SU‐E‐T‐672: Comparisons of Single and Multiple Isocenter Stereotactic IMRT Treatment Planning for Multiple Brain Metastases Treatment

Abstract

Purpose: To compare quality of single and multiple isocenter stereotactic IMRT treatment plans for multiple intracranial targets. Methods: Five patients (two with three and three with two brain metastatic tumors) treated with multiple isocenters using 9 to 12 non‐coplanar beams per lesion were replanned for single isocenter 10 to 12 non‐coplanar beams. Identical contour sets and dose‐volume constraints were applied. Plans were developed using BrainLab iPlan system for delivery with Varian TrueBeam STx machine. The prescribed dose to each target was 25 Gy in five fractions and minimum 95% dose was required to cover > 95% of target volume. Results: All plans satisfied the dose‐volume constraints, with no significant differences in dose conformity between single and multiple isocenter plans. The mean Paddick conformity index (CI) for two target single and multiple isocenter plans was 0.76 and 0.75 (p = 0.93), and for three target single and multiple isocenter plans was 0.73 and 0.70 (p = 0.37), respectively. Normal brain tissue doses were higher for single isocenter plans compared to multiple isocenter plans. The average normal brain volumes receiving 15 and 10 Gy for two target plans (single vs. multiple isocenter) were: (4.8% vs. 2.1%) and (8.9% vs. 4.5%), respectively. For three target plans these volumes were: (2.0% vs. 1.5%) and (4.6% vs. 3.4%). The estimated total treatment time (patient set‐up, imaging‐verification, beam‐on time at 600 MU/min, etc.) were approximately 1.75 and 2.5 times lower with two and three target single isocenter delivery, respectively. Conclusion: Single isocenter plans were capable of producing quality treatment plans similar to multiple isocenter plans. Treatment delivery times were much higher and the normal brain tissue doses were only slightly lower at 10 and 15 Gy dose levels for multiple isocenter plans compared to single isocenter plans. Clinical consequences of these normal tissue doses are however unknown.