Abstract
Respiratory motion has been considered a clinical challenge for lung tumor treatments due to target motion. In this study, we aimed to perform an experimental evaluation based on dynamic phantoms using MLC‐based beam tracking. TrackBeam, a prototype real‐time beam tracking system, has been assembled and evaluated in our clinic. TrackBeam includes an orthogonal dual‐layer micro multileaf collimator (DmMLC), an on‐board mega‐voltage (MV) portal imaging device, and an image processing workstation. With a fiducial marker implanted in a moving target, the onboard imaging device can capture the motion. The TrackBeam workstation processes the online MV fluence and detects and predicts tumor motion. The DmMLC system then dynamically repositions each leaf to form new beam apertures based on the movement of the fiducial marker. In this study, a dynamic phantom was used for the measurements. Three delivery patterns were evaluated for dosimetric verification based on radiographic films: no‐motion lung‐tumor (NMLT), three‐dimensional conformal radiotherapy (3DCRT), and four‐dimensional tracking radiotherapy (4DTRT). The displacement between the DmMLC dynamic beam isocenter and the fiducial marker was in the range of 0.5 mm to 1.5 mm. With radiographic film analysis, the planar dose histogram difference between 3DCRT and NLMT was 48.6% and 38.0% with dose difference tolerances of 10% and 20%, respectively. The planar dose histogram difference between 4DTRT and NLMT was 15.2% and 4.0%, respectively. Based on dose volume histogram analysis, 4DTRT reduces the mean dose for the surrounding tissue from 35.4 Gy to 19.5 Gy, reduces the relative volume of the total lung from 28% to 18% at V20, and reduces the amount of dose from 35.2 Gy to 15.0 Gy at D20. The experimental results show that MLC‐based real‐time beam tracking delivery provides a potential solution to respiratory motion control. Beam tracking delivers a highly conformal dose to a moving target, while sparing surrounding normal tissue.PACS number: 87.55.de, 87.55.ne, 87.56.nk
Highlights
22 Liu et al.: Beam Tracking Delivery for moving target with dynamic phantom of several centimeters. This compromises the benefits of highly conformed dose delivery with three-dimensional conventional radiotherapy (3DCRT) or intensity modulated radiotherapy (IMRT) techniques.[1,2,3] Differences between planned and delivered radiation treatments may occur due to the respiration-induced tumor motion, leading to insufficient dose to the tumor and excess dose to the surrounding normal structures.[4,5] Existing methods that attempt to account for tumor motion can be grouped into two categories: discrete delivery methods, and continuous delivery methods, known as beam tracking.[6,7,8,9,10]
We have investigated real-time beam tracking delivery based on dynamic phantoms
The dosimetric analysis between the 3DCRT and no-motion lung-tumor (NMLT) experiments indicate that a total of 48.6%, 38.0%, 31.1%, 22.5%, and 11.1% of the pixels in the region of interest (ROI) of the dose image exceed the dose difference tolerances of 10%, 20%, 30%, 40% and 50%, respectively
Summary
22 Liu et al.: Beam Tracking Delivery for moving target with dynamic phantom of several centimeters. This compromises the benefits of highly conformed dose delivery with three-dimensional conventional radiotherapy (3DCRT) or intensity modulated radiotherapy (IMRT) techniques.[1,2,3] Differences between planned and delivered radiation treatments may occur due to the respiration-induced tumor motion, leading to insufficient dose to the tumor and excess dose to the surrounding normal structures.[4,5] Existing methods that attempt to account for tumor motion can be grouped into two categories: discrete delivery methods (such as gating), and continuous delivery methods, known as beam tracking.[6,7,8,9,10]. A gating duty cycle of 30% to 50% leads to an increase in delivery time by a factor of 2 to 3.(17,18) For one feasibility study reported in the literature, the respiratory gating increased the delivery time by a factor of 4 to 15.(1,18-19)
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