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Dosimetric comparison of three photon radiosurgery techniques for an elongated ellipsoid target
1Department of Radiation Oncology, University of Southern California School of Medicine, Los Angeles 90033-0804, USA. chengyu@hsc.usc.edu
Purpose:
To examine the dosimetric differences among three radiosurgery techniques: gamma knife, linac multiple arcs, and conformally-shaped static fields.
Methods And Materials:
A simulated target was taken to be a prolate ellipsoid, 25 mm in diameter, 35 mm in length, centrally located in a three-dimensional (3D) model of a patient head taken from MR images. Single isocenter linac treatment plans were developed, 9 portals for the static shaped field technique, and a 7-arc plan for the multiple arc method. A total of 13 isocenters with 3 different collimators were used in the gamma knife plan.
Results:
At dose levels from 25% to 50% of the reference dose, multiple arc and shaped-field plans treated a greater volume than the gamma knife plan. The linac plans, however, delivered the dose more homogeneously across the target volume as compared to the gamma knife plan. For the dose levels between 50-100%, the shaped fields and gamma knife plan have a similar dose distribution, and treated slightly less volume than the multiple arc plan.
Conclusion:
For a target of limited volume and essentially any shape, one can obtain closely conformal dosimetry with the gamma knife. For a regular-shaped target, the single isocenter multiple arc technique gives a more homogenous dose distribution within the target. Static shaped fields offer an alternative radiosurgery technique, with dosimetry similar to the multiple arc method, applicable to targets of any shape.