Research: 2018 – Montreal

Project Title:
Generating a population-based recurrence risk map based on PSMA-PET imaging to guide radiotherapy.
Dr. Cynthia Ménard, Centre de recherche du CHUM
The primary focus of my scholarly activity is to better individualize radiation therapy through the development, validation, and clinical application of imaging techniques to radiation treatment planning, response assessment, and treatment adaptation. Throughout my career I have invested my efforts to improving radiotherapy for patients with prostate cancer. I have a unique background in the development and clinical deployment of advanced imaging techniques in prostate cancer.
Project Abstract:
Increased PSA level detected shortly following prostatectomy indicates cancer recurrence and affects 15 to 20% of treated patients [Stephenson]. Recurrent cancer cells should be completely encompassed in the clinical targeted volume (CTV) during radiation treatment planning to improve favorable patient outcomes. The emergence of PSMA-PET imaging, which has increased sensitivity in locating sites of disease recurrence when compared to conventional methods, still lacks the required imaging resolution to identify some microscopic-sized disease. The presence of such sites increases the risk of local recurrence in the pelvic region. The pipeline for treatment planning could therefore benefit from previous assessment of recurrence in the pelvic area from the diseased patient population. The patterns of local recurrence in this population, accompanied by risk factors, could guide CTV delineation for evidence-based planning. This combination of information could be presented as an anatomical map showing probability of recurrence in the pelvic area. Disease recurrence related to anatomical structures can be evaluated from the alignment of individual patient PSMA-PET/CT images. The probability map can be derived from the evaluation of occurrence related to location of disease in the patient population. Such a population-based probability map is promising for treatment planning and disease coverage during radiotherapy planning.
Scientific Abstract:
CTV assessment for targeted irradiation therapy following pelvic recurrence after prostatectomy could benefit from the creation of a population-based recurrence probability map derived from PSMA-PET/CT images. A population-based probability map depicting sites of recurrence in the diseased population can be obtained by combining individual patient PSMA-PET/CT images. A previous registration method by Brock et al. [Brock] was employed to register gross tumor volume (GTV) from T2-weighted MR to the CTV from CT images. This biomechanical-based algorithm, termed Morfeus, is based on the finite element method and requires the segmentation of anatomical structures. Semi-automatic segmentation of pelvic organs will be provided to this non-linear deformable image registration (DIR) algorithm. Subsequent computation will employ a voxel-based approach to evaluate probability of recurrence over anatomical structure of the pelvis following prostatectomy. A per-voxel probability density assessment will be derived from the map of recurrence sites, as shown from PSMA-PET/CT images, combined with risk factor data. The resulting novel population-based recurrence probability map will guide radiation oncologist in dose planning while estimating the CTV for radiation therapy.
Impact on prostate cancer patients:
For patients with recurrence following prostatectomy, there is a risk that microscopic recurrence sites may remain after therapeutic treatment. Our hope is that including the anatomical pattern of recurrence from the general population for planning the CVT in individual patients might lower the risk of leaving untreated recurrence sites out of the CVT.