Ten-step method of high-dose LDR ¹²⁵ I brachytherapy for intermediate-risk prostate cancer

Dose escalation is key for improved outcomes in intermediate-risk prostate cancer, including unfavorable intermediate-risk (UIR) cases. This educational report is designed to provide information about our quality high-dose ¹²⁵ I seed implantation monotherapy technique in which a biologically effective dose (BED) ≧ 200 Gy is applied for treatment of intermediate-risk prostate cancer. This protocol is named the "Ten-step Method," where the rationale and principle of the method are based on the following four goals: (1) The entire prostate should be covered by the prescription isodose distribution with a sufficient margin from the prostatic capsule, achieving high D90 and V100 values by ¹²⁵ I seed implantation. (2) The high-dose cloud (240 Gy) should not invade the urethra or rectum. (3) In order to achieve goals (1) and (2), make the high-dose cloud intentionally along the periphery (bilateral wall to anterior wall) away from the urethra and rectum. (4) In order to achieve goal (3), seeds at the periphery, except those anterior to the rectal wall, should be placed just 1mm inside the capsule. The data obtained from a total of 137 patients with intermediate-risk prostate cancer treated with low-dose-rate (LDR) monotherapy are shown. The dosimetry parameters were monitored at 1 month after seed implantation by using CT and MRI fusion guidance. The data at 1 month after LDR were: Average D90, BED, and V100 of ¹²⁵ I LDR monotherapy were 194.1 Gy, 207.3 Gy, and 99%, respectively. This ten-step method was reproducible in 137 patients with intermediate-risk prostate cancer, allowing administration of high-dose monotherapy with excellent clinical outcomes.