BERKELEY, CA (UroToday.com) - Because the external-beam radiotherapy treatment of prostate cancer typically is delivered in up to 40 treatment fractions, the reproducible positioning of the target for irradiation is a major source of concern.
Image-guided radiotherapy (IGRT) uses imaging in the radiotherapy treatment room to localize the prostate and secure its correct position relative to the irradiation beams.(1, 2) As a result, the exposure of normal tissues is minimized. This increased accuracy has been exploited to escalate the radiation dose to the prostate for improving tumor control, without increasing the toxicity of the treatment.(3)
While the positioning uncertainties between treatment fractions are minimized, the movement of the prostate during the actual irradiation on any given day (intrafraction motion) still is a problem. For prostate, as for other organs in the pelvic region, an important cause of intrafraction motion is thought to be moving gas pockets inside the rectum. The hypothesis is that an antiflatulent diet diminishes the amount of gas pockets and causes a more stable rectal filling. However, the results of the present study show that an antiflatulent diet during radiotherapy in clinical practice increases the intrafraction prostate motion.
An explanation for the increased prostate motion with the use of an antiflatulent diet might be the age of the patient population. Epidemiologic studies demonstrated a high prevalence of constipation and laxative use in the elderly with a suggested prevalence for constipation as high as 50%.(4) The exact biologic mechanism is unclear, but advancing aged is associated with altered mechanical properties, structural changes and altered control of the pelvic floor.(5) To keep a regular bowel movement, many elderly have their specific food pattern.(5) A dietary advice might disturb this precarious balance, leading to more variation in rectal filling instead of the intended stable rectal filling. This leads to the conclusion that manipulation of rectal filling in the rather elderly prostate cancer patients is problematic.
Another explanation for the failure in reducing the intrafraction prostate motion could be that the hypothesis of intrafraction motion being caused by gas and rectal filling is not correct. Despite studies that suggest gas as a major source,(6-8) the predominant source of intrafraction motion might be different, for example due to clenching of the pelvic muscle, bladder filling, leg motion, or pelvic rotation.(6, 9-11)
Therefore, the exact cause of intrafraction prostate movement needs to be investigated further. Once the mechanism is well understood, we might be able to come up with a theoretical new solution for the problem. Before such an attempt to reduce the intrafraction motion an be introduced in clinical practice, the benefit should be proven first, and it has to be verified whether an advantage in reducing the intrafraction motion also counterbalances the negative aspect of a method.
- Smitsmans MH, Wolthaus JW, Artignan X, et al.: Automatic localization of the prostate for on-line or off-line image-guided radiotherapy. Int J Radiat Oncol Biol Phys 60:623-635, 2004
- Nederveen AJ, Dehnad H, van der Heide UA, et al.: Comparison of megavoltage position verification for prostate irradiation based on bony anatomy and implanted fiducials. Radiother Oncol 68:81-88, 2003
- Lips IM, Dehnad H, van Gils CH, et al.: High-dose intensity-modulated radiotherapy for prostate cancer using daily fiducial marker-based position verification: Acute and late toxicity in 331 patients. Radiat Oncol 3:15, 2008
- Higgins PD, Johanson JF: Epidemiology of constipation in North America: A systematic review. Am J Gastroenterol 99:750-759, 2004
- Bouras EP, Tangalos EG: Chronic constipation in the elderly. Gastroenterol Clin North Am 38:463-480, 2009
- Nederveen AJ, van der Heide UA, Dehnad H, et al.: Measurements and clinical consequences of prostate motion during a radiotherapy fraction. Int J Radiat Oncol Biol Phys 53:206-214, 2002
- Nichol AM, Warde PR, Lockwood GA, et al.: A cinematic magnetic resonance imaging study of milk of magnesia laxative and an antiflatulent diet to reduce intrafraction prostate motion. Int J Radiat Oncol Biol Phys 77:1072-1078, 2010
- Ghilezan MJ, Jaffray DA, Siewerdsen JH, et al.: Prostate gland motion assessed with cine-magnetic resonance imaging (cine-MRI). Int J Radiat Oncol Biol Phys 62:406-417, 2005
- Padhani AR, Khoo VS, Suckling J, et al.: Evaluating the effect of rectal distension and rectal movement on prostate gland position using cine MRI. Int J Radiat Oncol Biol Phys44:525-533, 1999
- O'Doherty UM, McNair HA, Norman AR, et al.: Variability of bladder filling in patients receiving radical radiotherapy to the prostate. Radiother Oncol 79:335-340, 2006
- Mah D, Freedman G, Milestone B, et al.: Measurement of intrafractional prostate motion using magnetic resonance imaging. Int J Radiat Oncol Biol Phys 54:568-575, 2002
Irene M. LIps, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.