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Purpose To investigate the inconsistency of recent literature on the effect of magnetic field on the response of radiochromic films, we studied the influence of 0.35 T magnetic field on dosimetric response of EBT3 and EBT-XD GafchromicTM films. Methods Two different models of radiochromic films, EBT3 and EBT-XD, were investigated. Pieces of films samples from two different batches for each model were irradiated at different dose levels ranging from 1 to 20 Gy using 6 MV flattening filter free (FFF) x-rays generated by a clinical MR-guided radiotherapy system (B = 0.35 T). Film samples from the same batch were irradiated at corresponding dose levels using 6 MV FFF beam from a conventional linac (B = 0) for comparison. The net optical density was measured 48 h postirradiation using a flatbed scanner. The absorbance spectra were also measured over 500-700 nm wavelength range using a fiber-coupled spectrometer with 2.5 nm resolution. To study the effect of fractionated dose delivery to EBT3 (/EBT-XD) films, 8 (/16) Gy dose was delivered in four 2 (/4) Gy fractions with 24 h interval between fractions. Results No significant difference was found in the net optical density and net absorbance of the films irradiated with or without the presence of magnetic field. No dependency on the orientation of the film during irradiation with respect to the magnetic field was observed. The fractionated dose delivery resulted in the same optical density as delivering the whole dose in a single fraction. Conclusions The 0.35 T magnetic field employed in the ViewRay® MR-guided radiotherapy system did not show any significant influence on the response of EBT3 and EBT-XD GafchromicTM films.

Three types of films, Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55, were used to measure relative output factors of 4 and 8 mm collimators of the Leksell Gamma Knife Perfexion. The optical density to dose calibration curve for each of the film types was obtained by exposing the films to a range of known doses. Ten data points were acquired for each of the calibration curves in the dose ranges from 0 to 4 Gy, 0 to 8 Gy, and 0 to 80 Gy for Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55 films, respectively. For the measurement of relative output factors, five films of each film type were exposed to a known dose. All films were scanned using EPSON EXPRESSION 10000 XL scanner with 200 dpi resolution in 16 bit gray scale for EDR2 film and 48 bit color scale for Gafchromic films. The scanned images were imported in the red channel for both Gafchromic films. The background corrections from an unexposed film were applied to all films. The output factors obtained from film measurements were in a close agreement both with the Monte Carlo calculated values of 0.924 and 0.805 for 8 and 4 mm collimators, respectively. These valuesmore » are provided by the vendor and used as default values in the vendor's treatment planning system. The largest differences were noted for the Kodak EDR 2 films (-2.1% and -4.5% for 8 and 4 mm collimators, respectively). The best agreement observed was for EBT Gafchromic film (-0.8% and +0.6% differences for 8 and 4 mm collimators, respectively). Based on the present values, no changes in the default relative output factor values were made in the treatment planning system.« less

The capability of the new GafChromic EBT prototype B for external beam dose verification is investigated in this paper. First the general characteristics of this film(dose response, postirradiation coloration, influence of calibrationfield size) were derived using a flat-bed scanner. In the dose range from 0.1 to 8 Gy , the sensitivity of the EBT prototype B film is ten times higher than the response of the GafChromic HS, which so far was the GafChromic film with the highest sensitivity. Compared with the Kodak EDR2 film, the response of the EBT is higher by a factor of 3 in the dose range from 0.1 to 8 Gy . The GafChromic EBT almost does not show a temporal growth of the optical density and there is no influence of the chosen calibrationfield size on the dose response curve obtained from this data. A MatLab program was written to evaluate the two-dimensional dose distributions from treatment planning systems and GafChromic EBT film measurements. Verification of external beam therapy (SRT, IMRT) using the above-mentioned approach resulted in very small differences between the planned and the applied dose. The GafChromic EBT prototype B together with the flat-bed scanner and MatLab is a successful approach for making the advantages of the GafChromic films applicable for verification of external beam therapy.

Dry-processing film systems have become popular particularly in a network environment. This is mainly due to its ability to produce high quality images without wet chemistry processing. In this paper we describe a monthly monitoring program on five Model 8700 DryView™ Laser Imagers in our institution. A SMPTE pattern is generated via DryView™ Laser Imager software. The 100% patch is used for checking the base-plus-fog of the Imager. The 40% patch is used as the speed index. The optical density difference between patches 10% and 70% is used as the contrast index. These numbers are plotted for testing system consistency. In addition, the SMPTE pattern is examined to verify the sharpness of the bar patterns and the visibility of subtle contrasts—95% inset in the 100% patch and a 5% inset in the 0% patch. The clinical films are checked for processor artifacts, such as residuals from the drum. Stability of the dry processors has also been studied using three strips per day obtained at three different times of the day over a period of ten consecutive working days. The coefficient of variation is 0.05 for the speed index and 0.04 for the contrast index. The monthly monitoring program has been carried out in our institution since January 1997. The problems found by this monthly monitoring program assess the necessity of routine QC for DryView™ Laser Imagers. The instability of the post-processing dry silver films, and, consequently, the film handling requirements, are also discussed.

GafChromic MD-55 is a fairly new, thin film dosimeter that develops a blue color (lambda max = 676 nm) when irradiated with ionizing radiation. The increase in absorbance is roughly proportional to the absorbed dose. In this study, GafChromic MD-55 was irradiated with 60Co gamma rays. A double irradiation method was used in which a dosimeter is given an unknown dose followed by a known, calibration dose. With this method, GafChromic MD-55 was used to measure doses in the vicinity of 6 Gy with an uncertainty of less than 1%. It was found that the measured optical density of GafChromic MD-55, as presently fabricated, is affected by the polarization of the analyzing light, an important consideration when using GafChromic MD-55 as a precision dosimeter. GafChromic MD-55 was found to consist of seven layers. The response to polarized light was measured for the whole dosimeter and for the three Mylar films which form part of the dosimeter.

The results of quality control (QC) tests on 70 mammography units in Southern California from 1986 to 1990 are reported. Thirteen facilities, selected because they housed all of the mammography units in three communities involved in a National Institutes of Health research project, had their units tested twice at an interval of 1 year. Fourteen self‐selected units were also tested twice at intervals ranging from 1–3 years. Forty‐three self‐selected units in 31 additional facilities had testing only once. All 70 units underwent measurement of focal spot size or resolution, tube output, half‐value layer (HVL), automatic exposure control (AEC) accuracy, relative kVp accuracy, mean glandular dose, and imaging of several test objects. The test results for the units tested once showed no significant differences compared to those tested twice. For the latter, once the units were tested and determined to be acceptable, retesting showed differences only in overall film optical density, dose, and AEC performance.

An electro-optical, photographic dodging technique, called light equalization radiography (LER), has been developed. The use of LER extends the dynamic range of radiographic film by enhancing the film contrast in the "toe" region of a radiographic film. Contrast recorded above some predetermined optical density is unaffected. The use of LER permits high-contrast films to be used in radiographic exams where low-contrast, "latitude" film types have been used traditionally, e.g., in chest radiography.

Purpose: 3D-gel dosimetry provides high-resolution treatment validation; however, scanners aren't widely available. In remote dosimetry, dosimeters are shipped out from a central base institution to a remote site for irradiation, then shipped back for scanning and analysis, affording a convenient service for treatment validation to institutions lacking the necessary equipment and resources. Previous works demonstrated the high-resolution performance and temporal stability of PRESAGE. Here the newest formulation is investigated for remote dosimetry use. Methods: A new formulation of PRESAGE was created with the aim of improved color stability post irradiation. Dose sensitivity was determined by irradiating cuvettes on a Varian Linac (6MV) from 0–15Gy and measuring change in optical density at 633nm. Sensitivity readings were tracked over time in a temperature control study to determine long-term stability. A large volume study was performed to evaluate the accuracy for remote dosimetry. A 1kg dosimeter was pre-scanned, irradiated on-site with an 8Gy 4field box treatment, post-scanned and shipped to Princess Margaret Hospital for remote reading on an identical scanner. Results: Dose sensitivities ranged from 0.0194–0.0295 ΔOD/(Gy*cm)—similar to previous formulations. Post-irradiated cuvettes stored at 10°C retained 100% initial sensitivity over 5 days and 98.6% over 10 weeks while cuvettes stored at room temperature fell to 95.8% after 5 days and 37.4% after 10 weeks. The immediate and 5-day scans of the 4field box dosimeter data was reconstructed, registered to the corresponding eclipse dose-distribution, and compared with analytical tools in CERR. Immediate and 5-day scans looked visually similar. Line profiles revealed close agreement aside from a slight elevation in dose at the edge in the 5-day readout. Conclusion: The remote dosimetry formulation exhibits excellent temporal stability in small volumes. While immediate and 5-day readout scans of large volume dosimeters show promising agreement, further development is required to reduce an apparent time dependent edge elevation.

Purpose: To evaluate the effect of different dose rates on the optical density (OD) for the commercially available GAFCHROMIC EBT3 film using a Novalis TX. Methods: 3×3 cm2 pieces of GAFCHROMIC EBT3 (A12141101) were placed on the surface of a 20×20×20 cm3 solid water phantom. A 2 cm thick block of solid water was placed on the film for build up. The machine output was monitored using a Farmer‐type chamber located at a depth of 10 cm below the films. Chamber ion recombination as a function of dose rate was accounted for, and pressure and temperature were monitored throughout. The monitor unites were calculated such that a certain dose (50, 100, 500 cGy) was delivered at the level of the film. The dose rate was varied between 50 and 1000 cGy/min through changing both machine settings (100–600 MU/min, 1000 MU/min in SRS mode and source‐to‐surface distance SSD (75–135 cm). The films were scanned 24 hours post irradiation, and the resulting changes in net OD were compared against the corresponding dose rate. Results: Preliminary examination of net OD results shows a small dependence on dose rate, but within the uncertainty of the measurements. As such, within the uncertainties of clinical film dosimetry, the GAFCHROMIC EBT3 films are independent of dose rate (50–1000 cGy/min) irrespective of the total delivered dose (between 50–500 cGy). Conclusion: Results suggest GAFCHROMIC EBT3 films to be dose rate independent to within 3% for a wide range of dose rates (and total delivered doses) that are normally used in clinical settings.

Purpose: To quantify the sensitivity and stability of the Presage dosimeter in sheet form for different concentrations of chemicals and for a diverse range of clinical photon energies. Methods: Presage polymer dosimeters are formulated to investigate and optimize their sensitivity and stability. The dosimeter is composed of clear polyurethane base, leucomalachite green reporting dye, and bromoform radical initiator in 1mm thick sheets. The chemicals are well mixed together, cast in an aluminum mold, and left to cure at 60 psi for a minimum of 2 days. Dosimeter response will be characterized at multiple energies including Co-60, 6 MV, 15 MV, 50 kVp, and 250 kVp. The dosimeters are read by an Epson 10000 XL scanner at 800 dpi, 2^16 bit depth. Red component images are analyzed with ImageJ. Results: Analysis of optical density verse dose for Co-60 energies indicates that the bromoform containing Presage was able to quantify dose from 0 to 300 Gy, with saturation beyond 300 Gy. Initial results show two regions of linear response, 0–100 Gy and 150–300 Gy. The 150–300 Gy region has a sensitivity of 0.0024 net OD/Gy. Further results on other energies are still in progress. Conclusions: This work shows the potential for use of thin sheets of Presage dosimeter as a dosimeter capable of being analyzed with a flatbed scanner.

The performance of commercially available light sensitometers was compared with two other methods of x-ray sensitometry to determine whether commercially available sensitometers are viable for evaluating clinical performance of mammography film. X-ray sensitometry was performed using mammography screens that were modified to accommodate a graded optical step tablet (screen sensitometry). Finally, a means for performing intensity-scale x-ray sensitometry was configured (inverse-square sensitometry). Clinical mammography x-ray exposure conditions were used and film processing quality was closely monitored during the study. Statistical results for chi-square probabilities on the resulting contrast curves yielded good agreement for most of the configurations investigated. Comparison of film gradient versus optical density curves showed good agreement for maximum contrast values and the corresponding optical density for maximum contrast for three of the four screen-film combinations used when comparing light sensitometry to screen sensitometry. A similar comparison of light sensitometers to inverse-square sensitometry showed good agreement for maximum contrast, but less agreement for the corresponding optical density of maximum contrast. Based on these results, the authors concluded that commercially available sensitometers could be used to estimate clinical film performance for the screen-film systems tested. In particular they can be used to determine the range of optical densities that provide optimal film contrast.

Purpose: To compare how the inclusion of the uncertainties in dose and optical density affects the results of the calibration of Gafchromic® EBT3 radiochromic films. Methods: Five methods of least square minimization were compared for calibration of radiochromic films. These differed in the way in which the uncertainties of dose and optical density are taken into account. The comparison was made by simulating the calibration fit at an increasing number of points measured in the calibration table and in the gamma analysis of ten real IMRT verifications. Results: According to the results of the simulations, the methods that take into account all the variability in dose and optical density are superior to those that do not use them. The improvements are reflected in lower bias of the parameters, lower variability and faster convergence when the number of the points increases in the calibration table. When these methods are employed in the gamma analysis comparison, the statistical significance of the results depends on how restrictive the parameters are that define this comparison. Conclusions: Methods that take into account all the variability both in dose and in optical density should be used in the calibration process.

Purpose: This study investigated if the dose‐response of EBT2 film can be modeled as a bimolecular reaction of the monomers that composes the active layer of the EBT2 film. The LET dependence of EBT2 films was explored using the models developed in this study. Methods: To build a dose‐response curve a set of films was exposed to pristine proton beams of 161.61 MeV, with doses ranging from 0.93 Gy to 14.82 Gy at a depth of 2 cm in water. The same procedure was applied to a film using a lower energy beam, 85.55 MeV. Because the chemical models predict different values for the maximum optical density of the film, another set of films was exposed to a higher dose, about 200 Gy, to determine which chemical model would better predict the film parameters. Fluence‐averaged LET curves were computed by calculating the ratio of the dose and fluence in water. Proton energy spectra were also computed at selected depths for both energies. Results: The unimolecular and the bimolecular models were able to accurately fit the experimental data, with both having R2 = 0.9996. The maximum optical density values found were 0.901 +/− 0.050 by the unimolecular model and 1.276 +/− 0.077 by the bimolecular model. Exposing a set of EBT2 films to 200 Gy yielded a measured optical density of 1.360 +/− 0.070, which indicated larger systematic uncertainties in the unimolecular model compared to the bimolecular model. Conclusions: Although both the unimolecular and the bimolecular models fit the experimental data with similar accuracy, only the bimolecular model could predict the maximum optical density of the EBT2 film with acceptable accuracy. We also observed that the energy spectra at the measurement depths play a role in the LET response of the EBT2 films when described as a bimolecular reaction. This project is supported in part by P01CA021239 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

Purpose: To evaluate the characteristics of commercial‐grade flatbed scanners and medical‐grade scanners for radiochromic EBT film dosimetry.Methods: Performance aspects of a Vidar Dosimetry Pro Advantage (Red), Epson 750 Pro, Microtek ArtixScan 1800f, and Microtek ScanMaker 8700 scanner for EBT2 Gafchromic film were evaluated in the categories of repeatability, maximum distinguishable optical density (OD) differentiation, OD variance, and dose curve characteristics. OD step film by Stouffer Industries containing 31 steps ranging from 0.05 to 3.62 OD was used. EBT films were irradiated with dose ranging from 20 to 600 cGy in 6×6 cm2field sizes and analyzed 24 hours later using RIT113 and Tomotherapy Film Analyzer software. Scans were performed in transmissive mode, landscape orientation, 16‐bit image. The mean and standard deviation Analog to Digital (A/D) scanner value was measured by selecting a 3×3 mm2 uniform area in the central region of each OD step from a total of 20 scans performed over several weeks. Repeatability was determined from the variance of OD step 0.38. Maximum distinguishable OD was defined as the last OD step whose range of A/D values does not overlap with its neighboring step. Results: Repeatability uncertainty ranged from 0.1% for Vidar to 4% for Epson. Average standard deviation of OD steps ranged from 0.21% for Vidar to 6.4% for ArtixScan 1800f. Maximum distinguishable optical density ranged from 3.38 for Vidar to 1.32 for ScanMaker 8700. A/D range of each OD step corresponds to a dose range. Dose ranges of OD steps varied from 1% for Vidar to 20% for ScanMaker 8700. Conclusions: The Vidar exhibited a dose curve that utilized a broader range of OD values than the other scanners. Vidar exhibited higher maximum distinguishable OD, smaller variance in repeatability, smaller A/D value deviation per OD step, and a shallower dose curve with respect to OD.

Purpose: To investigate the effects of optical density (OD) sensitivity and growth with time post‐irradiation on intensity‐modulated radiation therapy(IMRT)dosimetry with gafchromic films (EBT1 and EBT2). Method and Materials:EBT1 and EBT2 films were used to perform IMRTquality assurance, which were exposed to IMRT plans created in treatment planning system using 6 MV photon beam from a Trilogy Varian linac.Calibrationfilms were exposed to graded doses from 78–399cGy in order to convert OD to dose. The films were scanned using a flat panel scanner several times starting from 4 to 480 hours post‐irradiation. Gray scale and red colors for both EBT1 and EBT2 films were used to evaluate film sensitivity on IMRT analysis. The IMRTfilms were analyzed with calibrationfilms that were scanned synchronously and at different times post‐irradiation to quantify the effect of OD growth.Dose difference and gamma analysis of the dose distributions measured by film and calculated by treatment planning system were used to evaluate the effects of OD growth and sensitivity. Result: OD variations show that EBT1 grows slower, however, reaching higher values (14%) than EBT2 (13%) after long time post‐irradiation. The gray color values grow higher (13–14%) than red values (6%) for both EBT1&2 films after 480 hours. The results of dose difference and gamma parameter with more than 85% and 97% passing rates, respectively, using acceptance criteria (5%, 5mm) were better for films analyzed with synchronized calibration and red color values than non‐synchronized calibration and grayscale. Conclusion: The measurement of dose distributions agrees well with those calculated by treatment planning for synchronized IMRT and calibrationfilms where variation due to OD growth is minimized. Red color values provide better gamma for IMRT analysis with EBT1&2 films because of lower OD growth and high sensitivity than gray color values.

Purpose: The goal of this work is to evaluate the uniformity of International Specialty Products Gafchromic EBT2 film with a high‐resolution metric. The effect on uniformity of the marker dye (blue‐channel) correction and time post‐exposure are investigated. Methods: Film uniformity was quantified by using EBT2 and Kodak EDR2 film to measure the flatness of a cobalt‐60 field. EBT2 films were digitized 24, 48, and 72 hours post‐exposure and analyzed using three Methods: the manufacturer‐recommended blue‐channel correction, an in‐house blue‐channel correction, and a net optical density (OD) measurement in the red color channel. The field flatness was calculated from the horizontal and vertical dose profiles taken through the center of the cobalt‐60 field for each analysis method and compared to the EDR2 results. Results: The blue‐channel correction methods improved the flatness measured with EBT2 film by up to 1% over the net OD method. Additionally, the percent standard deviations of the flatness measurements with the blue‐channel correction methods were up to 0.7% (1‐sigma) lower than the net OD method. The flatness measured with EDR2 film was 1.4% to 1.8% better than the flatness measured with EBT2 film using the net OD method. The flatness did not exhibit any unidirectional change with time and showed a maximum change of 0.4%. Conclusions: Using field flatness as a metric for response uniformity, EBT2 film analyzed with the net OD method demonstrates substantial non‐uniformities relative to EDR2 film. The blue‐channel correction considerably improves the uniformity of EBT2 response and reduces the film‐to‐film response variation relative to the net OD method. The uniformity of EBT2 is independent of post‐exposure time. The blue‐channel correction can be used to reduce uncertainty in relative dosimetric measurements with EBT2 film.

Purpose: The use of polymergels dosimeters were investigated as suitable dosimeters for assessing internal radionuclide dosimetry of Tc‐99m. Material and Methods: 25–5000 MBq of Tc‐99m was introduced by syringe into aqueous PAGAT polymergel dosimeter mixtures which had been sealed in nitrogen‐filled P6 glass vials. After irradiation the polymergel dosimeters were assessed using optical spectrophotometry and MRI more than 48 hours (8 half‐lives) after preparation. The dose delivered to the each P6 vial was calculated empirically and also computed using GATE Monte Carlo software.Results:Spectrophotometry optical density or MRI R2 relation rate versus total activity curves were obtained and used to evaluate the relationship between the amount of gelpolymerization and the dose deposited by the radionuclide. A linear dose response was exhibited up to 1000 MBq (corresponding to 20Gy) and was still behaving monotonically at 5000 MBq. Conclusion: PAGAT polymergel dosimeters offer the potential to measure radiation dose from Tc‐99m three‐dimensionally. Further work will extend these techniques to use with I‐131, F‐18, Y‐90 and other particle emitting radionuclides.

Routine IMRT QA is often performed using radiographic film in combination with a film analysis software package. In addition to differences in film batches, various factors could affect the film developing process such as temperature, transport rate, or replenishment rate. The conversion of the degree of blackening of the film, as measured by optical density, to dose is achieved by applying a sensitometric, or characteristic curve, to the film; thus converting it to a dose map. These curves need to be constructed at the beginning of the start of film IMRT QA. In order to account for processing variations, and film batch differences, our practice is to expose a single reference film to a known dose at the time of each IMRT QA and adjust the “baseline” film sensitometric curve accordingly; in effect assuming that the shape of the curve remains unchanged and it is only shifted by a fixed amount to a higher or lower dose. The validity of this assumption and the degree to which film processing can affect it are investigated here. We have analyzed the sensitometric curves and reference films used for adjusting the curves at two institutions over a three‐year period. Our data show that sensitometrically‐derived doses from the reference films vary from the delivered doses by up to 17% in one institution and 12% in another. Analysis of curves generated for different film batches, or over time, shows that this method of scaling the dose to shift the sensitometric curve results in an acceptable match when curves for the same film type are compared, validating our simple QA technique. Other factors, such as a good processor QA, may affect the results.

To establish whether GafChromic EBT medium is suitable for real‐time fibre‐based in vivodosimetry, we are investigating whether dose‐rate and temperature fluctuations introduce extraneous uncertainties to change in optical density (ΔOD) measurements. 1 cm × 1cm pieces of film were irradiated with a 6 MV beam within a 30 cm × 30 cm × 10 cm Solid Water phantom fitted with optical fibres for real‐time measurements, using a 10 cm × 10 cm field at SAD, 100 cm SAD, and 1.5 cm depth. Each exposure delivered a dose of 5, 10, 25, 50, 100, 250, 500 or 1000 cGy at a dose‐rate of 14, 32, 65, 130, 260 or 520 cGy/min. Change in OD obtained immediately at the end of each exposure were compared. The percent uncertainty in ΔOD for a given dose was calculated by using all the values obtained, regardless of the dose‐rate used. The percent uncertainty ranged between 1.8% and 3.6%, with an average of 2.8%. The expected variation in ΔOD within a single sheet of GafChromic EBT film for a given dose is 1.5% (two standard deviations). This suggests that there is an increase in uncertainty of real‐time ΔOD measurements when variations in dose‐rate are introduced for the doses in 5–1000 cGy range, and dose‐rates between 14 and 520 cGy/min. The average increase in uncertainty is 4%.

Purpose: Presage is a new radiochromic material with substantial promise as a practical and convenient 3D dosimeter. Here we investigate new formulations of PRESAGETM to determine formulations that have high sensitivity, high stability, and/or are amenable to repeat measurements.Method and Materials: PRESAGETM formulations were manufactured in 2 mL glass vial samples and were irradiated in a 6MV photon beam to a dose of 5 Gy. Fifteen formulations were studied, eight of which were variations containing leucomalachite green (LMG) and seven variations containing leuco crystal violet (LCV). The transmission spectra (500–700 nm) were measured in a spectrophotometer for each sample pre‐irradiation and then approximately one hour post‐irradiation. Subsequent spectrum acquisitions were recorded at 2, 24, 48, and 72 hours post‐irradiation to ascertain the stability of optical density changes. Results: Overall, the LCV formulations show greater sensitivity than the formulations containing LMG. The most promising LCV formulations exhibit a 15 – 33 % increase in post‐irradiation absorption relative to pre‐irradiation. The LCV formulations had minimal post‐irradiation color bleaching from 2 to 72 hours, while the LMG formulations varied widely in stability post‐irradiation. A number of the LMG samples returned to their pre‐irradiation optical density, suggesting the possibility of a formulation which could be reusable. In addition, two of the formulations which contained polymeric acrylates along with the leuco dyes increased transmission relative to pre‐irradiation, illustrating the intriguing potential of an ‘inverse radiochromic dosimeter’ (i.e. a dosimeter that becomes clearer after irradiation). Conclusions: Absorption changes post‐irradiation identified LCV formulations with the initial response and stability for application in 3D dosimetry. In addition, LMG formulations were identified that may permit the unique potential for ‘inverse radiochromic dosimetry’ and reusability.

Purpose: Over the last few decades, various groups have investigated optical fiber‐based dosimeters for in vivomeasurements. Recently, two radiochromic films have also been considered for real‐time in vivo point‐based optical dosimetry, and both GafChromic MD‐55 and GafChromic EBT films faired well in several criteria. However, GafChromic MD‐55 was shown to have the change in optical density depend both on dose rate and on temperature, as measured immediately at the end of a given exposure. To continue with the search for a suitable medium for real‐time fiber‐based in vivodosimetry, GafChromic EBT film is also being investigated for dose rate and temperature effects. Method and Materials: 1 cm × 1cm pieces of film were irradiated with a 6 MV beam within a 30 cm × 30 cm × 10 cm Solid Water phantom fitted with optical fibers for real‐time measurements, using a 10 cm × 10 cm field at SAD, 100 cm SAD, and 1.5 cm depth. Each exposure delivered a dose in 5 to 1000 cGy range at a dose rate in 14 to 520 cGy/min range. Changes in OD obtained immediately at the end of each exposure were compared. The percent uncertainty in ΔOD for a given dose was calculated by using all the values obtained, regardless of the dose‐rate used. Results: The percent uncertainty ranged between 1.8% and 3.6%, with an average of 2.8%. The expected variation in ΔOD within a single sheet of GafChromic EBT film for a given dose is 1.5% (two standard deviations). The average increase in uncertainty is 4%. Conclusion: An increase in uncertainty of real‐time ΔOD measurements is observed when variations in dose‐rate are introduced for the doses in 5 to 1000 cGy range, and dose‐rates between 14 and 520 cGy/min.

This study describes the phantoms and methods for performance evaluation of 23 phototimers used in mammography. The evaluation is primarily based on an analysis of the optical densities of image receptors (films). According to the results, the kVp compensation, the response capability, the saturation, and the density controls of the phototimers are very poor. The variation in optical film density exceeded +/- 0.3 optical density (OD) in 87% of the phototimers for the tube voltage range 25-40 kVp and for the 2-6-cm-thick phantoms. The operation of the density controls should be adjusted in 70% of the phototimers. Recommendations are presented.

The effects of scatter radiation on signal‐to‐noise ratio and optical density contrast are quantitatively compared for three tissue interfaces at 85, 110, and 240 kVp in mobile chest techniques. It is shown that scatter in the mediastinal portion of the radiograph is virtually independent of energy, while it substantially increases with energy in the lung fields.