“We had a much higher-risk group,” he elaborated (with 55% of patients having a nodal risk exceeding 35%), and PSMA PET was used in the workup in the large majority of patients, improving diagnostic sensitivity.
In delivering radiation, “we made sure to include the common iliac nodes and to go up to L4 and L5 and the common iliac junction,” Dr. Murthy further noted.
Also, the POP-RT trial had a higher prostate dose (biological equivalent dose of 129.6 Gy), used image-guided intensity-modulated radiotherapy, and administered ADT for much longer than the other trial (2 years vs. 4-8 months).
“Prophylactic radiotherapy in this trial improved biochemical failure–free survival and disease-free survival in high-risk prostate cancer patients. The improvement in outcomes was seen in spite of giving long-term ADT and in spite of doing dose escalation,” Dr. Murthy summarized. “There is no overall survival difference as of yet, but that remains to be seen.”
“Based on these results, it would be fair to say that whole-pelvis radiotherapy should be considered for these patients with high-risk and very-high-risk prostate cancer,” he concluded.
Practice-changing findings
“Overall, I’m very impressed with this study,” commented Colleen A. Lawton, MD, of Medical College of Wisconsin, Milwaukee. “The primary endpoint of biochemical failure–free survival is not a great one, but fortunately, the distant metastasis-free survival, a secondary endpoint, was statistically improved also.”
Dr. Colleen A. Lawton
The POP-RT results are not surprising given other lines of evidence, she noted. For example, early results of a trial among postprostatectomy patients (RTOG 0534) suggest a benefit of pelvic lymph node radiation, and findings from studies in other adenocarcinomas, such as breast and rectal, show that treating the lymph nodes improves outcomes.
“I think the data are practice changing. … mostly because there is so much retrospective data suggesting a benefit from lymph node radiotherapy for prostate cancer, especially with adequate doses, but this is the first prospective randomized trial to use proper dosing to the primary and lymph nodes, and adequate ADT,” Dr. Lawton said. “The use of PSMA PET is also important from a selection perspective in identifying patients more likely to have microscopic versus gross lymph node involvement and in follow-up to identify which patients fail in the lymph nodes.”
“I agree with the authors’ conclusions and would definitely recommend lymph node radiotherapy for these high- and very-high-risk patients in addition to the ADT,” she concluded. “The dose to the lymph nodes at 50 Gy in 25 fractions is a bit higher than has been used in all of the RTOG trials (45 Gy in 25 fractions), and I do believe that adequate doses are critical in seeing a benefit to treatment.”
The POP-RT trial was funded by Tata Memorial Centre, the Uro-Oncology Disease Management Group, and the Terry Fox Foundation. Dr. Murthy disclosed no conflicts of interest. Dr. Lawton disclosed that she was a coauthor of the RTOG 9413 trial.
SOURCE: Murthy V et al. ESTRO 2020, Abstract OC-0613.