Design and implementation of a "cheese" phantom-based Tomotherapy TLD dose intercomparison.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• TomoTherapy machines require specific quality assurance (QA) protocols due to their unique beam delivery.
• External dose intercomparisons are crucial for ensuring accurate radiation delivery.
• The 2014 Swiss Society of Radiobiology and Medical Physics (SSRMP) dosimetry intercomparison aimed to evaluate different phantom setups for TomoTherapy QA.

Purpose of the Study:

• To compare the suitability of two different phantom setups for external dose intercomparisons in TomoTherapy.
• To assess the accuracy of dose measurements using the standard calibration plans for TomoHelical and TomoDirect techniques.

Main Methods:

• Two phantoms were used: a cylindrical Perspex phantom and the manufacturer-provided "cheese" phantom.
• Standard calibration plans for TomoHelical and TomoDirect irradiation were applied.
• Thermoluminescent dosimetry (TLD) was used to measure the dose, and the ratio of measured dose (Dm) to calculated dose (Dc) was assessed for 20 TomoTherapy machines.

Main Results:

• The standard deviation of Dm/Dc ratios for the "cheese" phantom was 1.9% for TomoHelical and 1.2% for TomoDirect.
• For the Perspex phantom, the standard deviations were 2.8% for TomoHelical and 1.8% for TomoDirect.
• The "cheese" phantom demonstrated lower variability in dose measurements.

Conclusions:

• The "cheese" phantom setup, without individual planning, is more suitable for TomoTherapy dose checks compared to the Perspex phantom setup.
• Future SSRMP dosimetry intercomparisons for TomoTherapy will utilize the "cheese" phantom setup.