Head and Neck Cancer

PV QA 2 - Poster Viewing Q&A 2

MO_35_2826 - Geometric variations of the clinical target volume in neck sublocations for image-guided radiation therapy of nasopharyngeal cancer

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Geometric variations of the clinical target volume in neck sublocations for image-guided radiation therapy of nasopharyngeal cancer
W. Tan1,2, M. Yang2, W. Sheng1, D. HU3, and X. Li2; 1Department of Oncology, Southern Medical University Shenzhen Hospital, Shenzhen, China, 2Department of Oncology, Shenzhen People Hospital, Shenzhen, China, 3Hubei Cancer Hospital, Wuhan, China

Purpose/Objective(s): Both the tumor and normal tissues associated with head and neck cancer change substantially over the course of radiation therapy, including subregional variations. This study aimed to quantify the residual errors of the clinical target volume (CTV) for the neck and to estimate the planning target volume (PTV) margins at various sublocations for image-guided radiotherapy of nasopharyngeal cancer.

Materials/Methods: Twenty patients with locally-advanced NPC had a planning, as well as 6 weekly repeated computed tomography (CT) scans (CTplan, CTrepeat, respectively) during chemoradiotherapy treatment. The sternocleidomastoid muscle (SCM) and their various sublocations, as well as the body contours of transverse CT sections were manually defined. The systematic errors, random errors, and the vector displacements of neck sublocations were calculated, and PTV margins were estimated.

Results: The left- and right-side SCM volume decreased by 3.7% ± 9.6% (1.9%, 5.4%) and 5.1% ± 6.7% (3.9%, 6.3%), respectively, and the center of mass shifted medially by 0.8–0.9 mm. An anisotropic PTV margin was required to maintain geometric coverage in the left-right (2–4 mm) and anterior-posterior (1–5 mm) directions. The geometric changes in the upper-middle neck (1–3 mm) were smaller than those in the lower neck (3–5 mm). And those in the anterior part of the neck (2–3 mm) were smaller than in the posterior (3–5 mm). Though the rigid image registration-induced geometric errors were less than 3%, it had considerable variability in the middle and lower neck sublocations.

Conclusion: The neck CTV geometrical changes were substantial and showed sublocation heterogeneity. An anisotropic CTV-PTV margin with 1–5 mm that depended on the neck sublocation is recommended to maintain geometrical coverage of imaging-guided radiation therapy for nasopharyngeal cancer.

Author Disclosure: W. Tan: None. M. Yang: None. W. Sheng: None. D. HU: None.

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