Increasing Number of Fractions in the Case of Non-Uniform Dose and Fixed Nominal BED Leads to Increased Cell Killing in the Treatment Target

Authors: Kuperman VY* and Spradlin GS

DOI: 10.23880/psbj-16000277

Volume 8, Issue 2

Abstract

Purpose: To evaluate how heterogeneity of the target dose affects cell survival in the target and biologically effective dose (BED) depending on the number of fractions ( ). Methods: Effect of dose non-uniformity on the probability of cell survival in the target volume is studied by using the linearquadratic model. In this work we compare cell killing for different fractionation schedules under the assumption that the nominal biologically effective dose is fixed. Results: It is theoretically shown that in the case the probability of cell survival in the target decreases with increasing for an arbitrary ratio , where denote variance and mean of the target dose, respectively. This result is valid for an arbitrary distribution of the target dose. To demonstrate dependence of BED on and , we computed BEDs by using DVHs for 57 clinical cases of early-stage, non-small cell lung cancer. The computed BEDs demonstrate potential increase in cell kill for the considered cases when is increased from 5 to 20 for a fixed . Conclusion: Small variations in the target dose (i.e., ) can significantly reduce BED in Stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery (SRS). The magnitude of decrease in BED can be reduced by increasing . The obtained results indicate that moderate hypo fractionation with can yield higher BED as compared to the frequently used SBRT schedules with five or fewer fractions.

Keywords: Heterogeneous Target Dose; BED; Hypofractionation; SBRT

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