Use of jaw tracking in intensity modulated and volumetric modulated arc radiation therapy for spine stereotactic radiosurgery.

Abstract

This study was conducted to evaluate the advantages of jaw tracking for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in spine radiosurgery. VMAT and IMRT plans were retrospectively generated for 10 RTOG 0631 spine radiosurgery protocol patients. A total of 8 plans for each patient were created for a Varian TrueBeam equipped with a Millennium 120 multileaf collimator. Plans were created to compare IMRT and VMAT plans with and without jaw tracking, as well as with different flattening-filter-free energies: 6 MV unflattened (6U) and 10 MV unflattened (10U). The plans were prescribed to the 90% isodose line to either 16 or 18 Gy in 1 fraction. Planning target volume coverage, conformity index, dose to the spinal cord, and distance to falloff from the 90% to 50% isodose line were evaluated. Ion chamber and film measurements were performed to verify calculated dose distributions. Jaw tracking decreased spinal cord dose for both IMRT and VMAT plans, but a larger decrease was seen with the IMRT plans (P = .004 vs P = .04). The average D(10%) for the spinal cord (dose that covered 10% of the spinal cord) was least for the 6U IMRT plan with jaw tracking and was greatest for the 10U IMRT plan without jaw tracking. Measurements showed greater than 98.5% agreement for planar dose gamma analysis and less than 2.5% for point dose analysis. The addition of jaw tracking to IMRT and VMAT can decrease spinal cord dose without a change in calculation accuracy. A lower dose to the spinal cord was achieved with 6U than with 10U, although in some cases, 10U may be justified.