# Long-Term Control With Proton Beam Therapy for Recurrent Prostate Cancer in the Right Perineum Following Intensity-Modulated Radiation Therapy: A Case Report

## TL;DR

A patient with recurrent prostate cancer in the perineum was successfully treated with proton beam therapy after previous radiation and chemotherapy, showing long-term control with no complications.

## Contribution

This case report demonstrates the effectiveness of proton beam therapy for a rare recurrence site in prostate cancer following IMRT.

## Key findings

- Proton beam therapy led to no mass lesions in the prostate or surrounding tissues five years post-treatment.
- PSA levels remained below 0.008 ng/ml with no late complications observed.
- The patient experienced gradual pain relief after switching to cabazitaxel chemotherapy.

## Abstract

Radiation therapy (RT) is commonly used for the treatment of prostate cancer, with intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT) being the utilized modalities. This case report outlines the treatment course of a recurrent prostate cancer lesion in the right perineal musculature managed with proton therapy following IMRT. A 64-year-old Japanese man, diagnosed with prostate cancer and categorized as high risk according to the National Comprehensive Cancer Network guidelines, underwent six months of androgen deprivation therapy, which included bicalutamide and degarelix acetate. Six months after completing 78 Gy in 39 fractions of IMRT, the patient reported perineal to anal pain. Laboratory tests showed an elevated serum prostate-specific antigen (PSA) level, and pelvic MRI showed a mass lesion in the right perineal musculature. Consequently, the patient was diagnosed with recurrent prostate cancer. Thereafter, the patient underwent eight cycles of systemic chemotherapy with docetaxel; however, his pain progressively worsened. Subsequently, the treatment was switched to 12 cycles of cabazitaxel, which led to gradual pain relief. The patient received PBT at 60 Gy relative biological effectiveness in 30 fractions for the recurrent lesion. Five years after PBT, pelvic MRI showed no mass lesions in the prostate or surrounding tissues. The PSA levels remained low, less than 0.008 ng/ml, and there were no apparent late complications.