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Traditional Linear Accelerators
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
There are two types of secondary collimators – diaphragms or jaws and multi-leaf collimators. Essentially, the secondary collimators convert the circular x-ray beam emerging from the primary collimator into a more clinically useful beam shape with a uniform dose profile. This is done by the collimators moving to define the required field shape and blocking the x-rays outside this field shape.
Radiotherapy Physics
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Andrea Wynn-Jones, Caroline Reddy, John Gittins, Philip Baker, Anna Mason, Greg Jolliffe
A Multi-Leaf Collimator (MLC), such as that shown in Figure 6.5, provides yet more control over beam shaping. The MLC allows the treatment fields to conform closely to the target volume, compared to simply using square fields defined by the secondary collimators.
Mammography and Interventional Breast Procedures
Published in Raymond Taillefer, Iraj Khalkhali, Alan D. Waxman, Hans J. Biersack, Radionuclide Imaging of the Breast, 2021
Collimator: Collimators regulate the size and the shape of the x-ray beam. Beam collimation is intended to decrease scatter radiation and unnecessary patient exposure. In mammography, rectangular collimation is used to match the shape of the image receptor [19].
Modeling of dose and linear energy transfer homogeneity in cell nuclei exposed to alpha particles under various setup conditions
Published in International Journal of Radiation Biology, 2023
Adrianna Tartas, Mateusz Filipek, Marcin Pietrzak, Andrzej Wojcik, Beata Brzozowska
The use of a collimator was simulated for the bottom-up setup, with a 5 mm thick aluminum collimator placed 1 mm of air above the source and 1 mm of air below the Mylar foil, as shown in Figure 1. The collimator had a dimension of 6 cm × 5 cm and a thickness of 5 mm. The 140 hexagonal holes with a diagonal of 5 mm were separated with 0.25 mm thick wall. The fourth irradiation setup included rotating collimator. To simulate the rotation, the hexagonal shape of the central hole (where the diagonals of the collimator intersected) was divided into six equilateral triangles. The rotation axis was set at 1/3 of the height of one of the triangles (the bottom one), dropped onto the side of the hexagon as it was shown in Figure 2. The collimator was rotated in steps of 5 degrees. The angular speed should be adjusted to the time of irradiation in such a way that the collimator would make a full rotation. If the speed must be higher, the number of rotations should be an integer. Rotating the collimator allowed to minimize the radiation attenuation by the collimator walls.
Progress in large field-of-view interventional planar scintigraphy and SPECT imaging
Published in Expert Review of Medical Devices, 2022
Martijn M.A. Dietze, Hugo W.A.M de Jong
The next system concerns the smart integration of two existing imaging modalities: planar scintigraphy and fluoroscopy. This combined imaging modality is named ‘Interventional X-ray and Scintigraphy Imaging’ (IXSI) (see Figure 2a) [42–46]. The scanner consists of an x-ray flat panel detector that is positioned in front of a gamma camera that is mounted with a cone-beam collimator. The detector stack is placed together with an x-ray tube on a custom-made gantry. The focal length of the cone-beam collimator is approximately the same as is the distance of the x-ray tube to the flat panel detector so that x-ray and nuclear projections are intrinsically registered. By rotating the detector around the patient (using parameterized non-circular orbits), SPECT and CBCT reconstructions can furthermore be acquired. The CBCT reconstruction can be used for attenuation correction so that the SPECT reconstruction becomes quantitative.
Stereotactic Body Radiation Therapy (SBRT) in Pelvic Lymph Node Oligometastases
Published in Cancer Investigation, 2020
Leonid B. Reshko, Martin K. Richardson, Kelly Spencer, Charles R. Kersh
Intensity-modulated radiotherapy and volumetric-modulated arc therapy planning techniques were considered. A gross tumor volume (GTV) was contoured and a clinical target volume was kept equivalent to the GTV. A non-uniform planning target volume of five millimeters was added to account for localization and targeting uncertainties. The radiotherapy dose was prescribed to this volume. The treatment planning techniques included non-coplanar static aperture arcs and non-coplanar static fields. Treatments were delivered using a linear accelerator with four-millimeter multileaf collimator leaf width and a robotic couch. Cone-beam CT was obtained prior to each treatment. The fractions were delivered weekly. The radiotherapy treatment technique did not undergo any major changes between 2007 and 2017. The BED was calculated by the formula: nd[1 + d/(α/β)]. Equivalent doses of 2-Gy fractions (EQD2) were calculated from the BED with the following formula: nd[(d + α/β) ÷ (2 + α/β)]. α/β is a ratio unique for a given tissue, d = dose per fraction, and n = number of fractions (26). α/β of 10 was used for our calculations (27). The specific dose constraints depended on the tumor location and were based on the prior studies and on our institutional experience (28). Radiologic imaging and clinical follow-up were performed at 3-month intervals or more frequently to assess treatment response.