Purpose: Estimates of the probability of induction of second cancers following radiotherapy requires several modifications and extensions to the traditional linear dose-risk relationship. In this paper, two models, based on cell kill and an hypothetical "flat" risk response respectively, are modelled and compared using organ dose data from realistic simulations of radiotherapy of the prostate and larynx.
Materials and methods: A general model for cancer induction is used, which in principle takes into account the age profile of radiotherapy patients, a dose dependent DDREF and a general modifying factor which modifies induction probabilities at arbitrarily high doses. The model is applied to measurements of organ doses derived from simulation of a radical prostate treatment delivering 74 Gy to the target volume and a larynx treatment delivering 50 Gy to the target.
Results: A suggested set of realistic conditions gives a total second cancer induction risk of 2.2 - 8.2 cancers per 104 person years for the prostate and 4.4 - 4.7 cancers per 104 person years for the larynx, assuming a DDREF of 1. Widely varying values may be derived if certain key parameters in the models are varied.
Conclusion: Absolute determination of second cancer risk is subject to large uncertainties, but could be used to assess the relative dose and risk burden of alternative radiotherapy treatments, particularly those involving the same clinical site.
Harrison RM. The estimation of second cancer risk following radiotherapy: a discussion of two models. Biomed Imaging Interv J 2007; 3(2):e54.
Dr. Roger Harrison, NGH Unit, Newcastle upon Tyne. Tel: +44 (0)191-233-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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Regional Medical Physics Department, a Clinical Directorate of the Newcastle upon Tyne Hospitals NHS Foundation Trust.
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