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

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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.



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