SU‐E‐T‐727: Evaluation of Eclipse AAA Dose Calculation Accuracy in the Presence of a Titanium Spinal Fixation Device

T. he, W. Laub, S. Pillai, Brian Ragel, C. Kubicky

Research output: Contribution to journalArticle

Abstract

Purpose: To determine whether the Eclipse's AAA algorithm can accurately predict doses in the presence of hardware. Methods: A titanium spinal fixation device was attached to a spine model to mimic its spatial orientation in patient. The model was immobilized to a plastic plate to form a rigid device. Posterior spine irradiation was simulated by positioning the device inside a PTW water tank with 270 degree gantry irradiation. Absolute doses and relative dose distributions were measured using ion chamber and OSLD. Lateral spine irradiation was simulated by placing the device in a water tank with 0 degree gantry irradiation. Planar doses were measured using a SunNuclear MapCheck device for 6 MV open and intensity‐modulated beams. Above experiement setups were reproduced in Eclipse from CT images with correct electron densities assigned to materials used in the experiments, e.g. electron density 4.0 for the titanium device. Doses were calculated using AAA 8.9 algorithm and compared with measurements. Results: In posterior spine irradiation, doses were measured respectively for 7×10 and 10×15 cm open fields. Measured dose outputs agreed with calculations within 2.5% at all selected locations along the spinal canal and under the titanium cage. Excellent agreements (< 1%) on relative depth doses along beam axis were observed. Dose profiles at depths below the device generally agreed with calculations within 3%, although discrepancies in some regions were as large as 5%. Eclipse's AAA algorithm seems to predict doses well in the regions shadowed by the titanium material while under‐estimate doses in adjacent regions outside the shadows. In lateral spine irradiation, the 3mm/3% gamma analysis demonstrated > 98% agreements between the measured and the calculated planar doses for all tested open and intensity‐modulated fields. Conclusions: Eclipse's AAA 8.9 algorithm can reasonably accurately predict doses in the spine region in the presence of a titanium spinal fixation device.

Original languageEnglish (US)
Number of pages1
JournalMedical Physics
Volume38
Issue number6
DOIs
StatePublished - Jun 2011

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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