Evaluation of a single‐scan protocol for radiochromic film dosimetry

Abstract

The purpose of this study was to evaluate a single‐scan protocol using Gafchromic EBT3 film (EBT3) by comparing it with the commonly used 24‐hr measurement protocol for radiochromic film dosimetry. Radiochromic film is generally scanned 24 hr after film exposure (24‐hr protocol). The single‐scan protocol enables measurement results within a short time using only the verification film, one calibration film, and unirradiated film. The single‐scan protocol was scanned 30 min after film irradiation. The EBT3 calibration curves were obtained with the multichannel film dosimetry method. The dose verifications for each protocol were performed with the step pattern, pyramid pattern, and clinical treatment plans for intensity‐modulated radiation therapy (IMRT). The absolute dose distributions for each protocol were compared with those calculated by the treatment planning system (TPS) using gamma evaluation at 3% and 3 mm. The dose distribution for the single‐scan protocol was within 2% of the 24‐hr protocol dose distribution. For the step pattern, the absolute dose discrepancies between the TPS for the single‐scan and 24‐hr protocols were 2.0±1.8 cGy and 1.4±1.2 cGy at the dose plateau, respectively. The pass rates were 96.0% for the single‐scan protocol and 95.9% for the 24‐hr protocol. Similarly, the dose discrepancies for the pyramid pattern were 3.6±3.5 cGy and 2.9±3.3 cGy, respectively, while the pass rates for the pyramid pattern were 95.3% and 96.4%, respectively. The average pass rates for the four IMRT plans were 96.7%±1.8% for the single‐scan protocol and 97.3%±1.4% for the 24‐hr protocol. Thus, the single‐scan protocol measurement is useful for dose verification of IMRT, based on its accuracy and efficiency.PACS number: 87.55.Qr

Gafchromic EBT3 film dosimetry in electron beams — energy dependence and improved film read‐out

“…Several studies have been published presenting the dosimetric characteristics of the EBT3 film, often comparing to the previous EBT2 model (7,8,9,10,11,12,13) . Many groups have also published dosimetry protocols or comprehensive sets of dosimetry procedures based on the use of the EBT3 film (14,15,16,17,18,19,20) . It has been widely used for various applications, for example verification of IMRT treatment plans, (21) stereotactic radiotherapy, (22,23) in vivo dosimetry, (24) and brachytherapy (25) .…”

Minimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer

“…A dose difference of 2% and a distance to agreement of 2 mm were selected for the gamma analysis to evaluate regions receiving at least 30% of the maximum dose. 9 implies a more modulated/complex plan, and it was assumed that more modulated plans can produce more interplay. A smaller amplitude may cause a smaller interplay, therefore the value of the MCSv divided by the amplitude was smaller for a more dose variation.…”