Abstract
Multimodality imaging has become an important adjunct of state-of-the-art radiation therapy (RT) treatment planning. Recently, simultaneous PET/MR hybrid imaging has become clinically available and may also contribute to target volume delineation and biological individualization in RT planning. For integration of PET/MR hybrid imaging into RT treatment planning, compatible dedicated RT devices are required for accurate patient positioning. In this study, prototype RT positioning devices intended for PET/MR hybrid imaging are introduced and tested toward PET/MR compatibility and image quality. A prototype flat RT table overlay and two radiofrequency (RF) coil holders that each fix one flexible body matrix RF coil for RT head/neck imaging have been evaluated within this study. MR image quality with the RT head setup was compared to the actual PET/MR setup with a dedicated head RF coil. PET photon attenuation and CT-based attenuation correction (AC) of the hardware components has been quantitatively evaluated by phantom scans. Clinical application of the new RT setup in PET/MR imaging was evaluated in anin vivo study. The RT table overlay and RF coil holders are fully PET/MR compatible. MR phantom and volunteer imaging with the RT head setup revealed high image quality, comparable to images acquired with the dedicated PET/MR head RF coil, albeit with 25% reduced SNR. Repositioning accuracy of the RF coil holders was below 1 mm. PET photon attenuation of the RT table overlay was calculated to be 3.8% and 13.8% for the RF coil holders. With CT-based AC of the devices, the underestimation error was reduced to 0.6% and 0.8%, respectively. Comparable results were found within the patient study. The newly designed RT devices for hybrid PET/MR imaging are PET and MR compatible. The mechanically rigid design and the reproducible positioning allow for straightforward CT-based AC. The systematic evaluation within this study provides the technical basis for the clinical integration of PET/MR hybrid imaging into RT treatment planning.
Highlights
For years computed tomography (CT) has been the basis for radiation therapy (RT) treatment planning and is still the main imaging modality for precise dose planning and target volume definition
The axial z-direction was not evaluated since both RF coil holders slide into the track of the RT table overlay that fixes the z-direction
Two RT devices have been tested in this context, a flat tabletop that is placed on top of the spine array RF coil on the Biograph mMR integrated positron emission tomography (PET)/Magnetic resonance (MR) system and two RF coil holders that allow for head/neck imaging
Summary
For years computed tomography (CT) has been the basis for radiation therapy (RT) treatment planning and is still the main imaging modality for precise dose planning and target volume definition. It provides highly accurate three-dimensional (3D) anatomical information of the patient as well as linear attenuation coefficients (LACs) of tissues and a direct relation to the electron density needed for dose calculation. 072505-2 potential use of functional imaging parameters.[3] Some studies even suggested RT planning based on only MR images without the additional use of CT.[4,5] positron emission tomography (PET) or PET/CT is increasingly used as an additional imaging modality improving the accuracy of the target volume delineation.[6,7]
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