Development of a deformable phantom for experimental verification of 4D Monte Carlo simulations in a deforming anatomy. (July 2018)

• Record Type: Journal Article
• Authors: Gholampourkashi, Sara; Cygler, Joanna E.; Lavigne, Bernie; Heath, Emily
• Is Part Of: Physica medica. Volume 51(2018)
• Page Start: 81
• Page End: 90
• Publication Date: 2018-07
• Subjects: Monte Carlo -- Deformable lung phantom -- 4D dose calculation -- VMAT; 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.2018.05.012
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: A realistic and reproducible tissue-equivalent novel deformable lung phantom is built. RADPOS recorded phantom motion is used in 4D MC simulations. 4DdefDOSXYZnrc user code accurately simulates dose delivered to the phantom. Accuracy of deformation vectors affects the accuracy of 4D dose calculations. RADPOS combined with our 4D Monte Carlo code is a valid tool for 4D simulations. Abstract: Purpose: To verify the accuracy of 4D Monte Carlo (MC) simulations, using the 4DdefDOSXYZnrc user code, in a deforming anatomy. We developed a tissue-equivalent and reproducible deformable lung phantom and evaluated 4D simulations of delivered dose to the phantom by comparing calculations against measurements. Methods: A novel deformable phantom consisting of flexible foam, emulating lung tissue, inside a Lucite external body was constructed. A removable plug, containing an elastic tumor that can hold film and other dosimeters, was inserted in the phantom. Point dose and position measurements were performed inside and outside the tumor using RADPOS 4D dosimetry system. The phantom was irradiated on an Elekta Infinity linac in both stationary and moving states. The dose delivery was simulated using delivery log files and the phantom motion recorded with RADPOS. Results: Reproducibility of the phantom motion was determined to be within 1 mm. The phantom motion presented realistic features like hysteresis. MC calculations and measurements agreed within 2% at the center of tumor. Outside the tumor agreements were better than 5% which were within the positional/dose reading uncertainties at the measurement points. More than 94% of dose points from MC simulations agreed within 2%/2 mm compared to film measurements. Conclusion: The deformable lung phantom presented realistic and reproducible motion characteristics and its use for verification of 4D dose calculations was demonstrated. Our 4DMC method is capable of accurate calculations of the realistic dose delivered to a moving and deforming anatomy during static and dynamic beam delivery techniques.