Abstract
Radiation therapy has made tremendous progress in oncology over the last decades due to advances in engineering and physical sciences in combination with better biochemical, genetic and molecular understanding of this disease. Local delivery of optimal radiation dose to a tumor, while sparing healthy surrounding tissues, remains a great challenge, especially in the proximity of vital organs. Therefore, imaging plays a key role in tumor staging, accurate target volume delineation, assessment of individual radiation resistance and even personalized dose prescription. From this point of view, radiotherapy might be one of the few therapeutic modalities that relies entirely on high-resolution imaging. Magnetic resonance imaging (MRI) with its superior soft-tissue resolution is already used in radiotherapy treatment planning complementing conventional computed tomography (CT). Development of systems integrating MRI and linear accelerators opens possibilities for simultaneous imaging and therapy, which in turn, generates the need for imaging probes with therapeutic components. In this review, we discuss the role of MRI in both external and internal radiotherapy focusing on the most important examples of contrast agents with combined therapeutic potential.
Highlights
Radiotherapy (RT) has become an indispensable tool in oncology, representing non-surgical treatment by cytotoxic ionizing radiation with the ability to destroy cancerous cells
A small Gd(III)-complex designed for radiosensitization combined with Magnetic resonance imaging (MRI) is porphyrin-like macrocycle motexafin gadolinium (MGd) (Figure 2) that belongs to the texaphyrins class of drugs, which proved effective to mediate radiation of tumors and brain metastasis in particular [19]
Translation of MRI-assisted radiotherapy into the clinic requires interdisciplinary efforts taking into account the beneficial aspects of each modality as well as the limitations and challenges
Summary
Radiotherapy (RT) has become an indispensable tool in oncology, representing non-surgical treatment by cytotoxic ionizing radiation with the ability to destroy cancerous cells. One of the main objectives of a successful treatment is an accurate delivery of a correct therapeutic dose to the target while avoiding radiation exposure of the surrounding healthy tissues This requires careful delineation of tumor by detecting its extension as well as assessing morphology, physiology, and biochemistry prior to therapy. Its poor soft-tissue contrast is in many cases limiting the spatial accuracy, which is important for the correct determination of tumor margins, especially when cancers in the proximity to the vital organs are at stake Another concern in external RT is patient misalignment as a result of internal motions, such as swallowing, respiration or muscle contraction/relaxation. As a non-invasive imaging modality without implication of ionizing radiation, it relies on the observation of water molecule protons, based on their density and relaxation dynamics These parameters lead to visualization of the differences in tissues by generation of either T1 - (positive/bright) or T2 -weighted (negative/dark) contrast. ERT/MRI [36] (CAs), TheSPIONs/dextran-NH lack of sensitivity by145 administration of contrast agents γFe2O3/Fe3O4/citrate
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