Separating the Rectum from the Prostate during Proton Beam Radiotherapy of Prostate Cancer Patients Reduces Rectal Side Effects

English

Reviewer: William Levin
Abramson Cancer Center of the University of Pennsylvania
Ultima Vez Modificado: 29 de mayo del 2007

Presenter: K. Nilsson
Presenter's Affiliation: Uppsala University, Sweden
Type of Session: Scientific

Background

Radiation therapy is one of the mainstays of treatment for localized prostate cancer.
Common side effects of this treatment include acute and late rectal toxicity.
Many investigators and clinicians have attempted to reduce the risk of rectal toxicity by displacing the rectum posteriorly, away from the prostate gland.
By displacing the rectum, increased radiation doses can be administered to the prostate gland while decreasing radiation to uninvolved rectum.

Materials and Methods

In the current study, comparative treatment plans were generated for patients with and without retraction of the rectum.
Nine patients with biopsy proven prostate cancer were studied.
Patients received four gold markers implanted in the prostate to verify daily positioning of the gland.
For the rectal immobilization portion of the study a cylindrical rod was inserted into the rectum.
This device was then retracted dorsally in order to maximize the separation between the prostate gland and rectal wall.

Results

On average, the 90% isodose line covered the rectum without the use of rectal retraction, while the 50-70% isodose line covered the rectum with the use of the rectal retraction technique.
There was a 77% reduction in the dose to the outer rectal wall with the use of rectal retraction, p<0.01.
There was a 92% reduction in the dose to the rectal mucosa, favoring the rectal retraction technique p<0.01.
Furthermore, there was a significant reduction in the maximal dose to the rectal wall and mucosa with the use of rectal retraction.

Author's Conclusions

The rectal retraction technique was easily producible and well tolerated.
This technique showed the ability to decrease radiation dose to the rectum during prostate radiotherapy.

Clinical/Scientific Implications

Several randomized prospective trials have shown that there is a dose response for radiation in the treatment of prostate cancer.
Until recently, before the advent of IMRT and proton therapy, higher doses have not been achievable because of acute and late complications to the rectum.
These newer methods of radiation delivery are allowing for increased dose.
Utilizing techniques such as rectal displacement may further minimize rectal toxicity as radiation doses are escalated.
However, there are other studies that have looked at rectal balloons and fluid placed in the rectum with conflicting data.
It will most likely require individualized evaluation in each patient to see if these techniques are appropriate in each specific case.