Abstract
BackgroundInterest in MR-only treatment planning for radiation therapy is growing rapidly with the emergence of integrated MRI/linear accelerator technology. The purpose of this study was to evaluate the feasibility of using synthetic CT images generated from conventional Dixon-based MRI scans for radiation treatment planning of lung cancer.MethodsEleven patients who underwent whole-body PET/MR imaging following a PET/CT exam were randomly selected from an ongoing prospective IRB-approved study. Attenuation maps derived from the Dixon MR Images and atlas-based method was used to create CT data (synCT). Treatment planning for radiation treatment of lung cancer was optimized on the synCT and subsequently copied to the registered CT (planCT) for dose calculation. Planning target volumes (PTVs) with three sizes and four different locations in the lung were planned for irradiation. The dose-volume metrics comparison and 3D gamma analysis were performed to assess agreement between the synCT and CT calculated dose distributions.ResultsMean differences between PTV doses on synCT and CT across all the plans were −0.1% ± 0.4%, 0.1% ± 0.5%, and 0.4% ± 0.5% for D95, D98 and D100, respectively. Difference in dose between the two datasets for organs at risk (OARs) had average differences of −0.14 ± 0.07 Gy, 0.0% ± 0.1%, and −0.1% ± 0.2% for maximum spinal cord, lung V20, and heart V40 respectively. In patient groups based on tumor size and location, no significant differences were observed in the PTV and OARs dose-volume metrics (p > 0.05), except for the maximum spinal-cord dose when the target volumes were located at the lung apex (p = 0.001). Gamma analysis revealed a pass rate of 99.3% ± 1.1% for 2%/2 mm (dose difference/distance to agreement) acceptance criteria in every plan.ConclusionsThe synCT generated from Dixon-based MRI allows for dose calculation of comparable accuracy to the standard CT for lung cancer treatment planning. The dosimetric agreement between synCT and CT calculated doses warrants further development of a MR-only workflow for radiotherapy of lung cancer.
Highlights
Lung cancer comprises nearly 33% of all cancers with relatively high mortality rate in every ethnic group and gender [1]
The aim of this study is to investigate the feasibility of using a Magnetic Resonance (MR)-generated synCT for treatment planning of lung cancer where the impact of inhomogeneity is expected to be significant, and to evaluate the dosimetric differences between synCT and conventional Computed tomography (CT)-planned doses
Synthetic CT Mean Hounsfield unit (HU) in Organ at risk (OAR) were measured on synCT and planCT for each of the eleven patients (Table 1)
Summary
Lung cancer comprises nearly 33% of all cancers with relatively high mortality rate in every ethnic group and gender [1]. Radiation therapy is the main treatment option for lung cancer. The 5-year overall survival rate after radiotherapy in patients with stage 1 non-small cell lung cancer is nearly 50%. Common practice is to register the MR images to planning CT, and to transfer MR-contoured structures to the planCT for treatment planning. This process can potentially introduce systematic errors due to uncertainties in the MRto-CT registration. Interest in MR-only treatment planning for radiation therapy is growing rapidly with the emergence of integrated MRI/linear accelerator technology. The purpose of this study was to evaluate the feasibility of using synthetic CT images generated from conventional Dixon-based MRI scans for radiation treatment planning of lung cancer
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