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Introduction In small fields conditions, the acquisition of dosimetry data used for beam commissioning can become a real challenge. The use or not of a reference chamber, the detectors positioning, their sizes and composition imply adapted acquisition protocols. The goal of this work is to determine acquisition parameters and positioning protocol for each detector, in order to realize a comparative analysis of their responses according to the type of acquisition. Methods As part of this work, several detectors: MicroDiamond 60019 (PTW), Razor Diode (IBA), ionization chambers CC01 and CC04 (IBA), Stealth transmission chamber, have been used to acquire dosimetry data : beams profiles , percentage depth dose and output factor (OF). These measurements have been realized for fields ranging from 0.4 cm × 0.4 cm to 3.2 cm × 3.2 cm with a Plateform Synergy Beam Modulator Accelerator and a Blue Phantom 2 water tank (IBA). According to the type of detector, acquisition protocols are configured (resolution and integration time). Comparative measurements are achieved with and without a reference chamber (Stealth) so as to study the impact of the latter on the results. A comparison of percentage depth dose, beams profiles and OF acquired with these different detectors is realized to characterize their differences in term of response. Results The first results show that specific positioning and acquisition protocols are necessary for each detector. The reference chamber allows to save a significant amount of time during the data acquisition without apparently perturbing the beam quality. For OF, significant differences appear among different detectors for fields inferior to 2.4 cm × 2.4 cm. Measurements are undergoing. Conclusions Dosimetry measurements in small fields conditions require adapted acquisition parameters and precise detectors positioning. The complementarity of these detectors seems to be adapted to the dosimetry data acquisition in small fields conditions. The MicroDiamond and the Razor diode, by their conception and their small sensitive volume, seem to be the best adapted detectors for fields inferior to 1 cm × 1 cm. [ABSTRACT FROM AUTHOR]

Introduction During total body irradiation (TBI), the control of the dose received by the patient during each fraction of the treatment is necessary. The aim of this study was to verify that the EDD-53G diodes could be used in the TBI conditions and afterward to set up a measurement protocol for in vivo dosimetry during the fractions of treatment. Methods The diodes used were IBA’s EDD-53G (black) diodes with an OmniPro-InViDos supports DPD-12 electrometer. All measurements were made with the patient’s treatment conditions for a TBI: gantry at 270°, collimator at 45°, irradiation fields size 40 cm by 40 cm and source-skin distance (SSD) of 303 cm, 333 cm, 373 cm or 403 cm (clinically used SSD). Diode calibration was carried out with diodes placed at the input and the output of a phantom of 20 cm composed of RW3 polystyrene plaque with a FARMER ionization chamber (IBA FC65-P) positioned at mid-thickness. During the evaluation phase of the diodes, repeatability and reproducibility studies were carried out. The diodes angulation influence on the irradiation incidence and the diodes influence on each other were evaluated. A verification of the diode’s dose linearity was also carried out. Secondly, thickness correction factors (from 4 cm to 30 cm) were established at the four SSD, taking the patient’s different thicknesses compared to the reference conditions into account. Results In the study of the diodes angulation influence, an anisotropy of the diodes according to their rotation axis was established: relative mean deviation σ average = 1.2% (max deviation of 4%) σ average = 0.3% if the diode is always placed in accordance with the same axis. Therefore, the repeatability and reproducibility studies were carried out taking into account this effect and positioning the diode always at the same angle of incidence with the beam. These two studies yielded the following results: σ average = 0.08% for repeatability (σmax = 1.55%) and σ average = 0.88% for reproducibility (σmax = 0.11%). The diode presence in the vicinity of another did not show influence on the measurement (σ average = 0.09%). The response linearity of the diodes according to the delivered dose has been demonstrated (slope coefficient = 1.000 ± 0.001). For each SSD, a correction factor curve to be applied as a function of the thickness of the phantom was performed. Conclusions The first results obtained with these diodes were satisfying. Subsequently, an anthropomorphic phantom test is considered to verify the in vivo dosimetry measurement protocol with the diodes. [ABSTRACT FROM AUTHOR]

Introduction Prolonged exposures in interventional radiology can lead to increased skin doses (Dskin) and to determinist side effects. The increasing frequency of Rotational mode (RM) acquisitions implies significant Dskin rises. The Dskin calculation method for a fluorography can be performed manually or with dedicated software. However, currently, such methods do not exist for RM. The aim of this study is to evaluate the feasibility of Dskin calculation with the PCXMC 2.0 Rotation software (STUK) for RM in interventional neuroradiology, then to validate this estimation by using a manual method combined with PCXMC use and fluorography. Methods This study is performed for an Allura Xper FD20/10 (Philips) system. The available RM are the XperCT (207°/rotation, 622 images) and the Propeller (240°/rotation, 122 images). For these acquisitions, mean dose is calculated by PCXMC for each organ, but this software is not able to obtain a reliable Dskin, which is averaged over the whole phantom skin. The objective is to determine the possible existence of a factor to convert mean organ dose during the acquisition to Dskin. Considering neuroradiology interventions, the mean brain dose (Dbrain) was chosen as convertible to Dskin for different points on the skin. Hence several measurements were carried out on an anthropomorphic ART phantom (Radiology Support Devices Inc.) with Thermo Luminescent Dosimeters (TLDs) which were calibrated at radiological energies and with a homogeneity below 5%. In a second phase, a manual calculation based method was created to estimate Dskin with a dedicated software which cannot consider RM: a trigonometric estimation was performed to evaluate the number of projections per rotation that could contribute to Dskin at each point. Fluorographies were then simulated on PCXMC for these points, based on each corresponding number of projections. Then, Dbrain for each fluorography was converted in RM Dskin. Experimental TLDs measurements were carried out in order to validate this method. Results For the XperCT, the posterior Dskin measured with TLDs is 34,53 mGy, 2,67 mGy for the Propeller. For these RM, the first Dskin estimations from Dbrain lead to the Dskin measured with TLDs within a 20% accuracy interval. Conclusion In addition to the Dskin determination with PCXMC for the two RM in interventional neuroradiology, its estimation with the fluorography conversion method seems possible. [ABSTRACT FROM AUTHOR]

Introduction The objective of this study is to evaluate the overall performances of the new Elekta Gamma Knife Icon via End-to-End tests. Methods This study consists of three different End-to-End tests: misalignment, point dose and dose distribution discrepancies. The first study evaluates the misalignment of the dose delivery by using a phantom made of plexiglass wherein radiochromic films have been inserted. CBCT images of this phantom have been acquired and were using for the dose planning. The dose planning consisted of positioning 4 mm isocenters on specific localizations. Films were analyzed with ImageJ software. The second study evaluates point dose discrepancies. We used the anthropomorphic CIRS STEEV phantom and a PTW PinPoint ionization chamber. A dose planning, consisting of a single 4 mm isocenter centered on the sensitive volume of the ionization chamber, were performed on the CT of the phantom and the whole workflow including mask and pillow personalization and CBCT repositioning were followed step-by-step. Deviation of ten dose measurements was analyzed. The third study evaluates dose distribution discrepancies. We used the anthropomorphic CIRS STEEV phantom and a film stack insert filled with seven radiochromic films. A realistic dose planning (25 isocenters (4 and 8 mm collimators, some plugged), prescription dose of 4.8 Gy at the 50% isodose) was performed on the CT of the phantom using the Convolution algorithm then the whole workflow including mask and pillow personalization and CBCT acquisitions were followed. Film distribution doses were compared with theoretical distribution using 3%/1mm gamma index analysis via FilmQA Pro software (Ashland). Results Misalignment errors found were 0.25 mm and 0.27 mm in x and z directions. Point dose discrepancy found was 0.18% when the phantom has been moved and when the re-alignment procedure with CBCT acquisition was performed. Average number of pixels passing the 3%/1 mm gamma index criteria is 97.5% (min. 93.6% and max. 99.45%). Conclusions The sum of these results demonstrates the overall quality of the new Elekta Gamma Knife ICON and offers the guarantee of high quality procedures for hypo fractionated and frameless treatment. Informations given by the CBCT (ie. Leksell coordinates here) are enough trustable to assure the quality of treating a patient at the right localization and with the right dose. [ABSTRACT FROM AUTHOR]

Introduction The objective of this study is to evaluate performance and accuracy of each part of the new Leksell Gamma Knife ICON. Methods The evaluation was based on four criteria: quality of the image, dose due to the image (CBDI and dose distribution into the patient) mechanical performance, monitoring system (HDMM). The CBCT Image quality was evaluated using the Catphan 503 phantom (The Phantom Laboratory) coupled to MyQA software (IBA). The phantom was daily scanned with the two acquisition presets (high and low dose) over a period of two months. The contrast noise ratio (CNR), overall uniformity, scaling discrepancy, geometric distortion and spatial resolution were measured. The CBDI were measured with the two available presets (low and high dose) with a Raysafe X2 CT chamber and a CTDI phantom (The Phantom Laboratory). The dose distribution evaluation were evaluated by using thermoluminescent detectors (TLD) and an anthropomorphic head phantom RANDO (The Phantom Laboratory).The mechanical performances, consisting of comparisons between Leksell and real coordinates of four objects, have been evaluated with the Diode tool+ provided by Elekta. A series of 100 measurements enable us to quantify the repeatability and reproducibility of the system. The HDMM system was assessed using a micrometer screw on which we mounted a patient marker allowing movement visualization by the infrared cameras. Movements in three directions were applied and recognition assessed. Results Image quality results are: CNR: 1.41 ± 0.1/2.24 ± 0.17 (low/high), overall uniformity: 83.14 ± 0.98/86.57 ± 0.66 (low/high). For the scaling discrepancy: 0.26 ± 0.20/0.21 ± 0.1 mm (low/high), the geometric distortion: 0.33 ± 0.05/0.21 ± 0.03 mm (low/high) and resolution space 0.49 ± 0.02/0.48 ± 0.01 lp/mm (low/high). CBDI values are 2.23 and 5.9 mGy (low/high). The dose distribution into the head phantom shows a large heterogeneity: doses measured are between 2.24 and 7.28 mGy when scanning with the high dose preset. The mechanical performance with the Diode Tool+ show us a maximum discrepancy of 0.17 ± 0.02 mm and the average manual measurements are between 0.16 and 0.19 ± 0.05 mm. The accuracy of the HDMM system was equal to 0.01 mm with a maximum error of 0.05 mm. Conclusions The sum of these results demonstrates the overall quality of the new Leksell Gamma Knife ICON and offers the guarantee of high quality procedures for hypo fractionated and frameless treatment. [ABSTRACT FROM AUTHOR]