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. 2015 Sep 14:8:2545-53.
doi: 10.2147/OTT.S87159. eCollection 2015.

Different setup errors assessed by weekly cone-beam computed tomography on different registration in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy

Jiqing Su  1 , Wen Chen  2 , Huiyun Yang  2 , Jidong Hong  2 , Zijian Zhang  2 , Guangzheng Yang  2 , Li Li  2 , Rui Wei  2
Affiliations

Different setup errors assessed by weekly cone-beam computed tomography on different registration in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy

Jiqing Su et al. Onco Targets Ther. .

Abstract

The study aimed to investigate the difference of setup errors on different registration in the treatment of nasopharyngeal carcinoma based on weekly cone-beam computed tomography (CBCT). Thirty nasopharyngeal cancer patients scheduled to undergo intensity-modulated radiotherapy (IMRT) were prospectively enrolled in the study. Each patient had a weekly CBCT before radiation therapy. In the entire study, 201 CBCT scans were obtained. The scans were registered to the planning CT to determine the difference of setup errors on different registration sites. Different registration sites were represented by bony landmarks. Nasal septum and pterygoid process represent head, cervical vertebrae 1-3 represent upper neck, and cervical vertebrae 4-6 represent lower neck. Patient positioning errors were recorded in the right-left (RL), superior-inferior (SI), and anterior-posterior (AP) directions over the course of radiotherapy. Planning target volume margins were calculated from the systematic and random errors. In this study, we can make a conclusion that there are setup errors in RL, SI, and AP directions of nasopharyngeal carcinoma patients undergoing IMRT. In addition, the head and neck setup error has the difference, with statistical significance, while patient setup error of neck is greater than that of head during the course of radiotherapy. In our institution, we recommend a planning target volume margin of 3.0 mm in RL direction, 1.3 mm in SI direction, and 2.6 mm in AP direction for nasopharyngeal cancer patients undergoing IMRT with weekly CBCT scans.

Keywords: PTV margins; cone-beam computed tomography; intensity-modulated radiation therapy; nasopharyngeal carcinoma; setup error.

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Figures

Figure 1
Figure 1
Image registration by automatic bone matching and manual fine-tuning method in head. Notes: (A) The cross section, coronal plane, and sagittal plane in an NPC patient’s planning CT, and we use nasal septum as a bony landmark for automatic bone matching and manual fine-tuning method (the yellow frame represents registration area); (B) the cross section of the head in planning CT image; (C) the cross section of the head in cone-beam CT image; (D) a typical fusion image with planning CT. The areas circled in red indicate the primary gross volume (GTVnx). Abbreviations: NPC, nasopharyngeal carcinoma; CT, computed tomography.
Figure 2
Figure 2
Image registration by automatic bone matching and manual fine-tuning method in upper neck. Notes: (A) The cross section, coronal plane, and sagittal plane in an NPC patient’s planning CT, and we use 1–3 cervical vertebrae as a bony landmark for automatic bone matching and manual fine-tuning method (the yellow frame represents registration area); (B) the cross section of upper neck in planning CT image; (C) the cross section of upper neck in cone-beam CT image; (D) a typical fusion image with planning CT. The areas circled in red indicate the involved lymph nodes (GTVnd). Abbreviations: NPC, nasopharyngeal carcinoma; CT, computed tomography.
Figure 3
Figure 3
Image registration by automatic bone matching and manual fine-tuning method in lower neck. Notes: (A) The cross section, coronal plane, and sagittal plane in an NPC patient’s planning CT, and we use 4–6 cervical vertebrae as a bony landmark for automatic bone matching and manual fine-tuning method (the yellow frame represents registration area); (B) the cross section of lower neck in planning CT image; (C) the cross section of lower neck in cone-beam CT image; (D) a typical fusion image with planning CT. The areas circled in red indicate the involved lymph nodes (GTVnd). Abbreviations: NPC, nasopharyngeal carcinoma; CT, computed tomography.
Figure 4
Figure 4
Setup errors of 30 patients in the (A) right–left direction; (B) superior–inferior direction, and (C) anterior–posterior direction (the mean ± SD). Abbreviations: RL, right–left; SI, superior–inferior; AP, anterior–posterior; SD, standard deviation.
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