Dose distribution in pediatric CT head examination using a new phantom with radiochromic film

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

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“…Gafchromic films are also applicable to X‐ray dose measurements in computed tomography (CT) 6 , 7 , 8 , 9 , 10 , 11 , 12 …”

Section: Introductionmentioning

confidence: 99%

Correction of nonuniformity error of Gafchromic EBT2 and EBT3

Katsuda

Gotanda

et al. 2016

J Applied Clin Med Phys

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“…Particularly, sheet role phantom for radiochromic films has been developed to measure computed tomography (CT) dosimetry in diagnostic examinations. [1,2] In addition, separated cylindrical phantom that sandwiched radiochromic films has also been developed. [3] These measurement manoeuvres enable three-dimensional dose distribution.…”

Section: Introductionmentioning

confidence: 99%

Noise reduction of radiochromic film: median filter processing of subtraction image

Katsuda

Gotanda

et al. 2015

IFMBE Proceedings

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Abstract-Pre-ultraviolet rays exposure is a useful method to reduce non-uniformity error of radiochromic films. However, dust and scratch noises such as spike noise disturb precise measurement. To reduce these , median filter processing is applied for pre-subtraction and subtraction images.To reduce non-uniformity error of the thickness unevenness of Gafchromic EBT film, ultraviolet rays were exposed to correct data. There were three kinds of images obtained: first ultraviolet exposure image, second ultraviolet exposure image and the subtraction image of both. Median filer processing was performed on all these images. Eleven kinds of median filter radius factors (0.0 to 5.0) were applied using image analysis software. Data and graphs were then estimated.The maximum pixels value of dust was 229 on the second ultraviolet exposure image of film 3. After median filter preprocessing, the pixel value of the noises were similar to the minimum value. A 2.0-radius median filer is a useful factor for processing.Noise reduction that affected data of estimated images may be applied to measure radiation doses on a variety of radiochromic films. Ultraviolet exposure and subtraction method with median filter processing enable precise measurement and high spatial resolution dose distribution.

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“…Thus, SRCT-P was flexible in terms of the phantom size and shape, and the depth of the measurement position in the phantom was determined according to where the RFs were inserted between the sheets. In addition, identification of the maximum dose position in the SRCT-P, evaluation of the absorbed dose in a local area, and the detailed dose distribution in the phantom were facilitated [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…To measure the detailed dose distribution, a sheet roll CT dosimetry phantom (SRCT-P) with Radiochromic film (RF) was developed [4,5]. RFs have been developed for measurement of the absorbed dose of low-energy photons IFMBE Proceedings Vol.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Dose Distribution According to Patient Setup Errors in Pediatric Head CT Examination: A Phantom Study

et al. 2015

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Abstract-Radiation doses during computed tomography (CT) examinations are generally evaluated by CT dose index (CTDI). The CTDI is measured by means of a CTDI phantom, which is placed in the center of the CT gantry aperture. However, patients are not always positioned in the centered in clinical settings. In this study, dose distributions associated with patient setup errors and head size were evaluated using phantoms developed for pediatric patients. The phantoms were made using flexible acrylic sheets in a cylindrical shape [diameters of 6 (premature baby), 8 (neonate), 10 (infant), and 12 cm (child)] and placed on the end of the CT bed. The bed position was lowered from the center by up to a radius length for each phantom size. Dose distributions in the phantoms were measured using radiochromic film. By lowering the bed position, the surface doses at 0° increased and those at 180° and the center doses decreased. However, the other measurement positions exhibited complex changes depending on the phantom size. In addition, the shapes of the dose profile curves varied according to the distance from the X-ray tube (i.e. location in the gantry aperture). In this study, the surface doses became smaller with decreasing distance from the X-ray tube. Therefore, decreasing the distance from the lens to the X-ray tube would be an effective way to reduce the absorbed dose of the lens. However, the dose distributions in the phantoms varied in a complex manner depending on patient setup errors and phantom size. In addition, beam slice width and pitch were important factors in determining the amount of the CT dose. To keep radiation doses during CT examination as low as reasonably achievable, it is important to clarify the influence of CT scanning settings on CT dose.

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Dose distribution in pediatric CT head examination using a new phantom with radiochromic film

Cited by 21 publications

References 15 publications

Correction of nonuniformity error of Gafchromic EBT2 and EBT3

Correction of nonuniformity error of Gafchromic EBT2 and EBT3

Noise reduction of radiochromic film: median filter processing of subtraction image

Evaluation of Dose Distribution According to Patient Setup Errors in Pediatric Head CT Examination: A Phantom Study

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