Purpose: This work investigates the potential implications on tumour control probability (TCP) for external beam prostate cancer treatment when considering the bystander effect in partial exposure scenarios.
Materials and Methods: The biological response of a prostate cancer target volume under conditions where a sub-volume of the target volume was not directly irradiated was modelled in terms of surviving fraction (SF) and Poisson-based TCP. A direct comparison was made between the linear-quadratic (LQ) response model, and a response model that incorporates bystander effects as derived from published in vitro data (McMahon et al., 2013, McMahon et al., 2012). Scenarios of random and systematic misses were considered.
Results: Our results suggest the potential for the bystander effect to deviate from LQ predictions when even very small (< 1 %) sub-volumes of the target volume were directly irradiated. Under conditions of random misses for each fraction, the bystander model predicts a 3 % and 1 % improvement in tumour control compared to that predicted by a LQ model when only 90 % and 95 % of the prostate cells randomly receive the intended dose. Under conditions of systematic miss, if even a small portion of the target volume is not directly exposed, the LQ model predicts a TCP approaching zero, whereas the bystander model suggests TCP will improve starting at exposed volumes of around 85%.
Conclusions: The bystander model, when applied to clinically relevant scenarios, demonstrates the potential to deviate from the TCP predictions of the common local LQ model when sub-volumes of a target volume are randomly or systematically missed over a course of fractionated radiation therapy.
Written by:
Balderson MJ, Kirkby C. Are you the author?
University of Calgary, Department of Physics and Astronomy, 2500 University Drive, NW, Calgary, T2N 1N4 Canada.
Reference: Int J Radiat Biol. 2013 Nov 25. Epub ahead of print.
doi: 10.3109/09553002.2014.868617
PubMed Abstract
PMID: 24266432
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