[Measurement of setup error in conformal radiotherapy for nasopharyngeal carcinoma].
OBJECTIVE
Setup error is the key factor in determining the margin of planning target volume (M(PTV)) for conformal radiotherapy of nasopharyngeal carcinoma (NPC). This study was to establish a method using radiopaque fiducial markers which were embedded in occlusal splint ("occlusal splint method") to acquire setup errors to calculate M(PTV) in CRT for NPC.


METHODS
The occlusal splint method was performed in 22 NPC patients who received CRT. Setup errors were calculated by comparing the coordinates of 3 fiducial markers read from portal images with those read from computed tomography (CT) data. According to the formulation, the size of MPTV with or without consideration of organ motion was also calculated.


RESULTS
The standard deviations of systematic errors (Sigma) were 1.13 mm, 1.47 mm, and 1.31 mm in X (medio-lateral), Y (antero-posterior) and Z (cranio-caudal) axes, respectively; the standard deviations of random errors were 0.81 mm, 0.45 mm, and 0.80 mm in X, Y, and Z axes, respectively. Without consideration of organ motion, the sizes of M(PTV) were 3.40 mm, 3.98 mm, and 3.83 mm in X, Y, and Z axes, respectively; with consideration of organ motion, the sizes of M(PTV) were 3.75 mm, 4.35 mm, and 4.16 mm in X, Y, and Z axes, respectively.


CONCLUSIONS
Using the "occlusal splint method", each institution can precisely calculate setup error data, and stipulate the size of M(PTV) adequate to one's own situation.
Pan
Jian-Ji
JJ
Department of Radiotherapy, Fujian Provincial Tumor Hospital, Fujian Medical University, Fuzhou, Fujian 350014, P. R. China. panjianji@msn.com
Zheng
Bu-Hong
BH
Zhang
Yu
Y
Chen
Chuan-Ben
CB
Li
Jin-Lian
JL
Zhang
Xiu-Chun
XC
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011187:Posture; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*