PRIAPUS-PCa Study: Stereotactic Body Radiation Therapy (SBRT) and Androgen Deprivation Therapy (ADT) Impact on Sexual Function on Men With Unfavorable Intermediate Risk Prostate Cancer

This study examines how two standard combination treatment for prostate cancer - a highly targeted form of radiation called Stereotactic Body Radiation Therapy (SBRT) and a hormone-blocking treatment called Androgen Deprivation Therapy (ADT) - impact sexual function in men with unfavorable intermediate risk prostate cancer. Participants will complete study questionnaires before treatment or Baseline, and after treatment, on Month 3, 9, 15, and 24.

• SBRT combined with ADT (Combination product): SBRT combined with Zoladex

Primary outcomes

• Change in erectile dysfunction severity from baseline to 24 months, as measured by the change in International Index of Erectile Function 5-item version (IIEF-5) score. [Baseline, 3, 9, 15, and 24 months post-SBRT]: Outcome Measure Title: Change in Erectile Function Score as Measured by the International Index of Erectile Function-5 (IIEF-5 / SHIM) Measurement Tool: International Index of Erectile Function-5 (IIEF-5, also known as SHIM) Unit of Measure: Total IIEF-5 score (range 1-25; higher scores indicate better erectile function) Derived Unit: Change in IIEF-5 score from baseline to 24 months (continuous variable, points)

Secondary outcomes

• Proportion of patients with clinically significant (moderate to severe) erectile dysfunction [Baseline, 3, 9, 15, and 24 months]: Measurement Tool: IIEF-5 (SHIM) Unit of Measure: Percentage (%) of patients with IIEF-5 score ≤ 11
• Change in sexual function, as measured by the Expanded Prostate Cancer Index Composite 26-item version (EPIC-26) sexual domain score [Baseline, 3, 9, 15, and 24 months]: Measurement Tool: EPIC-26 Questionnaire - Sexual Domain Unit of Measure: Standardized domain score (0-100 scale; higher scores indicate better sexual function)
• Hormonal Domain Score of the Expanded Prostate Cancer Index Composite (EPIC-26) [Baseline, 3, 9, 15, and 24 months]: Measurement Tool: EPIC-26 Questionnaire - Hormonal Domain Unit of Measure: Standardized domain score (0-100 scale; higher scores indicate better hormonal function)
• Ejaculatory Function Score as Measured by the Male Sexual Health Questionnaire - Ejaculation Scale (MSHQ-ES-8) [Baseline, 3, 9, 15, and 24 months]: Measurement Tool: Male Sexual Health Questionnaire - Ejaculation Scale (ES-8) Unit of Measure: Total ES-8 score (range 3-40; higher scores indicate worse ejaculatory function)
• Health-Related Quality of Life Score as Measured by EORTC QLQ-ELD14 [Baseline, 3, 9, 15, and 24 months (for patients >70 years)]: Measurement Tool: European Organization for Research and Treatment of Cancer Quality of Life Questionnaire - Elderly Module (EORTC QLQ-ELD14) Unit of Measure: Standardized subscale scores (0-100 scale): Functional scales (higher = better functioning) Symptom scales (higher = greater symptom burden)

Sex: Male, ages: 18 Years to 80 Years

Inclusion Criteria:

* Men aged 18-80 years with biopsy-proven UIR-PCa (National Comprehensive Cancer Network \[NCCN\] criteria: Gleason score 7 (4+3), PSA 10-20 ng/mL, or clinical stage T2b-T2c)
* Planned treatment with SBRT (36.25-37.5 Gy in 5 fractions) and ADT (6 months)
* Baseline sexual function assessment available (International Index of Erectile Function \[IIEF-5, also known as SHIM\] score ≥ 12 or pre-selection erection status score of 1-3: erection insufficient for intercourse, sufficient but not optimal, or normal)
* Eastern Cooperative Oncology Group (ECOG) performance status 0-1.
* Written informed consent to participate.

Exclusion Criteria:

* Prior pelvic radiotherapy, prostate surgery, ADT, or chemotherapy
* Pre-existing severe sexual dysfunction (IIEF-5 score < 12 or pre-selection erection status score of 0: no erection)
* Hypogonadism at presentation (baseline testosterone below normal range)
* Contraindications to SBRT or ADT
* Metastatic disease, second malignancy, or previous malignancies.
* Benign or malignant penile diseases.
* Use of medications altering ejaculation (e.g., 5-alpha reductase inhibitors)
* Psychiatric conditions affecting questionnaire completion or QoL assessment
* Severe comorbidities affecting QoL assessments (e.g., advanced cardiovascular disease).

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