Evaluating the dosimetric effect of treatment-induced changes in virally mediated @entity135 XXXX .

@entity1 @entity135 @entity5
INTRODUCTION: @entity1 with virally mediated @entity135 (VMHNC) often present with advanced nodal disease that is highly radioresponsive as demonstrated by @entity5 and nodal regression during treatment. The resultant changes may impact on the planned dose distribution and so adversely affect the therapeutic ratio. The aim of this study was to evaluate the dosimetric effect of treatment-induced anatomical changes in VMHNC @entity1 who had undergone a replan. METHODS: Thirteen @entity1 with virally mediated oropharyngeal or nasopharyngeal @entity5 who presented for definitive radiotherapy between 2005 and 2010 and who had a replan generated were investigated. The dosimetric effect of anatomical changes was quantified by comparing dose-volume histograms (DVH) of primary and nodal gross target volumes and organs at risk (OAR), including spinal cord and parotid glands, from the original plan and a comparison plan. RESULTS: Eleven three-dimensional conformal radiation therapy (3DCRT) and two intensity modulated radiation therapy (IMRT) plans were evaluated. Dose to the spinal cord and brainstem increased by 4.1% and 2.6%, respectively. Mean dose to the parotid glands also increased by 3.5%. In contrast, the dose received by 98% of the primary and nodal gross @entity5 volumes decreased by 0.15% and 0.3%, respectively, when comparing the initial treatment plan to the comparison plan. CONCLUSION: In this study, treatment-induced anatomical changes had the greatest impact on OAR dose with negligible effect on the dose to nodal gross @entity5 volumes. In the era of IMRT, accounting for treatment-induced anatomical changes is important as focus is placed on minimizing the acute and long-term side effects of treatment.
