Optimization of the margin expanded from the clinical to the planned target volume during intensity-modulated radiotherapy for nasopharyngeal carcinoma
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Wang Fangzheng1,2,*, Sun Quanquan1,2, Jiang Chuner3,*, Ye Zhimin1,2, Yang Shuangyan4, Yu Huanhuan4, Shi Jianfang4, Masoto Sakamoto5, Qin Weifeng1,2, Fu Zhenfu1,2, Jiang Yangming6 and Wang Yuezhen1,2
1Department of Radiation Oncology, Zhejiang Cancer Hospital, Hangzhou 310022, China
2Radiobiology Research Unit Key Laboratory of Radiation Oncology of Zhejiang Province, Hangzhou 310022, China
3Department of Breast Surgery, Zhejiang Cancer Hospital, Hangzhou 310022, China
4Department of Physics, Zhejiang Cancer Hospital, Hangzhou 310022, China
5Department of Radiology, Fukui Red Cross Hospital, Fukui 918-8501, Japan
6Department of Digital Earth, Institute of Remote Sensing and Digital Earth, CAS, Beijing 100101, China
*These authors have contributed equally to this work
Jiang Yangming, email: [email protected]
Wang Yuezhen, email: [email protected]
Keywords: nasopharyngeal carcinoma; intensity-modulated radiotherapy; margins; clinical target volume; megavoltage computed tomography
Received: May 25, 2017 Accepted: November 03, 2017 Published: November 20, 2017
During the radiotherapy process, the emergence of set-up errors is nearly inevitable. Because set-up errors were not detected and corrected daily, planned target volumes were formed by expanding the clinical target volume according to each unit’s experience. We optimized the margins of clinical and planned target volumes during administration of intensity-modulated radiotherapy for nasopharyngeal carcinoma. A total of 72 patients newly diagnosed with non-metastatic nasopharyngeal carcinoma and treated with Tomotherapy were prospectively enrolled in the study. For each patient, one megavoltage computed tomography scan was obtained after conventional positioning, online correction, and daily tomotherapy delivery. The interfraction set-up errors were determined using a planning CT based on the registered scan. The mean interfraction errors were -2.437±2.0529 mm, 0.0652±2.3844 mm, 0.318±1.8314 mm, and 0.197±1.8721° for the medial-lateral, superior-inferior, and anterior-posterior directions, and the direction of rotation, respectively. The total MPTV in the three directions was 7.53 mm, 1.83 mm, and 2.08 mm, respectively. The 3-mm margins in the superior-inferior and anterior-posterior directions uniformly expanded from the clinical target volume should be sufficient, and the marging in the medial-lateral direction was up to 7.5 mm. These results suggest that personalized MPTV may be adopted for intensity-modulated radiotherapy planning.
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