To investigate the efficacy and safety of radiotherapy for all metastases in patients with metachronous oligo-metastatic prostate cancer after radical treatment.

From October 2011 to February 2021, 41 patients with prostate cancer with less than 5 metastases after radical treatment were retrospectively analyzed in a single center. The median age at radiotherapy was 68 (57-81) years. Forty patients (98%) received androgen deprivation therapy (ADT). There were 28 patients in the hormone sensitive (HSPC) group and 13 patients in the hormone resistant (CRPC) group. The median initial PSA was 24.4 (7.4-399.0) ng/ml. Tumor stage: T₂ stage 11 patients, T₃ stage 27 patients, T₄ stage 3 patients.30 patients were in N₀ stage and 11 patients in N₁ stage. Gleason score was 7 in 12 patients, 8 in 9 patients, 9 in 18 patients, and 10 in 2 patients.33 patients were treated with surgery, and 8 patients were treated with radiotherapy. The time span from diagnosis to metastasis was 3.1 (0.2-1.8) years. Conventional imaging examination (CT/ MRI/bone scan) before radiotherapy was used in 7 patients, and PSMA PET/CT examination was used in 34 patients.The median PSA before radiotherapy was 1.3(0.1-33.8) ng/ml. There were 62 metastases in 41 patients, including 1 lesion in 28 patients, 2 lesions in 9 patients, 3 lesions in 2 patients, and 5 lesions in 2 patients. Fifty-four patients had bone metastases and eight had retroperitoneal lymph node metastases. Twenty-two bone metastases were located in the pelvis, 18 in the vertebral body, 12 in the ribs, one in the femur and one in the sternum.The median metastatic volume was 5.8(0.2-81.7) cm³.Daily image-guided rotational intensity modulated radiotherapy was used to cover all metastases.Dose segmentation modes include 37.5Gy/7.5Gy/5F, 60Gy/3Gy/20F, 65-70Gy/2.6-2.8Gy/25F.The median biological effective dose (BED₃) was 120 (67-147) Gy. The primary endpoint was biochemical progression-free survival (BPFS), the secondary endpoints were acute and late toxic side effects, local relapse-free survival (LPFS), and overall survival (OS).

The median follow-up time was 21 months (range 5-72 months). All patients completed radiotherapy, and 16 patients had grade 1 to 2 acute toxicity and side effects, and no grade 3 or above acute and late stage side effects. 1-year LPFS was 97.1%.The 1-year and 2-year BPFS were 77.5% and 59.2%, respectively. The median BPFS time was 29 months (range 13.9-44.2 months). Univariate analysis showed that the HSPC group (P<0.001) and the group with total metastatic volume ≤ 5.8cm³ (P=0.010) had higher BPFS. The median BPFS time was 37 months in the retroperitoneal lymph node metastases subgroup and 17 months in the bone metastases subgroup (P=0.141). In the HSPC group, the median BPFS was 30(22-38) months. After radiotherapy, PSA decreased in all 28 patients, and increased in 6 patients. The median BPFS was 12(4-18) months. In the CRPC group, the median BPFS was 4(0-8) months. PSA decreased in 10 patients (76.9%) after radiotherapy, and PSA decreased in 6 patients. The median BPFS was 5(3-28) months. Three patients’PSA did not decrease after radiotherapy, and they were treated with new endocrine therapy drugs, chemotherapy, immunotherapy and other systemic therapy.

For patients with metachronous metastases after radical treatment, full coverage radiotherapy has good safety and high local control rate. HSPC patients and patients with low tumor load could be recommended to receive radiotherapy for all metastatic lesions preferentially, and patients with only retroperitoneal lymph node metastases may have better prognosis after radiotherapy than patients with bone metastases.

Prostatic neoplasms; Oligo-metastasis; Oligo-progressive; Radiation therapy