Faculty of Physics - University of Bucharest

UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-23 18:12

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Conference: Bucharest University Faculty of Physics 2023 Meeting

Section: Biophysics; Medical Physics

Title:

The impact of Gamma analysis on acceptability criteria in pacient specific quality assurance

Authors:

Alexa Teodora CREȚU(1), Mihai Th. DUMITRACHE(2), Maria VLĂSCEANU(2), Alina DUMITRACHE(2), Claudia Gabriela CHILOM(1)

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Affiliation:

1) Department of Electricity, Solid Physics and Biophysics, Faculty of Physics, University of Bucharest, Măgurele, Romania

2) “Dr. Carol Davila” Central Military Emergency University Hospital Bucharest, Romania

E-mail

cretualexa99@yahoo.com

Keywords:

IMRT, Gamma analysis, acceptability criteria, action limits, γ index, passing rates

Abstract:

Intensity Modulated Radiation Therapy (IMRT) is a precise and effective treatment technique used in cancer therapy, in terms of conforming high doses of radiation to the target volume, while the organs at risk receive a much smaller dose. The beam delivery system used to irradiate patients generally provides a dose distribution that includes regions of high gradient and must be verified before the treatment. For this reason, every designed treatment plan using the IMRT technique should be verified before the first fraction will be delivered to the patient. During the specific verification of the treatment plan, the ability of the treatment equipment to properly deliver the plan is analyzed. Over time, a large number of quality assurance methods have been developed, including Gamma analysis [1]. Gamma analysis mathematically compares the dose distribution generated by the computerized planning system to that measured by a two-dimensional detector array, in terms of spatial resolution and dose. This method combines the dose difference test with the distance to agreement criteria. The gamma (γ) index, calculated independently for each reference point, is the minimum distance in the renormalized multidimensional space between the evaluated distribution and the reference point. If the value of the γ index is less or equal to 1, the evaluated point passes the test. The aim of this study was to establish the action limits based on the Gamma test’s passing rates, for various acceptability criteria (3%/3mm G, 3%/3mm L, 2%/2mm G, 2%/2mm L, 3%/2mm G). The action limits are defined as the amount the quality measures are allowed to deviate to maintain the quality of treatment delivery as well as defining the action levels for various anatomical sites [2]. For each tumor localization (ORL, lung, prostate), the Gamma test was performed on 50 treatment plans. Based on the results, the confidence and action limits were calculated for each criterion.

References:

[1]. Jabbari K., Pashaei F., Ay M.R., Amouheidari A., Tavakoli M.B., Evaluating the Impact of Various Parameters on the Gamma Index Values of 2D Diode Array in IMRT Verification, J Med Signals Sens, 8, 31-32, 2018. DOI:10.4103/jmss.JMSS_15_17.

[2]. Miften M., Olch A., Mihailidis D., Moran J., Pawlicki T., Molineu A., Li H., Wijesooriya K., Shi J., Xia P., Papanikolaou N., Low D. A., Tolerance Limits and Methodologies for IMRT Measurement-Based Verification QA: Recommendations of AAPM Task Group No. 218, Medical Physics, 2018. DOI:10.1002/mp.12810.