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It Is Not Safe to Apply Popular CTV-PTV Margins for Patients with Tomotherapy

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Y Tong

Y Tong1,2*, G Gong1 , P Cheng2 , Y Yin1 , (1) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong Province,China. (2) School of Nuclear Science and Technology, University of South China, Hengyang, Hunan Province,China.


SU-I-GPD-T-400 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The purpose of this study was to evaluate CTV₋PTV margins of tumors for Tomotherapy.

Methods: Setup errors were analyzed for 151 patients receiving helical tomotherapy treatment, 53 patients had head and neck tumors, 45 had thoracic tumors, 20 had abdominal tumors, and 33 had pelvic tumors. The setup errors were calculated in ₊Χ (left), ₋Χ (right), ₊Υ(head), ₋Υ(foot), ₊Ζ(ventral) and ₋Ζ(dorsal) six directions after Megavoltage CT images were registered to simulation CT images. The CTV₋PTV margins subsequently were calculated.

Results: The setup errors along the ₊Ζ direction were higher than that along the other directions. The distributions range of systematic errors (Σ) and random errors(σ) were 0.8₋1.4 mm and 1.1₋1.4 mm, 1.0₋2.7 mm and 1.8₋2.5 mm, 0.9₋2.4 mm and 1.5₋2.4 mm, 1.0₋2.3 mm and 1.3₋2.8 mm for head and neck tumors, thoracic tumors, abdominal tumors and pelvic tumors, respectively. The CTV₋PTV margins on ₊Χ, ₋Χ, ₊Υ, ₋Υ, ₊Ζ and ₋Ζ directions were 4.3mm, 2.8mm, 3.1mm, 4.0mm, 4.1mm , 4.6mm for head and neck tumors; 3.7mm, 3.8mm, 7.8mm, 5.9mm,5.2mm,8.4mm for thoracic tumors; 3.5mm,6.5mm,5.9mm,3.6mm,3.9mm,7.7mm for abdominal tumors; and 3.7mm, 4.6mm, 4.8mm, 5.2mm, 3.3mm, 7.7mm, respectively, for pelvic tumors. The CTV₋PTV margins on six directions were asymmetric for all tumors, and the heterogeneity were more remarkable on ₊Ζ and ₋Ζ directions.

Conclusion: The CTV₋PTV margins for patients with different parts tumors had heterogeneity during Tomotherapy. The traditional symmetrical popular margins from CTV to PTV could bring risks to the target and organs at risk, and individual CTV₋PTV margins should be expend on ₊Χ, ₋Χ,₊Υ, ₋Υ, ₊Ζ, and ₋Ζ directions, respectively.

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