Film Scanner Research Articles

A new approach to concordance in mid-infrared spectromicroscopy mapping of malignant tumors

Mid-infrared spectromicroscopy studies on biological tissue sections require accurate identification of tumor-bearing areas in histology-stained and infrared-unstained tissue sections. Concordance was achieved as follows: paired stained and unstained thin (5 microm) human brain tumor cryosections mounted on slides were scanned with a Nikon Coolscan 4000 film scanner at 4000 dpi, edited with Adobe Photoshop CS2 software, and both digital images saved. A digital tractile grid, developed in our laboratory, was overlaid onto both images. Boundaries of tumor-containing areas in stained sections were identified by light microscopy, and a digital boundary map constructed. The map was transferred onto the unstained spectromicroscopy tissue image, and finally layered onto the gridded, equisized, spectromicroscope-generated overview image prior to Fourier transform infrared spectromicroscopy. Accurate identification of tumor-bearing areas, normal brain tissue and transitional zones allowed for meaningful interpretation of respective spectral patterns in detecting subtle differences within biochemical profiles. This is the first reported method of a standardized technique for ensuring concordance in mapping of malignant tumors by mid-infrared spectromicroscopy. This technique is applicable to all biological thin tissue sections, and serves to enhance accuracy of concordance between globar- and synchrotron-light generated infrared data with that obtained by conventional light microscopy.

Mechanical calibration and alignment of an aerial photogrammetric film scanner based on a 2D array camera

AbstractMechanical calibration and alignment are fundamental steps in the development of any new aerial photogrammetric scanner. One aim of a film scanner in the digital era is to digitise the accumulated historic archives of images belonging to photogrammetric institutes. The present analysis is centred on a scanner with a translating 2D array camera. Two phases of equal importance can be outlined: the first phase is the alignment of all the mechanical parts inside the scanner, and the second is mechanical calibration, when the systematic effects in the camera positioning are measured and compensated. Among the design requirements of this scanner was to avoid the need for geometrical modification of the scanned images: they should be acquired in the correct position and not require a posteriori correction with a software routine. The proposed solutions lead to a final result of a metrologically satisfactory scanner with a geometric uncertainty of 2 μm or less throughout the frame (250 mm × 250 mm), a value definitely smaller than the pixel size (10 μm/pixel).

SU-GG-T-82: Clinical Experiences and Dosimetric Comparison of the Model 6711 and 9011 I-125 for Intra-Operative Prostate Implant

Purpose:This study compares the film dosimetric characteristics of seed model 9011 I‐125 (THIN) and model 6711 I‐125 (Both sources from Oncura). The THIN seed uses a smaller 20 gauge needle diameter compared to the 18 gauge standard used for model 6711. Method and Materials: Twenty patients (pts) underwent transperineal brachytherapy; 10 each with model 9011 and model 6711 seeds, respectively. Both groups were implanted with dynamic intra‐operative technique using the MICK applicator. The source activity range was 0.45 −0.5 mCi. Three weeks after the implant, a chest x‐ray, pelvic x‐ray and pelvic CT were obtained. The intra‐operative and post‐implant evaluations were done with Variseed 8.0.1. Additionally, Model 9011 and 6711 seeds were exposed to Gafchromic EBT2 films and scanned with the Vida Pro Advantage film scanner. The dosimetric properties of the two models were analyzed and compared using RIT software. Results: Film dosimetry demonstrated that the dosimetric parameters for THIN seed model 9011 were similar to those of model 6711. Anisotropy and radial dose function were slightly different, within 1% for r>1cm. Intra‐operatively, the thin needles were better‐visualized and easier to track on ultrasoundimages. Visualization of individual sources on pelvic X‐ray films for model 6711 and 9011 were similar. There was no seed migration to the lung for either group. For post‐implant evaluation model 9011 seeds were more difficult to identify on pelvic CTimages using Seed Finder module of Veriseed software. Conclusion: The dosimetric characteristics of THIN seed model 9011 and model 6711 are similar. Intra‐operative visualization of the THIN seed improved source capture on the intra‐operative planning system. Post implant source localization was more difficult on CTimages.

SU-GG-T-243: Quality Assurance Measurements for Varian/ RapidArc

Purpose: As Varian revealed “RapidArc radiotherapy technology is a major advance from Varian Medical Systems that improves dose conformity while significantly shortening treatment times.” It delivers IMRTtreatment plan with 360 degree rotation of linear accelerator gantry. The purpose of this analysis is to perform Quality Assurancemeasurements by using regular IMRT QA tools to verify the doses delivered with the new RapidArc radiotherapy technology. Method and Materials: 20 treatment plans had been validated which generated from VARIAN/ Eclipse (RapidArc Progressive Resolution Optimizer V.8.6.15). All plans were measured with two different dosimetric systems. The first system included Plastic‐Water phantom, EDR2 films (Kodak), Ion Chamber (Wellhofer) and Electrometer (FLUKE F35040). The other system contained PTW “Seven‐29 Ion Chamber Array” with two 5‐cm thick Plastic‐Water phantoms. Film Dosimetry was performed by VIDAR's DosimetryPRO Advantage film scanner. The dose distribution analysis and comparison were completed by PTW/ VeriSoft tool to verify dose distributions measured in phantom with dose distributions computed by a RTPS using RapidArc radiotherapy technology. Results: The results show both Dosemeasurements are within acceptable criteria (the ±5% tolerance limit). The data from ion chambermeasurements shows %Diff are within 2%. It is more accurate if comparing it to the results from PTW's IMRT plan verification tool. After normalized the Dose at measured QA point, both results show the ISO Dose line are well comparable to the Dose distribution generated from Eclipse/RapidArc treatment plans. Data from PTW shows 94%–100% of the measured points passing criteria Gamma ≤ 1.0 (acceptance criteria 3%/3mmDTA). Conclusion: For all two dosimetric systems, fine agreement was experimental between measured and calculated doses distribution. Results show that 2 independent QA tools (PTW & Ion‐Chamber with EDR2 films) could capably perform Quality Assurance Test for MU & Dose distrubutionVerification in RapidArc Treatment Planning.

Engineered Anisotropic Microstructures for Ultrathin-Layer Chromatography

The strong dependence of separation behavior on ultrathin-layer chromatography (UTLC) stationary phase microstructure motivates continued UTLC plate design optimization efforts. We fabricated 4.6-5.3 mum thick normal phase silica UTLC stationary phases with several types of in-plane macropore anisotropies using the glancing angle deposition (GLAD) approach to engineering nanostructured thin films. The separation behaviors of two new media, isotropic vertical posts and anisotropic bladelike films, were compared to that of anisotropic chevron media. Channel-like structures within the anisotropic media introduced preferential mobile phase flow directions that could be exploited to give separation tracks diagonal to the development direction. Extraction of chromatograms from these angled tracks required the development of a new analytical approach that involved a commercial flatbed film scanner and custom numerical image analysis software. GLAD stationary phase performance was quantified using the Dimethyl Yellow dye separated from a lipophilic dye mixture over migration distances less than approximately 10 mm. The limits of detection were 10 +/- 4 ng for the vertical posts and 11 +/- 3 ng for the bladelike media. We obtained theoretical plate heights that varied with film microstructure between 12 and 28 mum. Unoptimized separation performance was comparable to that of other planar chromatography media. Macropore anisotropies engineered by GLAD may expand the capabilities of future UTLC stationary phases.

Evaluation of a commercial flatbed document scanner and radiographic film scanner for radiochromic EBT film dosimetry

The purpose of this study was to quantify the performance and assess the utility of two different types of scanners for radiochromic EBT film dosimetry: a commercial flatbed document scanner and a widely used radiographic film scanner. We evaluated the Epson Perfection V700 Photo flatbed scanner and the Vidar VXR Dosimetry Pro Advantage scanner as measurement devices for radiochromic EBT film. Measurements were made of scan orientation effects, response uniformity, and scanner noise. Scanners were tested using films irradiated with eight separate 3×3 cm2 fields to doses ranging from 0.115–5.119 Gy. ImageJ and RIT software was used for analyzing the Epson and Vidar scans, respectively. For repeated scans of a single film, the measurements in each dose region were reproducible to within ±0.3% standard deviation (SD) with both scanners. Film‐to‐film variations for corresponding doses were measured to be within ±0.4% SD for both Epson scanner and Vidar scanners. Overall, the Epson scanner showed a 10% smaller range of pixel value compared to the Vidar scanner. Scanner noise was small: ±0.3% SD for the Epson and ±0.2% for the Vidar. Overall measurement uniformity for blank film in both systems was better than ±0.2%, provided that the leading and trailing 2 cm film edges were neglected in the Vidar system. In this region artifacts are attributed to the film rollers. Neither system demonstrated a clear measurement advantage. The Epson scanner is a relatively inexpensive method for analyzing radiochromic film, but there is a lack of commercially available software. For a clinic already using a Vidar scanner, applying it to radiochromic film is attractive because commercial software is available. However, care must be taken to avoid using the leading and trailing film edges.PACS number: 87.55.Qr

Dosimetric Impact of Surgical Clips in Electron Beam Treatment of Breast Cancer

Titanium clips are commonly used to delineate the location of the tumor bed during breast cancer surgery. Electron beams are frequently used to boost radiation dose to the breast cavity. This research investigated the effect on such boost treatments as a result of metallic clip perturbation potentially exhibited through attenuation and scatter processes using measurements with Gafchromic film and treatment planning simulation with both generalized Gaussian pencil beam and electron Monte Carlo algorithms. Results showed that the potential effect of clip interference is unidentifiable from both algorithms. Dosimetry with Gafchromic external beam therapy film did detect dose perturbations caused by the titanium clips in proximal plane, 0.23 mm away, resulting in 3.0% backscatter and 2.4% attenuation at 6 MeV and 2.0% backscatter and 6.7% attenuation at 9 MeV. The noise contribution of the film scanner is estimated to be about 0.4% and nearly 2% uncertainty in film calibration. As a result, we conclude that the magnitude of dose perturbations from clip is negligible for clinical findings.

Performance of Convenient Film Scanner System for Automatic Counting of Track Etched Pits on PADC Detectors

Performance of Convenient Film Scanner System for Automatic Counting of Track Etched Pits on PADC Detectors

Anywhere But the Home: The Promiscuous Afterlife of Super 8

Anywhere But the Home: The Promiscuous Afterlife of Super 8

SU‐EE‐A1‐06: Quality Control of External Beam Treatment Delivery: Mechanical Parameters

Purpose: The focus of this study is to develop a methodology using statistical process control (SPC) that provides effective quality control of mechanical parameters in external beam treatment delivery. Materials and Methods: A four‐field box clinical treatment technique was used as the evaluation tool. Parameters tested were gantry angle, table height, table lateral, and collimator field size. The dosimeter, GafChromic EBT film, was placed vertically in a pelvic phantom in the transverse plane at isocenter. All films were digitized and evaluated using a Vidar film scanner and RIT, Inc. software. Dose distributions of accurate treatment delivery were measured and compared to treatment delivery with a single mechanical parameter deviated at 0.5, 1.0 and 1.5 times the TG‐40 parameter specification. Each distribution was sampled in the penumbra region using three sampling sets (SS). Each SS consisted of different (size and/or position) regions of interest (ROI). Set‐A and B were 1.5cm × 1.5cm while Set‐C was 0.8cm × 1.0cm. Set‐A and C were centered in the same locations along each beam entry 7cm from isocenter. Set‐B was positioned at the corners of the dose box in the distribution. Results: Two process behavior charts (PBC) were prepared for each SS, evaluating the mean dose and mean dose range. PBC for Set‐A were unable to distinguish between accurate and inaccurate distributions. Set‐B detected all mechanical parameters deviated at 1.0 and 1.5 times the TG‐40 specification but also indicated four false‐positives. These PBC were also effectively unable to distinguish between the accurate and inaccurate distributions. Set‐C PBC detected all mechanical parameters deviated at the 1.0 and 1.5 level and reliably indicated the inaccurate distributions. Conclusions: Small and therefore more homogeneous, strategically located ROI can be effective in SPC to detect inaccurately delivered treatments. Quality control of linac mechanical parameters can be performed using SPC‐based methodology.

Camera Scans – Using a Digital Camera as a Film Scanner

Individual photographers and institutions are struggling with large film archives that require digitizing. Digital cameras can fill an important gap in the scanning environment, enabling large collections to be scanned on-site with low-cost equipment and easily-trained operators. Digital camera scans can now produce very high-quality images, suitable for nearly any kind of reproduction. This paper will discuss the issues surrounding implementation of camera scanning systems, including scan quality, hardware, software and workflow considerations.In addition to an outline of the technical processes, this paper will discuss how the dramatic cost reductions provided by camera scanning shifts the resource allocation in the workflow, repositioning highest-skilled work from the start of the workflow to the end.

다엽콜리메이터의 임상적용을 위한 효율적인 정보 취득 기술

최근 방사선치료의 중추적 역할을 담당하고 있는 다엽콜리메이터는 사용의 편리성 때문에 기존의 납합 금 차폐물을 급속도로 대체하고 있다. 그러나 다엽콜리메이터는 엽간 누설선량이나 디지털 신호를 입출력 알고리즘에 따른 오류가 발생할 수 있다. 저자는 미국 Varian사에서 제공하는 다엽콜리메이터의 입력 방법에 따른 차이를 모의치료장치 프로그램(XimaVision)값을 기준으로 전자펜 정보 전송장치(MLC shaper)와 디지털 변환장치(film scanner)에서의 오차와 유효 조사야를 여러 형태의 차폐윤곽으로 비교하였다. 기준 값과 비교하여 기본적인 차폐 윤곽(test1-5)에서 전자펜 전송방식은 <TEX>$0{\sim}0.29cm$</TEX>, <TEX>$0.23{\sim}3.59cm^2$</TEX>, 디지털 변환장치 방식은 <TEX>$0{\sim}0.20cm$</TEX>, <TEX>$0.72{\sim2.59cm^2$</TEX> 차이를 보였다. 임상에서 적용되는 차폐 윤곽에서 전자펜 전송방식은 <TEX>$0{\sim}0.54cm$</TEX>, <TEX>$0.04{\sim}1.68cm^2$</TEX>, 디지털 변환장치 방식은 <TEX>$0{\sim}0.78cm$</TEX>, <TEX>$0.24{\sim}3.89cm^2$</TEX> 차이를 보였고, 대부분 선속 중심선에서 멀어질수록 조사야가 클수록 오차범위가 증가함을 알 수 있었다. 다엽콜리메이터의 임상적용을 위한 다양한 정보 입력과정에서 기준점으로부터 수 mm 이내에서 오차가 잇었다. 그리고 유효 조사야는 실제 면적에 대하여 수 <TEX>$cm^2$</TEX>이내에서 오차가 발생하여 기계적 선량(Monitor Unit)이나 조사야 내 선량변화에 관여하지 않았다. 그러나 임계장기를 차폐 할 경우 장기의 움직임으로 표적용적의 일부가 포함되지 않을 수 있기 때문에 문제의 여지가 있다. 그러므로 오류를 최소화하기 위한 다엽콜리메이터의 입력과정에 세심한 주의를 기울여야 한다. The MLC(multi leaf collimator) in charge of important role in radiation therapy field recently have been exchanging from shielding block into it rapidly, owing to being convenient. However, MLC can be occurred the leakage dose of inter_leaves and the error of algorithm in imput and output from digital signal. We compared the difference of imput method to MLC made by Varian Cop. with the error and effective field induced by MLC shaper and film scanner based on XimaVision value as using MLC layer of various shapes. According to comparing standard value with them to basic MLC layer (test1-5), MLC shaper was <TEX>$0{\sim}0.29cm$</TEX>, <TEX>$0.23{\sim}3.59cm^2$</TEX> and film scanner was <TEX>$0{\sim}0.78cm$</TEX>, <TEX>$0.24{\sim}3.89cm^2$</TEX>. At the MLC layer to be applied in clinic, MLC shaper was <TEX>$0{\sim}0.54cm$</TEX>, <TEX>$0.04{\sim}1.68cm^2$</TEX> and film scanner was <TEX>$0{\sim}0.78cm$</TEX>, <TEX>$0.24{\sim}3.89cm^2$</TEX>. The more distance and field from axis of central line increase, the more bigger the error value increases. There is a few mm error from standard point at the process which imput various information to apply MLC in clinic. and effective field did not have variation of monitor unit and dose owing to being a few cm2 error against real field. But there are some problem to shield critical organs because some part of target volume induced by the movement of organs can be not included, therefore we have to pay attention on the process to imput MLC layer

SU‐GG‐T‐276: Comparison of the Epson Perfection V700 Photo Flatbed and the Vidar VXR‐16 Dosimetry PRO AdvantageTM Film Scanners for Use with Radiochromic Film

Purpose: The purpose of this study was to compare the performance and utility of a commercially available flatbed scanner with that of a widely‐used medical film scanner for use with radiochromic film. Method and Materials: This project compares the Vidar VXR Dosimetry Pro and the Epson Perfection V700 Photo flatbed scanner. Using radiochromic EBT film irradiated to a known range of doses 0–512 cGy using eight 3×3 cm fields on a single film, both scanners were characterized for scan repeatability, orientation effects, uniformity, and scanner noise. RIT V5.0 was used to determine pixel value (PV) of Vidar scans, while ImageJ software was used for the Epson scans. Results: For the range of doses measured, average pixel values of a central 1.5×1.5 cm region of interest (ROI) were reproducible within 0.1% standard deviation with Vidar and approximately 0.2% with Epson. Epson mean PV differed by up to 18% for all dosed regions from landscape to portrait orientation, while only up to 5% for Vidar. From 0 to 512 cGy, identical films showed a 10% wider PV range for Vidar than Epson. Scanner noise was minimal; Epson showed a maximum SD of 1.00% from the mean of the central ROI, Vidar showed 1.14%. In both systems, cross profiles for an unirradiated film showed deviations in PV no more than 2% of the mean. Conclusion: No clear significant accuracy advantage was noted in either system, provided the leading and trailing 1 cm film edges were neglected with the Vidar system. Although the Epson scanner is a relatively inexpensive method for analyzing radiochromic film, the lack of commercially available software for it could be a major disadvantage. Hence, an institution already having a Vidar system may find its use with radiochromic film attractive.

Accurate dosimetry with GafChromic™ EBT film of a 6MV photon beam in water: What level is achievable?

This paper focuses on the accuracy, in absolute dose measurements, with GafChromicTM EBT film achievable in water for a 6 MV photon beam up to a dose of 2.3 Gy. Motivation is to get an absolute dose detection system to measure up dose distributions in a (water) phantom, to check dose calculations. An Epson 1680 color (red green blue) transmission flatbed scanner has been used as film scanning system, where the response in the red color channel has been extracted and used for the analyses. The influence of the flatbed film scanner on the film based dose detection process was investigated. The scan procedure has been optimized; i.e. for instance a lateral correction curve was derived to correct the scan value, up to 10%, as a function of optical density and lateral position. Sensitometric curves of different film batches were evaluated in portrait and landscape scan mode. Between various batches important variations in sensitometric curve were observed. Energy dependence of the film is negligible, while a slight variation in dose response is observed for very large angles between film surface and incident photon beam. Improved accuracy in absolute dose detection can be obtained by repetition of a film measurement to tackle at least the inherent presence of film inhomogeneous construction. We state that the overall uncertainty is random in absolute EBT film dose detection and of the order of 1.3% (1 SD) under the condition that the film is scanned in a limited centered area on the scanner and at least two films have been applied. At last we advise to check a new film batch on its characteristics compared to available information, before using that batch for absolute dose measurements.

Liquid embolisation material reduces the delivered radiation dose: a physical experiment

To test a new hypothesis that the glue/contrast admixture used for embolisation reduces the dose delivered to AVMs using an experimental model. A model was created using a block of "solid water" (6 x 5 x 2 cm) with twelve wells of different depths. Different concentrations of the glue admixture (Enbucrilate + Lipiodol) were used. The model was irradiated using a 5MV beam with a clinical LINAC system and the dose was checked upstream and downstream. Dose was measured using Kodak XV film, a Vidar 16 bit film scanner and software for therapeutic film dosimetry measurements (RIT software). The radiation dose varied with the distance beyond the glue solid water interface. For distances of 0, 2 and 5 mm to the film, the mean reduction was 13.65% (SD = 2.94), 6.87% (SD = 1.95) and 1.75% (SD = 1.14), respectively. There was also correlation with the Lipiodol concentration in the mixture. The maximum reductions for 80, 50 and 20% Lipiodol concentrations were 16.1% (SD = 1.32), 14.85% (SD = 0.98) and 10% (SD = 1.21), respectively. There was no correlation between the glue depth and the dose delivered. The hypothesis that the glue mixture used for embolisation reduces the radiation dose delivered was experimentally confirmed with this study.

A prototype quantitative film scanner for radiochromic film dosimetry

We have developed a high resolution, quantitative, two-dimensional optical film scanner for use with a commercial high sensitivity radiochromic film (RCF) for measuring single fraction external-beam radiotherapy dose distributions. The film scanner was designed to eliminate artifacts commonly observed in RCF dosimetry. The scanner employed a stationary light source and detector with a moving antireflective glass film platen attached to a high precision computerized X-Y translation stage. An ultrabright red light emitting diode (LED) with a peak output at 633 nm and full width at half maximum (FWHM) of 16 nm was selected as the scanner light source to match the RCF absorption peak. A dual detector system was created using two silicon photodiode detectors to simultaneously measure incident and transmitted light. The LED light output was focused to a submillimeter (FWHM 0.67 mm) spot size, which was determined from a scanning knife-edge technique for measuring Gaussian optical beams. Data acquisition was performed with a 16-bit A/D card in conjunction with commercial software. The linearity of the measured densities on the scanner was tested using a calibrated neutral-density step filter. Sensitometric curves and three IMRT field scans were acquired with a spatial resolution of 1 mm for both radiographic film and RCF. The results were compared with measurements taken with a commercial diode array under identical delivery conditions. The RCF was rotated by 90 deg and rescanned to study orientation effects. Comparison between the RCF and the diode array measurements using percent dose difference and distance-to-agreement criteria produced average passing rates of 99.0% using 3%/3 mm criteria and 96.7% using 2%/2 mm criteria. The same comparison between the radiographic film and diode array measurements resulted in average passing rates 96.6% and 91.6% for the above two criteria, respectively. No measurable light-scatter or interference scanner artifacts were observed. The RCF rotated by 90 deg showed no measurable orientation effect. A scan of a 15 x 15 cm2 area with 1 mm resolution required 22 min to acquire. The LED densitometer provides an accurate film dosimetry system with 1 mm or better resolution. The scanner eliminates the orientation dependence of RCF dosimetry that was previously reported with commercial flatbed scanners.

SU-FF-T-185: Dosimetry Along Edges of An Irregular MLC Field with Different Stepping Angles

Purpose: To measure dose profiles along edges of an irregular MLC field with different leaf stepping angles. So that dependences of dosimetric parameters for the profile on the stepping angle can be measured and investigated. Methods and Materials: Seven diamond‐shaped MLC fields enclosed by a 10 × 10 cm2 square with different stepping angles namely 21.8°, 31.0°, 38.7°, 45.0°, 51.3°, 59.0° and 68.2° were generated using the Varian SHAPER program. The fields were input to the console of a Varian 21 EX linac with a MLC of 120 leaves. Radiographic films were used to measure dose profiles parallel to the field edges. The film was placed at SAD = 100 cm, with 5 cm of solid water slab on top. Photon beam of 6 MV was used for the irradiation. The irradiated film was then developed and digitized using the Vidar VXR‐16 film scanner. Film dosimetric analysis was carried out using the RIT 113 system. Results: Width of profile measured at the 50% relative dose increases with the leaf stepping angle from 21.8° to 45° and then decreases when angle > 45°. Both width of ripple and its relative peak height decrease with increase of the stepping angle. However, profiles having different tongue‐and‐groove arrangements measured at the positive and negative in‐line axis (between the Y1 and Y2 jaw) have similar results. Conclusions: This study provides measured results to understand the dosimetry along the edge of an irregular MLC field when the leaf stepping angle is varying. The data are expected to benefit the physics modeling of the MLCdosimetry, particularly at the penumbra region for the treatment planning system, and the Monte Carlo simulation related to the irregular segmental MLC field for IMRT.

SU‐FF‐T‐410: The Influence of Scanner Parameters On the Accuracy of Film Dosimetry: A Comparison of the Epson Expression 1680 Flatbed and the Vidar VXR‐16 Dosimetry PRO Film Scanners

Purpose: To investigate the properties of Vidar VXR‐16 Dosimetry PRO™ and Epson Expression 1680 film scanners with Gafchromic EBT and EDR2 radiographic films for dosimetry applications. Method and Materials: The EDR2 and EBT films are irradiated with 10 × 10 cm2 6 MV X‐ray beams in solid water. Dose calibration curves are obtained using an MLC generated stepwedge. Each EDR2 or EBT film is scanned in both vertical and horizontal orientation with Vidar and Epson scanners in transmission mode and analyzed using FilmQA™ (3cognition LLC) software. The RIT (Radiological Imaging Technology, Colorado Springs) software is used with the Vidar only. Epson scans are done without color correction in the 48‐bit RGB mode, resolution 75 dpi. The R channel image is used for analysis. Vidar scans are done with resolution 71 dpi, logarithmic and linear translation tables, and the 16‐bit grayscale image is analyzed. Results: For the EDR2 film no differences are observed for different scan orientations on either Epson or Vidar scanners with both RIT and FilmQA software. The EBT scans show no difference for different scan directions on either scanner. However, artifacts are associated with different translation tables with the Vidar while up to 2% differences are observed in the penumbra with Epson. Scanning measurement, calibration, and background films in the same direction estimates doses on central axis with 2% accuracy for both film types and scanners. However, inconsistent scan directions result in errors up to 10% on Epson and 41%‐45% on Vidar scanner. Conclusion: Calibration curve differences depend on the type of scanner, scanning mode, scanning software, and film orientation. The EDR2 on either scanner reproduces relative profiles and dose to better than 2% regardless of orientation. For the EBT the scanner parameters, orientation, and software corrections become important for accurate dosimetry results and to avoid artifacts.

SU‐FF‐T‐444: Variability of EDR2 Dose Calibration Films Taken for IMRT Dose Verification

Purpose: To report the consistency of EDR2 calibration films taken for IMRT absolute dose verification. Method and Materials: 180 sets of dose‐optical (OD) calibration films for IMRT dose validation were taken on 4 Linacs on two campuses using Kodak EDR2 film from Nov. 2005 to Dec. 2006. Each calibration datum contained at least 5 dose points (i.e. 0 cGy, 60 cGy, 120 cGy, 180 cGy and 240 cGy). All calibration films were processed on the same Kodak film processor, were scanned with the same Vidar 1600Pro film scanner, and analyzed using RIT dosimetry software. A second order polynomial function was applied to create the H‐D curve using averaged dose‐OD data from each Linac separately. The range of dose variation (maximum, minimum and standard deviation) was determined. Results: Overall, one standard deviation of the OD corresponded to ±5.3 cGy at 60 cGy, ±8.1 cGy at 120 cGy, ±11.1 cGy at 180 cGy, and ±11.7 cGy at 240 cGy. The maximum and minimum recorded OD numbers of 180 cGy dose point corresponded to 221.4 cGy and 152.5 cGy respectively. Variability was greater for the films taken at one campus and transported (usually overnight) to the main campus for processing and analysis. Had a single dose point film (e.g. 180 cGy) been taken, dose errors (2 SD) of ±24.4 cGy at 240 cGy and ±16.5 cGy at 120 cGy would have occurred. There was no correlation of consistency with processor service. Conclusions: The OD calibration curves with EDR2 film varied significantly, not only in absolute OD value but also in curvature. In order to achieve +/−3% accuracy for IMRT dose verification films, EDR2 calibration films must be taken for each set of IMRT films.

SU‐FF‐T‐262: Indications of Effective Depth Reversal for Cylindrical Ion Chambers in Electron Beams

Purpose: Cylindrical ionization chamber measurements of electron beam depth dose are corrected for the effective depth of measurement and water/air stopping power ratio. The purpose of this presentation is to examine whether a unidirectional upstream shift from physical to effective depth of measurement as often used in data acquisition systems makes sense. Method and Materials: Ionization chamber measurements of depth dose corrected for effective depth by a unidirectional shift and water/air stopping power ratio at depth are compared with diode and EBT film measurements for standard electron beam cone sizes over the nominal energy range of 6 MeV to 20 MeV. The diode results are obtained with a NIST traceable electrometer and are used without correction for any change in water/silicon stopping power ratio vs depth. The EBT film density is converted to dose based on a characteristic curve from films exposed in plastic water at the nominal depth of dose maximum. EBT film results are used without additional corrections for any change in water/EBT film stopping power ratio vs depth. The EBT film density is evaluated with a pin‐hole densitometer as well as a VIDAR film scanner. Results: Good agreement of all measurements at depth from 80 to 10 percent suggest ignoring variation in stopping power ratio for both diode and EBT film has little impact on the results. Both diode and film suggest a slightly deeper depth of dose maximum and a more rapid drop in dose from Dmax towards the surface. Conclusion: Agreement between ionization chamber results and the high resolution solid detector results would improve if the shift in the effective depth of measurement of the ionization chamber is based on dose gradient and reverses as the gradient reverses with perhaps no shift at the zero gradient position. This may impact on calibration protocols.