Volumetric modulated arc remedy remedy planning of thoracic vertebral metastases utilizing stereotactic physique radiotherapy.
J Appl Clin Med Phys. 2018 Mar;19(2):54-61
Authors: Mallory M, Pokhrel D, Badkul R, Jiang H, Lominska C, Wang F
PURPOSE/OBJECTIVES: To retrospectively consider the plan high quality, remedy effectivity, and accuracy of volumetric modulated arc remedy (VMAT) plans for thoracic backbone metastases utilizing stereotactic physique radiotherapy (SBRT).
MATERIALS/METHODS: Seven sufferers with thoracic vertebral metastases handled with noncoplanar hybrid arcs (NCHA) (1 to 2 3D-conformal partial arcs +7 to 9 IMRT beams) have been re-optimized with VMAT plans utilizing three coplanar arcs. Tumors have been situated between T2 and T7 and PTVs ranged between 24.three and 240.1 cc (median 48.1 cc). All prescriptions have been 30 Gy in 5 fractions with 6 MV beams handled utilizing the Novalis Tx linac outfitted with excessive definition multileaf collimators (HDMLC). MR photos have been fused with planning CTs for goal and OAR contouring. Plans have been in contrast for goal protection utilizing conformality index (CI), homogeneity index (HI), D90, D98, D2, and Dmedian. Regular tissue sparing was evaluated by evaluating doses to the spinal wire (Dmax, D0.35, and D1.2 cc), esophagus (Dmax and D5 cc), coronary heart (Dmax, D15 cc), and lung (V5 and V10). Knowledge evaluation was carried out with a two-sided t-test for every set of parameters. Dose supply effectivity and accuracy of every VMAT plan was assessed through high quality assurance (QA) utilizing a MapCHECK system. The Beam-on time (BOT) was recorded, and a gamma index was used to check dose settlement between the deliberate and measured doses.
RESULTS: VMAT plans resulted in improved CI (1.02 vs. 1.36, P = zero.05), HI (zero.14 vs. zero.27, P = zero.01), D98 (28.four vs. 26.eight Gy, P = zero.03), D2 (32.9 vs. 36.zero Gy, P = zero.02), and Dmedian (31.four vs. 33.7 Gy, P = zero.01). D90 was improved however not statistically vital (30.four vs. 31.zero Gy, P = zero.38). VMAT plans confirmed statistically vital enhancements in regular tissue sparing: Esophagus Dmax (22.5 vs. 27.zero Gy, P = zero.03), Esophagus 5 cc (17.6 vs. 21.5 Gy, P = zero.02), and Coronary heart Dmax (13.1 vs. 15.eight Gy, P = zero.03). Enhancements have been additionally noticed in spinal wire and lung sparing as nicely however weren’t statistically vital. The BOT confirmed vital discount for VMAT, four.7 ± zero.6 min vs. 7.1 ± 1 min for NCHA (not accounting for sofa kicks). VMAT plans demonstrated an correct dose supply of 95.5 ± 1.zero% for scientific gamma passing charge of three%/three mm standards, which was just like NCHA plans.
CONCLUSIONS: VMAT plans have proven improved dose distributions and regular tissue sparing in comparison with NCHA plans. Important reductions in remedy time might probably reduce affected person discomfort and intrafraction motion errors. VMAT planning for SBRT is a gorgeous possibility for the remedy of metastases to thoracic vertebrae, and additional investigation utilizing different fractionation schedules is warranted.
PMID: 29349867 [PubMed – indexed for MEDLINE]