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Intensity modulated operating mode of the rotating gamma system
Author(s) -
Sengupta Bishwambhar,
Gulyas Laszlo,
Medlin Donald,
Koroknai Tibor,
Takacs David,
Filep Gyorgy,
Panko Peter,
Godo Bence,
Hollo Tamas,
Zheng Xiao Ran,
Fedorcsak Imre,
Dobai Jozsef,
Bognar Laszlo,
Takacs Endre
Publication year - 2018
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12887
Subject(s) - imaging phantom , collimator , monte carlo method , dosimetry , radiosurgery , nuclear medicine , physics , linear particle accelerator , penumbra , optics , beam (structure) , mathematics , medicine , radiation therapy , radiology , statistics , ischemia , cardiology
Purpose The purpose of this work was to explore two novel operation modalities of the rotating gamma systems (RGS) that could expand its clinical application to lesions in close proximity to critical organs at risk (OAR). Methods The approach taken in this study consists of two components. First, a Geant4‐based Monte Carlo (MC) simulation toolkit is used to model the dosimetric properties of the RGS Vertex 360™ for the normal, intensity modulated radiosurgery (IMRS), and speed modulated radiosurgery (SMRS) operation modalities. Second, the RGS Vertex 360™ at the Rotating Gamma Institute in Debrecen, Hungary is used to collect experimental data for the normal and IMRS operation modes. An ion chamber is used to record measurements of the absolute dose. The dose profiles are measured using Gafchromic EBT3 films positioned within a spherical water equivalent phantom. Results A strong dosimetric agreement between the measured and simulated dose profiles and penumbra was found for both the normal and IMRS operation modes for all collimator sizes (4, 8, 14, and 18 mm diameter). The simulated falloff and maximum dose regions agree better with the experimental results for the 4 and 8 mm diameter collimators. Although the falloff regions align well in the 14 and 18 mm collimators, the maximum dose regions have a larger difference. For the IMRS operation mode, the simulated and experimental dose distributions are ellipsoidal, where the short axis aligns with the blocked angles. Similarly, the simulated dose distributions for the SMRS operation mode also adopt an ellipsoidal shape, where the short axis aligns with the angles where the orbital speed is highest. For both modalities, the dose distribution is highly constrained with a sharper penumbra along the short axes. Conclusions Dose modulation of the RGS can be achieved with the IMRS and SMRS modes. By providing a highly constrained dose distribution with a sharp penumbra, both modes could be clinically applicable for the treatment of lesions in close proximity to critical OARs.