Radiation therapy: Treatment with 2 separate HDR brachytherapy implants, each with one fraction of 13.5 Gray (Gy) with an interval of 7-14 days between treatments.

Radiation therapy in the study consists of treatment with 2 separate interstitial HDR brachytherapy procedures with temporary interstitial catheters, each with one fraction of 13.5 Gray (Gy). Both procedures will be done in an identical manner. The 2 procedures will be separated by an interval of 7-14 days Treatments will be done with interstitial catheters inserted transperineally with transrectal ultrasound guidance under sterile conditions. Optimization of treatment plan will be done with Brachyvision software (Varian, Palo Alto CA) based on CT-scan imaging done post-implant. Optimization parameters will be the following:

Prostate :

• V100 > 95%
• V150 30-35%
• V200 < 15%
• D90 > 90% (12,15Gy)

Bladder

• V75 < 1cc

Rectum

• V75 < 1cc

Urethra

V125 = 0cc D10 < 120%

Treatments will be carried out with an Iridium-192 afterloader. Source and all catheters will be removed from the patient at the end of the procedure.

Disease free survival as evaluated by absence of biochemical recurrence (Phoenix criteria) and absence of clinically/radiologically diagnosed local, regional or distant recurrence.

Toxicity according to International prostate symptom score (IPSS) and Expanded Prostate Index Composite (EPIC) questionnaires.

Toxicity according to Expanded Prostate Index Composite (EPIC) questionnaires.