What this Trial Is About

Radiotherapy (RT) is an established treatment option for localized prostate cancer (PCa), with cure rates similar to those of radical prostatectomy. In the last decade, conventionally fractionated RT (1.8-2.0 Gy per fraction to 78-80 Gy) has been replaced by moderately hypofractionated RT (2.3-3.65 Gy per fraction to 56-70 Gy). The rationale behind this change is the scientific level 1 evidence that a higher dose per fraction may improve the cost-benefit of RT due to the specific radiobiology of PCa (a lower alpha/beta than that of adjacent healthy tissues). Additionally, there is a practical advantage both for patients and the radiation department due to a reduced number of fractions. More recently, extreme hypofractionation or stereotactic body radiotherapy (SBRT) (7-9.5 Gy per fraction to 36-43 Gy in 4-7 fractions) has been introduced as RT modality, and proved to be an effective and safe treatment option for patients with low and intermediate clinically-localized PCa, with similar incidence of late toxicity and 5-year disease free survival outcomes when compared to hypofractionated and conventional radiotherapy regimens. International guidelines endorse extreme hypofractionated SBRT as routine treatment option for low and intermediate risk PCa patients. For high-risk prostate cancer, preliminary results of ongoing prospective studies are promising, but these data are not yet mature enough to recommend extreme hypofractionated SBRT in high-risk prostate cancer. Upon this, ongoing prospective trials handle strict eligibility criteria hereby selecting patients with few comorbidities. This may not necessarily fully reflect the real life patient population. Indeed, patients with a large prostate size, a history of transurethral resection of the prostate (TURP), or 'significant' urinary baseline symptoms may be at risk for experiencing increased toxicity. Based on this concern, these patients were excluded from ongoing clinical trials. However, whether these patients will really develop more toxicity, is a theoretical concern, not yet based on clinical evidence. It is our hypothesis that using modern radiotherapy such as volumetric arc therapy (VMAT) and image-guided radiotherapy (IGRT) - both standard technologies at the Radiation-Oncology department in Leuven University Hospitals - extreme hypofractionated SBRT can be successfully implemented in the treatment of intermediate risk and a select group of high-risk PCa patients and/or patients with pre-existing urinary morbidity.

Observational Study on Extreme Hypofractionation for Localized Prostate Cancer