A dosimetric comparison of two-phase adaptive intensity-modulated radiotherapy for locally advanced nasopharyngeal cancer

• Main Authors: Chitapanarux I., Chomprasert K., Nobnaop W., Wanwilairat S., Tharavichitkul E., Jakrabhandu S., Onchan W., Traisathit P., Van Gestel D.
• Format: Article
• Published: Japan Radiation Research Society 2015
• Subjects: Health, Toxicology and Mutagenesis; Radiology, Nuclear Medicine and Imaging; Radiation
• Online Access: http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=84929912587&origin=inward; http://cmuir.cmu.ac.th/handle/6653943832/38968
• Institution: Chiang Mai University

© 2015 The Author. The purpose of this investigation was to evaluate the potential dosimetric benefits of a two-phase adaptive intensity-modulated radiotherapy (IMRT) protocol for patients with locally advanced nasopharyngeal cancer (NPC). A total of 17 patients with locally advanced NPC treated with IMRT had a second computed tomography (CT) scan after 17 fractions in order to apply and continue the treatment with an adapted plan after 20 fractions. To simulate the situation without adaptation, a hybrid plan was generated by applying the optimization parameters of the original treatment plan to the anatomy of the second CT scan. The dose-volume histograms (DVHs) and dose statistics of the hybrid plan and the adapted plan were compared. The mean volume of the ipsilateral and contralateral parotid gland decreased by 6.1 cm³ (30.5%) and 5.4 cm³ (24.3%), respectively. Compared with the hybrid plan, the adapted plan provided a higher dose to the target volumes with better homogeneity, and a lower dose to the organs at risk (OARs). The Dmin of all planning target volumes (PTVs) increased. The Dmax of the spinal cord and brainstem were lower in 94% of the patients (1.6-5.9 Gy, P < 0.001 and 2.1-9.9 Gy, P < 0.001, respectively). The D<inf>mean</inf> of the contralateral parotid decreased in 70% of the patients (range, 0.2-4.4 Gy). We could not find a relationship between dose variability and weight loss. Our two-phase adaptive IMRT protocol improves dosimetric results in terms of target volumes and OARs in patients with locally advanced NPC.