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Increasing dose gradient and uniformity in small fields using modulation: Theory and prototypes for cone‐based stereotactic radiosurgery
Author(s) -
Bender Edward T.
Publication year - 2014
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 - 10.1118/1.4870380
Subject(s) - collimator , dosimetry , collimated light , imaging phantom , radiosurgery , optics , intensity modulation , context (archaeology) , modulation (music) , fluence , cone beam computed tomography , mathematics , physics , nuclear medicine , computed tomography , phase modulation , acoustics , radiation therapy , medicine , paleontology , laser , radiology , phase noise , biology
Purpose: To investigate the theoretical limits to the tradeoff between dose gradient and uniformity when modulation is used in the context of cone based SRS, and to design a prototype collimation device that allows for steeper dose gradients and/or higher target uniformity as compared to a standard circular collimator.Methods: An inverse planning optimization is performed in the context of idealized phantom geometry to determine the ideal fluence pattern that best approximates a “rect function” dose distribution. Ideal fluence patterns were approximated in a prototype device and radiochromic film dosimetry was utilized to compare the prototype device to a standard circular collimator.Results: For choices of prescription isodose lines above approximately 50%, utilizing modulation allows for an improved tradeoff between dose gradient index and dose heterogeneity index. Compensators placed within the circular collimator can achieve the necessary modulation.Conclusions: Using modulation with features on a submillimeter distance scale, it is possible to increase the dose gradient and/or uniformity in small fields.