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[en] Radiotherapy is commonly utilised as standard treatment in the so called mucosa-associated lymphoid tissues (MALT), due to the low probability of distant relapse.The particularities of the lesion, make necessary both energy degradation and beam conformation. To keep homogeneity within acceptable limits, a lengthener attached to the electron applicator has been devised to closely fit the anatomy of the patient. Considering the small area of the outcoming field, film dosimetry is preferred, since the dimensions of an ionisation chamber and even of a semiconductor probe might be comparable to the field size. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)
[en] Purpose: This paper presents a model for dose–response curves of radiochromic films. It is based on a modified version of single-hit model to take into account the growth experienced by lithium salt of pentacosa-10,12-diynoic acid polymers after irradiation. Methods: Polymer growth in radiochromic films is a critical phenomenon that can be properly described by means of percolation theory to provide an appropriate distribution function for polymer sizes. Resulting functional form is a power function featuring a critical exponent and two adjustable parameters. Moreover, these parameters act as scaling factors setting a natural scale for sensitometric curves where the dependence on channel sensitivity is removed. A unique reduced response curve is then obtained from all the color channels describing film behavior independently of film dosimetry system. Results: Resulting functional form has been successfully tested in several sensitometric curves from different Gafchromic EBT models, providing excellent agreement with experimental data in a wide dose range up to about 40 Gy and low dose uncertainty. Conclusions: The model presented in this paper describes accurately the sensitometric curves of radiochromic films in wide dose ranges covering all typical ranges used in external radiotherapy. Resulting dose uncertainty is low enough to render a reasonably good performance in clinical applications. Due to cross-correlation, only one of the adjustable parameters is totally independent and characterizes film batches
[en] To investigate the characteristics of the newly marketed, Insight dental X-ray film. Kodak Ultraspeed (DF-58), E-speed, Agfa Dentus M2, and Kodak Insight (IP-21) films were radiographed using a Trophy intra-oral radiographic machine. 10 step exposure times were prepared and each step exposure was monitored using a FH 40G (ESM Eberline Instruments) dosimeter for each of the 4 types of intra-oral film. All films were manually processed and the radiographic densities at 6 site of each processed film were measured, and the characteristic curves of each of the 4 types intra-oral films were created utilizing these dosimetric data and radiographic densities, based on ISO 5779. The film contrast, speed, and base plus fog density of Insight film were compared with those of the 3 other films examined in this experiment. E-speed film showed greatest average gradients followed by Insight film. E-speed and Ultraspeed film showed great average gradients at low density levels. Insight film showed the fastest speed followed by E-speed, Dentus M2 and Ultraspeed film. Dentus M2 film showed greatest base plus fog density level followed by Insight film. Kodak Insight film showed fastest film speed with comparable film contrast on characteristic curve.
[en] Accuracy of relative dose distributions calculated by TPS was within tolerance levels for all the evaluated test cases; however, TPS monitor unit (MU) computations were not acceptable, so the system was not clinically commissioned for that purpose. an experimental method was validated for estimation of the characteristic β angle and subsequent calculation or required MU. The proposed system has been dosimetrically commissioned and pilot tested clinically on a real patient; a high percentage short term tumor remission has been observed, accompanied with acceptable radiation complications, making the methodology very promising. (Author)
[en] Kodak X-Omat V radiographic film has been tested for its polarization properties when using polarized and non-polarized light sources and detectors. The radiographic film has been shown to produce a relatively small but not negligible (less than 5%) variation in 90 degrees cycles in measured optical density within the visible spectrum when the light source is fully linear polarized and the film is rotated through 360 degrees angle. Negligible variations are seen when the detector is linearly polarized. If both light source and detector are linearly polarized, variations in measured optical density can reach 35% when the film is rotated through 360 deg. angle. This seems to be due to variations in the degree and axis of rotation in polarized light caused by the radiographic film and is independent of exposure level as the intensity of variation in absolute optical density is relatively the same for all film exposures. We recommend that a polarization test be performed on a densitometry system to establish the extent of its polarization properties before accurate dosimetry is performed with radiographic film. (note)
[en] This study evaluates the ImageJ software as dosimetric tools for analyzing the film dosimeter in high energy photons and electrons. The percentage depth dose of photons of 6 and 10 MV and electrons of 6 and 9 MeV were measured using the Gafchromic EBT2 film dosimeter. The films were scanned and analyzed using the Verisoft software and ImageJ. The beam profiles at nominal photon and electron beam parameters were also evaluated using the two methods. The PDD measured in ImageJ at high energy photons were in good agreement within 1 % percentage of discrepancy at all depths in comparison to the Verisoft software. The PDD measured in ImageJ at high energy electrons also showed good agreement to Verisoft software within 8 % percentage of discrepancy at all depths. The measured flatness of beam profiles at Dmax, R_5_0, R_8_0 and R_9_0 in ImageJ were also in good agreement to Verisoft software with flatness value between 4 and 8 %. The results indicated the suitability of ImageJ software as dosimetric tool for analyzing EBT2 film dosimeter at high energy photon and electrons.(author)
[en] Introduction The optical properties of the Radiochromic film, expressed for its optical density (OD), change as the absorbed energy varies. The film to use should be defined in terms of its capability of modification in OD for different dose adsorbed levels, besides of the spatial response and linearity. For this study, we use the GafChormic XR-RV2 film, in a dose range from 0 Gy to 10 Gy, cut in small pieces and irradiated with 100 kVp and 150 kVp energies. The samples will be measured with a spectrophotometer and compared with the result obtained with commercial scanner. The aim of this work is focused on obtaining calibration curves for the same samples of films, using a spectrophotometer comparing the results of measurements with a graphic scanner. Materials and Methodology A kilovoltage x-ray beam (50 kVp to 150kVp) from an Xstrahl 150 X-ray therapy Unit used for superficial treatment, was employed in this study. It was calibrated following the protocol described in Report-76 by TG-61 of the AAPM. The film XR-RV2, is composed in its interior by a block of three layers; the adhesive sensitive (12.0 mm thick), surface (3.0 mm) and active (17.0 mm), and is coated on both sides by layers of polyester one of yellow color and another one of white color, both of 97.0 mm thick. The dose was delivered to the center of the Gafchromic XR-RV2 films by a circular field cone with diameter of 5.0 cm, positioned on a 30.0 x 30.0 x 5.0 [U+3016]cm[U+3017]ˆ3 solid water phantom with the film at surface. The films, were cut into small samples (4x4 cm2) from the same sheet, and each sample was irradiated with one of two beam qualities (100 kVp or 150 kVp), considering doses from 0 to 10 Gy in steps of 100 cGy calculated at the surface, where the sample with 0 cGy will be measured for background reference.
[en] This study clarified the mechanical performance of volumetric modulated arc therapy (VMAT) plans for prostate cancer generated with a commercial knowledge-based treatment planning (KBP) and whether KBP system could be applied clinically without any major problems with mechanical performance. Thirty consecutive prostate cancer patients who underwent VMAT using extant clinical plans were evaluated. The mechanical performance and dosimetric accuracy of the single optimized KBPs, which were trained with other 51 clinical plans, were compared with the clinical plans. The mechanical performance metrics were mean field area (MFA), mean asymmetry distance (MAD), cross-axis score (CAS), closed leaf score (CLS), small aperture score (SAS), leaf travel (LT), modulation complexity score (MCSv), and monitor unit (MU). The γ passing rates were evaluated with ArcCheck and EBT3 film. The mean mechanical performance metrics (clinical plan vs. KBP) were as follows: 18.28 cm2 vs. 17.25 cm2 (MFA), 21.08 mm vs. 20.47 mm (MAD), 0.54 vs. 0.55 (CAS), 0.040 vs. 0.051 (CLS), 0.20 vs. 0.23 (SAS5mm), 458.5 mm vs. 418.8 mm (LT), 0.27 vs. 0.27 (MCSv), and 618.2 vs. 622.1 (MU), respectively. Significant differences were observed for CLS and LT. The average γ passing rates (clinical plan vs. KBP) were as follows: 99.0% vs. 99.1% (3%/3 mm) and 92.4% vs. 92.5% (2%/2 mm) with ArcCHeck, and 99.5% vs. 99.4% (3%/3 mm) and 95.2% vs. 95.4% (2%/2 mm) with EBT3 film, respectively. The KBP used lower multileaf collimator (MLC) travel and more closed or small MLC apertures than the clinical plan. The KBP system of VMAT for the prostate cancer was acceptable for clinical use without any major problems.