Presentation Influence of dose uncertainty with fractionation effect on tumor control probability in carbon-ion therapy

Sakama, Makoto  ,  Kanematsu, Nobuyuki  ,  Inaniwa, Taku

2016-05-27
Description
In light ion radiotherapy, the dose concentration is highly sensitive to some uncertainties such as setup and range errors. Here we propose a method for evaluating the influence of dose uncertainty from spatial and range uncertainties with fractionation effect on tumor control probability (TCP) in carbon-ion therapy using the concept of equivalent stochastic dose, which was defined as a voxel dose that gives the mean expected survival fraction (SF) for the stochastically variable dose. Assuming that the probability density functions of dose and alpha variation for given errors are Gaussian distribution, the mean expected survival fractions were calculated with consideration of the correlation of setup and range errors between the fractions. Using this SF, equivalent stochastic clinical dose (ESCD) distributions, i.e. RBE-weighted dose distributions, of lung and prostate cases for various errors were calculated. To account for spatial dose heterogeneity, equivalent uniform stochastic clinical doses(EUSCD)were calculated by using the mean expected survival fraction in the volume of interest. Tumor control probability curves were calculated for assumed each error considering inter-patient sensitivity variation and dose uncertainty with fractionation effect, and affected by the contribution of setup and range errors and correlation of the errors. EUSCDs agreed well with TCP results except for case of large errors. The proposed evaluation method with EUSCD and TCP calculations will be useful for the stable indicator of tumor dose to improve treatment planning in carbon-ion therapy.
The 55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG55)

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