Biologically consistent dose accumulation using daily patient imaging

Nina I Niebuhr,Asja Pfaffenberger,Ralf O Floca,Clemens M Hentschke,Markus Alber,Peter Huber,Tilman Bostel,Mona Splinter,Joao Seco,Nils H Nicolay,Juliane Hörner-Rieber

doi:10.1186/s13014-021-01789-3

Abstract

BackgroundThis work addresses a basic inconsistency in the way dose is accumulated in radiotherapy when predicting the biological effect based on the linear quadratic model (LQM). To overcome this inconsistency, we introduce and evaluate the concept of the total biological dose, bEQDd.MethodsDaily computed tomography imaging of nine patients treated for prostate carcinoma with intensity-modulated radiotherapy was used to compute the delivered deformed dose on the basis of deformable image registration (DIR). We compared conventional dose accumulation (DA) with the newly introduced bEQDd, a new method of accumulating biological dose that considers each fraction dose and tissue radiobiology. We investigated the impact of the applied fractionation scheme (conventional/hypofractionated), uncertainties induced by the DIR and by the assigned α/β-value.ResultsbEQDd was systematically higher than the conventionally accumulated dose with difference hot spots of 3.3–4.9 Gy detected in six out of nine patients in regions of high dose gradient in the bladder and rectum. For hypofractionation, differences are up to 8.4 Gy. The difference amplitude was found to be in a similar range to worst-case uncertainties induced by DIR and was higher than that induced by α/β. ConclusionUsing bEQDd for dose accumulation overcomes a potential systematic inaccuracy in biological effect prediction based on accumulated dose. Highest impact is found for serial-type late responding organs at risk in dose gradient regions and for hypofractionation. Although hot spot differences are in the order of several Gray, in dose-volume parameters there is little difference compared with using conventional or biological DA. However, when local dose information is used, e.g. dose surface maps, difference hot spots can potentially change outcomes of dose-response modelling and adaptive treatment strategies.

Highlights

This work addresses a basic inconsistency in the way dose is accumulated in radiotherapy when pre‐ dicting the biological effect based on the linear quadratic model (LQM)
It can be seen that the lower the α/β-value used in the Biological equivalent dose (bEQDd) calculation, the higher the difference between bEQDd and Total dose (Da)
For example the highest impact in the given example can be seen for a standard fractionated treatment in the high dose regime with the highest dose variation magnitude where the difference of bEQDd(α/β = 1 Gray [dose unit] (Gy)) to b EQDd(α/β = 10 Gy) is 9.5 Gy. This dependency induces an uncertainty in the calculation of bEQDd based on the uncertainty of the α/β-value which is analyzed in the patient data results

Summary

Introduction

This work addresses a basic inconsistency in the way dose is accumulated in radiotherapy when pre‐ dicting the biological effect based on the linear quadratic model (LQM). To overcome this inconsistency, we introduce and evaluate the concept of the total biological dose, bEQDd. Fractionation is a key principle in the success of radiotherapy treatments, exploiting the biological advantages of different tissue radiosensitivities to open up the therapeutic window described by the commonly used linear quadratic model (LQM) for cell survival [1]. While the fractionated treatment scheme is based on the use of the LQM and daily imaging is available to gain information about the daily dose, both principles are not yet consistently used together.

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