Prostate Rectum Spacers
Prostate cancer is the second most common cancer in men worldwide. Around 900,000 cases of prostate cancer were recorded in 2008, with 258,000 deaths. One of the most frequently selected treatment options is radiation therapy, either delivered as brachytherapy or external beam radiotherapy. While prostate radiotherapy has advantages relative to other treatments, one concern is radiation injury to the rectum (radiation proctitis), since the rectum is positioned immediately posterior to the prostate. Rectal radiation injury can result in diarrhea, rectal urgency, mucous production and bleeding, symptoms that may take up to 6-12 months to appear but can occur any time post-irradiation up to 30 years after exposure.
One emerging strategy for reducing this rectal injury is to position a spacer between the two structures, effectively pushing the rectum away from the high dose radiation field.
Researchers have been able to create such spacers by placing different materials into the potential space between the prostate and rectum. Hyaluronic acid (HA) injection into the prostate –rectum space resulted in > 1 cm additional space with no complaints of tenesmus or sensation of rectal filling. Patients treated with HA had a significantly smaller incidence of rectal mucosal damage at proctoscopic examinations (5% vs. 36%, p=0.002) and no macroscopic rectal bleeding (0% vs. 12%, p=0.047) relative to those without HA spacer. A similar study was performed using collagen injections into the same space achieving an average 1.1 cm space between the prostate and anterior rectum resulting in an over 50% reduction in rectal radiation dose during prostate radiotherapy. Researchers evaluating an absorbable balloon inserted into the prostate-rectum space found almost 2 cm space creation with a calculated reduction in rectal radiation. Finally, evaluations of an injectable, absorbable hydrogel (currently in US clinical trials) injected into the same space resulted in about 1 cm of additional space, with over 60% reduction in rectal radiation (rV70).
While still under clinical evaluation, prostate-rectum spacers hold considerable promise to not only reduce unintended rectal radiation and the resulting complications, but to allow for higher doses of cancer radiation, potentially improving patient survival. Additionally, a higher dose per treatment should allow for complete treatment with fewer visits, resulting in increased patient convenience and considerable healthcare cost savings.
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