Preclinical Radiation Research Research Articles

220: Advancing the small animal radiation research platform for pre-clinical radiation research

220: Advancing the small animal radiation research platform for pre-clinical radiation research

Accuracy of Off-Line Bioluminescence Imaging to Localize Targets in Preclinical Radiation Research

In this study, we investigated the accuracy of using off-line bioluminescence imaging (BLI) and tomography (BLT) to guide irradiation of small soft tissue targets on a small animal radiation research platform (SARRP) with on-board cone beam CT (CBCT) capability. A small glass bulb containing BL cells was implanted as a BL source in the abdomen of 11 mouse carcasses. Bioluminescence imaging and tomography were acquired for each carcass. Six carcasses were setup visually without immobilization and 5 were restrained in position with tape. All carcasses were setup in treatment position on the SARRP where the centroid position of the bulb on CBCT was taken as "truth". In the 2D visual setup, the carcass was setup by aligning the point of brightest luminescence with the vertical beam axis. In the CBCT assisted setup, the pose of the carcass on CBCT was aligned with that on the 2D BL image for setup. For both 2D setup methods, the offset of the bulb centroid on CBCT from the vertical beam axis was measured. In the BLT-CBCT fusion method, the 3D torso on BLT and CBCT was registered and the 3D offset of the respective source centroids was calculated. The setup results were independent of the carcass being immobilized or not due to the onset of rigor mortis. The 2D offset of the perceived BL source position from the CBCT bulb position was 2.3 mm ± 1.3 mm. The 3D offset between BLT and CBCT was 1.5 mm ± 0.9 mm. Given the rigidity of the carcasses, the setup results represent the best that can be achieved with off-line 2D BLI and 3D BLT. The setup uncertainty would require the use of undesirably large margin of 4-5 mm. The results compel the implementation of on-board BLT capability on the SARRP to eliminate setup error and to improve BLT accuracy.

An Integrated X-Ray/Optical Tomography System for Pre-clinical Radiation Research.

The current Small Animal Radiation Research Platform (SARRP) is poor for localizing small soft tissue targets for irradiation or tumor models growing in a soft tissue environment. Therefore, an imaging method complementary to x-ray CT is required to localize the soft tissue target's Center of Mass (CoM) to within 1 mm. In this paper, we report the development of an integrated x-ray/bioluminescence imaging/tomography (BLI/BLT) system to provide a pre-clinical, high resolution irradiation system. This system can be used to study radiation effects in small animals under the conebeam computed tomography (CBCT) imaging guidance by adding the bioluminescence imaging (BLI) system as a standalone system which can also be docked onto the SARRP. The proposed system integrates two robotic rotating stages and an x-ray source rated at maximum 130 kVp and having a small variable focal spot. A high performance and low noise CCD camera mounted in a light-tight housing along with an optical filter assembly is used for multi-wavelength BL tomography. A three-mirror arrangement is implemented to eliminate the need of rotating the CCD camera for acquiring multiple views. The mirror system is attached to a motorized stage to capture images in angles between 0-90° (for the standalone system). Camera and CBCT calibration are accomplished.

Accuracy of Off-Line Bioluminescence Imaging to Localize Targets in Preclinical Radiation Research.

In this study, we investigated the accuracy of using off-line bioluminescence imaging (BLI) and tomography (BLT) to guide irradiation of small soft tissue targets on a small animal radiation research platform (SARRP) with on-board cone beam CT (CBCT) capability. A small glass bulb containing BL cells was implanted as a BL source in the abdomen of 11 mouse carcasses. Bioluminescence imaging and tomography were acquired for each carcass. Six carcasses were setup visually without immobilization and 5 were restrained in position with tape. All carcasses were setup in treatment position on the SARRP where the centroid position of the bulb on CBCT was taken as "truth". In the 2D visual setup, the carcass was setup by aligning the point of brightest luminescence with the vertical beam axis. In the CBCT assisted setup, the pose of the carcass on CBCT was aligned with that on the 2D BL image for setup. For both 2D setup methods, the offset of the bulb centroid on CBCT from the vertical beam axis was measured. In the BLT-CBCT fusion method, the 3D torso on BLT and CBCT was registered and the 3D offset of the respective source centroids was calculated. The setup results were independent of the carcass being immobilized or not due to the onset of rigor mortis. The 2D offset of the perceived BL source position from the CBCT bulb position was 2.3 mm ± 1.3 mm. The 3D offset between BLT and CBCT was 1.5 mm ± 0.9 mm. Given the rigidity of the carcasses, the setup results represent the best that can be achieved with off-line 2D BLI and 3D BLT. The setup uncertainty would require the use of undesirably large margin of 4-5 mm. The results compel the implementation of on-board BLT capability on the SARRP to eliminate setup error and to improve BLT accuracy.

Abstract 5725: Accuracy of off-line bioluminescence imaging to localize targets in pre-clinical radiation research

Abstract Introduction Pre-clinical methods of delivering focal radiation to biological targets have made significant advances. Our group has developed the Small Animal Radiation Research Platform (SARRP), which is capable of using x-ray cone-beam CT (CBCT) to accurately guide delivery of conformal radiation. However, CBCT is deficient in localizing small orthotopic soft-tissue tumors. Bioluminescent imaging (BLI) is an affordable, accessible and sensitive ancillary method of detecting such tumors. In this study, we evaluate the setup accuracy of off-line BLI as a means to guide focal irradiation of small tumor volumes. Methods Athymic nude mice were used in accordance with institutional guidelines. Human pancreatic carcinoma cells (MiaPaCa-2) stably expressing luciferase were injected into a small glass bulb and sutured intra-abdominally to the tail of the pancreas in euthanized mice. Two methods of animal repositioning were employed during this process in which the animals were either unrestrained (n=6) or restrained (n=5). Two dimensional (2D) BLI and 3D bioluminescent tomography (BLT) were acquired of each supine mouse carcass. An ink-dot marked the “visual” centroid of the surface BL image. Carcasses were then transported to a SARRP for CBCT localization. Three methods of image guidance were applied. Using visual setup, the animal was positioned to align the ink-dot with the central axis of the SARRP. In the CBCT-aided setup, the pose of each carcass was adjusted to recapitulate its pose at the time of BLI. The 2D radial offset of the “true” bulb centroid in CBCT from the central axis of the SARRP was measured. In the 3D setup, the 3D contours of CBCT and BLT contours were registered and the 3D radial offset between the 2 centroids was calculated. Results Using the visual set up, single plane offsets of 2.2 mm +/- 1.2 mm and 2.5 mm +/- 1.5 mm were calculated between the isocenter of the vertical beam and the centroid of the bulb in unrestrained and restrained mice, respectively. After fusing the coronal 2D BL image to a corresponding coronal CBCT image, the central axis of the vertical beam was again aligned to the skin mark. The offset distances in a single plane were 2.2 mm +/- 1.2 mm and 2.4 mm +/- 1.1 mm in unrestrained and restrained mice, respectively. Finally, the offsets between the center of mass of the BL source and the CBCT glass bead after 3D fusion were 1.5 mm +/- 1 mm and 1.6 mm +/- 0.8 mm in unrestrained and restrained mice, respectively. Conclusion Restraining mice between modalities did not result in significant reduction of set up uncertainty. Similarly, use of 2D-BLI did not improve upon the visual set up method. The 3D-BLT fusion represents the best that can be achieved with off-line localization. An on-board approach with further improvement in BLT using prior information of anatomic and optical properties should be investigated to further improve localization uncertainty. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5725. doi:1538-7445.AM2012-5725

Image Registration and Localization Accuracy of a Micro IGRT System

The μIGRT systems bridge the technology gap between pre-clinical radiation research and clinical radiation therapy. Image registration enables accurate target localization based on reference data used for treatment plan design. The purpose of this research was to quantify the registration and localization accuracy of a μCBCT guided radiation therapy system. Images of a cylindrical phantom with five embedded fiducial markers and two mouse cadavers were acquired with a μCT scanner (eXplore Ultra, GE Healthcare, London, ON) and/or the CBCT scanner of a μIGRT system (XRad 225Cx, Precision Inc X-rays, North Branford, USA). Voxel sizes were 0.15x0.15x0.15 mm3 and 0.2x0.2x0.2 mm3 for the μCT scan and μCBCT scans respectively. Dicom images were imported into an in-house developed image registration software package. Fiducial markers for the phantom and naturally occurring calcifications in the abdomen for the mice were manually identified and their locations were stored in the coordinate system of the irradiator. Corresponding scans were aligned using local rigid registration with a shaped region of interest and correlation-ratio as a similarity measure. For the phantom, the fiducial markers were excluded from the region of interest. After registration the distance between the manually placed landmarks was calculated. To quantify the overall localization accuracy, a cylindrical phantom containing a Gafchromic film with a small pinched hole was scanned on the μIGRT system, imported into the image registration tool as a reference scan and the hole was marked as the treatment iso-center. The phantom was manually displaced, rescanned and imported as the localization scan. Following image registration the phantom was repositioned using a robotic couch adjustment. Finally the film was exposed to 8 equi-angular spaced beams and the distance between the pinched hole and the center of the beam intersection was manually determined. This was repeated 5 times. For the phantom the residual landmark distance was 19 μm ± 94 μm (1 SD) in the axial plane and 121 μm ± 86 μm in the longitudinal direction. For the mice cadavers this was about 40 μm ± 60 μm in all directions. The average localization accuracy was 167 μm ± 72 μm (1 SD). We quantified the registration and localization accuracy of a μIGRT system and observed an overall delivery accuracy better than 200 μm including manual landmark identification. Multi-modality image registration and quantification of the localization accuracy for living specimen are subject of further study.