Volumetric Modulated Arc Radiotherapy is an innovative technique currently utilized to efficiently deliver complex treatments. Dose rate, speed of rotation, and field shape are continuously varied as the radiation source rotates about the patient. Patient specific quality assurance is performed to verify that the delivered dose distribution is consistent with the plan formulated in a treatment planning system. The purpose of this work is to present novel methodology using a Gafchromic EBT3 film image of a patient plan in a cylindrical phantom and calculating the delivered MU per control point. Images of two dimensional plan dose matrices and film scans are analyzed using MATLAB with the imaging toolbox. Dose profiles in a ring corresponding to the film position are extracted from the plan matrices for comparison with the corresponding measured film dose. The plan is made up of a series of individual static Control Points. If we consider these Control Points a set of basis vectors, then variations in the plan can be represented as the weighted sum of the basis. The weighing coefficients representing the actual delivered MU can be determined by any available optimization tool, such as downhill simplex or non-linear programming. In essence we reconstruct an image of the delivered dose. Clinical quality assurance is performed with this technique by computing a patient plan with the measured monitor units and standard plan evaluation tools such as Dose Volume Histograms. Testing of the algorithm with known changes in the reference images indicated a correlation coefficient greater than 0.99.

Date Published: 19 March 2014
PDF: 6 pages
Proc. SPIE 9033, Medical Imaging 2014: Physics of Medical Imaging, 90335D (19 March 2014); doi: 10.1117/12.2041449

Published in SPIE Proceedings Vol. 9033:
Medical Imaging 2014: Physics of Medical Imaging
Bruce R. Whiting; Christoph Hoeschen, Editor(s)