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SU‐E‐T‐685: Impact of Lesion Morphology and Separation On One‐Versus Two‐Isocenter Frameless Radiosurgery
Author(s) -
Roper J,
Chanyavanich V,
Betzel G,
Dhabaan A
Publication year - 2013
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 - 10.1118/1.4815112
Subject(s) - isocenter , radiosurgery , nuclear medicine , lesion , medicine , radiation therapy , radiology , surgery , imaging phantom
Purpose: To investigate the dosimetric and localization effects of one‐versus two‐isocenter SRS. Methods: A library of 50 retrospective patient plans was compiled for cases of two brain lesions. One‐and two‐isocenter plans were generated. One‐isocenter plans consisted of four non‐coplanar‐VMAT arcs; isocenter was positioned midway between two lesions. In the two‐isocenter approach, each lesion was planned separately using four non‐coplanar DCA. DCA plans were summed. All plans were normalized so that 21 Gy covers 100% of the PTVs. Dosimetry and localization errors were studied for one‐and two‐isocenter plans. Normal tissue dose, V12, was evaluated as a function of lesion morphology and separation distance. Plans were exported to Velocity, where localization errors were simulated using rotations of 0°, 0.5°, 1°, and 2° about each isocenter. The effect of rotational misalignments on PTV coverage was compared for D95 and minimum dose. Results: Findings from 10 cases are reported. Analysis of one‐versus two‐isocenter plans shows that the V12 is comparable at lesion separations of 8 cm or less, while V12 is higher for one‐isocenter plans at greater separations. As lesion volume increases, V12 increases more for one‐isocenter plans. The effects of localization errors on target coverage were investigated. For 2° rotational errors on one‐isocenter plans, D95 decreases on average by 7%, whereas the decrease for two‐isocenter plans is 0.5%. Minimum PTV dose decreases more substantially: 12% versus 1% respectively for the one‐and two‐isocenter plans. The above values are averaged over all lesion separations. For the largest separation of 15 cm, minimum PTV dose decreases by 37% for the one‐isocenter plan. Conclusions: Localization becomes more important as separation increases for one‐isocenter SRS. Findings suggest that lesion morphology and separation should be considered when deciding between one‐and two‐isocenter SRS because of the effects on normal tissue dose and target coverage.