Please use this identifier to cite or link to this item: https://doi.org/10.1016/j.radonc.2015.09.032
Title: Measuring radiotherapy setup errors at multiple neck levels in nasopharyngeal cancer (NPC): A case for differential PTV expansion
Authors: Cheo, Timothy
Loh, Yvonne
Chen, Desiree
Lee, Khai Mun
Tham, Ivan 
Keywords: Science & Technology
Life Sciences & Biomedicine
Oncology
Radiology, Nuclear Medicine & Medical Imaging
Nasopharyngeal Carcinoma
Setup errors
PTV margin
INTENSITY-MODULATED RADIOTHERAPY
PLANNING TARGET VOLUME
HEAD
CARCINOMA
UNCERTAINTIES
DELINEATION
TOMOGRAPHY
POSITION
THERAPY
MARGINS
Issue Date: 1-Dec-2015
Publisher: ELSEVIER IRELAND LTD
Citation: Cheo, Timothy, Loh, Yvonne, Chen, Desiree, Lee, Khai Mun, Tham, Ivan (2015-12-01). Measuring radiotherapy setup errors at multiple neck levels in nasopharyngeal cancer (NPC): A case for differential PTV expansion. RADIOTHERAPY AND ONCOLOGY 117 (3) : 419-424. ScholarBank@NUS Repository. https://doi.org/10.1016/j.radonc.2015.09.032
Abstract: Background and purpose We aim to quantify the magnitude of the systematic and random setup errors at three different anatomical levels of the neck in Nasopharyngeal Carcinoma (NPC) when clivus matching is used, and recommend appropriate PTV margins for each level. Material and methods Thirty-six patients undergoing image-guided radiotherapy (IGRT) each with 9 scheduled CBCTs were reviewed. The magnitude of setup errors were measured at the level of the clivus, C4 and C7 vertebrae, before and after CBCT correction. The 3D displacements, systematic and random errors were calculated for each level. The appropriate PTV expansion was determined using Van Herk's formula. Results Mean 3D displacement was 1.88, 2.66 and 3.35 mm at the clivus, C4 and C7 before correction. The differences were statistically significant (p < 0.05). The PTV margin required without correction was 2.33, 4.33 and 6.52 mm respectively. These were reduced to 1.20, 3.72 and 6.08 mm after CBCT corrections. Conclusions Variability is seen in setup errors at the clivus, C4 and C7 vertebral levels. A variable planning margin approach with reduced margin at the clivus is recommended. Use of daily CBCT allows the PTV expansion to be reduced to 1.2 mm.
Source Title: RADIOTHERAPY AND ONCOLOGY
URI: https://scholarbank.nus.edu.sg/handle/10635/206007
ISSN: 01678140
18790887
DOI: 10.1016/j.radonc.2015.09.032
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