The goal of this study is to assess the feasibility of high-dose radiotherapy (Single-Dose Radiotherapy, SDRT) of 24 Gy in patients with localized low and intermediate risk prostate cancer using a special system of internal and external immobilization of the prostate gland.

Patients eligible for this study are classified according to the National Comprehensive Cancer Network (NCCN) guidelines as low or intermediate risk prostate cancer (Stage T1-T2c and/or Prostate Specific Antigen (PSA) level ≤20 ng/mL and/or Gleason score of ≤7).

The study will examine the technical feasibility of image-guided volumetrically-modulated arc therapy (VMAT-IGRT) with an emphasis on normal tissue sparing and precision of radiation delivery using dedicated devices (an air-filled endorectal balloon and a Foley catheter) that ensure target immobilization and reproducibility of prostate anatomical localization using a special external patient immobilization system, including patient placement on the patient transfer trolley, which allows patient transfer without removing the endorectal balloon and urinary catheter during all stages of simulation and treatment planning (MR, CT, Positron emission tomography (PET) / CT-simulation) and during the treatment session on the linear accelerator.

Previously untreated patients with localized prostate cancer of the low risk and favorable intermediate risk (NCCN) groups will receive SDRT at a dose of 24 Gy. In patients from the unfavourable intermediate risk (NCCN) group with a visible dominant intraprostatic lesion (DIL), local escalation of the DIL dose to 30 Gy will be performed.

Patients will be followed up at one week and one month after completion of treatment, then every 3 months for 24 months (+/- 4 weeks), and every 6 months thereafter. Evaluation of early and late adverse events will focus, although not exclusively, on the genitourinary and gastrointestinal toxicity, primarily the rectal toxicity. Serum prostate-specific antigen (PSA) levels will be determined according to the clinical follow-up schedule. Multiparametric magnetic resonance imaging (mpMRI) with intravenous contrast will be performed at baseline and at 6-, 12-, and 24-months post-intervention. Participants of the study will be followed up for at least 2 years after treatment.

This study evaluates the clinical outcomes and potential adverse events associated with external beam single-dose radiotherapy (SDRT) using a dedicated internal and external target immobilization system in patients with low- and intermediate-risk localized prostate adenocarcinoma.

The findings from recently published randomized trial demonstrate that five-fraction SBRT is a robust and viable alternative to moderately fractionated radiotherapy for prostate cancer, demonstrating equivalent efficacy with enhanced convenience for patients. The high 5-year biochemical control rates, tolerability of treatment, coupled with the significant advancements in radiotherapy delivery, underscore the potential of Stereotactic Body Radiation Therapy (SBRT) use in prostate cancer treatment.

The feasibility of Single-Dose RadioTherapy (SDRT) in localized prostate cancer was tested in the randomized PROSINT trial comparing 5-session ultra-hypofractionated radiotherapy course with a Single Dose of 24 Gy radiotherapy. The 4-year results of this trial were recently published. The adverse event profile in both comparison groups was exceptionally good, with no severe adverse events of 3 or higher according to the NCI CTCAE v.4.0 scale and similar biochemical tumor response to both treatment regimens.

Patients enrolled in this trial will undergo volumetric intensity modulation arc therapy (VMAT-IGRT) using state-of-the-art dosimetric radiation therapy planning and quality assurance procedures with an emphasis on normal tissue sparing and precision of radiation delivery using dedicated devices that ensure target immobilization and reproducibility of prostate anatomical localization. A special endorectal balloon filled with air will be used for immobilization of the target in the prostate gland and anatomical reproducibility, while a urethral Foley catheter will be used to ensure reproducibility of the urethral position and online tracking of the prostate gland position (during the entire radiotherapy session). The study will also examine the technical feasibility of using a special external patient immobilization system, including patient positioning on a patient transfer trolley, which allows for patient transfer without removing the endorectal balloon and urinary catheter from the table at all stages of pre-radiation preparation (MR, CT, Positron emission tomography (PET) / CT simulation) and during the treatment session on the linear accelerator. Previously untreated patients with localized prostate cancer in the low risk and favorable intermediate risk (NCCN) groups will receive SDRT at a dose of 24 Gy. In patients in the unfavourable intermediate risk (NCCN) group with a visible dominant intraprostatic lesion (DIL), local dose escalation per DIL to 30 Gy will be performed.

Patients will be followed up at one week and one month after completion of treatment, then every 3 months for 24 months (+/- 4 weeks), and every 6 months thereafter. Evaluation of early and late adverse events will focus, although not exclusively, on the genitourinary and gastrointestinal tracts, primarily the rectum. Serum prostate-specific antigen (PSA) levels will be determined according to the clinical follow-up schedule. Multiparametric magnetic resonance imaging (mpMRI) with intravenous contrast will be performed at baseline and at 6-, 12-, and 24-months post-intervention. The study participants will be followed up for at least 2 years.

Inclusion Criteria:

• Signed study specific informed consent form;
• Histologic confirmation of adenocarcinoma of the prostate by biopsy;
• Biopsy Gleason score ≤ 7;
• Up to 6 months of previous hormonal therapy is allowed (but not required);
• PSA ≤ 20 prior to hormone therapy (if given);
• No direct evidence of regional or distant metastases after appropriate staging studies (CT, MRI, 68Ga-Prostate-Specific Membrane Antigen (PSMA) Positron emission tomography (PET) / CT)
• Age ≥ 18;
• Performance Status 0-2;
• International Prostate Symptom Score (IPSS) must be ≤ 15 (alpha blockers allowed)
• Computerized Tomography (CT) or Magnetic Resonance Imaging (MRI) or Ultrasound-based volume estimation of prostate gland ≤ 100 cc

Exclusion Criteria:

• Positive lymph nodes or metastatic disease from prostate cancer on imaging studies (CT, MRI, 68Ga-Prostate-Specific Membrane Antigen (PSMA) Positron emission tomography (PET) / CT);
• Tumour Clinical stage T3 or T4 on MRI;
• Gleason score > 7;
• PSA > 20 ng/mL;
• Previous pelvic radiotherapy;
• Previous surgery for prostate cancer;
• Recent transurethral resection of the prostate (TURP) (less than 3 months);
• Previous hormonal therapy given for more than 6 months prior to therapy;
• Prior invasive malignancy unless disease free for a minimum of 3 years;
• Previous significant urinary obstructive symptoms;
• Significant psychiatric illness;
• Ultrasound or CT or MRI estimate of prostate volume > 100 cc;
• Severe, active co-morbidity.
• Inability to fulfill all dosimetric criteria for target dose coverage and restrictions for the organs at risk according to study protocol;