Effectiveness of a Patient-Specific Immobilization and Positioning System to Limit Interfractional Translation and Rotation Setup Errors in Radiotherapy of Prostate Cancers
Effectiveness of a Patient-Specific Immobilization and Positioning System to Limit Interfractional Translation and Rotation Setup Errors in Radiotherapy of Prostate Cancers作者机构：Department of Clinical Oncology Tuen Mun Hospital Hong Kong China
出 版 物：《International Journal of Medical Physics, Clinical Engineering and Radiation Oncology》 (医学物理学、临床工程、放射肿瘤学（英文）)
年 卷 期：2016年第5卷第3期
页 面：184-195页
学科分类：0502[文学-外国语言文学] 050201[文学-英语语言文学] 05[文学]
主 题：Immobilization Prostate CBCT Margin Interfractional Motion
摘 要：Objective: To evaluate the effectiveness of a patient-specific immobilization and positioning device in prostate radiotherapy. Methods: Eighty patients were immobilized and positioned by a patient-specific device. Prostate translations and rotations were estimated from daily cone beam computed tomography scans using a contour-based approach assisted by auto-registration and quantified by the group mean GM, systematic Σ and random σ errors. Dosimetric impacts of residual prostate rotations where the translation errors were corrected were evaluated by robustness plan analysis. Results: Using the patient-specific immobilization alone without online image-guidance, the GM, Σ and σ of the prostate translations were 0.8, 1.7, and 1.5 mm (left-right;LR), 0.8, 2.1, and 1.9 mm (superior-inferior;SI), and 0.5, 1.7 and 1.5 mm (anterior-posterior;AP), while for the prostate rotations they were 0.0°, 0.6°, and 0.7°(pitch), 0.2°, 0.5°, and 0.6°(roll), and 0.2°, 0.5°, and 0.6°(yaw). The resulting van Herk’s margin was 5.8 (LR), 7.3 (SI) and 5.8 (AP) mm. With adaptive online image-guidance based on estimates from the first 5 fractions, Σ were reduced by 0.7 - 1.2 mm for the prostate translations, resulting in a margin reduction by 2 - 3.5 mm. Changes of Σ and σ in the prostate rotations were insignificant regardless of translation corrections. Dosimetric impacts of residual rotation errors were negligible if a 2 mm margin was applied. Conclusions: Our patient-specific immobilization system can effectively limit the prostate translations and rotations, which is important without 6D treatment couches or using ultrasound image-guidance without rotational corrections.
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