title: Dose variations in tumor volumes and organs at risk during IMRT for head-and-neck cancer.
abstract: Many head-and-neck cancer (HNC) patients treated with radiotherapy suffer significant anatomical changes due to tumor shrinkage or weight loss. The purpose of this study was to assess dose changes over target volumes and organs at risk during intensity-modulated radiotherapy for HNC patients. Sixteen HNC IMRT patients, all requiring bilateral neck irradiation, were enrolled in the study. A CTplan was performed and the initial dose distribution was calculated. During the treatment, two subsequent CTs at the 15th (CT15) and 25th (CT25) fractions were acquired. The initial plan was calculated on the CT15 and CT25, and dose-volume differences related to the CTplan were assessed. For target volumes, mean values of near-maximun absorbed dose (D2%) increased at the 25th fraction, and doses covering 95% and 98% of volume decreased significantly at the 15th fraction. Contralateral and ipsilateral parotid gland mean doses increased by 6.1% (range: -5.4, 23.5%) and 4.7% (range: -9.1, 22.3%), respectively, at CT25. The D2% in the spinal cord increased by 1.8 Gy at CT15. Mean absorbed dose increases at CT15 and CT25 were observed in: the lips, 3.8% and 5.3%; the oral cavity, 3.5% and 2.5%; and lower middle neck structure, 1.9% and 1.6%. Anatomical changes during treatment of HNC patients affect dose distribution and induce a loss of dose coverage to target volumes and an overdosage to critical structures. Appropriate organs at risk have to be contoured and monitored in order to know if the initial plan remains suitable during the course of the treatment. Reported dosimetric data can help to identify patients who could benefit from adaptive radiotherapy.
authors.affiliation: Servei de Física,Servei d’Oncologia Radioteràpica, Hospital Universitari Vall d’Hebron, Universitat Autònoma de Barcelona, Barcelona 08035, Spain . mbeltran@vhebron.net
authors.forename: Mercè
authors.initials: M
authors.lastname: Beltran
authors.forename: Mónica
authors.initials: M
authors.lastname: Ramos
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Rovira
authors.forename: Santiago
authors.initials: S
authors.lastname: Perez-Hoyos
authors.forename: Marc
authors.initials: M
authors.lastname: Sancho
authors.forename: Enrique
authors.initials: E
authors.lastname: Puertas
authors.forename: Sergi
authors.initials: S
authors.lastname: Benavente
authors.forename: Merce
authors.initials: M
authors.lastname: Ginjaume
authors.forename: Jordi
authors.initials: J
authors.lastname: Giralt
mesh_terms: D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D058958:Organs at Risk; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D047368:Tumor Burden