Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy. Med Phys 2016 Aug;43(8):4797
Date
08/05/2016Pubmed ID
27487897DOI
10.1118/1.4959534Scopus ID
2-s2.0-84979775187 (requires institutional sign-in at Scopus site) 42 CitationsAbstract
PURPOSE: The integration of MRI with a linear accelerator (MR-linac) offers great potential for high-precision delivery of radiation therapy (RT). However, the electron deflection resulting from the presence of a transverse magnetic field (TMF) can affect the dose distribution, particularly the electron return effect (ERE) at tissue interfaces. The purpose of the study is to investigate the dose effects of ERE at air-tissue and lung-tissue interfaces during intensity-modulated radiation therapy (IMRT) planning.
METHODS: IMRT and volumetric modulated arc therapy (VMAT) plans for representative pancreas, lung, breast, and head and neck (HN) cases were generated following commonly used clinical dose volume (DV) criteria. In each case, three types of plans were generated: (1) the original plan generated without a TMF; (2) the reconstructed plan generated by recalculating the original plan with the presence of a TMF of 1.5 T (no optimization); and (3) the optimized plan generated by a full optimization with TMF = 1.5 T. These plans were compared using a variety of DV parameters, including V100%, D95%, DHI [dose heterogeneity index: (D20%-D80%)/Dprescription], Dmax, and D1cc in OARs (organs at risk) and tissue interface. All the optimizations and calculations in this work were performed on static data.
RESULTS: The dose recalculation under TMF showed the presence of the 1.5 T TMF can slightly reduce V100% and D95% for PTV, with the differences being less than 4% for all but one lung case studied. The TMF results in considerable increases in Dmax and D1cc on the skin in all cases, mostly between 10% and 35%. The changes in Dmax and D1cc on air cavity walls are dependent upon site, geometry, and size, with changes ranging up to 15%. The VMAT plans lead to much smaller dose effects from ERE compared to fixed-beam IMRT in pancreas case. When the TMF is considered in the plan optimization, the dose effects of the TMF at tissue interfaces (e.g., air-cavity wall, lung-tissue interfaces, skin) are significantly reduced in most cases.
CONCLUSIONS: The doses on tissue interfaces can be significantly changed by the presence of a TMF during MR-guided RT when the magnetic field is not included in plan optimization. These changes can be substantially reduced or even eliminated during VMAT/IMRT optimization that specifically considers the TMF, without deteriorating overall plan quality.
Author List
Chen X, Prior P, Chen GP, Schultz CJ, Li XAAuthors
Guang-Pei Chen PhD Associate Professor in the Radiation Oncology department at Medical College of WisconsinXiaojian Chen PhD Assistant Professor in the Radiation Oncology department at Medical College of Wisconsin
Phillip Prior PhD Assistant Professor in the Radiation Oncology department at Medical College of Wisconsin
Christopher J. Schultz MD Chair, Professor in the Radiation Oncology department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
HumansMagnetic Fields
Magnetic Resonance Imaging
Neoplasms
Radiation Dosage
Radiotherapy Dosage
Radiotherapy, Image-Guided
Radiotherapy, Intensity-Modulated
