Evaluation of a novel triple-channel radiochromic film analysis procedure using EBT2

This study investigates an X‐ray dose measurement method for computed tomography using Gafchromic films. Nonuniformity of the active layer is a major problem in Gafchromic films. In radiotherapy, nonuniformity error is reduced by applying the double‐exposure technique, but this is impractical in diagnostic radiology because of the heel effect. Therefore, we propose replacing the X‐rays in the double‐exposure technique with ultraviolet (UV)‐A irradiation of Gafchromic EBT2 and EBT3. To improve the reproducibility of the scan position, Gafchromic EBT2 and EBT3 films were attached to a 3‐mm‐thick acrylic plate. The samples were then irradiated with a 10 W UV‐A fluorescent lamp placed at a distance of 72 cm for 30, 60, and 90 minutes. The profile curves were evaluated along the long and short axes of the film center, and the standard deviations of the pixel values were calculated over large areas of the films. Paired t‐test was performed. UV‐A irradiation exerted a significant effect on Gafchromic EBT2 (paired t‐test; p=0.0275) but not on EBT3 (paired t‐test; p=0.2785). Similarly, the homogeneity was improved in Gafchromic EBT2 but not in EBT3. Therefore, the double‐exposure technique under UV‐A irradiation is suitable only for EBT2 films.PACS number(s): 87.53 Bn

Section: Introductionmentioning

confidence: 99%

Correction of nonuniformity error of Gafchromic EBT2 and EBT3

Katsuda

Gotanda

et al. 2016

“…Radiation dose information is provided by a red channel, and information on the degree of uniformity is provided by a blue channel, which information is used for nonuniformity corrections 16 , 17 . However, the uniformity of Gafchromic EBT2 in a single red channel using a double exposure technique (pre‐exposure technique) was equal to that of a triple‐channel method (8) . Therefore, thickness‐unevenness of the active layer was enhanced by uniformly irradiating with UV rays, such as UV exposure to Gafchromic EBT film (7) …”

Section: Discussionmentioning

confidence: 99%

“…In these films, a yellow dye is included in an active layer to reduce nonuniformity errors. A study has shown that the uniformity of Gafchromic EBT2 with a single red channel in a double‐exposure technique (pre‐irradiation technique) is equal to that of a triple‐channel method (8) . Thus, UV could be used for pre‐exposure to improve uniformity.…”

Section: Introductionmentioning

confidence: 99%

Comparing three UV wavelengths for pre‐exposing Gafchromic EBT2 and EBT3 films

Katsuda

Gotanda

et al. 2015

Gafchromic films are used for X‐ray dose measurements during diagnostic examinations and have begun to be used for three‐dimensional X‐ray dose measurements using the high‐resolution characteristics of Gafchromic films for computed tomography. However, the problem of unevenness in Gafchromic film active layers needs to be resolved. Double exposures using X‐rays are performed during therapeutic radiology, although this is difficult for a diagnostic examination because of a heel effect. Thus, it has been suggested that ultraviolet (UV) radiation be used as a substitute for X‐rays. However, the appropriate UV wavelength has not been determined. Thus, we conducted this study to decide an appropriate UV wavelength. UV peak wavelengths of 245 nm (UV‐A), 310 nm (UV‐B), and 365 nm (UV‐C) were used to irradiate EBT2 and EBT3 films. Each UV wavelength was irradiated for 5, 15, 30, and 60 min, and irradiation was then repeated every 60 min up to 360 min. Gafchromic films were scanned after every irradiation using a flatbed scanner. Images were split into RGB images, and red images were analyzed using ImageJ, version 1.44, image analysis software. A region of interest (ROI) one‐half inch in diameter was placed in the center of subtracted Gafchromic film images, and UV irradiation times were plotted against mean pixel values. There were reactions in the front and back of Gafchromic EBT3 and the back of Gafchromic EBT2 with UV‐A and UV‐B. However, UV‐C resulted in some reactions in both sides of Gafchromic EBT2 and EBT3. The UV‐A and UV‐B wavelengths should be used.PACS number(s): 87.53 Bn

“…Furthermore, the gamma pass rates with a DD of 3% and DTA of 3 mm were over 95% for all plans. Van Hoof et al (15) assessed the multichannel method using EBT2 film and reported that the dose discrepancies from the TPS were small, in the order of 0 to 5 cGy for a single square beam. Hayashi et al (14) also performed a similar assessment and reported that the average gamma pass rates in the IMRT and VMAT dose verification were

97.2 % \pm 0.8 %

.…”

Section: Discussionmentioning

confidence: 99%

“…This method allows the separation of the dose‐dependent and dose‐independent parts of the scanned signal, and the multichannel method shows a significant improvement in spatial homogeneity. Hayashi et al (14) and Van Hoof et al (15) reported on the usefulness of the multichannel method compared to the single‐channel method. Moreover, Pevez Azorin et al (16) developed an improved multichannel method by considering the information on unirradiated film.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a single‐scan protocol for radiochromic film dosimetry

Shimohigashi

Araki

Maruyama

et al. 2015

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