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Trends in Cancer Research   Volumes    Volume 16 
Abstract
The advanced dose gradient index without the deficiencies of Paddick’s dose gradient index
Markus Wösle
Pages: 55 - 74
Number of pages: 20
Trends in Cancer Research
Volume 16 

Copyright © 2021 Research Trends. All rights reserved

ABSTRACT
 
The ICRU Report 91 recommends, inter alia, Paddick’s dose gradient index (GI) for reporting the values of dose gradients in stereotactic radiotherapy. Nevertheless, the GI shows false positive characteristics on a decreasing physical dose gradient D. One aim of ICRU Report 91 is to better associate treatment complications with the values of dose gradient indices. In this context, the GI is not suitable. Therefore, the author developed an advanced dose gradient index (aGI) to get rid of the deficiencies of the GI. A function of the volume product of the isodoses of interest was used to define the aGI instead of the volume ratio that defines the GI. The dose gradient distributions were quantified by the superficially averaged dose gradient (SADG). The values of the SADG, aGI, and GI were determined for the linac-based stereotactic radiosurgery and radiotherapy of 13 brain metastases and 25 choroidal melanomas, respectively. The aGI was proportional to ΔD/SADG with true characteristics in both irradiation series; ΔD = const. is the dose difference of the isodoses of interest. Pearson’s correlation coefficients were r ≥ 0.647. Contrary to the aGI, the GI showed false positive regression lines with r ≤ -0.511. The growing aGI on a decreasing |SADG| is reasonable because the aGI is nearly a reciprocal dose gradient measure in the form of a radius difference Δr = ΔD/||·D||. The utilisation of the aGI entails no limitations of the comparability of dose gradient values. The GI and other dose gradient indices based on volume ratios of the isodoses of interest should no longer be used for reporting dose gradient values.
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