A Prospective Stage IIS Clinical Trial Evaluating Hemi-Ablative Low Dose Rate (LDR) Brachytherapy for Localised Prostate Cancer

This is a pilot Stage IIS study to evaluate the feasibility of performing a larger multicentre trial.The HAPpy study is a prospective development study offering hemi ablative LDR brachytherapy to 34 men with histologically proven low or intermediate risk localised prostate adenocarcinoma which affects a single lobe of the prostate.The data obtained from these 34 patients will be compared to matched patients from a retrospective cohort of whole gland brachytherapy patients treated in the same institution.Precise mapping and characterisation of the disease will be established using mp-MRI (T2-weighted and DCE(gadolinium)) imaging and transperineal template biopsy (TTB). Only the lobes with disease (left or right half of the gland) will be treated provided that the contralateral side is free of disease. Patients will be followed for two years post treatment at which time a further mp-MRI and TTB will confirm disease control outcomes.

Focal therapy for prostate cancer is a new idea and is considered an experimental treatment which needs to be evaluated within carefully conducted clinical trials . Rather than investigating focal therapy in a strict sense where only known areas of disease are treated, a more conservative approach needs to be taken until more information can be obtained regarding the outcomes of changing treatment techniques. Hemi-ablative focal therapy is considered to be a low-risk treatment and investigations into the performance of the technique should provide a pathway for future investigations of less conservative methodologies. Hemi-ablative focal therapy treats half of the prostate gland with a treatment margin, effectively treating at least 50% of the whole gland with a prescription dose. In theory, this should lessen the side effects associated with radical treatment while still maintaining disease control.This type of treatment is only suitable for patients with unilateral disease.

An international group of experts was established to form a consensus on how to design and conduct an LDR focal brachytherapy program for clinical trials. The group's findings were published by Langley et al and a dosimetric modelling study by Al Qaisieh et al.

Focal hemi gland brachytherapy will be delivered by means of an adaptation of same real-time planning technique (denominated 4D Brachytherapy) used to deliver whole gland LDR prostate brachytherapy. Stranded iodine 125 sources are implanted on the periphery of the prostate gland and loose iodine 125 sources are implanted within the central volume of the gland. Because all planning and dosimetry are done in real-time, radiotherapy physics will be able to adhere to the strict planning protocols required for this study.

Treatment planning: For standard whole-gland treatment, the whole prostate gland is delineated to form the Planning Target Volume (PTV) and the V100 is planned such that it covers the entire PTV plus a 0.5cm margin. For hemi-ablative focal treatments, the prostate will be divided into half and a new HTV (called the HemiTreatment Volume) is outlined on the side of the prostate determined to have clinically significant disease. A treatment margin of 0.5cm is considered around the HTV, which is similar when planning whole-gland treatment. In this way, >95% of the HTV is aimed to receive 100% of the prescription dose (V100). The V150 is situated in a semi-horseshoe shape in order to spare the urethra from high doses of radiation.