Prostate Stereotactic Radiation and Radio-induced Lymphocyte Apoptosis for Predicting Late Toxicities in Prostate Cancer (PROSTERA)

PROSTERA is a prospective, single-arm, monocentric interventional study (RIPH-2) designed to evaluate the prognostic performance of the Radio-induced Lymphocyte Apoptosis (RILA) assay to predict late radiation-induced toxicities in patients with localized prostate cancer treated with stereotactic body radiotherapy (SBRT).

The primary objective is to determine whether pre-treatment RILA (percentage of apoptotic T-lymphocytes measured ex-vivo after controlled irradiation) is predictive of clinically meaningful late toxicities graded ≥2 according to CTCAE v5.0 within 24 months after SBRT. Secondary objectives include PSA kinetics, patient-reported outcomes (EORTC QLQ-PR25, QLQ-C30 and IPSS), dosimetric correlations, and estimation of diagnostic performance metrics (AUC, sensitivity, specificity) of the RILA assay.

A single peripheral blood sample (2 mL) is collected at the time of CT simulation (inclusion visit). Samples are transported to the designated laboratory (LIRS/RunResearch) and processed according to the RILA SOP: cells are placed in culture (RPMI 1640 + 20% FBS, dilution 1:10) within 4 hours of collection, incubated 16-24 hours, then irradiated ex-vivo (8 Gy; conformational irradiation using institutional accelerator) and incubated for an additional 48 hours. After post-irradiation incubation cells are stained for CD4/CD8 and propidium iodide and analysed by flow cytometry (FACS) on 10,000 events in triplicate to derive the percentage of apoptotic CD4+ and CD8+ T-cells. All assay timings and plate/aliquot identifiers are recorded in laboratory logs. The collected sample is entirely consumed for the assay (no sample retention).

Eligible participants are adult males with localized prostate adenocarcinoma meeting the protocol inclusion criteria (e.g. clinical stage T1-T2, Gleason score 6-7, PSA \<15 ng/mL as per protocol), able to provide written informed consent and compliant with follow-up procedures. Key exclusions include prior pelvic radiotherapy, metastatic disease, inability to consent, and other criteria listed in the protocol. Enrollment will be consecutive to limit selection bias.

All participants receive SBRT delivered according to institutional conformational technique (protocol-specified dose constraints and organ-at-risk delineation per RTOG recommendations; typical stereotactic schedule described in the protocol). Imaging data (centering CT and any low-dose CT), treatment plans and dose-volume histograms (DVH) will be collected and stored in the electronic CRF for dose-toxicity correlation analyses.

Safety and patient-reported outcomes will be recorded during routine follow-up visits at baseline (pre-SBRT) and at 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54 and 60 months post-radiotherapy; CTCAE v5.0 will be used for toxicity grading and the EORTC QLQ-PR25, QLQ-C30 and IPSS questionnaires for quality-of-life and urinary symptom assessment. PSA will be measured at the same scheduled timepoints. No additional study-specific clinic visits are required beyond standard care.

The planned sample size is 220 subjects (calculated to achieve the desired precision for the RILA AUC estimate; \~166 evaluable subjects minimally required), with an anticipated inclusion period of 24 months and maximum individual follow-up of 61 months (total study duration ≈ 88 months). Data will be recorded in a pseudonymized electronic CRF and source documents will remain available in patient medical records. The study will be conducted under the applicable ethical and regulatory framework (CPP approval, MR-001, GDPR).

• Mortality rate of T-CD8+/-CD4+ lymphocytes [Time frame: After in vitro culture and irradiation at 8 Gy]
• Clinical and biological variables of patients [Time frame: At baseline and during follow-up (up to 60 months post-radiotherapy)]
• Quality of life - EORTC QLQ-PR25 [Time frame: Baseline, 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months post-radiotherapy]
• Quality of life - EORTC QLQ-C30 [Time frame: Baseline, 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months post-radiotherapy]
• Urinary symptoms - International Prostate Symptom Score (IPSS) [Time frame: Baseline, 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months post-radiotherapy]
• Treatment tolerance - Number of participants with adverse events [Time frame: Baseline, 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months post-radiotherapy]