Clinical evaluation for the difference of absorbed doses calculated to medium and calculated to water by Monte Carlo method

Abstract

BackgroundTo evaluate the difference of absorbed doses calculated to medium and to water by a Monte Carlo (MC) algorithm based treatment planning system (TPS), and to assess the potential clinical impact to dose prescription.MethodsThirty patients, 10 nasopharyngeal cancer (NPC), 10 lung cancer and 10 bone metastases cases, were selected for this study. For each case, the treatment plan was generated using a commercial MC based TPS and dose was calculated to medium (Dm). The plan was recalculated for dose to water (Dw) using the same Monitor Units (MU) and control points. The differences between Dm and Dw were qualitatively evaluated by dose-volume parameters and by the plan subtraction method. All plans were measured using the MapCheck2, and gamma passing rates were calculated.ResultsFor NPC and Lung cases, the mean differences between Dw and Dm for the targets were less than 2% and the maximum difference was 3.9%. The maximum difference of D2% for the organs at risk (OARs) was 6.7%. The maximum differences between Dw and Dm were as high as 10% in certain high density regions. For bone metastases cases, the mean differences between Dw and Dm for the targets were more than 2.2% and the maximum difference was 7.1%. The differences between Dw and Dm for the OARs were basically negligible. At 3%&3 mm criterion, the gamma passing rate of Dw plan and Dm plan were close (> 94%).ConclusionThe differences between Dw and Dm has little clinical impact for most clinical cases. In bony structures the differences may become clinically significant if the target/OAR is receiving doses close to its tolerance limit which can potentially influence the selection or rejection of a particular plan.

Report dose-to-medium in clinical trials where available; a consensus from the Global Harmonisation Group to maximize consistency

“…The uncertainties from dose reporting, although not unimportant, are small compared to the biological uncertainties. The use of D m,m versus D w,m for clinical nasopharyngeal or lung patients results in minimal DVH differences in the target or organs at risk [39]. There is potential for clinically important differences for bony structures with doses already close to the tolerance limit.…”

The status of medical physics in radiotherapy in China

“…After 2015, the number of publications is increased significantly. There are 9 publications in 2016 [118][119][120][121][122][123][124][125][126], 7 publications in 2017 [127][128][129][130][131][132][133], 10 publications in 2018 [134][135][136][137][138][139][140][141][142][143], 9 publications in 2019 [144][145][146][147][148][149][150][151][152] and 8 publications in 2020 [153][154][155][156][157][158][159][160]. Within the subspecialty of radiation therapy, the numbers of publications in the fields of clinical implementation, plan optimization, plan evaluation and quality assurance are 23 papers (37%), 16 papers (26%), 14 papers (23%) and 9 papers (14%), respectively.…”

Dosimetric Impact of Acuros XB Dose-to-Water and Dose-to-Medium Reporting Modes on Lung Stereotactic Body Radiation Therapy and Its Dependency on Structure Composition

“…Several studies have assessed the implications of using AXB for lung SBRT treatment planning [7][8][9][18][19][20][21][22][23][24][25][26][27][28][29][30] . In most cases, the impact in dose-volume parameters is below 2% except for the target coverage, which is considerably lower, and the Dw maximum dose in bony structures, which is significantly higher, in AXB-recalculated plans, as happens when MC is adopted 31 . Certain studies used an older version of AXB (v10) [7][8][9]21,25,26,30 , which differs from more recent versions in many respects, most importantly with regard to CT-to-material conversions 32,33 .…”

“… 7 , 8 , 9 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 In most cases, the effect in dose-volume parameters is below 2% except for the target coverage, which is considerably lower, and the Dw maximum dose in bony structures, which is significantly higher, in AXB-recalculated plans, as happens when MC is adopted. 31 Certain studies used an older version of AXB (v10), 7 , 8 , 9 , 21 , 25 , 26 , 30 which differs from more recent versions in many respects, most importantly with regard to computed tomography (CT)-to-material conversions. 32 The number of dose-volume parameters for organs at risk (OARs) is limited in all studies, particularly those examining Dw, which is a better estimate of dose to sensitive tissue in bone than Dm.…”