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TH‐CD‐204‐06: Diffusion MRI for Treatment Response Assessment of MRI‐Guided Tri‐Cobalt 60 Radiotherapy
Author(s) -
Yang Y,
Low D,
Cao M,
Sheng K,
Lamb J,
Thomas D,
Kamrava M,
Hu P
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4926253
Subject(s) - nuclear medicine , imaging phantom , pulse sequence , effective diffusion coefficient , diffusion mri , medicine , magnetic resonance imaging , radiation therapy , diffusion imaging , diffusion , image quality , materials science , nuclear magnetic resonance , radiology , physics , computer science , image (mathematics) , artificial intelligence , thermodynamics
Purpose: To develop a diffusion MRI pulse sequence on the 0.35T MRI in a commercially available MRI‐guided tri‐Cobalt 60 radiotherapy system (Viewray), and demonstrate the initial utility of this pulse sequence on a patient undergoing radiation therapy. Methods: The pulse sequence is a diffusion‐weighted spin echo (SE) single‐shot echo planar imaging (EPI) sequence. The pulse sequence parameters included: flip angle=90°, repetition time (TR) = 1500ms, echo time (TE) = 140ms, EPI factor = 128, b values = 0, 300, 500 s/mm2, 5 averages, and total scan time of 27sec. To assess the apparent diffusion coefficient (ADC) calculation accuracy, a uniform water phantom was scanned using the developed diffusion sequence on the Viewray system and on a 1.5T Siemens system at the same ambient temperature. The diffusion MRI sequence was further tested in a patient with sarcoma at the thigh who underwent a 25‐fraction treatment regime. A single 2D slice diffusion images were acquired on the Viewray system immediately after her 20th fraction treatment while she remained on the treatment couch. Results: In the phantom, the calculated ADC value was 1.94×10−3 s/mm2 based on the Viewray images, which agreed well with the results based on the 1.5T Siemens images (2.03×10−3 s/mm2). The diffusion image acquired on the sarcoma patient had excellent image quality and showed heterogeneous structure within the gross tumor volume (GTV). The ADC was 2.36×10−3 s/mm2 at the bladder and 1.44×10−3 s/mm2 at the tumor. Conclusion: This is the first in vivo study of a diffusion MRI sequence on a hybrid MRI‐Radiotherapy system. We demonstrate the feasibility of diffusion MRI on the hybrid MRI‐60Co radiotherapy system with 0.35 Tesla magnet and it may be a powerful tool for assessing the longitudinal changes in tumor ADC, the tumor response to radiotherapy and for adaptive radiotherapy.