Abstract
Recent publications indicate α/β for prostate carcinoma could be lower than assumed. Therefore, hypofractionation might increase the therapeutic ratio. However, patient repositioning and organ motion may affect hypofractionated treatments more than conventional treatments. Our purpose is to evaluate the potential impact of geometric uncertainties on hypofractionated treatments.Tumor control probability (TCP) and normal tissue complication probability (NTCP) are calculated for simulated conventional and hypofractionated treatments, assuming α/β of 1.5 Gy for prostate and 3.0 Gy for rectum. A Monte Carlo simulation randomly samples systematic and random displacements and produces the cumulative dose distribution for the prostate and rectum. The limiting number of fractions and the impact of different α/β values are also explored.A consistent but small reduction in TCP is seen with hypofractionation (generally <1%) as a result of geometric uncertainties. Escalated hypofractionation seems to allow large TCP gains (∼20%) without increasing NTCP. Treatments of five fractions seem to affect outcome minimally. The α/β value has a much greater impact on TCP than geometric uncertainties.The potential increased influence of geometric uncertainties on hypofractionation seems small. Limited knowledge of radiobiologic response is likely a greater obstacle to prostate hypofractionation than geometric uncertainties.
Published Version
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