Effects of coefficient of variation of target dose on biologically equivalent dose and equivalent uniform dose in stereotactic body radiotherapy of liver cancer
10.3969/j.issn.1005-202X.2025.05.005
- VernacularTitle:肝癌SBRT治疗计划的靶区剂量分布变异系数对BED和EUD的影响
- Author:
Yufeng QIN
1
;
Bo ZHAO
Author Information
1. 清华大学医学院,北京 100084
- Publication Type:Journal Article
- Keywords:
liver cancer;
stereotactic body radiation therapy;
coefficient of variation;
biologically equivalent dose;
equivalent uniform dose
- From:
Chinese Journal of Medical Physics
2025;42(5):581-588
- CountryChina
- Language:Chinese
-
Abstract:
Objective To explore the quantitative relationship between coefficient of variation(CV)and biologically equivalent dose(BED)in the stereotactic body radiotherapy(SBRT)plans for liver cancer.Methods For 38 clinical liver cancer SBRT plans,the standard deviation of target dose was firstly calculated.Under the condition that the coefficient of variation(CV=σ/(D),where σ represents the standard deviation of the dose and (D)represents the mean dose)equaled 0.055,which was consistent with the mathematical approximation of CV?1,BED was expanded using a Taylor expansion around (D),and the first two terms were taken to derive the functional relationship between BED and CV,as well as BED value.Then,assuming that the dose follows a Gaussian distribution with a variance of σ2 centered at (D),BED value and the functional relationship between BED and CV were derived.Finally,BED value was calculated using the dose-volume histogram,and the BED values obtained from the 3 methods were compared.Results For the two approximate methods,the percentage change in BED for non-uniform dose distributions was as follows:when the SBRT plan had a CV of 0.02,the BED was decreased by approximately 2％using the Taylor expansion and by approximately 2％using the Gaussian distribution.The fitted relationship between CV and BED percentage change showed a BED percentage change of 7.1％.When the SBRT plan had a CV of 0.035,the BED was decreased by 6.1％using the Taylor expansion and by 6.6％using the Gaussian distribution.The fitted relationship between CV and BED percentage change showed a BED percentage change of 20％for a CV of 0.035 99.When the SBRT plan had a CV of 0.09,the BED for a non-uniform dose distribution was decreased by 29％using both the Taylor expansion and the Gaussian distribution as compared with a uniform dose distribution.The fitted relationship between CV and BED percentage change showed a BED decrease of 64.59％for a CV of 0.09.For a conventional 2 Gy×35 fraction plan,a CV of 0.09 resulted in a BED decrease of 14.93％.Conclusion Liver cancer SBRT plans are affected by CV.Even small degrees of non-uniformity can lead to significant reductions in BED and equivalent uniform dose.This reduction increases with higher single-fraction doses when the CV is small.The BED changes caused by the CV in SBRT plans are greater than those in conventional 2 Gy radiotherapy.When the CV is small,the percentage decrease in BED can be predicted using a fitted equation,but the error increases significantly when the CV is large.
