Separating the Rectum from the Prostate during Proton Beam Radiotherapy of Prostate Cancer Patients Reduces Rectal Side Effects
Reviewer: William Levin
Abramson Cancer Center of the University of Pennsylvania
Last Modified: May 29, 2007
Presenter: K. Nilsson
Presenter's Affiliation: Uppsala University, Sweden
Type of Session: Scientific
- 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.
- 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.
- 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.
- 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.