A comprehensive geometric quality assurance framework for preclinical microirradiators

Abstract

Purpose: The mechanical and geometric accuracy of small animal image-guided radiotherapy (SA-IGRT) systems is critical and is affected by a number of system-related factors. Because of the small dimensions involved in preclinical radiotherapy research, such factors can individually and/or cumulatively contribute to significant errors in the small animal radiation research. In this study, we developed and implemented a comprehensive quality assurance (QA) framework for characterizing the mechanical and geometric constancy and accuracy of the small animal radiation research platform (SARRP) system. Methods: We quantified the accuracy of gantry and stage rotation isocentricity and positional stage translations. We determined the accuracy and symmetry of field sizes formed by collimators. We evaluated collimator assembly system performance by characterization of collimator axis alignment along the beam axis during gantry rotation. Furthermore, we quantified the end-to-end precision and accuracy of image-guided delivery by examining the congruence of intended (e.g., imaging) and actual delivery (measured during experiment) isocenters. Results: The fine and broad beams showed different central axes. The center of the beam was offset toward the cathode (0.22 AE 0.05 mm) when switching the beam from a fine to a broad focus. Larger (custom-made) collimators were more symmetrically centered than smaller (standard) collimators. The field formed by a 1-mm circular collimator was found to deviate from the circular shape, measuring 1.55 mm and 1.25 mm in the X and Y directions, respectively. The 40-mm collimator showed a field that was 1.65 (4.13%) and 1.3 (3.25%) mm smaller than nominal values in the X and Y directions, respectively, and the 30-mm collimator field was smaller by 0.75 mm (2.5%) in the X direction. Results showed that fields formed by other collimators were accurate in both directions and had ≤2% error. The size of the gantry rotation isocenter was 1.45 AE 0.15 mm. While the gantry rotated, lateral and longitudinal isocenter displacements ranged from 0 to À0.34 and À0.44 to 0.33 mm, respectively. Maximum lateral and longitudinal displacements were found at obliques gantry angles of À135°and 45°, respectively. The stage translational accuracies were 0.015, 0.010, and 0 mm in the X, Y, and Z directions, respectively. The size of the stage rotation runout was 2.73 AE 0.3 mm. Maximum displacements of the stage rotational axis were À0.38 (X direction) and À0.26 (Y direction) mm at stage angles of À45°and À135°, respectively. We found that displacements of intended and actual delivery isocenters were 0.24 AE 0.10, 0.12 AE 0.62, and 0.12 AE 0.42 mm in the X, Y, and Z directions, respectively. Conclusion: We used the SARRP built-in electronic portal imaging device (EPID) to perform most of the geometric QA tests, demonstrating the utility of the EPID for characterizing the geometric accuracy and precision of the SA-IGRT system. However, in principle, the methodology and tests developed here are applicable to any digita...

Online dose delivery verification in small animal image‐guided radiotherapy

“…In order to avoid the impact of these uncertainties, the EIPD dosimetry method was tested for cone sizes of 5-40 mm, and smaller field sizes (<5 mm) were not considered. 17,18 However, since small fields (<5 mm) are frequently used in preclinical radiation research, there is ongoing research in our lab to minimize these geometrical uncertainties and extend the EPID dosimetry to these field sizes.…”

“…Because current version of image acquisition software is not capable of acquiring integrated images over a long period of time, the EPID was used to estimate dose rate rather than dose. As outlined in previous works, 17,18 the EPID's pixel pitch is equal to 69 and 50 µm at the EPID and isocenter planes respectively. The nominal SAD and the x-ray source-to-detector distance (SDD) are approximately 35 and 47 cm respectively.…”

“…We have characterized and quantified them and the capability of an imager to detect such errors. [16][17][18] In recent work, we developed an EPID-based transit/exit dosimetry for kV x-ray beams. We validated this technique against film and ion chamber (IC) in homogeneous and heterogeneous materials.…”

A failure modes and effects analysis quality management framework for image‐guided small animal irradiators: A change in paradigm for radiation biology

“…In practice, the Xstrahl SARRP Muriplan (version 3) has been shown to have dosimetric deficiencies of up to 20% near a phantom surface. 14,53 Finally, the manual use of treatment accessories without electronic interlocks to verify the correct filter and cone sizes were seen as the largest risk of failure (128-360). Given that electronic interlocks are common in other radiation equipment, it is curious that these have not yet been introduced in more recent versions of IGSAI.…”

“…However, despite the rapid influx of new technology, comprehensive quality assurance (QA) protocols similar to the AAPM TG-142 5 for linear accelerator are still virtually nonexistent, and radiation biology study protocols present wide variations from site to site. [6][7][8][9][10] Many attempts have been made to produce rigorous systematic and prescriptive QA [11][12][13][14][15][16][17] methodologies similar to those employed in the clinic for patient radiation therapy (RT) such as the AAPM Task Group 40 18 and 142. 5 These approaches typically focus on comprehensive dosimetry and geometrical tests performed by physics specialists with knowledge and access to specialized equipment such as special dosimetric phantoms, 16,19 GAFChromic EBT film, 15,20 alanine detectors, 21 and ionization chamber measurements.…”