Monte carlo

rloIntroduction
The M.D. Anderson Cancer Center (MDACC) has developed an anthropomorphic head phantom for remote monitoring of stereotactic radiosurgery (SRS) treatments. The phantom contains a 1.9 cm imageable target as well as TLD and radiochromic film. The
TLD allow us to estimate dose to the center of the target with an accuracy of ± 3%. The radiochromic film allow us to measure the location of the dose gradients (field edges) within ± 1 mm along three orthogonal axis. This phantom has been provided to the community through the Radiological Physics Center (RPC) and the Radiation Dosimetry
Services (RDS) since 1995. The design of the phantom is presented as well as a summary of the data obtained through the last four years of monitoring. The data includes dose to the center of the target, alignment of isodose distributions, and comparisons of radiation treatment area with that determined by the institution’s treatment planning system. We have also been able to compile data to compare dosimetry
(dose and localization precision) between Gamma-Knife and Linac based stereotactic treatments. We have also collected demographic information on the modalities for localization, planning and delivering SRS treatments in our monitored population.

Materials and Methods
The remote monitoring system, shown in figure 1, consists of a water filled head shaped plastic shell (The Phantom Laboratories, Salem, NY), this shell has been fitted to accept inserts through the neck, these inserts are 7.5 cm diameter cylinders that reproducibly align to a high degree of precision (0.1 mm). One insert, the imaging insert, is used to establish a target in stereotactic space. This insert is water filled with a 1.9 cm (3/4”) nylon ball suspended at a know location. This combination of nylon and water allows localization with either CT or MRI. A second insert, the dosimetry insert, locates two
TLD capsules and two pieces of radiochromic film at a know location with