Based on a recent study conducted at the University of Colorado Cancer Center and published in the journal Physics in Medicine and Biology reveals that endorectal balloons generally used during exact radiation treatment for prostate cancer can distort the prostate in a way that could make radiation miss its target.
"Use of a balloon allows you to stabilize the anatomy. But what we show is that imprecision with balloon placement could reduce radiation dose coverage over the intended area," said investigator at the CU Cancer Center and chief physicist at the University of Colorado School of Medicine Department of Radiation Oncologym, Moyed Miften, PhD, FAAPM.
In particular, Miften and peers including Bernard Jones, Gregory Gan, and Brian Kavanagh studied the method known as stereotactic body radiation, in which powerful, accurately-targeted radiation is delivered only to cancerous sites of the prostate with the intent of eradicating tumor tissue.
An endorectal balloon is required to hold the prostate in place while this high dose is delivered. The study utilized 71 images of 9 patients to demonstrate an average endorectal balloon placement error of 0.5 cm in the inferior direction. Additionally, these placement errors led to less specific radiation targeting and to patchy radiation dose coverage over cancerous sites.
"In radiation oncology, we use a CT scan to image a patient's prostate and then plan necessary treatment. But if during treatment the prostate doesn't match this planning image, we can deliver an imprecise dose," said Miften.
With the employment of endorectal balloon, Miften and colleagues discovered prostates could be slightly pushed or squeezed, causing the prostate to deform slightly from its original shape and also sometimes tilting slightly from its original position in the body. Subsequently these deformations can push parts of the prostate outside the areas that are then rendered unreachable by the targeted radiation.
"What we see is that whether or not a clinician chooses to use an endorectal balloon along with stereotactic body radiation for prostate cancer, it's essential to perform the procedure with image guidance. The key is acquiring images immediately prior to treatment that ensure the anatomy matches the planning CT," concluded Miften.