title: Design and implementation of a "cheese" phantom-based Tomotherapy TLD dose intercomparison.
abstract: BACKGROUND
  The unique beam-delivery technique of Tomotherapy machines (Accuray Inc., Sunnyvale, Calif.) necessitates tailored quality assurance. This requirement also applies to external dose intercomparisons. Therefore, the aim of the 2014 SSRMP (Swiss Society of Radiobiology and Medical Physics) dosimetry intercomparison was to compare two set-ups with different phantoms.
  
  
  METHODS
  A small cylindrical Perspex phantom, which is similar to the IROC phantom (Imaging and Radiation Oncology Core, Houston, Tex.), and the "cheese" phantom, which is provided by the Tomotherapy manufacturer to all institutions, were used. The standard calibration plans for the TomoHelical and TomoDirect irradiation techniques were applied. These plans are routinely used for dose output calibration in Tomotherapy institutions. We tested 20 Tomotherapy machines in Germany and Switzerland. The ratio of the measured (Dm) to the calculated (Dc) dose was assessed for both phantoms and irradiation techniques. The Dm/Dc distributions were determined to compare the suitability of the measurement set-ups investigated.
  
  
  RESULTS
  The standard deviations of the TLD-measured (thermoluminescent dosimetry) Dm/Dc ratios for the "cheese" phantom were 1.9 % for the TomoHelical (19 measurements) and 1.2 % (11 measurements) for the TomoDirect irradiation techniques. The corresponding ratios for the Perspex phantom were 2.8 % (18 measurements) and 1.8 % (11 measurements).
  
  
  CONCLUSIONS
  Compared with the Perspex phantom-based set-up, the "cheese" phantom-based set-up without individual planning was demonstrated to be more suitable for Tomotherapy dose checks. Future SSRMP dosimetry intercomparisons for Tomotherapy machines will therefore be based on the "cheese" phantom set-up.
authors.affiliation: Department of Radiation Oncology, Medical Physics Group, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland. johann.schiefer@kssg.ch.
authors.forename: Hans
authors.initials: H
authors.lastname: Schiefer
authors.affiliation: Department of Radiation Oncology, Medical Physics Group, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland.
authors.forename: Konrad
authors.initials: K
authors.lastname: Buchauer
authors.affiliation: Department of Radiation Oncology, Medical Physics Group, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Heinze
authors.affiliation: Department of Radiation Oncology, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland.
authors.forename: Guido
authors.initials: G
authors.lastname: Henke
authors.affiliation: Department of Radiation Oncology, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Plasswilm
mesh_terms: D032701:Biomimetics / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013819:Thermoluminescent Dosimetry / Q000295:instrumentation*
keywords: Cylinder phantom; Dose intercomparison; TLD, thermoluminescent dosimetry; Tomotherapy; “Cheese” phantom