Fiducial marker matching versus vertebral body matching: Dosimetric impact of patient positioning in carbon ion radiotherapy for primary hepatic cancer
Marker matching and vertebral body matching were evaluated for effectiveness.
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They were performed for 20 cases of primary hepatic cancer in carbon ion therapy.
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Eight cases with vertebral body matching were not clinically acceptable.
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All cases with marker matching were clinically acceptable.
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Marker matching was more robust than vertebral body matching.
Abstract
Purpose
The aim of this study was to compare the dose-volume parameters of fiducial marker matching (MM) with vertebral body matching (VM) in patient positioning for carbon ion radiotherapy for primary hepatic cancer.
Materials and methods
Twenty patients with primary hepatic cancer were retrospectively studied to assess changes in reproducibility of tumor position and dose distribution on two CT scans. One was for treatment planning and another was for dose confirmation, acquired the day before the first treatment day. The coverage of the clinical target volume (CTV) (D98) and normal liver volume excluding the CTV which received 20 Gy relative biological effectiveness (RBE) (V20) were used as evaluation parameters. Additionally, the correlation of tumor movement and D98 was calculated in VM and MM. The prescription dose was 60.0 Gy (RBE) delivered in four fractions (15 Gy/fx).
Results
The median (range) D98 for VM and MM was 57.9 (20.8–59.9) and 59.9 (57.2–60.3) Gy (RBE), respectively. The median (range) V20 for VM and MM was 17.9 (4.8–44.4) and 16.2 (4.7–44.9) Gy (RBE), respectively. The D98 for MM was significantly larger than that for VM (p = 0.001), although V20 showed no significant difference (p > 0.05). Twelve patients were clinically acceptable (D98 > 57 Gy (RBE)) with VM, while all patients were clinically acceptable with MM. Marker movement correlated with a decrease of D98 for VM (R = −0.814).
Conclusion
Compared with VM, MM was clinically acceptable in all patients. This suggests that MM is more robust than VM.