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- Title
Larynx motion considerations in partial larynx volumetric modulated arc therapy for early glottic cancer.
- Authors
Bahig, Houda; Nguyen‐Tan, Phuc Félix; Filion, Édith; Roberge, David; Thanomsack, Pensavan; Guise, Jacques; Blais, Danis; Doucet, Robert; Létourneau‐Guillon, Laurent; Lambert, Louise
- Abstract
<bold>Introduction: </bold>To assess laryngeal motion in early glottic cancer in order to determine safe margins for partial larynx volumetric modulated arc therapy (PL-VMAT), and to quantify dosimetric advantages of PL-VMAT.<bold>Methods: </bold>This prospective study included T1-2N0 glottic cancers treated with whole larynx VMAT (WL-VMAT). Pre- and mid-treatment 4D-computed tomography (4D-CT) and dynamic magnetic resonance imaging (MRI) allowed for assessment of larynx swallowing and respiratory motion. For 10 patients with lateralized lesions, PL-VMAT plans were calculated using margins derived from 4D-CT analysis.<bold>Results: </bold>Twenty patients were accrued from 2014 to 2016. Mean amplitude of larynx swallowing excursion was 23 mm and 6 mm in the superior and anterior directions, respectively. Mean respiratory motion reached 4 mm and 2 mm in superior-inferior and antero-posterior directions, respectively. Pre-treatment 4D-CT analysis identified one patient with planning CT acquired during swallowing. Mid-treatment 4D-CT revealed larynx shift relative to vertebrae in 30% of cases. PL-VMAT allowed for significant reduction of mean doses to ipsilateral carotid, contralateral carotid, thyroid gland, contralateral arytenoid and larynx. Using 8 mm internal margin for PL-VMAT, swallowing resulted in clinical target volume excursion beyond 95% isodose line during ≤1.5% of total treatment time in all patients.<bold>Conclusion: </bold>Although swallowing motion is rare, rapid and easily suppressed by patients, there is a risk of systematic miss-targeting if planning CT is acquired during swallowing. Larynx position shift relative to vertebrae occurs in 1/3 of patients over the course of radiotherapy. With soft-tissue image guidance and margins accounting for respiratory motion, PL-VMAT allows safe reduction of dose to organs at risk.
- Subjects
GLOTTIS cancer; LARYNGEAL cancer; RADIOTHERAPY treatment planning; MAGNETIC resonance imaging; INPATIENT care; RESPIRATORY therapist &; patient; COMPUTED tomography; DEGLUTITION; GLOTTIS; LARYNGEAL tumors; LONGITUDINAL method; COMPUTERS in medicine; MOTION; RADIATION doses; RADIOTHERAPY; TUMOR classification; TREATMENT effectiveness
- Publication
Journal of Medical Imaging & Radiation Oncology, 2017, Vol 61, Issue 5, p666
- ISSN
1754-9477
- Publication type
journal article
- DOI
10.1111/1754-9485.12612