SU-E-T-212: To Evaluate Significance of Gamma Index Between the Measurement of 2D Detector Arrays and the Calculated Patient 3D Dose Distribution

S Kim; Y Qiu; P Mavroidis; N Papanikolaou; S Stathakis

doi:10.1118/1.4814647

Dose distribution prediction of Gamma index using Random Forests Regression. A retrospective comparison

10.1063/5.0047862 ◽

2021 ◽

Author(s):

Stanislav Bozhikov ◽

Philipa Vassileva ◽

Karina Mitarova ◽

Desislava Aleksandrova ◽

Tsvetomira Hristova ◽

...

Keyword(s):

Random Forests ◽

Dose Distribution ◽

Retrospective Comparison ◽

Gamma Index

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Analysis of the Physical and Radiobiological Equivalence of the Calculated and Measured Dose Distributions for Prostate Stereotactic Radiotherapy

Medical Radiology and radiation safety ◽

10.12737/1024-6177-2021-66-3-68-75 ◽

2021 ◽

Vol 66 (3) ◽

pp. 68-75

Author(s):

E. Sukhikh ◽

L. Sukhikh ◽

A. Vertinsky ◽

P. Izhevsky ◽

I. Sheino ◽

...

Keyword(s):

Radiation Therapy ◽

Dose Distribution ◽

Three Dimensional ◽

Anterior Wall ◽

Dose Distributions ◽

Stereotactic Radiation ◽

Dose Volume Histograms ◽

Dose Volume ◽

Gamma Index ◽

Measured Dose

Purpose: Carrying out the analysis of the physical and radiobiological equivalence of dose distributions obtained during the planning of hypofractionated stereotactic radiation therapy of the prostate cancer and verification using a three-dimensional cylindrical dosimeter. Material and Methods: Based on the anatomical data of twelve patients diagnosed with prostate carcinoma, stage T2N0M0 with low risk, plans were developed for stereotactic radiation therapy with volumetric modulates arc therapy (VMAT). The dose per fraction was 7,25 Gy for 5 fractions (total dose 36,25 Gy) with a normal photon energy of 10 MV. The developed plans were verified using a three-dimensional cylindrical ArcCHECK phantom. During the verification process, the three-dimensional dose distribution in the phantom was measured, based on which the values of the three-dimensional gamma index and the dose–volume histogram within each contoured anatomical structures were calculated with 3DVH software. The gamma index value γ (3 %, 2 mm, GN) at a threshold equal to 20 % of the dose maximum of the plan and the percentage of coincidence of points at least 95 % was chosen as a criterion of physical convergence of the calculated and measured dose distribution according to the recommendations of AAPM TG-218. To analyze the radiobiological equivalence of the calculated and measured dose distribution, the local control probability (TCP) and normal tissue complication probability (NTCP) criteria were used based on the calculated and measured dose–volume histograms. Contours of the target (PTV) and the anterior wall of the rectum were used for the analysis. The approach based on the concept of equivalent uniform dose (EUD) by A. Niemierko was used to calculate the values of TCP/NTCP criteria. Results: The results of physical convergence of plans for all patients on the contour of the whole body were higher than 95 % for the criteria γ (3 %, 2 mm, GN). The convergence along the PTV contour is in the range (75.5–95.2)%. The TCP and NTCP values obtained from the measured dose-volume histograms were higher than the planned values for all patients. It was found that the accelerator delivered a slightly higher dose to the PTV and the anterior wall of the rectum than originally planned. Conclusion: The capabilities of modern dosimetric equipment allow us move to the verification of treatment plans based on the analysis of TCP / NTCP radiobiological equivalence, taking into account the individual characteristics of the patient and the capabilities of radiation therapy equipment.

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Interpretation of Gamma Index for Quality Assurance of Simultaneously Integrated Boost (SIB) IMRT Plans for Head and Neck Carcinoma

Polish Journal of Medical Physics and Engineering ◽

10.1515/pjmpe-2017-0016 ◽

2017 ◽

Vol 23 (4) ◽

pp. 93-97 ◽

Cited By ~ 1

Author(s):

Maria Atiq ◽

Atia Atiq ◽

Khalid Iqbal ◽

Quratul ain Shamsi ◽

Farah Andleeb ◽

...

Keyword(s):

Quality Assurance ◽

Head And Neck ◽

Dose Distribution ◽

Confidence Limit ◽

Passing Rate ◽

Gamma Analysis ◽

Gamma Index ◽

Integrated Boost ◽

Calculated Dose ◽

Dose Difference

Abstract Objective: The Gamma Index is prerequisite to estimate point-by-point difference between measured and calculated dose distribution in terms of both Distance to Agreement (DTA) and Dose Difference (DD). This study aims to inquire what percentage of pixels passing a certain criteria assure a good quality plan and suggest gamma index as efficient mechanism for dose verification of Simultaneous Integrated Boost Intensity Modulated Radiotherapy plans. Method: In this study, dose was calculated for 14 head and neck patients and IMRT Quality Assurance was performed with portal dosimetry using the Eclipse treatment planning system. Eclipse software has a Gamma analysis function to compare measured and calculated dose distribution. Plans of this study were deemed acceptable when passing rate was 95% using tolerance for Distance to agreement (DTA) as 3mm and Dose Difference (DD) as 5%. Result and Conclusion: Thirteen cases pass tolerance criteria of 95% set by our institution. Confidence Limit for DD is 9.3% and for gamma criteria our local CL came out to be 2.0% (i.e., 98.0% passing). Lack of correlation was found between DD and γ passing rate with R2 of 0.0509. Our findings underline the importance of gamma analysis method to predict the quality of dose calculation. Passing rate of 95% is achieved in 93% of cases which is adequate level of accuracy for analyzed plans thus assuring the robustness of SIB IMRT treatment technique. This study can be extended to investigate gamma criteria of 5%/3mm for different tumor localities and to explore confidence limit on target volumes of small extent and simple geometry.

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EPID – a useful interfraction QC tool

Polish Journal of Medical Physics and Engineering ◽

10.2478/pjmpe-2019-0029 ◽

2019 ◽

Vol 25 (4) ◽

pp. 221-228 ◽

Cited By ~ 1

Author(s):

Aleksandra Klimas ◽

Aleksandra Grządziel ◽

Dominika Plaza ◽

Barbara Bekman ◽

Bożena Woźniak ◽

...

Keyword(s):

Treatment Session ◽

Measured Signal ◽

Dose Distributions ◽

Imaging Device ◽

Detector Arrays ◽

X Ray ◽

Gamma Index ◽

Field Geometry ◽

Two Parameters ◽

Delivered Dose

Abstract Biomedical accelerators used in radiotherapy are equipped with detector arrays which are commonly used to obtain the image of patient position during the treatment session. These devices use both kilovolt and megavolt x-ray beams. The advantage of EPID (Electronic Portal Imaging Device) megavolt panels is the correlation of the measured signal with the calibrated dose. The EPID gives a possibility to verify delivered dose. The aim of the study is to answer the question whether EPID can be useful as a tool for interfraction QC (quality control) of dose and geometry repeatability. The EPID system has been calibrated according to the manufacturer’s recommendations to obtain a signal and dose values correlation. Initially, the uncertainty of the EPID matrix measurement was estimated. According to that, the detecting sensitivity of two parameters was checked: discrepancies between the planned and measured dose and field geometry variance. Moreover, the linearity of measured signal-dose function was evaluated. In the second part of the work, an analysis of several dose distributions was performed. In this study, the analysis of clinical cases was limited to stereotactic dynamic radiotherapy. Fluence maps were obtained as a result of the dose distribution measurements with the EPID during treatment sessions. The compatibility of fluence maps was analyzed using the gamma index. The fluence map acquired during the first fraction was the reference one. The obtained results show that EPID system can be used for interfraction control of dose and geometry repeatability.

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