Room: AAPM ePoster Library
Purpose: is an increasingly favored treatment option for patients with multiple brain metastases. One major treatment planning approach is using single isocenter to plan for multiple lesions with VMAT technique. Normal brain dose spillage is the primary challenge compare to conventional single isocenter single target treatment. Modern linear accelerator provides JTT to move jaws as close to MLC aperture as possible to reduce dose leakage and transmission through MLC. This study is performed to compare the dosimetric difference for SIMM-SRS with and without JTT.
Methods: patients with total thirty-seven lesions (range:3-11) treating with ten treatment isocenters of SIMM-SRS with SJT were selected and re-planned with JTT. Treatment plans were created with Eclipse treatment planning system (PO 15.6, AAA 15.6, 1mm dose calculation grid size) and were delivered with TrueBeam STX linear accelerator equipped with HDMLC and 6 DOF couch. Optimization criteria and dose normalization method were kept identical for both SJT and JTT. Normal brain dose at V1Gy, V3Gy, V5Gy, V10Gy and V12Gy were compared between two planning techniques. Two-tailed paired t-test was applied in this study for statistical significance comparison.
Results: the plans with both STT and JTT meet the clinical requirements on conformity index (CI), gradient index (GI) and OAR dose constraints. The average minimum dose to PTV, CI and GI were 97.97±1.89% vs. 97.18±2.22%, 1.34±0.14 vs. 1.31±0.12, and 4.98±1.23 vs. 5.19±1.35 for STJ and JTT, respectively. The average normal brain (brain-PTV) dose of SJT and JTT were V1Gy - 465.95±282.59cc vs. 420.52±42.54cc (p=0.004), V3Gy – 69.33cc±52.36 vs. 64.75±48.78cc (p=0.007), V5Gy – 21.66±15.21cc vs. 21.81±15.63cc (p=0.33), V10Gy – 5.88±3.81cc vs. 6.01±3.97cc (p=0.10) and V12Gy–3.98±2.55cc vs. 4.03±2.61cc (p=0.16).
Conclusion: can significantly reduce the low dose (1-3Gy) to normal brain while achieving similar treatment plan quality as SJT. Strong consideration should be made to apply JTT in SIMM-SRS treatment Planning.
Not Applicable / None Entered.