The goal of this study is to evaluate the recovery of erectile function at six months after hormonal therapy cessation in male patients affected by advanced prostate cancer and undergoing radiotherapy. The main questions are:

• How well and how quickly do patients recover their sexual function and overall quality of life after stopping hormone therapy and receiving radiotherapy?
• How do the details of the radiation treatment (like the dose and how it's delivered) relate to treatment success, side effects, and long-term outcomes such as cancer control, survival, and financial impact? Participants will receive hormonal therapy (Relugolix) following by radiotherapy. They will complete questionnaires on sexual function, quality of life, and financial impact before, during and after treatment, and attend follow-up visits for health assessments. The study will measure how many patients recover erectile function within six months of stopping hormonal therapy, how long recovery takes, how treatment doses relate to outcomes, and assess cancer control, side effects, quality of life, and survival.

Assessment of the International Index of Erectile Function-5 (IIEF-5) score at six months after hormonal therapy cessation, indicating recovery in at least 70% of the study population. Evaluation of Erectile Function Recovery 6 Months After Hormonal Therapy Completion The success of the study will be determined if erectile function recovery is observed in at least 70% of the population 6 months after the completion of hormonal therapy. Definition of "Erectile Function Recovery" for Individual Patients: A subject will be considered to have recovered erectile function if, at 6 months after the completion of hormonal therapy (Relugolix), their IIEF5 (International Index of Erectile Function - 5) score meets one of the following conditions:

• Achieving an IIEF5 score ≥ 17: This score indicates mild erectile dysfunction or no erectile dysfunction (as per IIEF5 categories: 22-25 no erectile dysfunction, 17-21 mild dysfunction). AND/OR;
• Significant increase in IIEF5 score compared to baseline: An increase of at least 5 points compared to the baseline (pre-treatment) IIEF5 score, indicating a clinically significant improvement in erectile function.

Recovery will only be evaluated in patients who had erectile dysfunction present (IIEF5 < 22) at baseline. The study will be considered "successful" if the proportion of patients meeting the individual definition of "erectile function recovery" (as specified above) at 6 months after the completion of hormonal therapy is greater than or equal to 70% of the studied population.

The secondary endpoints of this study aim to provide a comprehensive understanding of both the functional and oncological outcomes following the cessation of hormonal therapy with Relugolix. One key endpoint is the time to sexual function recovery (SFRT), defined as the interval between hormonal therapy cessation and the point at which a patient achieves an IIEF-5 score of 8 or higher, maintained across two consecutive assessments. This threshold was selected to reflect a clinically meaningful level of erectile function recovery, particularly in patients with moderate to severe dysfunction at baseline, and aligns with established literature and the study's primary endpoint criteria. Recovery will be assessed by comparing post-treatment IIEF-5 scores with each patient's baseline value. Additionally, the study will investigate the correlation between erectile function recovery and radiation dose exposure to critical anatomical structures involved in sexual function, including the penile bulb, crura, internal pudendal arteries, periprostatic neurovascular bundles, and testes, aiming to identify dose-dependent effects on functional outcomes. Other secondary endpoints include biochemical progression-free survival (bPFS), measured according to the Phoenix criteria (nadir PSA + 2 ng/mL), as well as local control (time to local recurrence or last follow-up without recurrence) and distant progression-free survival (dPFS), defined as the time to detection of distant metastases. The study will also evaluate acute and late urinary and rectal toxicity, using the RTOG criteria and International Prostate Symptom Score (IPSS) to assess the genitourinary and gastrointestinal side effects of therapy. To gauge broader patient well-being, quality of life (QoL) will be monitored using validated tools including the EORTC QLQ-C30, EORTC PR25, and IIEF-5 questionnaires. Furthermore, the study incorporates a financial toxicity assessment using the PROFFIT questionnaire, which measures the economic burden of treatment from the patient's perspective. Lastly, overall survival (OS) will be tracked, defined as the time from treatment initiation to death from any cause or the date of last follow-up, thereby offering a complete view of treatment impact across survival, function, toxicity, and patient-reported outcomes.

Inclusion Criteria:

• Male sex. (This criterion is required for the patient population being studied and for the correct data structuring in CTIS.)
• Age > 18 years;
• Diagnosis of prostate cancer via transperineal core biopsy;
• Classified as unfavorable intermediate-risk (T2b-2c, PSA ≤ 20 ng/mL, and Gleason score 7(4+3); ISUP grade 3);
• Signed informed consent for REDI-CaP protocol;
• Signed consent for REDI-CaP data processing;
• Prostate volume < 80 cc;
• No evidence of prostate capsule invasion (documented by multiparametric MRI of the prostate);
• Performance status: 0-1;
• Negative total-body CT with contrast and bone scan for metastases;
• Negative PSMA PET for secondary lesions;
• IIEF-5 score: > 8;
• Patient compliance with completing periodic questionnaires and attending regular follow-ups as required by the study.

Exclusion Criteria:

• Have prostate cancer classified as low-risk, favorable intermediate-risk, or high-risk;
• Exhibit erectile dysfunction at baseline (IIEF-5 score: < 8);
• Show positive PSMA PET results for metastases or pelvic lymph nodes;
• Have capsular involvement documented by multiparametric prostate MRI;
• Have contraindications to radiotherapy and/or hormone therapy;
• Are unable to undergo MRI;
• Cannot adhere to periodic tests and follow-ups;
• Refuse or have contraindications to the implantation of intraprostatic fiducials.