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Algorithm for dosimetry of multiarc linear‐accelerator stereotactic radiosurgery
Author(s) -
Luxton Gary,
Jozsef Gabor,
Astrahan Melvin A.
Publication year - 1991
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 - 10.1118/1.596593
Subject(s) - isocenter , linear particle accelerator , imaging phantom , dosimetry , radiosurgery , thermoluminescent dosimeter , beam (structure) , physics , optics , radiation treatment planning , computation , nuclear medicine , algorithm , radiation , computer science , radiation therapy , dosimeter , medicine
Treatment planning for multiarc radiosurgery is an inherently complex three‐dimensional dosimetry problem. Characteristics of small‐field x‐ray beams suggest that major simplification of the dose computation algorithm is possible without significant loss of accuracy compared to calculations based on large‐field algorithms. The simplification makes it practical to efficiently implement accurate multiplanar dosimetry calculations on a desktop computer. An algorithm is described that is based on data from fixed‐beam tissue‐maximum‐ratio (TMR) and profile measurements at isocenter. The profile for each fixed beam is scaled geometrically according to distance from the x‐ray source. Beam broadening due to scatter is taken into account by a simple formula that interpolates the full width at half maximum (FWHM) between profiles at isocenter at different depths in phantom. TMR and profile data for two representative small‐field collimators (10‐ and 25‐mm projected diameter) were obtained by TLD and film measurements in a phantom. The accuracy of the calculational method and the associated computer program were verified by TLD and film measurements of noncoplanar multiarc irradiations from these collimators on a 4‐MV linear accelerator. Comparison of film measurements in two orthogonal planes showed close agreement with calculations in the shape of the dose distribution. Maximal separation of measured and calculated 90%, 80%, and 50% isodose curves was ≤0.5 mm for all planes and collimators. All TLD and film measurements of dose to isocenter agreed with calculations to within 2%.