title: Fast dose calculation in magnetic fields with GPUMCD.
abstract: A new hybrid imaging-treatment modality, the MRI-Linac, involves the irradiation of the patient in the presence of a strong magnetic field. This field acts on the charged particles, responsible for depositing dose, through the Lorentz force. These conditions require a dose calculation engine capable of taking into consideration the effect of the magnetic field on the dose distribution during the planning stage. Also in the case of a change in anatomy at the time of treatment, a fast online replanning tool is desirable. It is improbable that analytical solutions such as pencil beam calculations can be efficiently adapted for dose calculations within a magnetic field. Monte Carlo simulations have therefore been used for the computations but the calculation speed is generally too slow to allow online replanning. In this work, GPUMCD, a fast graphics processing unit (GPU)-based Monte Carlo dose calculation platform, was benchmarked with a new feature that allows dose calculations within a magnetic field. As a proof of concept, this new feature is validated against experimental measurements. GPUMCD was found to accurately reproduce experimental dose distributions according to a 2%-2 mm gamma analysis in two cases with large magnetic field-induced dose effects: a depth-dose phantom with an air cavity and a lateral-dose phantom surrounded by air. Furthermore, execution times of less than 15 s were achieved for one beam in a prostate case phantom for a 2% statistical uncertainty while less than 20 s were required for a seven-beam plan. These results indicate that GPUMCD is an interesting candidate, being fast and accurate, for dose calculations for the hybrid MRI-Linac modality.
authors.affiliation: École Polytechnique de Montréal, Département de génie informatique et génie logiciel, 2500 Chemin de Polytechnique, Montréal, Québec H3T 1J4, Canada. sami.hissoiny@polymtl.ca
authors.forename: S
authors.initials: S
authors.lastname: Hissoiny
authors.forename: A J E
authors.initials: AJ
authors.lastname: Raaijmakers
authors.forename: B
authors.initials: B
authors.lastname: Ozell
authors.forename: P
authors.initials: P
authors.lastname: Després
authors.forename: B W
authors.initials: BW
authors.lastname: Raaymakers
mesh_terms: D003196:Computer Graphics; D006801:Humans; D060526:Magnetic Fields; D008297:Male; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D015203:Reproducibility of Results; D013997:Time Factors