Evaluating long-term outcomes for proton therapy in men with localized prostate cancer.

This study examined the long-term effectiveness and safety of proton therapy for localized prostate cancer. The data showed that proton therapy has favorable outcomes in these patients.

Localized prostate cancer (PCa) is a form of cancer that has not spread beyond the prostate gland. PCa can be treated by surgery, radiation, or hormone therapy. Men with PCa usually have high levels of prostate-specific antigen (PSA). PSA is a protein made by the cells of the prostate gland.

Proton therapy (PT) is a type of radiation therapy that uses a beam of special particles, called protons, instead of X-rays to destroy cancer cells. PT delivers the radiation dosage more precisely to the cancer cells and less to the surrounding healthy tissues such as the bladder and genitals. However, there are very few studies showing the benefits and long-term treatment results of PT for localized PCa.

This study involved 2021 patients with PCa at a single institution. The patients were classified into 6 risk groups: very low risk (V-LR), low risk (LR), favorable intermediate-risk (F-IR), unfavorable intermediate-risk (U-IR), high risk (HR), and very high risk (V-HR). Survival without biochemical relapse (BR) was the first outcome evaluated. If, after treatment, the PSA level increased by 2 ng/ml from the lowest value it was considered as evidence of recurring tumor activity (BR). The average follow-up time was 84 months.

Overall, 89.7% of all patients were alive without BR after 5 years. This percentage was 77.6% after 10 years. 

100% of the patients in V-LR groups were free from BR after 5 and 10 years. 98.5% of the LR group, 93% of the F-IR group, 89.7% of the U-IR group, 88.2% of the HR group, and 75.5% of the V-HR group were alive without BR after 5 years. 

After 10 years, 88.3% in the LR group, 85.5% of the F-IR group, 79.2% of the U-IR group, 68.4% of the HR group, and62.8% of the V-HR group were alive without BR.

Overall, 16.2% of patients had a relapse after an average of 54 months. 96.3% of all patients were alive after 5 years and 87.1% were alive after 10 years. Younger patients were more likely to experience BR.

Mild genital and urinary (GU) side effects occurred in 5.6% of patients after 5 years and moderate GU side effects occurred in 0.4% after 5 years. Mild bowel-related side effects were reported in 6.5% and moderate bowel-related side effects in 0.9% of patients after 5 years.

This study demonstrated that PT has a good long-term effectiveness and safety profile in localized PCa. 

The study is looked back in time at medical records. It was also conducted at a single institution and the PT dose used was lower than the current standard dose. The overall quality of life for patients was not reported.