An evaluation of the correlation between ExacTrac Dynamic and cone beam computed tomography (CBCT) imaging in prostate cancer patients with implanted fiducial markers receiving radiation therapy

Prostate movement during radiation therapy treatment has been clearly demonstrated. A major source of variation is differences in the patient's bladder and bowel preparation, required for treatment. This movement has been demonstrated both between treatments (interfraction) and during a treatment session (intrafraction) potentially leading to underdosing of the tumour volume and/or overdosing of surrounding healthy tissue. Traditionally, this movement has only been corrected immediately between treatments using cone beam computed tomography (CBCT). To ensure precise delivery of prostate radiation therapy, intrafraction monitoring of the prostate position is required. ExacTrac Dynamic (EXTD), a system that acquires kilovoltage (kV) images for radiation therapy treatment positioning, has recently released an implanted marker workflow that enables tracking of prostate movement during treatment. The aim of this retrospective study is to determine the correlation between initial positioning CBCT scans and EXTD images and evaluate prostate movement during treatment for prostate cancer patients. This will be evaluated by comparing the translational shifts from both imaging modalities. Intrafraction prostate movement will be evaluated by determining the frequency of occasions when the image shift magnitude is greater than the specified tolerance. This will inform and refine clinical protocols for patients receiving radiation therapy for prostate cancer.