Sensitivity and specificity analysis of 2D small field measurement array: Patient‐specific quality assurance of small target treatments and spatially fractionated radiotherapy

Abstract

The aim of this paper is to describe the tests carried out on a SRSMapCheck array, to verify its reliability and sensitivity for quality assurance (QA) of high gradient treatments as an alternative system to the use of high spatial resolution detectors, such as gafchromic film, whose processing requires meticulous and time-consuming procedures. Methods: In an initial step, general functionality tests were carried out to verify that the equipment meets the manufacturer's specifications. A study of the accuracy of the application of correction factors to compensate for variation in detector response due to dose rate, field size and beam angle incidence has been included. Besides, to assess the ability of the array to detect inaccurately delivered treatments, systematic errors corresponding to the deviation in the position of the leaves and the accuracy of the gantry position, have been introduced. Based on these results, an estimate of sensitivity and specificity values of the device has been completed. The final step included a study applied to high gradient treatment for real cases of spatially fractionated radiotherapy, where the results of SRSMapCheck measurements have been compared with gafchromic films. Results: General commissioning tests meet the manufacturer's specifications. dose rate (DR) response variation is better than 1.5% and for DR above 50 MU/min better than 1%. The results for beam incidences are better than 1% for all gantry angles, including beam incidences parallel to the array. Field size response differences are within the range of ±1% for sizes up to 2 × 2 cm 2 , with a maximum value obtained of 3.5%, for 1 × 1 cm 2 . From the systematic error study, using a Gamma function Γ (2%, 2 mm), the detector presents a high specificity with a value greater than 90% at its lower limit, while its sensitivity has a moderate mean value of 81%. Sensitivity values increase above 86% when we apply a Gamma function Γ (2%, 1 mm) is applied. Finally, the study of actual cases comprises 17 patients, distributed into 11 lung tumors, 3 gynecological and 3 soft tissue tumors. The gafchromic film showed a lower passing rate with an average value of Γ (2%, 2 mm) = 94.1% compared to Γ (2%, 2 mm) = 98.6% reached by the measurements with the array.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Evaluation of a high resolution diode array for CyberKnife quality assurance

“…Thus, it would be desirable to develop some alternative methods that would avoid the use of films, which is time and resource consuming. Recently, high‐resolution arrays have been developed for patient‐specific quality assurance (PSQA) of SRS and SBRT treatments and have proved their usefulness for this purpose 6–11 . Geometric and accuracy tolerances of the CyberKnife system are usually within the submillimeter range.…”

“…Recently, high‐resolution arrays have been developed for patient‐specific quality assurance (PSQA) of SRS and SBRT treatments and have proved their usefulness for this purpose. 6 , 7 , 8 , 9 , 10 , 11 Geometric and accuracy tolerances of the CyberKnife system are usually within the submillimeter range. Thus, whether a detector array has the sensitivity and resolution to discriminate such small errors should be investigated.…”