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A Potent Idea

A clinical trial will test a radiation regimen designed to preserve sexual function in men being treated for prostate cancer. 
BY Beth Fand Incollingo
PUBLISHED November 09, 2018
MEN WITH PROSTATE CANCER may find themselves choosing between numerous treatments that offer similar benefits. In the end, it’s what a man could lose as a result of treatment that often drives the decision.

In addition to causing urinary and/or bowel incon­tinence, prostate cancer treatments including surgery, radiation and hormone therapy can lead to impotence — a big concern for many patients.

That’s why researchers at the University of Texas (UT) Southwestern Medical Center in Dallas launched a clinical trial of a radiation treatment designed to both target cancer and spare nerve bundles and arteries crucial to potency.

The Prostate Oncologic Therapy While Ensuring Neurovascular Conservation (POTEN-C) trial builds on research conducted over a decade to improve radiation therapy for these patients, according to Neil Desai, M.D., M.H.S., an assistant professor of radiation oncology, a Dedman Family Scholar in Clinical Care and principal inves­tigator of the trial. “Nowadays, mortality after treatment for localized prostate cancer is as low as 1 percent at 10 years,” Desai said. “By contrast, as many as half of all patients being treated for prostate cancer will experience some decline in sexual function. It is appropriate, therefore, that our focus has shifted to this aspect of quality of life.”

TRIAL DESIGN
POTEN-C will include men whose cancer is localized to a single side of their prostate and has not spread to other parts of the body. In all, about half of men with localized prostate cancer fall into that category, Desai said. The study aims to determine if it is possible, using innovative technology, to minimize side effects and still preserve the effectiveness of radiation given in a focused manner.

Although men with this stage of prostate cancer are typically eligible for active surveillance, some opt for treat­ment because they worry about disease progression — or because their cancer is growing.

The men in the study will get a 40- to 45-gray dose of radiation on the affected side of their prostate and a reduced dose of 30 gray on the side with no or minimal disease. Stereotactic ablative radiotherapy (SAbR), a highly precise form of radiation, will be used, with a spacer gel (SpaceOAR) placed between the rectum and the prostate to further protect the nerve bundles needed for sexual function.

The trial will enroll 120 patients at up to nine major medical centers and follow them for two years. Half of the participants will be randomly assigned to the new radiation technique, and half will receive standard SAbR. Treatments will occur during five sessions given over a period of two or two-and-a-half weeks, with at least one day separating each treatment.

The researchers’ main goal is to compare the levels of erectile dysfunction experienced after treatment by men receiving single-side radiation versus the dual-side radiotherapy group. They will also track genitourinary and gastrointestinal side effects that occur within nine months of treatment, the length of time before disease progression occurs, recurrence in the original location, the number of deaths from prostate cancer, the appro­priateness of the selected radiation dosing, and the rectal spacer’s success in sparing neurovascular bundles.

To determine whether the technique works, researchers will rely on patient reports comparing potency before versus after treatment. “Our primary endpoint is the change in patient-reported sexual function at two years from therapy on a widely accepted and validated … patient-reported symptom survey for prostate cancer,” Desai said, adding that guidelines for evaluating potency will include whether men can get erections suitable for intercourse and whether they need to rely on medication for help.

RATIONALE
The radiation will be given as a monotherapy (not combined with other treatments) because doctors already know that SAbR by itself is very effective for men with these disease characteristics.

In 2016, for instance, men in the ProtecT trial had a 99 percent 10-year survival rate, regardless of whether they were treated with active surveillance, surgical removal of the prostate or radiotherapy, Desai said. Several other studies have also reported excellent cure rates with SAbR alone in this population, he said, including one at UT Southwestern that demonstrated a 98.6 percent survival rate without any biochemical indication of disease progression in 91 patients over five years.

“This is a population we expect not to die of disease after treatment but whom we are treating to minimize (a) risk of metastasis affecting quality of life and (b) progres­sion to higher-risk disease that would require more toxic multimodal therapy,” Desai said. “Thus, we feel confident that we can achieve high cure rates with SAbR alone, especially in this population.”

The idea that the spacer would be helpful emerged in a phase 1/2 trial of SAbR in men with this stage and form of the disease, also conducted at UT Southwestern. Treating patients with 50 gray of radiation without a spacer resulted in survival without any meaningful rise in prostate-specific antigen, a blood marker associated with prostate cancer’s progression, in 98 percent of participants over five years — but also a 6.6 percent rate of severe rectal toxicity. “Subsequent practice at our institution has been to lower the dose in low-intermediate risk patients and, most importantly, to standardly use SpaceOAR,” and that has eliminated high-grade rectal toxicity, Desai said.

Further impetus for POTEN-C came from a University of Michigan study that evaluated vessel-sparing radiotherapy. The study did not include a control group, but it showed a reduction in erectile dysfunction compared with the rates demonstrated in previous studies that did not use vessel-sparing techniques.

However, the Michigan study used conventional radiotherapy, typical dosages and no spacer. The updated techniques in POTEN-C could, according to Desai, “take the promising results of the Michigan experience to the next level in terms of potency preservation and prove its worth in a randomized fashion required for establishing a new technique in our field.”

ENROLLMENT CONSIDERATIONS
Kevin Stanfield of Mount Vernon, Texas, told UT Southwestern that he considered various options, including watch-and-wait surveillance, surgery and radiation, after learning he had prostate cancer, which had taken his grandfather’s life. He chose to enroll in the POTEN-C trial and receive SAbR.

“The potency was a big deal,” Stanfield said. “It’s not that I’m some sort of Romeo or anything, but my wife is a few years younger than me. We enjoy our time together.”

Additional trial locations will include the University of Michigan, UCLA, University of Pennsylvania, Gibbs Cancer Center & Research Institute in South Carolina, Miami Cancer Institute, University of Colorado and Cleveland Clinic. Enrollment will continue for two to three years. To inquire about enrolling in the trial (the identifier number is NCT03525262), call 214-645-8525 or 214-645-1477.

POTEN-C is funded by Augmenix of Massachusetts, the maker of SpaceOAR gel.
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