Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer

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 [Formula: see text] was performed and the initial dose distribution was calculated. During the treatment, two subsequent CTs at the 15th [Formula: see text] and 25th [Formula: see text] fractions were acquired. The initial plan was calculated on the [Formula: see text] and [Formula: see text] , and dose‐volume differences related to the [Formula: see text] were assessed. For target volumes, mean values of nearmaximun absorbed dose ([Formula: see text]) 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 [Formula: see text]. The [Formula: see text] in the spinal cord increased by 1.8 Gy at [Formula: see text]. Mean absorbed dose increases at [Formula: see text] and [Formula: see text] 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. PACS numbers: 87.53.Kn, 87.55.Dk