Abstract
Computed tomography (CT) has revolutionized external radiotherapy by making it possible to visualize and segment the tumors and the organs at risk in a three-dimensional way. However, if CT is a now a standard, it presents some limitations, notably concerning tumor characterization and delineation. Its association with functional and anatomical images, that are positron emission tomography (PET) and magnetic resonance imaging (MRI), surpasses its limits. This association can be in the form of a trimodality PET/CT/MRI. The objective of this mini-review is to describe the process of performing this PET/CT/MRI trimodality for radiotherapy and its potential clinical applications. Trimodality can be performed in two ways, either a PET/MRI fused to a planning CT (possibly with a pseudo-CT generated from the MRI for the planning), or a PET/CT fused to an MRI and then registered to a planning CT (possibly the CT of PET/CT if calibrated for radiotherapy). These examinations should be performed in the treatment position, and in the second case, a patient transfer system can be used between the PET/CT and MRI to limit movement. If trimodality requires adapted equipment, notably compatible MRI equipment with high-performance dedicated coils, it allows the advantages of the three techniques to be combined with a synergistic effect while limiting their disadvantages when carried out separately. Trimodality is already possible in clinical routine and can have a high clinical impact and good inter-observer agreement, notably for head and neck cancers, brain tumor, prostate cancer, cervical cancer.
Highlights
External radiotherapy consists of treating an internal lesion, superficial and/or external lesion with an external source of radiation
A following improvement was the control of the intensity of the treatment beams which opened in the new millennium the era of the intensity-modulated radiotherapy (IMRT) whose aim is to deliver a high dose to the target volume while sparing the adjacent tissues, notably organs at risk (OARs) [2]
A homogeneous dose is prescribed to the planning target volume (PTV) that considers uncertainty in treatment planning by encompassing the gross tumor volume (GTV, corresponding to the delineated macroscopic and radiologically measurable tumor) and the clinical target volume (CTV, which adds a margin to the GTV to cover nearby areas at risk of hosting microscopic disease) [3]
Summary
External radiotherapy consists of treating an internal lesion, superficial and/or external lesion with an external source of radiation. A following improvement was the control of the intensity of the treatment beams which opened in the new millennium the era of the intensity-modulated radiotherapy (IMRT) whose aim is to deliver a high dose to the target volume while sparing the adjacent tissues, notably OARs [2]. Multimodality is already possible in clinical routine with a high clinical impact and good inter-observer agreement [7] The aim of this mini-review is to present the concept of PET/ CT/MRI trimodality, its rationale for radiotherapy, and its potential interest in characterizing tumor, performing treatment planning, and doing ART
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
