Ultra-High Single-Dose Radiotherapy Promising in Some With Prostate Cancer

By David Douglas

March 18, 2021

NEW YORK (Reuters Health) - In certain patients with organ-confined prostate cancer, virtual prostatectomy via ultra-high single-dose radiotherapy (SDRT) compares well with curative extreme hypofractionated stereotactic body radiotherapy (SBRT), according to a small study.

"The current most advanced approach to cure localized prostate cancer with radiotherapy is delivered in five sessions," Dr. Carlo Greco of the Champalimaud Centre for the Unknown, in Lisbon, told Reuters Health by email. "We have been able to package the whole treatment into a 15-20-minute single session that yields the same results as the best produced by five sessions."

For their phase-2 trial, published in JAMA Oncology, Dr. Greco and colleagues randomized 30 men with intermediate-risk prostate cancer to receive SDRT or extreme hypofractionated SBRT. Androgen-deprivation therapy was not allowed.

The median age was 66 years in the SDRT group and 74 years in the SBRT group, but apart from age, baseline demographic characteristics were well balanced between the groups. The SDRT group received one 24 Gy radiation dose and those in the SBRT group got fractional dosing of 9 Gy per day for five days.

The researchers note that hydrogel spacers were not used to reduce rectal toxicity. "Rather," they say "rectal sparing was achieved through a noninvasive air-filled endorectal balloon approach to immobilize the prostate during treatment delivery."

Dr. Greco noted that this approach was used in both study groups "to achieve reproducible prostate repositioning with sub-mm accuracy and motion mitigation with a 2 mm tolerance."

Time to appearance and duration of acute and late toxic effects were similar in both groups. Cumulative late actuarial urinary toxic effects did not differ between groups. Actuarial grade-1 late gastrointestinal toxic effects were comparable and no higher-grade effects were seen.

None of the patients with favorable intermediate-risk disease experienced biochemical failure with either regimen and declines in prostate-specific antigen (PSA) level to less than 0.5 ng/mL were seen by 36 months in both study arms.

However, in those with unfavorable intermediate-risk, actuarial four-year PSA-relapse-free survival was 75.0% for SBRT and 64.0% for SDRT. Benign PSA bounces were similar in magnitude and rates of recurrence with both regimens.

"This proof-of-concept parallel-group randomized clinical trial confirms that 24 Gy SDRT is feasible and safe in the treatment of organ-confined prostate cancer," the researchers conclude.

"A major key to success," Dr. Greco added, "has been the ability to employ a new approach to prevent motion of the prostate during treatment, focusing the therapeutic dose onto the prostate and minimizing the risk of normal-tissue side effects."

Radiation oncologist Dr. Emily S. Weg of the University of Washington, in Seattle, who specializes in genitourinary cancers, told Reuters Health by email, "This study certainly represents the leading edge in stereotactic radiation therapy to the prostate."

"We will be eagerly awaiting the safety and efficacy outcomes data once they have longer follow-up," she said.

SOURCE: https://bit.ly/3vxAeHx JAMA Oncology, online March 11, 2021.

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