging, St. Joseph's Health Care and Western University, London, Canada., Division of Nuclear Medicine, London Health Sciences Centre and Western University, London, Canada., Department of Radiation Oncology, Odette Cancer Center, Sunnybrook Health Sciences Centre, Toronto, Canada., Department of Radiation Oncology, University of Toronto, Toronto, Canada., Urologic Cancer Centre for Research & Innovation and McMaster University, Hamilton, Canada., Department of Medical Biophysics, Lawson Health Research Institute and Western University, London, Canada., Department of Nuclear Medicine and Theranostics, St. Vincent's Hospital and University of New South Wales, Sydney, Australia.

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