Analysis of fractionation correction methodologies for multiple phase treatment plans in radiation therapy

Abstract

The use of the exact fractionation correction method, which is applying fractionation correction on the separate dose distributions of a multiple phase treatment before their summation was found to have a significant expected clinical impact. For regions of interest that are irradiated with very heterogeneous dose distributions and significantly different doses per fraction in the different treatment phases, the exact fractionation correction method needs to be applied since a significant underestimation of the true patient outcome can be introduced otherwise.

Practical aspects and uncertainty analysis of biological effective dose (BED) regarding its three-dimensional calculation in multiphase radiotherapy treatment plans

“…It has been shown that different tissues can receive the same total dose but display different biological responses due to their intrinsic radiobiological characteristics and the fractionation scheme used to deliver the dose. [1][2][3][4][5] In order to quantitatively explain the radiobiological effects from a differing prescribed dose and fractionation scheme, Barendsen introduced the "extrapolated response dose" (ERD) concept which was later renamed by J. F. Fowler as the "biological effective dose" (BED). 6,7 The BED expresses the radiobiological effectiveness of the physical dose (PD) delivered with a unique fractionation scheme.…”

“…Current practice is to approximate the maximum, cumulative BED by using a calculation method that excludes location within both phases and thus introduces potential errors and inaccuracies. Besides Jones et al 2 briefly discussing the multiphase BED mathematical properties, Mavroidis et al 4 used an approximate, voxel-based (coordinate sensitive) BED multiphase equation (BED A ) which analyzed the radiobiological responses of both the tumor and adjacent normal tissue by comparing the tumor control probability (TCP) and the normal tissue complication probability (NTCP). 2,4 The study concluded that when heterogeneous dose distributions exist, the BED A produced TCPs that significantly underestimated the actual radiobiological responses, whereas homogeneous dose distributions would render TCPs closer to the true response.…”

Direct evaluation of radiobiological parameters from clinical data in the case of ion beam therapy: an alternative approach to the relative biological effectiveness

“…Since the parameters γ and s are assumed to be radiation type independent, they were kept fixed to the values reported in literature from x-rays irradiations, γ = 4 for the tumor and γ = 3 and s = 0.18 for the bladder (Mavroidis et al 2013) (see table 2). …”

“…Our choice was derived from literature (Mavroidis et al 2013) and reference therein. Since these parameters have been fitted over a population response, it could be conceptually incorrect to directly use them in an individual model (Schinkel et al 2007, Stavrev et al 2010; however, we assumed that they were not too dissimilar to the putative individual ones in the range of the phenomenological estimates and in the clinically-relevant dose range.…”

“…The reference radiation LQ parameters used for the tumor and bladder are summarized in table 2. These values were derived from the 50% response dose D 50 , the maximum normalized value of the dose-response gradient γ and the ratio R = α X /β X , as reported in Mavroidis et al (2013).…”