Impact of geometric uncertainties on evaluation of treatment techniques for prostate cancer

Craig, Tim; Wong, Eugene; Bauman, Glenn; Battista, Jerry; Van Dyk, Jake

doi:10.1016/j.ijrobp.2004.09.016

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Volume 62, Issue 2 , Pages 426-436, 1 June 2005

Impact of geometric uncertainties on evaluation of treatment techniques for prostate cancer

Presented in part at the 2003 Annual Meeting of the American Association of Physicists in Medicine.

Tim Craig, Ph.D.
- Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada
- Department of Medical Biophysics, University of Western Ontario, London, ON, Canada
- T. Craig is currently at Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada.
Eugene Wong, Ph.D.
- Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada
- Department of Applied Mathematics, University of Western Ontario, London, ON, Canada
- Department of Oncology, University of Western Ontario, London, ON, Canada
Glenn Bauman, M.D.
- Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada
- Department of Oncology, University of Western Ontario, London, ON, Canada
Jerry Battista, Ph.D.
- Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada
- Department of Medical Biophysics, University of Western Ontario, London, ON, Canada
- Department of Oncology, University of Western Ontario, London, ON, Canada
Jake Van Dyk, M.Sc.
- Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada
- Department of Medical Biophysics, University of Western Ontario, London, ON, Canada
- Department of Oncology, University of Western Ontario, London, ON, Canada
- Reprint requests to: Jake Van Dyk, M.Sc., Department of Physics and Engineering, London Regional Cancer Program, London Health Sciences Centre, 790 Commissioners Rd. E., London, ON N6A 4L6 Canada. Tel: (519) 685-8300, ext. 58607; Fax: (519) 685-8658

Received 23 January 2004; received in revised form 14 September 2004; accepted 17 September 2004. published online 01 March 2005.

Purpose: To assess the impact of patient repositioning and internal organ motion on prostate treatment plans using three-dimensional conformal and intensity-modulated radiotherapy.

Methods and materials: Four-field, six-field, and simplified intensity-modulated arc therapy plans were generated for 5 prostate cancer patients. The planning target volume was created by adding a 1-cm margin to the clinical target volume. A convolution model was used to estimate the effect of random geometric uncertainties during treatment. Dose statistics, tumor control probabilities, and normal tissue complication probabilities were compared with and without the presence of uncertainty. The impact of systematic uncertainties was also investigated.

Results: Compared with the planned treatments, the delivered dose distribution with random geometric uncertainties displayed an increase in the apparent minimal dose to the prostate and seminal vesicles and a decrease in the rectal volume receiving a high dose. This increased the tumor control probabilities and decreased the normal tissue complication probabilities. Changes were seen in the percentage of prostate volume receiving 100% and 95% of the prescribed dose, and the minimal dose and tumor control probabilities for the target volume. In addition, the volume receiving at least 65 Gy, the minimal dose, and normal tissue complication probabilities changed considerably for the rectum. The simplified intensity-modulated arc therapy technique was the most sensitive to systematic errors, especially in the anterior-posterior and superior-inferior directions.

Conclusion: Geometric uncertainties should be considered when evaluating treatment plans. Contrary to the widely held belief, increased conformation of the dose distribution is not always associated with increased sensitivity to random geometric uncertainties if a sufficient planning target volume margin is used. Systematic errors may have a variable effect, depending on the treatment technique used.

Keywords: Prostate cancer , Patient repositioning , Organ motion , Convolution , Uncertainty