Gafchromic XR-QA2 Film Research Articles

Development and a feasibility study using Gafchromic XRQA2 film as a novel passive radon measurement technique

In the present paper, a novel passive-type radon measurement technique based on Gafchromic XRQA2 film was developed. A Gafchromic XRQA2 film was modified by peeling off a polyester layer to enhance the film sensitivity to alpha particles, which were mainly emitted from radon and its progeny, and the response of the modified Gafchromic XRQA2 film to alpha particles was investigated. The results indicated that, with the increase in time-integrated alpha activity, the darkness of the exposed modified Gafchromic film increased, and only a small alpha energy dependence with less than 2% relative difference in the film response was observed. Next, the modified Gafchromic XRQA2 film was deployed with a RADUET container for radon measurement to evaluate application feasibility, and the radon response of the modified Gafchromic XRQA2 film was compared with the traditional one of a RADUET with CR-39 detector. The radon calibration was investigated using the radon exposure chamber. The obtained calibration functions showed that the net optical density of modified Gafchromic XRQA2 film was directly proportional to the accumulated radon concentration over the exposure period. From the calibration, the minimum and maximum detectable radon concentrations for a three-month measurement period were estimated to be about 390 Bq m−3 and 15,000 Bq m−3, respectively. Moreover, this technique enables to minimize the effect of thoron interference by the RADUET container design. These results suggest that this technique can be used for measuring radon, particularly in areas with potentially high radon concentrations, for example, underground mines and caves.

Comparison of sensitivity characteristics between GAFCHROMIC LD-V1 and GAFCHROMIC XR-QA2 in mammographic dosimetry.

In recent years, radiochromic films have begun to be used for dosimetry in mammography; however, the most sensitive GAFCHROMIC XR-QA2 (XR-QA2) film is no longer available owing to its discontinuation. In this study, we evaluated the sensitivity characteristics of GAFCHROMIC LD-V1 (LD-V1) as an alternative to XR-QA2 in the field of mammography, at a low dose and low energy. Our results show that the average ratio of the concentration change of LD-V1 divided by the concentration change of XR-QA2 at each absorbed dose was 53.7%, indicating the sensitivity of LD-V1 to be approximately half of XR-QA2. In addition, the linearity of the concentration change is sufficient even within a dose range of 0.59-14.52mGy, which is lower than the manufacturer's recommended dose range. Therefore, the LD-V1 is capable of accurate dose assessment even with a low dose and the low level of energy used in mammography.

P106] CT dose distribution of 10 cm (infants) and 16 cm (adults) by a head CT phantom

It is important to reduce X-ray dose in diagnostic radiology such as CT examination. In order to evaluate the head CT dose distribution of infants and adults. The diameters of the created two half cylindrical acrylic phantoms were 10 cm (infants) and 16 cm (adults). The Gafchromic film was sandwiched between the half of cylindrical acrylic phantoms. The head CT scan parameters were as follows; single scan, 2 cm scan thickness, 120 kV tube voltage, 300 mA tube current, and 1 s of rotation (Aquilion Toshiba Co., Japan). After head CT irradiation, the Gafchromic XR-QA2 film was scanned using an image scanner (EPSON ES-10000G, Seiko Epson Co., Nagano, Japan). Scanning data were analyzed in pixel values by image analysis application image J (National Institute of Health, Bethesda, MD), and CT dose distribution was evaluated. The pixel values of the CT irradiated area indicated the lowest value at the center of the phantom, gradually increased the pixel value to the surface of the phantom continuously. The ratio of the surface/center was 1.05 times for the infant’s phantom, and was 1.15 times for the adult’s phantom. The dose distribution in the head CT of infant’s and adult’s phantoms were evaluated using the half of cylindrical acrylic phantoms with Gafchromic XR-QA2 film. Dose distribution of the CT is able to evaluate using this method.

Gafchromic XRQA-2 film for Strontium-90/Yttrium-90 (Sr-90/Y-90) Detection

Gafchromic XRQA-2 radiochromic film is an effective tool for quality assurance and dose assessment in kilovoltage radiotherapy and diagnostic applications. This work is done to study the response of Gafchromic XRQA-2 film for beta particle detection. Materials investigated are the beta particle source, Sr-90/Y-90 and Gafchromic XRQA-2 film. The film is exposed to Sr-90/Y-90 for different duration of time and scanned with flatbed scanner. The film is analyzed by using a ImageJ software in the red mode. The result shows that the net reflected optical density (Net ROD) increased linearly with increase in time. The Net ROD and time integrated specific surface activity increased linearly with time. The Net ROD for Sr-90/Y-90 is from 0.00 to 0.13. Thus, the Net ROD is highly related to the duration of time exposed to the beta source.

P020] The influence of phantom diameter on X-ray CT dose evaluation using radiochromic film

Purpose In recent years, one of most important topic for X-ray CT examination is reducing radiation exposure. We have tried to establish the simple and accurate CT dosimetry method using radiochromic (RC) film. In this study, we investigated how the phantom diameter affects the pixel value distribution of RC film. This research is one step of quantifying dose distribution of X-ray CT using RC film. Methods The radiochromic film was exposed by a clinical CT scanner (Aquilion Lightning, Toshiba Medical Systems). Gafchromic XR-QA2 film was irradiated. The film-folding phantom consists of two acrylic semicylinder. In this study, the large phantom (cylinder cross-section diameter is 16 cm) and the small phantom (cylinder cross-section diameter is 10 cm) were used in this research. The scan parameters were as follows: non-helical scan, tube voltage = 120 kV, tube current = 300 mA, slice thickness = 2 cm, scan speed = 1 s per rotation. Image processing and analysis were performed by MATLAB (The Mathworks, Inc.) and Image J (National Institute of Health). The irradiated films were scanned by a commercial scanner (EPSON ES-10000G, Seiko Epson Co.). Results To compare the pixel value distribution using two differently sized phantom, we used the contour line analysis. The differences of distribution were observed between the large phantom and the small phantom. It was found that the distribution using the large phantom changes clearly. Conclusions In conclusion, our method may be useful for analyzing the distribution of pixel value on various conditions.

Measurement of backscatter factor for kilovoltage x-ray beam using ionization chamber and Gafchromic XR-QA2 film

Backscatter factor (BSF) is an important parameter in the determination of surface dose for kilovoltage X-ray beam. The purpose of this study was to measure the BSF for kilovoltage diagnostic X-ray beam, and compare the measured BSF between Gafchromic XR-QA2 film and shadow free (SFD) ionization chamber (IC). The parameters that may affect the BSF, such as tube voltage (kVp) and field size, were also studied. The results were in good agreement with the TRS 457, with deviation of less than 12 %. Based on the film study, the BSF obtained from the film measurement were found to be lower than that of the IC, with average difference of 26 %. It was also found that smaller field size resulted in lower effective energy, and the amount of photons which scattered back onto the surface were also smaller. This study demonstrated that the Gafchromic XR-QA2 film was not suitable for the application of small field size.

Differential dose absorptions for various biological tissue equivalent materials using Gafchromic XR-QA2 film in diagnostic radiology

Phantoms are devices that simulate human tissues including soft tissues, lungs, and bones in medical and health physics. The purpose of this work was to investigate the differential dose absorption in several commercially available low-cost materials as substitutes to human tissues using Gafchromic XR-QA2 film. The measurement of absorbed dose by different materials of various densities was made using the film to establish the relationship between the absorbed dose and the material density. Materials investigated included soft board materials, Perspex, chicken bone, Jeltrate, chalk, cow bone, marble, and aluminum, which have varying densities from 0.26 to 2.67gcm−3. The absorbed dose increased as the density and atomic number of the material increased. The absorbed dose to the density can be well represented by a polynomial function for the materials used.

Evaluation of the dose distribution according to tube voltage in pediatric head ct examination

Introduction In pediatric computed tomography (CT) examination, CT scanning with low tube voltage is suggested for increase the contrast enhancement. When the tube voltage is lowered, the tube current is raised to keep the image quality. Additionally, the dose distribution varies according to tube voltage and patient size. Purpose In this study, the dose distributions according to tube voltage were evaluated using developed phantoms and radiochromic film for CT dose dosimetry. Materials and methods The phantom shape was cylindrical and diameters were 100 and 140 mm. The dose distributions in the phantom were measured by GAFCHROMIC XR-QA2 film. The scanning tube voltages of CT (Supria; Hitachi Medical Corporation) were 80, 100, 120 and 140 kV. The tube currents were set based on CTDIvol (48.8 mGy) displayed on the CT console. Results In 100 mm phantom, the maximum doses of center or peripheral at 80 and 140 kV were 90.0 or 109.5, and 66.7 or 84.8 mGy, respectably. The maximum dose areas were at the surface in all tube voltage. However, the mean center dose was larger than mean peripheral dose. Additionally, the ratios of center to peripheral were increased according to increase tube voltage. Conclusion The results indicated the dose distribution in pediatric head CT become complex according to tube voltage and phantom size. Furthermore, tube current is important factor in determining the maximum dose. To appreciate the radiation risk, the pediatric CT dose should be evaluated by the dose distributions for each patient size and tube voltage. Disclosure We have no disclosure and financial support.

Calculation of conversion factor relating measured patient entrance skin dose and scanner registered computed tomography dose index during sinus examination

Introduction Radiochromic films (RF) have successfully been used in measuring radiation doses in computed tomography (CT). The films were reported to have the ability to picture radiation dose profile, to measure entrance surface dose (ESD), and the peak surface dose (PSD). Purpose The objective of this work was to study the feasibility of using RF as in vivo dosimeters to measure ESD from patients undergoing routine CT examination of the sinus and relate the measurements to the scanner calculated computed tomography dose index ( CTDI vol ) available at the scanner console. Materials and methods Gafchromic XR-QA2 film strips were calibrated against the reading from a 300 mm long pencil type ionization chamber calibrated in terms of CT dose length product (DLP). The in vivo measured ESD and PSD from 12 patients using films were used to calculate the conversion factors: C S = ESD / CTDI vol and C PK = PSD / CTDI vol . Results The calculated conversion coefficients C S and C pk were 0.88 and 1.18 respectively. The films were easily and effectively implemented as In-vivo dosimeter during CT imaging of the sinus allowing for a more accurate estimate of typical surface doses found in CT imaging. Conclusion The films had the advantage of not interfering with the patient setup and did not produce any image artifacts. The method can be used to study other CT examinations specially the ones with larger beam width and high pitch factor, to predict the peak skin dose, to examine the CT dose profile and the radiation dose distribution during annual QA. Disclosure we have nothing to disclose in relation with the presented work.

Energy response characteristics of radiochromic film at CT radiation quality

Introduction Radiochromic films (RF) have been developed for measurement of the absorbed dose of low-energy photons and to measure CT dose profiles. RF are self-developing and radiation sensitive, and the amount of darkening is proportional to the absorbed dose. RF are easy to handle due to their insensitivity to interior room light. Purpose In this study, energy response of GAFCHROMIC XR-QA2 film (XR-QA2) was evaluated to obtain an accurate measurement of CT dose. Materials and methods The measured dose and energy range of the XR-QA2 was designed to be 2–500 mGy and 20–200 kVp. XR-QA2 is a reflective-type film, and a flatbed scanner was used for the measurement of image density. To obtain the calibration curves, XR-QA2 were irradiated at 0–120 mGy (air-kerma) using 10–150 kVp (10 kVp intervals) photon beam with industrial X-ray System(Titan;GE). For image density acquisition, XR-QA2 were scanned before and after irradiate using a flatbed scanner (Epson GS-11000) in RGB (48 bit) mode, 150 dpi. Results The calibration curves varied according to the tube voltage. The energy response was best at 50 kVp and decreased according to increase tube voltage within the range of 50–150 kVp. Additionally, energy response was decreased rapidly below 40 kVp. Conclusion The dose differences were around 10% at 80–140 kVp. This indicated that single calibration curve is not adequate for CT dosimetry performed at different energies. To obtain an accurate measurement of CT dose, calibration curve has to make based on used energy. Disclosure We have no disclosure and financial support.

Estimation of Eye Lens Dose During Brain Scans Using Gafchromic Xr-QA2 Film in Various Multidetector CT Scanners.

The purpose of this study was to estimate eye lens dose during brain scans in 16-, 64-, 128- and 256-slice multidetector computed tomography (CT) scanners in helical acquisition mode and to test the feasibility of using radiochromic film as eye lens dosemeter during CT scanning. Eye lens dose measurements were performed using Gafchromic XR-QA2 film on a polystyrene head phantom designed with outer dimensions equivalent to the head size of a reference Indian man. The response accuracy of XR-QA2 film was validated by using thermoluminescence dosemeters. The eye lens dose measured using XR-QA2 film on head phantom for plain brain scanning in helical mode ranged from 43.8 to 45.8mGy. The XR-QA2 film measured dose values were in agreement with TLD measured dose values within a maximum variation of 8.9%. The good correlation between the two data sets confirms the viability of using XR-QA2 film for eye lens dosimetry.

Examination of the relevance of using radiochromic films in measuring entrance skin dose distribution in conventional digital mammography.

Based on manufacturer specifications, radiochromic films are sensitive enough to be used for dosimetry in digital mammography (DM). The aim of this work was to study the feasibility of measuring entrance surface dose (ESD) distribution using Gafchromic XR-QA2 films. The films were irradiated following a standard clinical two-view screening mammography protocol using a full-field digital mammography (FFDM) imaging system. The films were then digitised using a flatbed scanner. The calibration curve relating the readings from a calibrated ionisation chamber and the films' net optical density (NOD) could not be obtained. The examination of the calibration data revealed non-sensitivity of the films to resolve dose differences below 20 mGy at 28 kVp. Therefore, radiochromic films were found not to be suitable for measuring ESD profiles in DM. A 2D map of the NOD of the irradiated films obtained using in-house developed MATLAB computer program is presented.

An investigation into factors affecting the precision of CT radiation dose profile width measurements using radiochromic films.

To investigate the impact of x-ray beam energy, exposure intensity, and flat-bed scanner uniformity and spatial resolution on the precision of computed tomography (CT) beam width measurements using Gafchromic XR-QA2 film and an off-the-shelf document scanner. Small strips of Gafchromic film were placed at isocenter in a CT scanner and exposed at various x-ray beam energies (80-140 kVp), exposure levels (50-400 mA s), and nominal beam widths (1.25, 5, and 10 mm). The films were scanned in reflection mode on a Ricoh MP3501 flat-bed document scanner using several spatial resolution settings (100 to 400 dpi) and at different locations on the scanner bed. Reflection measurements were captured in digital image files and radiation dose profiles generated by converting the image pixel values to air kerma through film calibration. Beam widths were characterized by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of dose profiles. Dependences of these parameters on the above factors were quantified in percentage change from the baselines. The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within 4.5% and 7.6%, respectively. Increasing scanner spatial resolution significantly increased the uncertainty in both FWHM and FWTM, with FWTM affected by almost 8 times more than FWHM (48.7% vs 6.5%). When uncalibrated dose profiles were used, FWHM and FWTM were over-estimated by 11.6% and 7.6%, respectively. Narrower beam width appeared more sensitive to the film calibration than the wider ones (R(2) = 0.68 and 0.85 for FWHM and FWTM, respectively). The global and maximum local background variations of the document scanner were 1.2%. The intrinsic film nonuniformity for an unexposed film was 0.3%. Measurement of CT beam widths using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. With proper film calibration and scanner resolution setting, it can provide adequate precision for meeting ACR and manufacturer's tolerances for the measurement of CT dose profiles.

Innovative methodology for intercomparison of radionuclide calibrators using short half-life in situ prepared radioactive sources.

An original radionuclide calibrator method for activity determination is presented. The method could be used for intercomparison surveys for short half-life radioactive sources used in Nuclear Medicine, such as(99m)Tc or most positron emission tomography radiopharmaceuticals. By evaluation of the resulting net optical density (netOD) using a standardized scanning method of irradiated Gafchromic XRQA2 film, a comparison of the netOD measurement with a previously determined calibration curve can be made and the difference between the tested radionuclide calibrator and a radionuclide calibrator used as reference device can be calculated. To estimate the total expected measurement uncertainties, a careful analysis of the methodology, for the case of(99m)Tc, was performed: reproducibility determination, scanning conditions, and possible fadeout effects. Since every factor of the activity measurement procedure can influence the final result, the method also evaluates correct syringe positioning inside the radionuclide calibrator. As an alternative to using a calibrated source sent to the surveyed site, which requires a relatively long half-life of the nuclide, or sending a portable calibrated radionuclide calibrator, the proposed method uses a source preparedin situ. An indirect activity determination is achieved by the irradiation of a radiochromic film using (99m)Tc under strictly controlled conditions, and cumulated activity calculation from the initial activity and total irradiation time. The irradiated Gafchromic film and the irradiator, without the source, can then be sent to a National Metrology Institute for evaluation of the results. The methodology described in this paper showed to have a good potential for accurate (3%) radionuclide calibrators intercomparison studies for(99m)Tc between Nuclear Medicine centers without source transfer and can easily be adapted to other short half-life radionuclides.

TH-C-18A-05: Characteristics and Accuracy of CT Radiation Profile Width Measurements Using Radiochromic Films

Purpose: To investigate the impact of several acquisition and image analysis factors on the accuracy of CT beam width measurement using Gafchromic XR-QA2 film and an off the shelf document scanner. Methods: The film was carefully placed at the iso-center and exposed at various x-ray beam energies (80–140 kVp), exposure levels (50–400 mAs), and nominal beam widths (1.25, 5, and 10 mm). Films were scanned on a RICOH MP3501 flat-bed document scanner using reflection mode and various spatial resolutions (100 to 600 dpi) and locations within the scanner bed. Radiation dose profiles were derived by converting the net reflection measurements to dose values (in mGy) through film calibration (which is also described here). The beam widths were characterized by the FWHM and FWTM of the dose profiles and the deviations from the hybrid reference standards were quantified. The impact of x-ray beam energy, exposure intensity, film calibration, and the uniformity and spatial resolution of the document scanner were investigated. Results: The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within approximately 5%. Increasing scanner spatial resolution increased the uncertainty in both FWHM and FWTM (R2 = 0.35–0.71), with the FWTM affected by more than five times than the FWHM (28% vs. 4.9%). When uncalibrated dose profiles were used, the FWHM and FWTM were over-estimated by as much as 11.6% and 7.6%, respectively. Narrower beam width was more sensitive to the film calibration than the wider one (R2 = 0.68 and 0.85 for the FWHM and FWTM, respectively). Conclusion: Measurement of CT beam width using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. It can provide adequate accuracy for all practical purposes with appropriate film calibration and scanner spatial resolution (100 dpi or less).

SU‐E‐J‐152: Evaluation of TrueBeam OBI V. 1.5 CBCT Performance in An Adaptive RT Environment

Purpose:To evaluate the image quality and imaging dose of the Varian TrueBeam OBIv.1.5 CBCT system in a clinical adaptive radiation therapy environment, simulated by changing phantom thickness.Methods:Various OBI CBCT protocols(Head, Pelvis, Thorax, Spotlight) were used to acquire images of Catphan504 phantom(nominal phantom thickness and 10 cm additional phantom thickness). The images were analyzed for low contrast detectability(CNR), uniformity(UI), and HU sensitivity. These results were compared to the same image sets for planning CT(pCT)(GE LightSpeed 16‐ slice). Imaging dose measurements were performed with Gafchromic XRQA2 film for various OBI protocols (Pelvis, Thorax, Spotlight) in a pelvic‐sized phantom(nominal thickness and 4cm additional thickness). Dose measurements were acquired in the interior and at the surface of the phantom.Results:The nominal CNR[additional thickness CNR] for OBI was—Pelvis:1.45[0.81],Thorax:0.86[0.48], Spotlight:0.67[0.39],Head:0.28 [0.10]. The nominal CNR[additional thickness CNR] for pCT was— Pelvis:0.87[0.41],Head:0.60[0.22]. The nominal UI[additional thickness UI] for OBI was—Pelvis:11.5[24.1],Thorax:17.0[20.6], Spotlight:23.2[23.2], Head:15.6[59.9]. The nominal UI[additional thickness UI] for pCT was— Pelvis:9.2[8.6],Head:2.1[2.9]. The HU difference(averaged over all material inserts) between nominal and additional thickness scans for OBI: 8.26HU(Pelvis), 33.39HU(Thorax), 178.98HU(Head), 108.20HU (Spotlight); for pCT: 16.00HU(Pelvis), 19.85HU(Head). Uncertainties in electron density were calculated based on HU values with varying phantom thickness. Average electron‐density deviations (ρ(water)=1)for GE‐Pelvis, GE‐Head, OBI‐Pelvis, OBI‐Thorax, OBI‐Spotlight, and OBI‐Head were: 0.0182, 0.0180, 0.0058, 0.0478, 0.2750, and 0.3115, respectively. The average phantom interior dose was(OBI‐nominal):2.35cGy(Pelvis), 0.60cGy(Thorax), 1.87cGy(Spotlight); OBI‐increased thickness: 1.77cGy(Pelvis), 0.43cGy(Thorax), 1.53cGy (Spotlight). Average surface dose(OBI‐nominal): 2.29cGy(Pelvis), 0.56cGy(Thorax), 1.79cGy (Spotlight); OBI‐increased thickness: 1.94cGy(Pelvis), 0.48cGy(Thorax), 1.47cGy (Spotlight).Conclusion:The OBI‐Pelvis protocol offered comparable CNR and HU constancy to pCT for each geometry; other protocols, particularly Spotlight and Head, exhibited lower HU constancy and CNR. The uniformity of pCT was superior to OBI for all protocols. CNR and UI were degraded for both systems/scan types with increased thickness. The OBI interior dose decreased by approximately 30% with additional thickness.This work was funded, in part, under a grant with the Pennsylvania Department of Health. The Department of Health specifically declaims responsibility for any analyses, interpretations, or conclusions.

Investigation into image quality and dose for different patient geometries with multiple cone‐beam CT systems

To provide quantitative and qualitative image quality metrics and imaging dose for modern Varian On-board Imager (OBI) (ver. 1.5) and Elekta X-ray Volume Imager (XVI) (ver. 4.5R) cone-beam computed tomography (CBCT) systems in a clinical adaptive radiation therapy environment by accounting for varying patient thickness. Image quality measurements were acquired with Catphan 504 phantom (nominal diameter and with additional 10 cm thickness) for OBI and XVI systems and compared to planning CT (pCT) (GE LightSpeed). Various clinical protocols were analyzed for the OBI and XVI systems and analyzed using image quality metrics, including spatial resolution, low contrast detectability, uniformity, and HU sensitivity. Imaging dose measurements were acquired in Wellhofer Scanditronix i'mRT phantom at nominal phantom diameter and with additional 4 cm phantom diameter using GafChromic XRQA2 film. Calibration curves were generated using previously published in-air Air Kerma calibration method. The OBI system full trajectory scans exhibited very little dependence on phantom thickness for accurate HU calculation, while half-trajectory scans with full-fan filter exhibited dependence of HU calculation on phantom thickness. The contrast-to-noise ratio (CNR) for the OBI scans decreased with additional phantom thickness. The uniformity of Head protocol scan was most significantly affected with additional phantom thickness. The spatial resolution and CNR compared favorably with pCT, while the uniformity of the OBI system was slightly inferior to pCT. The OBI scan protocol dose levels for nominal phantom thickness at the central portion of the phantom were 2.61, 0.72, and 1.88 cGy, and for additional phantom thickness were 1.95, 0.48, and 1.52 cGy, for the Pelvis, Thorax, and Spotlight protocols, respectively. The XVI system scans exhibited dependence on phantom thickness for accurate HU calculation regardless of trajectory. The CNR for the XVI scans decreased with additional phantom thickness. The uniformity of the XVI scans was significantly dependent on the selection of the proper FOV setting for all phantom geometries. The spatial resolution, CNR, and uniformity for XVI were lower than values measured for pCT. The XVI scan protocol dose levels at the central portion of the phantom for nominal phantom thickness were 2.14, 2.15, and 0.33 cGy, and for additional phantom thickness were 1.56, 1.68, and 0.21 cGy, for the Pelvis M20, Chest M20, and Prostate Seed S10 scan protocols, respectively. The OBI system offered comparable spatial resolution and CNR results to the results for pCT. Full trajectory scans with the OBI system need little-to-no correction for HU calculation based on HU stability with changing phantom thickness. The XVI system offered lower spatial resolution and CNR results than pCT. In addition, the HU calculation for all scan protocols was dependent on the phantom thickness. The uniformity for each CBCT system was inferior to that of pCT for each phantom geometry. The dose for each system and scan protocol in the interior of the phantom tended to decrease by approximately 25% with 4 cm additional phantom thickness.

Three-dimensional dose distribution in contrast-enhanced digital mammography using Gafchromic XR-QA2 films: Feasibility study

This study was aimed to establish three-dimensional dose distributions for contrast-enhanced digital mammography (CEDM) using self-developed Gafchromic XR-QA2 films. Dose calibration and distribution evaluations were performed on a full-field digital mammography unit with dual energy (DE) contrast-enhanced option. Strategy for dose calibration of films in the DE mode was based on the data obtained from common target/filter/kVp combinations used clinically and the dose response model modified from Rampado's model. Dose derived from films were also verified by measured data from an ionization chamber. The average difference of dose was 8.9% in the dose range for clinical uses. Three-dimensional dose distributions were estimated using triangular acrylic phantom equipped with the mammography system. Five pieces of film sheets were separately placed between the acrylic slabs to evaluate the dose distribution at different depths. After normalizing the dose in each pixel to the maximum dose at the top-center position of the acrylic, normalized dose distribution for transverse, coronal and sagittal planes, could thus be obtained. The depth dose distribution evaluated in this study may further serve as a reference for evaluating the patient glandular dose at different depths based on the entrance exposure information.

Patient entrance surface dose measurements using XR-QA2 Gafchromic films during micturating cystourethrography procedures

The aim of this study was to test the feasibility of using Gafchromic XR-QA2 films in the measurements of patient entrance surface dose (ESD) during the micturating cystourethrogram (MCUG) examination in paediatric patients. Radiochromic films were used to map the entrance dose and to identify the location of peak surface dose (PSD). Direct in vivo measurements of entrance dose were conducted by placing a radiochromic film between the patient and the examination table. The measured ESD values for the commonly performed MCUG fluoroscopic examinations at the authors' institution was in the range of 1.2-7.8 mGy and the PSD in the range of 1.2-8.5 mGy per MCUG procedure for patients with age ranging from 1 to 12 y old. Gafchromic films (XR-QA2) were found to be an efficient and practical dosimetry method that can be easily used to measure clinical patient entrance doses during fluoroscopically guided procedures and potentially in other diagnostic investigations.

Evaluation of different techniques for CT radiation profile width measurement

This work has been conducted to demonstrate a procedure for using a Konica Minolta computed radiography (CR) system for the measurement of computed tomography (CT) radiation profile width, and to compare this method with conventional and GAFCHROMIC XR‐QA2 film measurements. The exposure and processing conditions of a Konica Minolta CR reader system were characterized to establish the relationship between exposure at the imaging plate (IP) and pixel value. A 6 cc ionization chamber was exposed at the isocenter of a CT scanner using 80 kVp, 0.4 sec with various mA settings. CR images were processed in fixed modes with various combinations of S and G values, establishing exposure and pixel value relationships. Appropriate exposure techniques and processing parameters were selected to avoid the saturation of the IP. Using the selected exposure and processing parameters, radiation profiles of various nominal collimation settings (40, 20, 10, and 5 mm) were acquired for measurement. Radiochromic film was characterized and utilized to compare with CR profiles and profiles obtained via conventional film. Appropriate exposures for both CR (80 kVp, large body filter, 4 and 8 mAs) and radiochromic films (120 kVp, large body filter, 300 mAs) were determined. Recommended CR processing settings (fixed mode with S=5 and G=1.81) were also determined. Compared to the conventional film results, the full width at half maximum (FWHM) results for CR agreed well within ±10%, while radiochromic film results showed maximum deviations of about 5%. In conclusion, FWHM of CT radiation profiles can be conveniently and accurately measured using a Konica Minolta CR system or XR‐QA2 film when appropriate exposure technique and processing parameters are used.PACS numbers: 87.57.Q‐, 87.57.qp, 87.59.bd, 87.57.uq