A randomized clinical trial of targeted stereotactic ablative radiotherapy (SABR) or stereotactic ablative radiotherapy (SBRT) for men with oligometastatic prostate cancer has been shown to be an effective treatment for patients who wish to delay hormone-suppression therapy.

The ORIOLE trial included 54 randomized patients whose cancer had spread to a limited number of sites outside the prostate after treatment with surgery or radiation. The patients were placed into 1 of 2 arms: a group who were observed but received no further treatment for 6 months and a group who were treated with SABR/SBRT to the metastatic sites outside of the prostate.

Men treated with SABR were significantly less likely to experience increases in their prostate-specific antigen levels and lived significantly longer without any detectable disease progression than patients who received no additional treatment. After 6 months, only 19% of patients treated with SABR saw their disease progress compared with 61% of those who did not receive SABR/SBRT treatment. The median progression-free survival (PFS) time for those in the observation arm was 5.8 months. Meanwhile, more than half of the patients in the SABR-treated arm were still progression-free more than a year after treatment.

When the researchers compared the blood cell samples taken before radiation therapy and the ones taken 90 days after treatment, they found significant, measurable changes in the T cells of patients in the SABR arm but no change in the T cells of those in the observation arm.

Researchers used a combination of traditional imaging technologies, such as bone scans, MRIs, and/or CT scans, as well as a more sensitive, advanced imaging technology known as a prostate-specific membrane antigen (PSMA) PET scan to reveal how high-dose radiation therapy may alter the course of prostate cancer spread or metastasis.

Thirty-six patients randomized to the SABR arm received radiation to all lesions detected by conventional imaging; however, they also underwent PSMA PET scans prior to and 180 days after treatment. The results of those scans were not made available to the physicians developing their treatment plans, they were used only for further analysis and comparison of cancer growth.

The findings indicated that the patients with no additional untreated lesions detected by the PSMA PET scan at baseline were significantly less likely to develop new metastatic lesions at 6 months than those whose PSMA PET scan showed at least 1 additional lesion at baseline. Patients with total consolidation of lesions also had a 4.8 times greater PFS than patients whose PSMA PET scans showed additional lesions.

Currently, PSMA PET scans are not widely available for physicians to use in treatment planning, but this study should add to the growing body of evidence of their usefulness, according to the study authors.

Reference
  1. Trial reports randomized evidence high-dose radiation is effective for men whose prostate cancer has spread [press release]. ASTRO website. Published September 15, 2019. https://www.astro.org/News-and-Publications/News-and-Media-Center/News-Releases/2019/Trial-reports-randomized-evidence-high-dose-radiat. Accessed September 27, 2019.