Individuals with intermediate risk, localized prostate cancer will be treated as effectively using fewer and better doses of radiation therapy delivered over five treatment sessions as they will with lower doses delivered over several weeks, a brand new phase III randomized trial suggests. The findings, that are the most recent from a series of studies investigating the advantages of stereotactic body radiation therapy (SBRT) for people diagnosed with prostate cancer, might be presented Monday on the American Society for Radiation Oncology (ASTRO) Annual Meeting.
The PACE B (Prostate Advances in Comparative Evidence) study found SBRT performed in addition to standard treatment with moderately fractionated radiation for people whose prostate cancer had not spread, demonstrating a five-year 96% disease control rate, in comparison with 95% for conventional radiation.
The outcomes for patients in each study arms were higher than we expected. To have the ability to sit down with a patient and say, ‘We will treat you with a low toxicity treatment in five days, and your likelihood of keeping the cancer at bay for five years is 96%, it is a positive conversation to have.”
Nicholas van As, MD, principal investigator for the trial, consultant clinical oncologist and Medical Director of The Royal Marsden NHS Foundation Trust and professor on the Institute of Cancer Research in London
Prostate cancer is some of the commonly diagnosed cancers within the U.S., second only to skin cancer for male patients. There are roughly 288,300 recent cases every year, with rates rising roughly 3% every year since 2014. “As patient volumes rise, substantially reducing the variety of times a patient needs to go to a cancer treatment center frees up worthwhile resources, allowing our radiation oncology teams to treat more patients in less time,” said Prof. van As.
Most prostate cancers are diagnosed before the cancer has grown beyond the prostate gland. The first treatment options for localized prostate cancer include lively surveillance, radiation therapy or surgery to remove the prostate gland.
SBRT is a complicated type of radiation therapy that shrinks or destroys tumors with fewer, higher doses of radiation delivered in a small variety of outpatient sessions. This approach uses advanced imaging and treatment planning techniques to deliver radiation with pinpoint accuracy, minimizing damage to surrounding healthy tissue. Patients who select radiation therapy for intermediate-risk prostate cancer typically receive treatment in 20 each day doses, or fractions, and as much as 40, while SBRT is usually given in five or fewer outpatient treatment sessions.
“There’s a number of evidence now that prostate cancer actually responds higher to a big fraction size given over a shorter time frame,” he said. “We have demonstrated now that the accelerated course is as effective because the protracted course.”
PACE B was a multi-center, international phase III randomized controlled study to analyze whether SBRT was non-inferior to traditional radiation for treating individuals with intermediate risk, localized prostate cancer. Non-inferiority was measured by whether patients remained freed from biochemical clinical failure (BCF), defined as a rise in PSA levels, distant metastases or other evidence the cancer was returning, or death from prostate cancer.
Drawing from 38 centers across the UK and Canada, PACE B researchers enrolled 874 individuals who preferred radiation treatment or were unsuitable for surgery. The median age was 69.8 years old.
Patients were randomly assigned to receive either SBRT (n=443) consisting of 5 fractions over one to 2 weeks (36.25 Gy total dose), or standard radiation (n=441) consisting of 39 fractions over 7.5 weeks (78 Gy) or 20 fractions over 4 weeks (62 Gy). Not one of the patients received hormonal therapy. Median follow-up was 73.1 months.
Five years after treatment, people treated with SBRT had a BCF-event free rate of 95.7% (93.2% – 97.3%), in comparison with 94.6% (91.9% – 96.4%) for those treated with conventional radiation, demonstrating that SBRT was non-inferior to CRT (90% CI, p-value for non-inferiority=0.007).
Unwanted effects were low in each groups, and never significantly different between treatment arms. At five years post-treatment, 5.5% of patients who received SBRT experienced grade 2 or higher negative effects affecting the genital or urinary organs, in comparison with 3.2% in the standard group (p=0.14). Just one person in each arm of the study experienced grade 2 or higher gastrointestinal negative effects (p=0.99).
“Standard radiation treatment is already highly effective and could be very well tolerated in individuals with localized prostate cancer,” Prof. van As said. “But for a healthcare system and for patients, to have this treatment delivered just as effectively in five days versus 4 weeks has huge implications.”
Though he expected SBRT to be non-inferior to traditional radiation, Prof. van As said he was surprised at the extent of disease control they were in a position to display. He attributed the high rates to improvements in image-guidance and technologies to deliver radiation in recent times.
“One among the things this study demonstrated is that outcomes of high-quality radiation therapy are outstanding,” he said. “We have turn into far more precise at tracking and reaching the targets. We’re in a position to put high doses of radiation in the proper place and avoid putting high doses in areas we don’t need it.”
He cautioned the outcomes couldn’t be extrapolated to all individuals with prostate cancer. “Ninety percent of our patients were intermediate risk, but they were the higher end of intermediate risk,” he said. “These results don’t apply to individuals with higher-risk cancer.”
Prof. van As’ team can also be examining using SBRT for patients with higher-risk disease. The PACE trials (NCT01584258) include three studies investigating the advantages of SBRT for individuals with localized prostate cancer. PACE A compared patient’s quality of life following SBRT or prostate surgery, finding fewer urinary and sexual negative effects from SBRT but the next risk for minor bowel problems. PACE C, which has accomplished accrual, investigates how well SBRT works for individuals with intermediate and high-risk prostate cancer who’re also being treated with hormone therapy.
Within the meantime, Prof. van As said, individuals with intermediate risk prostate cancer must be given the choice of SBRT as a substitute for longer courses of radiation or prostate surgery.