Stereotactic Re-irradiation of Local Recurrences of Prostate Cancer After Radiotherapy

The diagnosis of local recurrence after radiotherapy in patients with prostate cancer is a serious clinical problem. Interventional salvage treatment in the previously irradiated area is difficult with safety issues of special concern. According to the MASTER meta-analysis the effectiveness of various local salvage methods turned out to be comparable in patients with local recurrence after definitive radiotherapy. Stereotactic radiotherapy (SBRT) had the best toxicity profile, so this non-invasive treatment may be a suitable alternative to other methods. A particular problem is local recurrences after post-prostatectomy radiotherapy. The data on SBRT in such setting are even more scarce than in the case of relapses after definitive radiotherapy. Still, they show a low percentage of serious adverse events of grade ≥3 and good treatment tolerance.

Considering the own experience with re-irradiation of patients with prostate cancer, it was decided that re-irradiation should be carried out in the form of focal SBRT. With the objective of enhancing the safety and quality of salvage re-irradiation, and a comprehensive evaluation of the efficacy of this treatment it was determined that it should be implemented as a prospective phase II study- PROSTARE (PROstate cancer STereotActic Reirradiation).

The evaluation of the tolerance and effectiveness of stereotactic radiotherapy (SBRT) will be performed in patients with local recurrence after conventionally fractionated/moderately hypofractionated definitive radiotherapy (Group A), ultrahypofractionated definitive SBRT (Group C), or after prostatectomy and postoperative radiotherapy (Group B).

The study will be conducted as a single-centre study. The evaluation of the safety and effectiveness of such treatment could help develop qualification criteria for repeated irradiation. As a consequence, this should allow for the implementation of this form of treatment into radiotherapy protocols and then, in a controlled and safe way, into clinical practice.

The total sample size will comprise 55 patients. The expected recruitment period is 6 years (10 patients per year).

Requirements for reirradiation with SBRT:

• Both PET-PSMA and MR of the prostate or prostate bed are required in patients with recurrence after definitive radiotherapy or surgery followed by radiotherapy
• Fiducial implantation is not routinely required
• Empty rectum and partially empty/partially filled bladder (improved reproducibility)* during treatment planning and during each fraction of stereotactic radiotherapy
• Treatment with a linear accelerator is preferred
• CBCT must be performed before each fraction of SBRT with verification for tumour location (GTV)**
• Focal radiotherapy, i.e., irradiation of only the visible tumour with an appropriate margin
• Hormonal treatment is not routinely recommended (according to the ESTRO ACROP consensus) - up to the decision of the attending physician

• Principles of preparation with laxatives - Bisacodyl is advocated 4-5 hours before SBRT. If the diameter of the rectum on the CT for treatment planning exceeds 4 cm in diameter, the procedure should be repeated after appropriate preparation of the patient.

• If stereotactic radiotherapy is conducted on the CyberKnife - KV imaging and Tracking verification are required; additionally an assessment of bladder filling in ultrasonography should be performed

Inclusion criteria

• Local recurrence of prostate cancer after definitive radiotherapy

• biopsy proven or/and
• Consistent MRI and PET-PSMA results and PSA growth dynamics
• Time since primary radiotherapy - at least 2 years
• Good performance status (ZUBROD 0-1)

• If the results of the MRI and PET PSMA are inconsistent, and if there is no technical possibility of performing an MRI biopsy, the treatment is acceptable, but repeated imaging (PET or MRI) should be performed to assess the dynamics of the recurrence.

Exclusion criteria

• Polymetastatic dissemination in distant or regional lymph nodes (N1, M1) or oligometastatic dissemination, but not eligible for local forms of metastasis directed therapy (MDT)
• Tumour volume (GTV) > 14 cc
• Poor tolerability of primary radiotherapy (≥G3 toxicity) or persistent late toxicity ≥G2 interfering with re-irradiation
• Severe dysuria before repeated SBRT (e.g., IPSS ≥19)
• Diseases of the distal part of the rectum or anal canal that may affect SBRT tolerance (e.g., anal fissure)
• Previous prostate brachytherapy
• Substantial risk for further urologic interventions (e.g., TURB/TURP)