Presented by: Yoshiyuki Miyaji MD, PhD
Department of Urology, Kawasaki Medical School

Introduction

Focal therapy for prostate cancer in cases with low to intermediate risks is increasingly important. In this study, we examined the initial therapeutic outcomes of focal high-dose-rate brachytherapy (HDR-BT) for target lesions in patients with primary localized prostate cancer.

Materials

A prospective study was performed in 16 patients who underwent HDR-BT from April 1, 2020 to December 31, 2021. The suspect lesion on MRI was identified on transrectal 3D-US imaging to place an applicator needle through the perineal area. The planning target volume (PTV) was determined as the gross tumor volume (GTV) plus a margin of 5 mm, and a dose of 19 Gy/fraction was administered to the PTV. Follow-up schedule included prostate-specific antigen (PSA) measurement at 1 and every 3 months and MRI at 3 and every 6 months after treatment. Second look biopsy at treatment area and systematic biopsy were performed at one year after HDR-BT.

Results

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The 16 patients treated with HDR-BT had a median follow-up period of 22.5 (range 12-33) months. The median age was 73.5 (65-85) years, the median pre-treatment PSA level was 7.79 (2.37-14.17) ng/ml, the median prostate volume (PV) was 39.5 cm³, and the Gleason score was 3+3 in 4 cases and 3+4 in 12 cases. The median PTV was 4.52 cm³ and the median PTV to prostate volume (PTV/PV) ratio was 10.6% (4.7-25.6%). Scheduled treatment was provided for all patients without any problems and there were no unexpected adverse events. During follow-up, there were no genitourinary (GU) or gastrointestinal (GI) adverse events. The median PSA reduction rate at 6 months after treatment was 67.8% (4.6-92.5%) and reduction of ≥50% occurred in 10 patients (62.5%). Biochemical failure based on the Phoenix ASTRO consensus (nadir + 2) was 100% at 1 year and 78% at 2 years. MRI showed therapeutic effects on the target lesion in 12 cases (75%). The PSA reduction rate at 6 months of cases with therapeutic effects on MRI was significantly higher compared with those of cases with no therapeutic effects on MRI (p=0.0053).  The 2^nd look biopsy at one year after treatment were performed in 15 cases. Five cases detected viable cell in treatment area, and 4 cases detected ≥ Gleason score 3+4 cancer in non-treatment area. The PSA reduction rate at 6 months of cases with positive on 2^nd look biopsy was significantly lower compared with those of cases with benign on 2^nd look biopsy (p=0.0491).

Conclusion

MRI-US fusion-guided focal HDR-BT is a safe treatment that causes no GU and GI adverse events. These results may be due to the small PTV/PV ratio. However, the therapeutic range of HDR-BT is limited and the Phoenix ASTRO consensus for normal radiotherapy is not applicable. The PSA reduction rate at 6 months may be a useful alternative biochemical marker for prediction of the therapeutic effects of focal HDR-BT.

Funding

None

Lead Authors

Nobuhiko Kamitani, MD, PhD
Department of Radiology, Kawasaki Medical School General Medical Center

Co-Authors

Tsutomu Tamada, MD, PhD
Department of Radiology, Kawasaki Medical School

Shinjiro Simizu,
Department of Urology, Kawasaki Medical School

Seitetsu Sugiyama,
Department of Urology, Kawasaki Medical School General Medical Center

Yujiro Kawata,
Department of Radiology, Kawasaki Medical School

Ryuji Tokiya,
Department of Radiology, Kawasaki Medical School

Shintaro Takahashi,
Department of Urology, Kawasaki Medical School

Masataka Abe,
Department of Urology, Kawasaki Medical School

Shin Ohira,
Department of Urology, Kawasaki Medical School

Mikako Kaifu,
Department of Urology, Kawasaki Medical School

Tomohiro Fujii,
Department of Urology, Kawasaki Medical School

Kuniaki Katsui,
Department of Radiology, Kawasaki Medical School