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SU‐E‐T‐544: Dosimetric Evaluation of a Micro‐MLC Developed for a Robotic Stereotactic Radiosurgery/Radiotherapy Machine
Author(s) -
Li J S,
Fan J
Publication year - 2011
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 - 10.1118/1.3612506
Subject(s) - radiosurgery , monte carlo method , collimated light , leakage (economics) , tilt (camera) , materials science , optics , nuclear medicine , collimator , physics , mathematics , radiation therapy , geometry , medicine , laser , statistics , economics , macroeconomics
Purpose: To investigate the beam characteristics of a micro‐MLC developed for a robotic stereotactic radiosurgery/radiotherapy (SRS/SRT) system and to provide insight for the MLC design and the feasibility to replace traditional cones. Methods: A Monte Carlo simulation toolbox was developed in our in‐house Monte Carlo system to investigate the details of a micro‐MLC design and their dosimetric effects based on the beam properties of the robotic SRS/SRT system. The micro‐MLC is designed with a piecewise leaf end, no tongue‐and‐groove structure but a tilt angle to reduce the interleaf leakage. The leaf width is 2.5mm projected at 80cm source‐to‐ surface distance (SSD). The MLC leakage for various leaf thickness and tilt angle combinations was studied to derive the optimum leaf thickness and tilt angle. Penumbral widths (80%–20%) at different depths for different field sizes at 80cm SSD were investigated. The dose distributions were compared with those collimated by the cone collimators. Results: With the standard 60mm cone as a reference, the MLC leakage for 8cm tungsten leaves is about 1.9% under the leaves and 21.8% under the leaf ends when leaves are closed. When the leaf thickness is increased to 10cm, the leaf leakage dropped to 0.2% and 9.2%, respectively. When the leaf tilt angle was changed from 1 degree to 0.5 degree, the leakage does not change significantly. The penumbral widths at 1.5cm depth for MLC‐shaped circular field with a diameter of 60mm are 4.7mm and 6.2mm for the leaf‐ ends and lead‐sides. They are comparable to that of the standard 60mm cone, which is 6mm. At the 10cm depth, the penumbral widths become 5.8mm and 7.4mm, which are also comparable to that of the cone collimator (6.9mm). Conclusions: The Monte Carlo simulation results show that the dosimetric parameters of our micro‐MLC design are suitable for SRS/SRT with the robotic system.