MicroRT—Small animal conformal irradiator

Abstract

A novel small animal conformal radiation therapy system has been designed and prototyped: MicroRT. The microRT system integrates multimodality imaging, radiation treatment planning, and conformal radiation therapy that utilizes a clinical 192Ir isotope high dose rate source as the radiation source (teletherapy). A multiparameter dose calculation algorithm based on Monte Carlo dose distribution simulations is used to efficiently and accurately calculate doses for treatment planning purposes. A series of precisely machined tungsten collimators mounted onto a cylindrical collimator assembly is used to provide the radiation beam portals. The current design allows a source-to-target distance range of 1-8 cm at four beam angles: 0 degrees (beam oriented down), 90 degrees, 180 degrees, and 270 degrees. The animal is anesthetized and placed in an immobilization device with built-in fiducial markers and scanned using a computed tomography, magnetic resonance, or positron emission tomography scanner prior to irradiation. Treatment plans using up to four beam orientations are created utilizing a custom treatment planning system-microRTP. A three-axis computer-controlled stage that supports and accurately positions the animals is programmed to place the animal relative to the radiation beams according to the microRTP plan. The microRT system positioning accuracy was found to be submillimeter. The radiation source is guided through one of four catheter channels and placed in line with the tungsten collimators to deliver the conformal radiation treatment. The microRT hardware specifications, the accuracy of the treatment planning and positioning systems, and some typical procedures for radiobiological experiments that can be performed with the microRT device are presented.

Localized irradiation of mouse legs using an image-guided robotic linear accelerator

“…A literature search found few publications of a dedicated small animal irradiation system utilizing a kV beam energy source (5-7). Three publications describe prototype irradiation systems (8)(9)(10). However, there are no publications dealing with the positioning and tracking with robotic image guided precision irradiation of limited body parts of mice using a commercially available robotic linear accelerator.…”

Feasibility of small animal cranial irradiation with the microRT system

“…2 In brief review, microRT utilizes: ͑1͒ a clinical, high-dose rate ͑HDR͒ remote after-loading system with a 3.6 mm lengthϫ 0.65 mm diameter, cylindrical Ir-192 source ͑Nucletron, Columbia, Maryland͒; ͑2͒ a custom aluminum collimator assembly with tungsten collimator inserts ͑0.375 in. thicknessϫ 3.8 mm ID opening͒ at the 0°, 90°, 180°, and 270°treatment positions; ͑3͒ a translational threeaxis motor assembly for couch positioning ͑Velmex, Bloomfield, New York͒; ͑4͒ a multi-axis stepper motor amplifier ͑Primatics, Tangent, Oregon͒; ͑5͒ a LABVIEW-based software interface to control the motor assembly; ͑6͒ a custom Delrin ® animal couch with fiducial markers for CT registration; ͑7͒ a spatial digitizer for pretreatment couch-to-collimator calibration ͑Immersion, San Jose, California͒; ͑8͒ a DICOMcompliant custom treatment planning system, microRTP, based on a downloadable, in-house MATLAB-based software, CERR; 8 and ͑9͒ a rapid dose calculation model, based on Monte Carlo simulations and a modified parametric beam model.…”

“…In the original version of microRT, a spatial digitizer was used for the calibration procedure. 2 In these studies, the digitizer calibration was replaced by a LABVIEW-based program, which compared the rigid position of the microRT stage to the rigid positions of the limit switches on each of the three axes of the motor positioning system. Previously, the microRT positioning error during treatment was Ϯ0.5 mm, which was thought to be FIG.…”

“…To maintain conformality on a small-animal scale, error margins must be reduced by one order of magnitude to ϳ Ϯ 0.2 mm. 2,3 Given the dearth of animal-specific conformal radiotherapy systems and the intransitivity of clinical conformal irradiators to the animal arena, little progress has been made in animalmodeled, targeted radiotherapeutic response studies. While there has been progress in chemotherapeutic response experiments, the lack of an adequate radiotherapeutic analog has rendered the pursuit of combinatory cancer response studies exceedingly difficult.…”

The Development of Technology for Effective Respiratory-Gated Irradiation Using an Image-Guided Small Animal Irradiator

“…Two commercial systems are currently available: the Xstrahl, Small Animal Radiation Research Platform (SARRP), developed in collaboration with Johns Hopkins University (3, 4) with treatment planning using superposition convolution techniques (Muriplan from Xstrahl Life Sciences) (5), and the Precision X-ray, X-RAD 225Cx, developed in conjunction with the Princess Margaret Hospital (Toronto, Canada) (6) with treatment planning available using Monte Carlo methods (SmART-Plan from Precision X-ray, Inc.) (7). In addition, a number of other noncommercial small animal radiation research platforms have been developed to allow precise irradiation of structures in small animals (8)(9)(10)(11) along with a range of treatment planning solutions (12).…”