Radiation Oncologists' Perspectives on Oligometastatic Prostate Cancer: A Survey from Korean Oligometastasis Working Group

Abstract

Background: Interest in the oligometastatic prostate cancer (OMPC) is increasing, and various clinical studies have reported the benefits of metastasis-directed radiation therapy (MDRT) in OMPC. However, the recognition regarding the adopted definitions, methodologies of assessment, and therapeutic approaches is diverse among radiation oncologists. This study aims to evaluate the level of agreement for issues in OMPC among radiation oncologists.

Methods: We generated 15 key questions (KQs) for OMPC relevant to definition, diagnosis, local therapies, and endpoints. Additionally, three clinical scenarios representing synchronous metastatic prostate cancer (mPC) (case 1), metachronous mPC with visceral metastasis (case 2), and metachronous mPC with castration-resistance and history of polymetastasis (case 3) were developed. The 15 KQs were adapted according to each scenario and transformed into 23 questions with 6-9 per scenario. The survey was distributed to 80 radiation oncologists throughout the Republic of Korea. Answer options with 0.0-29.9%, 30-49.9%, 50-69.9%, 70-79.9%, 80-89.9%, and 90-100% agreements were considered as no, minimal, weak, moderate, strong, and near perfect agreement, respectively.

Results: Forty-five candidates voluntarily participated in this study. Among 23 questions, near perfect (n = 4), strong (n = 3), or moderate (n = 2) agreements were shown in nine. For the case recognized as OMPC with agreements of 93% (case 1), near perfect agreements on the application of definitive radiation therapy (RT) for whole metastatic lesions were achieved. While ≥70% agreements regarding optimal dose-fractionation for metastasis-directed RT (MDRT) has not been achieved, stereotactic body RT (SBRT) is favored by clinicians with higher clinical volume.

Conclusion: For the case recognized as OMPC, near perfect agreement for the application of definitive RT for whole metastatic lesions was reached. SBRT was more favored as a MDRT by clinicians with a higher clinical volume.

Keywords: local therapy; oligometastasis; prostate cancer; radiation therapy; survey study.

Figure 1

Flow of questionnaire generation and survey.

Figure 2

Clinical scenarios for the survey. (A) Case 1. A 74-year-old gentleman was shown to have a prostate-specific antigen (PSA) level of 24 ng/mL in a screening test. Transrectal ultrasonography (TRUS) and prostatic biopsy revealed a Gleason score of 8 (4 + 4), with adenocarcinoma in both sides. Magnetic resonance imaging (MRI) and computed tomography (CT) showed a prostatic mass with extraprostatic extension and right seminal vesicle invasion (yellow ellipse) and a lymph node (LN) with a short-axis size of 1 cm in the left obturator area (blue dot). An osteoblastic metastatic lesion with a long diameter of 2 cm in the right posterior iliac bone was confirmed on abdominopelvic (AP) CT and whole-body bone scan (WBBS). There is no evidence of other metastasis on CT and WBBS. Prostate-specific membrane antigen positron emission tomography (PSMA-PET) was not performed. (B) Case 2. A 65-year-old previously healthy gentleman was diagnosed with prostate cancer with clinical stage of T2aN0M0, a Gleason score of 7 (3 + 4), and a PSA of 12 ng/mL (yellow ellipse). The patient underwent a robotic radical prostatectomy. A pathological exam revealed the pathologic stage of pT2aN0 and clear resection margin. After surgery, the PSA level dropped to an undetectable level. However, PSA spiked to 30.4 ng/mL after 3 years. On PSMA-PET, metabolic uptakes were observed in the vertebral body of the 3rd lumber spine (red dot), right obturator LN (blue dot) and a nodule in the left lower lobe of the lung (black dot). There is no evidence of other metastasis. (C) Case 3. A 60-year-old previously healthy man was shown to have a PSA level of 13.8 ng/mL in a screening test. An initial workup revealed prostate adenocarcinoma in both sides of the prostate with a Gleason score of 9 (5 + 4) and clinical stage of T3bN1M0 (yellow ellipse). Two months after androgen-deprivation therapy (ADT), definitive radiation therapy of 70 Gy in 28 fractions was administered to the prostate, seminal vesicles, and elective nodal area. After 3 years of ADT administration, both prostate and right obturator lymph nodes showed complete remission, and PSA was maintained at 1.5 ng/mL without increase. However, the PSA increased to 2.1 ng/mL at 2 years after discontinuation of ADT and then continued to increase to 5.8 ng/mL 3 months later. AP CT and WBBS showed metastases in the 1st and 2nd lumbar spines (red dots), five or more para-aortic LNs (green dots), and left supraclavicular LN (brown dot). Therefore, ADT was resumed and apalutamide was administered. Thereafter, the PSA decreased to 1.5 ng/mL, and complete remission was confirmed by AP CT and WBBS. However, 1 year later, the PSA increased to 5 ng/mL again and 6 or more metastases were newly found in both lungs and liver with sizes of 2–3 cm on chest CT and AP CT (black dots). Bone metastasis was not noted. The patient was administered docetaxel every 3 weeks. AP CT and chest CT after four cycles of chemotherapy showed complete remission in metastatic tumors, except for metastatic lesions in the left upper lobe of the lung and segment 8 of the liver (black dots). In addition, the size of the persistent metastatic lesions increased from 1 cm to 1.5–2 cm. In PSMA-PET, no lesions showed metabolic uptake, other than the two persistent metastatic nodules. Abbreviations: RP, radical prostatectomy; PSMA-PET, prostate-specific membrane antigen positron emission tomography; PSA, prostate-specific antigen; ADT, androgen deprivation therapy; RT, radiation therapy; CTx, chemotherapy.