Monte Carlo evaluation of collapsed-cone convolution calculations in head and neck radiotherapy treatment plans
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The presence of air and bone interfaces makes the dose distribution for head and neck cancer treatments dif- ficult to accurately predict. This study compared planning sys- tem dose calculations using the collapsed-cone convolution algo- rithm with EGSnrc Monte Carlo simulation results obtained us- ing the Monte Carlo DICOM ToolKit software, for one orophar- ynx, two paranasal sinus and three nodal treatment plans. The difference between median doses obtained from the treatment planning and Monte Carlo calculations was found to be greatest in two bilateral treatments: 4.8% for a retropharyngeal node ir- radiation and 6.7% for an ethmoid paranasal sinus treatment. These deviations in median dose were smaller for two unilat- eral treatments: 0.8% for an infraclavicular node irradiation and 2.8% for a cervical node treatment. Examination of iso- dose distributions indicated that the largest deviations between Monte Carlo simulation and collapsed-cone convolution calcu- lations were seen in the bilateral treatments, where the increase in calculated dose beyond air cavities was most significant.
KeywordsRadiation therapy treatment planning dosimetry
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