Impact of lung density on isolated lung tumor dose in VMAT using inline MR-Linac. (December 2020)

• Record Type: Journal Article
• Authors: Ohno, Takeshi; Araki, Fujio; Anami, Naoki; Kubota, Takahiro; Yano, Masayuki; Ito, Shotaro
• Is Part Of: Physica medica. Volume 80(2021)
• Page Start: 65
• Page End: 74
• Publication Date: 2020-12
• Subjects: MR-Linac -- Isolated lung tumor -- Lung density -- Monte Carlo method; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2020.10.009
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Lung density varies greatly depending on whether inspiration breath hold or expiration breath hold is used. The dose impact of the inline magnetic field is larger in the low-density region. This study investigated the impact of lung density on lung tumor dose in an inline magnetic field. The 1 T inline magnetic field enhanced the 1–2 cm tumor dose more as the lung density was lower. For the 3 cm lung tumor, the lung tumor dose was independent of lung density at 0.5 T and 1.0 T. Abstract: Purpose: This study investigated the impact of lung density on the isolated lung tumor dose for volumetric modulated arc therapy (VMAT) in an inline magnetic resonance linear accelerator (MR-Linac) using the Monte Carlo (MC) simulation. Methods: CT images of the thorax phantoms with lung tumors of 1, 2, and 3 cm diameters were converted into voxel-base phantoms with lung densities of 0.1, 0.2, and 0.3 g/cm 3, respectively. The dose distributions were calculated for partial-arc VMAT. The dose distributions were compared using dose differences, dose volume histograms, and dose volume indices. Results: In all cases, the inline magnetic field significantly enhanced the lung tumor dose compared to that at 0 T. For the 1 cm lung tumor, the inline magnetic field of 1 T increased the minimum dose of 95% of the Planning target volume (PTV D95 ) by 14.0% in 0.1 g/cm 3 lung density as compared to that in 0.3 g/cm 3 at 0 T. In contrast, at 0 and 0.5 T, the PTV D95 in 0.3 g/cm 3 lung density was larger than that in lung density of 0.1 g/cm 3 . For the 2 cm lung tumor, a similar tendency to 1 cm was observed, whereas the dose impact of lung density was smaller than that for 1 cm. For the 3 cm lung tumor, the lung tumor dose was independent of lung density at 0.5 T and 1.0 T. Conclusion: The inline MR-Linac with the magnetic field over 1 T can enhance the PTV D95 for VMAT regardless of the lung density.