Stereotactic Focal Radiotherapy as an Alternative Treatment to Active Surveillance for Low and Intermediate Risk Prostate Cancer

Overview

\*Rationale : Active surveillance of prostate cancer helps to avoid the morbidity associated with curative radical prostatectomy /radiotherapy in patients with early stage disease. However, at 5 years and 15 years, respectively 35 % and nearly 50 % of patients require rescue interventional treatments. Numerous Phase II trials have reported using focal treatments (focused on the macroscopic tumor only while not involving the whole prostatic gland) in order to reduce the morbidity due to recurrence as well as the high anxiety rates under observation only. Stereotactic radiotherapy (highly focused radiotherapy technic to reduce the risk of side effects) is being proposed in the same way as it does not require any anaesthesia, as opposed to all the other focal methods. The purpose of this trial is to evaluate whether focal stereotactic radiotherapy treatments could reduce the rate of rescue treatments among patients eligible to an active surveillance program at first. * Major Inclusion Criteria : * 1\. Early stage prostate adenocarcinoma (CAPRA score ≤ 5) * 2\. No major urinary problems * 3\. Active Surveillance possible * Major Exclusion Criteria : * 1\. Age at diagnosis \< 50 years * 8\. Androgen-deprivation therapy * 9\. Any cancer within the last 5 years except skin basocellular carcinoma or any uncontrolled cancer * Trial : Phase II randomized trial comparing Stereotactic Radiation Therapy focused on the macroscopic tumor or Active Surveillance as the control arm. * Main objective : to compare the rescue treatment rates between the two arms

The stereotactic radiation therapy procedure involves at first placement of 3-4 fiducial markers, a planning computed tomography (CT) scan as well as a planning MRI, both fused thereafter based on fiducial markers. The delay between fiducial markers placement and planning CT Scan - MRI must be of at least 10 days. SBRT delivers 36.25 Gy in 5 fractions prescribed on the 80% isodose or higher. The fractions are delivered with a CyberKnife device every other day for 2 weeks. If constraints to organs at risk can be fulfilled with other radiation therapy devices, the latter can be used for treatment as well. Organs-at-risk (rectal wall, bladder wall, bladder neck, urethra, as well as contralateral neurovascular bundles, contralateral external sphincter and contralateral pudendal vessels) are delineated (see constraints used in the first citation). Gross target volume (GTV) is delineated on the MRI while considering the hypointense T2-weighted nodule, the hypointense apparent diffusion coefficient, and the hyperintense perfusion zone. At first, the GTV is expanded by 1cm in all directions to generate the clinical target volume (CTV). The CTV is then cropped to the limits of the prostate. If the volume ratio CTV/Prostate is under 30%, the expansion margin of the GTV is increased progressively within the prostate by 0.1 cm increments so that the CTV achieves at least 30% of the prostate volume. Hence, a maximum of 1.5 cm margin around the GTV is allowed and encouraged. The CTV is then expanded by 3 mm to generate the planning target volume (PTV).