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 nearmaximun absorbed dose (normalD2%) 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 normalD2% 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.PACS numbers: 87.53.Kn, 87.55.Dk

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Chylomicron retention disease, also known as Anderson's disease, is a rare hereditary hypocholesterolemic disorder, recessive inherited, characterized by nonspecific symptoms as abdominal distension, steatorrhea, and vomiting associated with failure to thrive. We describe a patient with failure to thrive, chronic diarrhea and steatorrhea who the diagnosis of chylomicron retention disease was established after several months of disease progression. The genetic study confirmed a homozygosity mutation in SAR1B gene, identifying a mutation never previous described [c.83_84delTG(p.Leu28Argfs*7)]. With this case report the authors aim to highlight for this very rare cause of failure to thrive and for the importance of an attempting diagnosis, in order to start adequate management with low fat diet supplemented with fat-soluble vitamins, reverting the state of malnutrition and avoiding possible irreversible and desvantating complications.

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