Dose Evaluation Of SBRT With/Without Simultaneous Integrated Boost With SIMRT, VMAT And HT Techniques For Spinal Metastasis

Part one:Dosimetric study of different fractionated schemas and PTV-cord distances for SBRT with/without simultaneous integrated boost in spinal metastasisPurpose:To investigate and quantify impact of different fractionation schemas and PTV-cord distances on dosimetry of stereotactic body radiation therapy (SBRT) with or without simultaneous integrated boost (SIB) in patients with spinal metastasis. Methods: Six modified planning target volumes (PTVs) in each of 5 patients with spinal metastases were created to ensure a specified minimum PTV-cord distance (0-5mm). The prescription dose (biologically equivalent dose, BED) was 70Gy with 4 fractionation schemes (1,3,5 and 10 fractions). PTV V100%, Dmin, D98%, D95%, conformity index (CI), V30% and dose of spinal cord were evaluated. Results:PTV-cord distance influenced PTV Dmin, D98% and D95%, and fractionation schemes influenced Dmin and D98%, with significant differences. A PTV-cord distance of≥2 mm,≥ 1 mm,≥ 1 mm, and≥ 0 mm met the dose requirements for the 1,3,5 and 10 fractionation schema, respectively. Spinal cord dose, PTV CI and V30% were not impacted by PTV-cord distance and fractionation schemes. Conclusions:PTV Dmin, D98%, D950%, were directly correlated with PTV-cord distance for SBRT with or without SIB in spinal metastasis. A PTV-cord distance of≥2 mm,≥1 mm,≥1 mm, and≥0 mm meet dose requirements in 1,3,5 and 10 fractionation schemas, respectively.Part two:Dosimetric study of sIMRT, VMAT and HT for SBRT with simultaneous integrated boost in spinal metastasisPurpose:To evaluate the dosimetric charateristics of step-and-shoot intensity modulated radiation therapy (sIMRT), volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) for SBRT with simultaneous integrated boost (SIB) for spinal metastasis, and to determine the most optimal treatment modality. Methods:Based on lesion location,16 spinal metastatic lesions were divided into 4 target types reflecting the target complexity. Three IMRT planning modalities including sIMRT, VMAT and HT were generated for each lesion. Boosted planning target volume (PTV-boost) and elective planning target volume (PTV-elective) were prescribed as 47.5 Gy and 30 Gy in 10 fractions, respectively. PTV V100%, Dmin, D98%, D95%, conformity index (CI), homogeneity index (HI), and maximum dose of the planning at risk volume for spinal cord (PRVsc) (Dmax),OARs dose, delivery time, monitor unit (MU) and QA (γ-test) were compared among the 3 techniques. Results:VMAT and HT were comparable, and capable of providing better PTV Dmin, D98%, D95%, CI and HI than IMRT. HT had a lower PRVsc Dmax than VMAT and sIMRT. No significant differences were detected among the 3 techniques for dose of other OARs. The delivery time per fraction was significantly shorter in VMAT than in IMRT and HT. Similarly, much less MUs were needed for VMAT than for IMRT and HT. Three techniques had equivalent Dmin in different target types, while HT and VMAT had better PTV V100%, D98%, D95%, CI and HI than IMRT in complex target types (type 3 and type 4). The plans of the 3 techniques met the QA criteria without significant differences. Conclusions:(1) SBRT with SIB in 10 fractions realized with sIMRT, VMAT and HT techniques meet dosimetric and QA requirements in spinal mestasis, even in MESCC. (2) VMAT has comparable dosimetric charateristics compared with HT, but with a higher treatment efficiency; while HT protects better the spinal cord. (3) VMAT and HT have dosimetric advantages in complex target types compared with IMRT.