[OA240] Comparison between four routine control devices detecting photon beam energy changes

Autor: Francisco Moreno, Joaquín Montes, Cristina Forastero Rodriguez, Rafael Guerrero Alcalde, Jose Manuel de la Vega, Antonio M. Lallena, Damián Guirado Llorente, Miguel Jiménez Melguizo
Rok vydání: 2018
Předmět:
Zdroj: Physica Medica. 52:90
ISSN: 1120-1797
Popis: Purpose The quality assurance (QA) program of a LINAC includes the control of the stability of the photon beam energy, through a control variable, the beam quality BQ. Our department owns four devices for this task. In this work a method to compare the performance of these QA devices is designed and applied. Methods Two photon beams with energies 6 and 15 MV, produced by a Siemens Artiste LINAC, were used to analyse the response of the following QA devices: StarTrack (Iba Dosimetry), QuickCheck and StarCheck (PTW) and IC Profiler (Sun Nuclear). They determine the BQ indirectly through their own control variable, BQ dev which shall be related to the BQ measured in reference conditions. To determine this relationship, the photon energy was modified by varying the bending magnet intensity I BM For each value of I BM , three PDD curves in water and three measurements for each device were taken. Through the measurements taken before and assuming that they follow a normal distribution, pairs of values of BQ and BQ dev were generated using Monte Carlo simulation methods. The pairs of simulated values are related between them by the relationship obtained previously. By comparing if the pair of values are inside or outside the tolerance interval, each simulation is classified as true positive TP, false positive FP, true negative TN or false negative FN. The tolerance interval chosen was 0.5%. Summing all the TP, FP, TN and FN, two parameters can be calculated: sensitivity and specificity. These parameters will allow to compare the performance between devices. Results For all devices, the relationship between BQ dev and BQ is linear, with a determination coefficient r 2 ≥ 0.9 . The QuickCheck and IC Profiler devices showed the best performance, with a sensitivity and a specificity higher than 95%. The StarTrack device had a good sensitivity, but a specificity of around 85%, for both energies. The StarCheck device showed a decent sensitivity, but a specificity of 67.7% and 78.7% for each energy, respectively. Conclusions The QuickCheck and IC Profiler devices showed the best performance, followed by StarTrack. The StarCheck device had a specificity much lower than the other three devices.
Databáze: OpenAIRE
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