A sparse orthogonal collimator for small animal intensity‐modulated radiation therapy part I: Planning system development and commissioning

Abstract

Purpose To achieve more translatable preclinical research results, small animal irradiation needs to more closely simulate human radiotherapy. Although the clinical gold standard is intensity‐modulated radiation therapy (IMRT), the direct translation of this method for small animals is impractical. In this study we describe the treatment planning system for a novel dose modulation device to address this challenge. Methods Using delineated target and avoidance structures, a rectangular aperture optimization (RAO) problem was formulated to penalize deviations from a desired dose distribution and limit the number of selected rectangular apertures. RAO was used to create IMRT plans with highly concave targets in the mouse brain, and the plan quality was compared to that using a hypothetical miniaturized multileaf collimator (MLC). RAO plans were also created for a realistic application of mouse whole liver irradiation and for a highly complex two‐dimensional (2D) dose distribution as a proof‐of‐principle. Beam commissioning data, including output and off‐axis factors and percent depth dose (PDD) curves, were acquired for our small animal irradiation system and incorporated into the treatment planning system. A plan post‐processing step was implemented for aperture size‐specific dose recalculation and aperture weighting reoptimization. Results The first RAO test case achieved highly conformal doses to concave targets in the brain, with substantially better dose gradient, conformity, and target dose homogeneity than the hypothetical miniaturized MLC plans. In the second test case, a highly conformal dose to the liver was achieved with significant sparing of the kidneys. RAO also successfully replicated a complex 2D dose distribution with three prescription dose levels. Energy spectra for field sizes 1 to 20 mm were calculated to match the measured PDD curves, with maximum and mean dose deviations of 4.47 ± 0.30% and 1.71 ± 0.18%. The final reoptimization of aperture weightings for the complex RAO test plan was able to reduce the maximum and mean dose deviations between the optimized and recalculated dose distributions from 10.3% to 6.6% and 4.0% to 2.8%, respectively. Conclusions Using the advanced optimization techniques, complex IMRT plans were achieved using a simple dose modulation device. Beam commissioning data were incorporated into the treatment planning process to more accurately predict the resulting dose distribution. This platform substantially reduces the gap in treatment plan quality between clinical and preclinical radiotherapy, potentially increasing the value and flexibility of small animal studies.

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.…”

“…However, preclinical radiation research technology is still behind that of clinical RT, and the advance techniques are underdeveloped. 42 – 44 With these technologies, one would expect that the dose conformality ( Fig. 5b1 – b3 , 5e ) can be improved.…”

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

“…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.…”

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.…”