Surface dose measurements with commonly used detectors: a consistent thickness correction method

Abstract

The purpose of this study was to review application of a consistent correction method for the solid state detectors, such as thermoluminescent dosimeters (chips (cTLD) and powder (pTLD)), optically stimulated detectors (both closed (OSL) and open (eOSL)), and radiochromic (EBT2) and radiographic (EDR2) films. In addition, to compare measured surface dose using an extrapolation ionization chamber (PTW 30‐360) with other parallel plate chambers RMI‐449 (Attix), Capintec PS‐033, PTW 30‐329 (Markus) and Memorial. Measurements of surface dose for 6 MV photons with parallel plate chambers were used to establish a baseline. cTLD, OSLs, EDR2, and EBT2 measurements were corrected using a method which involved irradiation of three dosimeter stacks, followed by linear extrapolation of individual dosimeter measurements to zero thickness. We determined the magnitude of correction for each detector and compared our results against an alternative correction method based on effective thickness. All uncorrected surface dose measurements exhibited overresponse, compared with the extrapolation chamber data, except for the Attix chamber. The closest match was obtained with the Attix chamber (−0.1%), followed by pTLD (0.5%), Capintec (4.5%), Memorial (7.3%), Markus (10%), cTLD (11.8%), eOSL (12.8%), EBT2 (14%), EDR2 (14.8%), and OSL (26%). Application of published ionization chamber corrections brought all the parallel plate results to within 1% of the extrapolation chamber. The extrapolation method corrected all solid‐state detector results to within 2% of baseline, except the OSLs. Extrapolation of dose using a simple three‐detector stack has been demonstrated to provide thickness corrections for cTLD, eOSLs, EBT2, and EDR2 which can then be used for surface dose measurements. Standard OSLs are not recommended for surface dose measurement. The effective thickness method suffers from the subjectivity inherent in the inclusion of measured percentage depth‐dose curves and is not recommended for these types of measurements.PACS number: 87.56.‐v

In search of a one plan solution for VMAT post‐mastectomy chest wall irradiation

“…Skin doses were evaluated with Gafchromic film (Ashland Advanced Materials, Bridgewater, USA) and nanoDot™ OSLDs (Landauer Inc., Glenwood, USA). OSLD measurements were performed with the dosimeter in its housing and with the dosimeter extracted from its housing (to minimize the effective depth of measurement compared to film 16,17 ). Data are clearly labeled with respect to the OSLD configuration in the subsequent sections.…”

Prediction of skin dose in low‐kV intraoperative radiotherapy using machine learning models trained on results of in vivo dosimetry

“…Gafchromic EBT3 (Ashland Special Ingredients, Bridgewater, NJ, USA) films were used to measure dose to the skin on patients who underwent TARGIT. Because the sensitive layer of the film is 0.125 mm from the surface of the patient, correction for the effective point of measurement is negligible for radiochromic films, and it can be safely assumed that EBT3 measures directly the skin dose. Before the surgical procedure, pieces of radiochromic films were wrapped by a nurse of the surgical staff in a thin sterile envelope.…”

Monte Carlo based investigations of electron contamination from telecobalt unit head in build up region and its impact on surface dose

“…The Theratron 780E telecobalt unit was modelled using the EGSnrc code along with the BEAMnrc user code [15,16] to study the depth dose distribution in water phantom. The component module CONESTAK was used to model the source and 5-cm-thick lead surrounding to the source.…”

“…Surface dose measurement on rectangular and curved surfaces using EBT2 film has been performed and found suitable for the surface dose measurement [14]. Use of EDR2 and EBT2 films for surface dose measurement using consistent thickness correction method has been reviewed and recommended by Reynolds et al [15].…”

“…From literature survey, it is clear that extensive research has been carried out to measure surface dose of telecobalt unit [3,[5][6][7][8][9][10][25][26][27] as well as medical linear accelerator [1,11,12,21,22,[28][29][30]. The researchers have used different measurement techniques such as extrapolation chamber [5], parallel plate chamber [5,6,7], TLD [5,7,8], Gafchromic films [13][14][15][16][17][18][19][20][21][22], MOSFET [31,32]. The Gafchromic EBT3 films have also used for measurement of dose in small X-ray field size [33].…”