Dose verification of 2 targets simultaneously for single-isocenter stereotactic radiation therapy and radiosurgery plans.

Most of conventional 2-dimensional (2D) methods verify dose of multiple targets separately one-by-one for Single-isocenter Multiple-target (SIMT) brain plans, which are inefficient and sub-optimal. This study presented a practical method to verify the dose of 2 targets simultaneously for improved efficiency and accuracy. Fifteen Stereotactic Radiation Therapy (SRT) and sixteen Stereotactic Radiosurgery (SRS) plans were used for this study. Each plan has 2 targets coincide with a plane through the plan isocenter. All plans were created in the Eclipse Treatment Planning System (TPS) using a 6 MV flattening filter free photon beam. A 2D detector array, myQA SRS was used for measurements. It has a spatial resolution of 0.4 mm and an active area of 120 × 140 mm. It can be rotated along the longitudinal axis with a cylindrical phantom with one-degree precision. All plans were delivered with the detector array centered at the plan isocenter and rotated to intersect 2 targets. Six plans with target separations less than 70 mm were crosschecked with the SRS MapCHECK, which has an active area of 77 × 77 mm. The measured 2D dose distributions were compared with those calculated from the TPS. Gamma-index analysis was performed using 3%/1 mm criteria and a 10% dose threshold. For all 31 SIMT brain plans measured with myQA SRS, the average and standard deviation of the gamma-passing rate was (96.8 ± 2.2)%. For 15 SRT plans and 16 SRS plans, that was (96.6 ± 2.4)% and (97.0 ± 2.1)%, respectively. For 6 plans crosschecked, the average gamma-passing rates were 96.8% vs. 94.8% with myQA SRS and SRS MapCHECK, respectively. A practical method to verify the dose of 2 targets simultaneously was demonstrated. It offers an efficient way for pretreatment verification of SIMT SRT and SRS plans with improved accuracy.