A Chvetsov*, University of Washington, Seattle, WA

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  A Chvetsov

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TU-D930-IePD-F3-5 (Tuesday, 7/12/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: Clinical studies in radiation therapy show that a reduction in the tumor control probability (TCP) with an increase in the total tumor volumes. To describe these clinical outcomes using the Equivalent Uniform Dose (EUD), a correction is needed that would take into account these tumor volume effects. We propose a correction for the absolute tumor volume in the EUD that would produce an equivalent variation in the TCP.

Methods: The equation for the TCP derived from the Poisson probability distribution predicts that a reduction in TCP with increasing initial tumor volume may be explained by several factors, including: 1) an increase in the initial number of clonogens (or tumor volume) and 2) an increase in the average cellular radiation resistance of the tumor clonogens. We consider the increase in the total tumor volume as an additional volume dependent radioresistance. To simulate this volume dependent radioresistance using the EUD, an equivalent TCP reduction is obtained by an increase in the cell survival fraction that in turn can be obtained by reducing the EUD.

Results: We computed the EUD correction for the absolute tumor volume using analytical and numerical methods. We have shown that the EUD decreases with an increase in the absolute tumor volume when the TCP decreases. The magnitude of the absolute tumor volume correction increases in the radiotherapy problems where the tumor volume effects are significant. The tumor volume effects are significant for the lower radiotherapy doses and for radioresistant tumors.

Conclusion: To improve the analysis of treatment outcomes and biological optimization of radiotherapy in the problems with significant tumor-volume effect. the EUD approach should include a correction for the absolute tumor volume that is consistent with the TCP.

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