The prostate’s next-door neighbor is the rectum, and even with the high accuracy of external-beam radiation therapy for prostate cancer, there is a risk of rectal proctitis (inflammation), with side effects including diarrhea, cramps, bleeding, and pain. Gel spacers – cushions of an injectable gel, which move the rectum farther from the prostate – have been shown to reduce these side effects. But there is room for improvement, says Hopkins radiation oncologist Daniel Song, M.D., Professor and Director of Genitourinary Radiotherapy.

Song and colleagues have been looking for a more precise and reproducible approach. Promising results of a recent trial suggest they have found one: a biodegradable balloon.

“We evaluated the efficacy and safety of a novel spacer balloon that goes between the prostate and rectum, which allows the potential for controlled, adaptable deployment,” says Song, who was first author of the study, published in the International Journal of Radiation Oncology, Biology, Physics . The study involved 222 participants from 16 centers who had T1-T3 prostate cancer and no MRI evidence that their cancer had extended beyond the prostate. Patients were randomly assigned either to a balloon or control group, and then they received intensity-modulated radiation therapy. The balloon was placed with a needle inserted through the perineum (the area between the scrotum and rectum) using transrectal ultrasound guidance.

The trial showed that the balloon was effective at shielding the rectum for the duration of radiation treatment, says Song: “98 percent of men received significantly lower doses of radiation to the rectum – and, as a result, had fewer side effects in this area.” In follow-up visits, the investigators found that the balloon material dissolved within six months after treatment in more than 98 percent of patients.