A sparse orthogonal collimator for small animal intensity‐modulated radiation therapy. Part II: hardware development and commissioning

Abstract

Purpose A dose‐modulation device for small animal radiotherapy is required to use clinically analogous treatment techniques, which will likely increase the translatability of preclinical research results. Because the clinically used multileaf collimator (MLC) is impractical for miniaturization, we have developed a simpler, better‐suited sparse orthogonal collimator (SOC) for delivering small animal intensity‐modulated radiation therapy (IMRT) using a rectangular aperture optimization (RAO) treatment planning system. Methods The SOC system was modeled in computer‐aided design software and fabricated with machined tungsten leaves and three‐dimensional (3D) printed leaf housing. A graphical user interface was developed for controlling and calibrating the SOC leaves, which are driven by Arduino‐controlled stepper motors. A Winston‐Lutz test was performed to assess mechanical alignment, and abutting field and grid dose patterns were created to analyze intra‐ and intercalibration leaf positioning error. Leaf transmission and penumbra were measured over the full range of gantry angles and leaf positions, respectively. Three SOC test plans were delivered, and film measurements were compared to the intended dose distributions. The differences in maximum, mean, and minimum, as well as pixelwise absolute dose differences, were compared for each structure, and a gamma analysis was performed for the target structures using criteria of 4% dose difference and 0.3 mm distance to agreement. Results The Winston‐Lutz test revealed maximum directional offsets between the SOC and primary collimator axes of 0.53 mm at 0° and 0.68 mm over the full 360°. Upper and lower abutting field patterns had maximum dose deviations of 18.8 ± 3.1% and 15.5 ± 2.9%, respectively, and grid patterns showed intra‐ and intercalibration repeatability of 93% and 91%, respectively. Extremely low midleaf (0.15 ± 0.05%) and interleaf (0.27 ± 0.22%) transmission was measured, with no significant rotational variation. The average penumbra was ~0.8 mm for all leaves at field center, with a range of 0.17 mm for all leaf positions. A highly concave test plan was delivered with a ~ 95% gamma analysis pass rate, and a realistic mouse phantom liver irradiation plan achieved a pass rate of ~98%. A highly complex dose distribution was also created with 551 SOC apertures averaging 2.4 mm in size. Conclusions A sparse orthogonal collimator was developed and commissioned, with promising preliminary dosimetry results. The SOC design, with its limited moving components and high dose‐modulation resolution, is ideal for delivering high‐quality small animal IMRT with our RAO‐based treatment planning system.

Feasibility of a Novel Sparse Orthogonal Collimator–Based Preclinical Total Marrow Irradiation for Enhanced Dosimetric Conformality

“…Although the 3D-TMI preclinical model was shown to be equivalent to the clinical TMI ( 16 ), the dose to the lungs and kidneys was relatively higher due to their proximity to the spine and lower 3D plan dose conformity. The SOC-TMI method is based on RAO planning ( 31 ) and SOC dose modulator ( 22 , 32 ) for IMRT planning. Compared with the MLC-based IMRT, SOC uses substantially fewer leaves while maintaining the modulation resolution.…”

“…Mouse position, immobilization, and CBCT imaging are the same as in the 3D-TMI preclinical model. The SOC system is designed and fabricated with four orthogonal, double-focused tungsten leaf pairs, which is programmed and controlled by the Rectangular Aperture Optimization (RAO) algorithm ( 21 , 22 ), which solves an inverse optimization problem for IMRT planning. The SOC can be installed on the small animal irradiator (Precision X-Ray, North Branford, CT) with a 3D printed adapter.…”

Quantitative Bioluminescence Tomography-Guided Conformal Irradiation for Preclinical Radiation Research

“…In clinic setting, one would use multi-leaf collimator combined with inverse planning to design optimal collimator opening and beam orientation to provide conformal dose coverage. However, pre-clinical radiation research technology is still behind that of clinic RT, and the advance techniques are underdeveloped (42)(43)(44). With these technologies, one would expect the dose conformality (Fig.…”

A method for generating intensity‐modulated radiation therapy fields for small animal irradiators utilizing 3D‐printed compensator molds

“…Recently, this model has been improved further to treat eight fields, with average leaf separation of 3.5 AE 1.4 mm, within 14 min using 225 kVp beam at 20 mA. 8,9 Compared to SOC technique, our treatment may be able to deliver a large field up to a 40 9 40 mm 2 square at a higher dose rate.…”

“…The technique has been integrated into XRAD‐225Cx at a relatively low cost using Arduino‐controlled stepper motors to move the collimators. Recently, this model has been improved further to treat eight fields, with average leaf separation of 3.5 ± 1.4 mm, within 14 min using 225 kVp beam at 20 mA 8,9 . Compared to SOC technique, our treatment may be able to deliver a large field up to a 40 × 40 mm 2 square at a higher dose rate.…”