Abstract
Advances in radiation technology, such as intensity-modulated radiation therapy (IMRT), have largely enabled a biological dose escalation of the target volume (TV) and reduce the dose to adjacent tissues or organs at risk (OARs). However, the risk of radiation-induced injury increases as more radiation dose utilized during radiation therapy (RT), which predominantly limits further increases in TV dose distribution and reduces the local control rate. Thus, the accurate target delineation is crucial. Recently, technological improvements for precise target delineation have obtained more attention in the field of RT. The addition of functional imaging to RT can provide a more accurate anatomy of the tumor and normal tissues (such as location and size), along with biological information that aids to optimize the therapeutic index (TI) of RT. In this review, we discuss the application of some common MRI-based functional imaging techniques in clinical practice. In addition, we summarize the main challenges and prospects of these imaging technologies, expecting more inspiring developments and more productive research paths in the near future.
Highlights
Radiation therapy (RT) is the cornerstone of curative cancer care [1]
Radiation oncology has undergone a huge transition in the last decades from 2D therapy to 3D conformal RT (3DCRT) and intensity-modulated RT (IMRT), and even to intensity-modulated proton therapy (IMPT), which allows for better performance in terms of dose escalation in the target volume (TV) and dose reduction in the organs at risk (OARs)
Narayana et al showed that Cho/Cr greater or equal to 3 defined by MR-spectroscopic imaging (MRSI) reduced 40% gross tumor volume (GTV) volumes (GTVs) compared with GTVs defined by T1-weighted magnetic resonance imaging (MRI) [49]
Summary
Radiation therapy (RT) is the cornerstone of curative cancer care [1]. Ideally, the optimal RT strategy is supposed to deliver the highest potential radiation dose to the tumor target volume (TV) without affecting nearby structures or organs at risk (OARs). We focus on photon-based RT techniques such as 3DCRT and IMRT, which are currently the main RT strategies in large-scale clinical practice, despite the lack of TI optimization during RT. In RT, imaging plays a critical role in tumor location, staging, target delineation, and outcome monitoring [3]. Functional imaging plays various roles in radiation oncology, such as tumor localization, staging, target delineation, assessment of early response to therapy, prognosis, and monitoring recurrence [4]. Functional imaging has widely enabled clinicians to improve TI ratios by reducing the risk of geographic miss and selectively increasing radiotherapy (RT) dose to the TV, and minimizing unnecessary dose exposure to the OARs simultaneously.
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