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Improvements in dosimetry in preclinical radiation research facilitate the application of results to the newest radiotherapy techniques, reducing gaps that hinder translation. Currently, guidelines for small-field kV photon dosimetry of small animal irradiators have not been published, and most of the publications are based on radiochromic film dosimetry. In this study, we evaluated the performance of four detectors, three ionization chambers (ICs): (PTW Advanced Markus, PTW Semiflex 31010, PTW PinPoint-3D 31016) and one solid-state detector (PTW 60017 unshielded Diode E) regarding their suitability for relative dosimetry of the small animal radiation research platform SARRP (220 kVp). The measurements were performed in a high-resolution 3D scanning phantom, centering the detectors in the field following the in-plane and cross-plane profiles method at two depths. Depth dose curves (PDDs) and profiles were measured in water for field sizes ranging from 40 × 40 mm2 to 5 × 5 mm2. Quantitative analysis was performed through global and local dose differences (DDs) between the PDDs and the Advanced Markus parallel plate IC data and through the gamma index (γ) criteria for profiles compared against data from EBT3 films provided by the manufacturer. Compared to the Advanced Markus IC, the PDD results suggest that PinPoint-3D is suitable for depth measurements at this beam quality, even near the surface, with agreements better than 1%. Semiflex 31010 was accurate to within 1.5% for measurements deeper than 5 mm. Diode E showed a dramatic DD and should not be recommended for the field sizes and kVp evaluated in this study. In agreement with γ analyses, PinPoint-3D and Diode E are good candidates for profile measurements of field sizes from 40 × 40 mm2 to 10 × 10 mm2. For 5 × 5 mm2 profiles, only Diode E showed good results, making it a recommended detector for profile measurements.

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A geometric acrylic phantom was designed and built for dose distribution verification in Stereotactic Radiosurgery. Acrylic objects representing the tumor tissue, (target volume (TV)), and the organ at risk (OAR), the brainstem, were inserted inside this phantom. The TV is represented by two semi-spheres of acrylic with a diameter of 13.0 mm, both having a central cavity for accommodation of a TLD-100 detector and a small radiochromic Gafchromic EBT film. The OAR is represented by the two parts of a 38.0 mm length acrylic cylinder with a diameter 18.0 mm and cavities along the cylinder central axis able to accommodate 5 TLD - 100 detectors and another of EBT film between the two cylinder parts. This experimental setup was submitted to a radiosurgical treatment, after which the TL dosimeters were evaluated and their responses were compared with the planned dose values. The radiochromic EBT films showed the dose distributions. The linear accelerator used was a Varian 2300 C/D, generating a 6 MV photon beam. The investigated phantom system was able to check the accuracy of dose delivery to predetermined points and the dose distribution due to stereotactic radiosurgery treatments and proved to be a good tool for quality control in these situations.

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In the last decade, radiochromic films (RCF) have been used extensively in medical physics for evaluating uniformity of radiation beams and dose distributions. These films are very sensitive to changes in temperature; therefore, one needs to know its thermal behavior to use them efficiently. Normally, the thermal assessment is done using optical methods on previously irradiated samples. Here, we report the use of a complementary dielectric method. We designed an experimental device that allows us to measure, simultaneously, the dielectric and optical properties as a function of temperature. We performed the measurements in real-time to temperature increases from 27 to 48 degrees C of EBT and MD-55 RCF previously exposed to UV. We found for both films a decrease in the real part of the dielectric permittivity as the temperature increases, but an increment and decrease in the dielectric loss factor for the EBT and MD-55 film, respectively.

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The performance of an L-alanine dosimeter with millimeter dimensions was evaluated for dosimetry in small radiation fields. Relative output factor (ROF) measurements were made for 0.5 x 0.5, 1 x 1, 3 x 3, 5 x 5, 10 x 10 cm(2) square fields and for 5-, 10-, 20-, 40-mm-diam circular fields. In beam profile (BP) measurements, only 1 x 1, 3 x 3, 5 x 5 cm2 square fields and 10-, 20-, 40-mm-diam circular fields were used. For square and circular field irradiations, Varian/Clinac 2100, and a Siemens/Mevatron 6 MV linear accelerators were used, respectively. For a batch of 800 L-alanine minidosimeters (miniALAs) the average mass was 4.3+/-0.5 (1 sigma) mg, the diameter was 1.22+/-0.07 (1 sigma) mm, and the length was 3.5+/-0.2 (l sigma) mm. A K-Band (24 GHz) electron paramagnetic resonance (EPR) spectrometer was used for recording the spectrum of irradiated and nonirradiated miniALAs. To evaluate the performance of the miniALAs, their ROF and BP results were compared with those of other types of detectors, such as an ionization chamber (PTW 0.125 cc), a miniTLD (LiF: Mg,Cu,P), and Kodak/X-Omat V radiographic film. Compared to other dosimeters, the ROF results for miniALA show differences of up to 3% for the smallest fields and 7% for the largest ones. These differences were within the miniALA experimental uncertainty (-5-6% at 1 sigma). For BP measurements, the maximum penumbra width difference observed between miniALA and film (10%-90% width) was less than 1 mm for square fields and within 1-2 mm for circular fields. These penumbra width results indicate that the spatial resolution of the miniALA is comparable to that of radiographic film and its dimensions are adequate for the field sizes used in this experiment. The K-Band EPR spectrometer provided adequate sensitivity for assessment of miniALAs with doses of the order of tens of Grays, making this dosimetry system (K-Band/miniALA) a potential candidate for use in radiosurgery dosimetry.

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GafChromic MD-55-2 film response was studied using a flatbed, reflective Microtek ScanMaker E3 scanner, under different conditions to optimize its use. Irradiations were performed using 60Co gamma rays in a 0-300 Gy dose interval to produce a calibrated step wedge. A 24-bit colour-scale mode along with image splitting into its red, green and blue components is suggested as an improved dosimetry method over a 256 grey level (8-bit) mode, extending the dynamic range for this film. Diverse film orientation and positioning, a black or a white background, and individual step film scanning were evaluated. Unwanted normalization is overcome by adding reference black and white steps adjacent to the radiochromic film, ensuring reproducibility. The use of a red filter was found to be equivalent to the use of the red component of the image after image colour splitting. The useful range for MD-55-2 film is extended up to 300 Gy if colour components, other than red, are used to evaluate the response. Comparisons with optical density measurements show that inexpensive commercial scanners might be a good alternative to densitometers.

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