The study aims to reduce the PTV (Planning Target Volume) safety margins to 1-2 mm in stereotactic prostate radiotherapy for low- and medium-risk prostate cancers while maintaining a dose of 36.25 Gy in 5 fractions per day. By reducing the hems, the investigators expect a reduction of acute and late toxicity on the organs at risk, dominantly the urethra, bladder, penile bulb, and rectum, and an improvement in the quality of life.

In this prospective study, a total of 100 patients will be treated over 2 years. Patients will be implanted with 4 contrast markers (fiducials) in the prostate - in the base, apex, and right and left lobes of the prostate. Subsequently, 3 planning examinations will be performed: 1. CT with a urinary catheter immediately after the implantation of fiducials (gold contrast markers), with a distance from implantation 2. planning CT and MR without a urinary catheter. The CTV (Clinical Target Volume) will be defined by the prostate, and the border on the PTV will be reduced from 3-5 mm to 1-2 mm isometrically to maximize the reduction of doses to the organs at risk (rectum, bladder, and urethra, penile bulb, testes), the organs at risk (OAR) will be marked in the radiation plan as OAR. Subsequently, the patients will be irradiated with a dose of 36.25 Gy in 5 fractions per day. Acute toxicity will be evaluated in the 1st and 3rd month after radiotherapy, and late toxicity after 4-6 months according to CTCAE criteria (Common Terminology Criteria for Adverse Events).

Inclusion Criteria:

• histologically verified, localized prostate cancer without regional lymphadenopathy or distant metastases
• low or intermediate risk - favorable risk
• staging according to NCCN recommendations:
• low risk: no staging required
• intermediate risk- favorable risk: CT abdomen and pelvis
• PSA up to 15
• age over 18 years
• signed informed consent form
• suitable position of fiducials (to be determined by the physicist)

Exclusion Criteria:

• a histological type other than acinar adenocarcinoma
• the presence of local lymphadenopathy or distant metastases
• a dominant lesion in the periphery that is in contact with the capsule or grows through it
• PSA over 15
• unsatisfactory position of fiducials (to be determined by the physicist)
• previous treatment with radiotherapy to the pelvic area

Only male patients with prostate cancer will be enrolled in the study.

There is no plan to make individual participant data available to other researchers. The data may be provided upon request.