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MR-CBCT Image-Guided System for Radiotherapy of Orthotopic Rat Prostate Tumors

T Chiu

S Stojadinovic , T Chiu*, T Arai , J Campbell , S Jiang , R Mason , UT Southwestern Medical Center, Dallas, TX


SU-E-FS1-7 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: Four Seasons 1

Purpose: Multi-modality image-guided radiotherapy is the standard of care in contemporary cancer management; however, due to hardware and software limitations, it is not common in the preclinical settings. Orthotopic prostate tumors are difficult to identify using cone beam computed tomography (CBCT). We characterized a research magnetic resonance (MR) scanner for preclinical studies and created a protocol for combined MR-CBCT image-guided small animal radiotherapy.

Methods: Two in-house dual-modality, MR and CBCT compatible, phantoms were designed and manufactured using 3D printing technology (MakerBot, New York, NY). The phantoms were used for quality assurance tests and to facilitate end-to-end testing for combined preclinical MR and CBCT based treatment planning. The phantoms’ MR and CBCT images were acquired utilizing the Varian 4.7 T scanner (Agilent Technologies, Santa Clara, CA) and the XRad-225Cx irradiator (PXI, North Branford, CT), respectively. The magnetic field distortion was assessed by comparing MR images to phantom blueprints and CBCT. The corrected MR scans were co-registered with CBCT and subsequently used for treatment planning.

Results: The fidelity of 3D printed phantoms compared to the blueprint design yielded favorable agreement as verified with the CBCT measurements. The geometric distortion of the magnetic field varied between 5 to 10% throughout the scanning volume. After correction, the MR images agreed within 1% relative to the CBCT for all geometric landmarks. The distortion free MR images were co-registered with the corresponding CBCT images and imported into SmART Plan (Maastro Clinic, Maastricht, Netherlands). This enabled contouring on MR data while the CBCT images were utilized for dose calculation.

Conclusion: The technology gap between preclinical and clinical sceneries has hindered preclinical explorations importance to human radiotherapy. An MR-CBCT based preclinical workflow was designed and implemented for small animal radiotherapy. Combined MR-CBCT image-guided radiotherapy for preclinical research potentially delivers enhanced relevance to human radiotherapy for various disease sites.

Funding Support, Disclosures, and Conflict of Interest: This research was supported in part by Cancer Prevention and Research Initiative of Texas (CPRIT) # RP140285. MRI was supported by P41 EB015908, 1P30 CA142543, and an ARRA supplement to 1U24 CA126608. Irradiation facilitated by Shared Instrumentation Grant (S10 RR028011).

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