Commissioning of an Upgraded Equinox-100 Cobalt-60 Radiation Therapy Unit in the Varian Eclipse Treatment Planning System

Abstract

The introduction of Cobalt 60 (Co 60) units in the 1950s established megavoltage radiation therapy worldwide. Unfortunately, advances for the Co 60 radiation treatment units were not heavily pursued over the years and Co 60 units have been steadily replaced by clinical linear accelerators (linacs) x ray systems, which can offer more precise radiation treatments. The Medical Physics Department at the Cancer Centre of Southeastern Ontario (CCSEO) has shown, however, that the Co 60 unit can be developed to enable modern radiation treatments similar to linacs. In 2015, the CCSEO collaborated with Best Theratronics (Kanata, Ontario) to upgrade a Theratron 780C Co 60 radiation therapy unit to an Equinox 100 external beam radiation therapy system. This was the first upgrade of a T780C Co-60 unit in the world, which represents an exciting opportunity to advance Co 60 radiation therapy to provide treatments equivalent to those available from modern linacs. In this thesis, an upgraded Equinox 100 unit is commissioned in the Varian Eclipse treatment planning systems (TPS) to ascertain if the Analytical Anisotropic Algorithm (AAA) in the Eclipse could be used to generate Co 60 3D based treatment plans. Firstly, mechanical commissioning of the upgraded unit was performed according to Task Group 45 report (AAPM) recommendations. Secondly, various commissioning beam measurements were acquired using an ion chamber in standard water phantom on the upgraded unit to model the beams in the Eclipse TPS. The AAA validation was performed to test the accuracy of the Eclipse TPS dose prediction based on the local percentage differences between the measurements and the Eclipse model calculations in various simple open and blocked plans using the ion chamber in the phantom. The mechanical acceptance tests are generally comparable to clinical linac tolerances, which suggest that upgrading conventional Co 60 units may improve treatments without compromising the mechanical accuracy. Similarly, the Eclipse model calculations of the validation plans show overall excellent agreements with measurements within the recommended clinical criteria for large fields starting at 5 × 5 cm2. This suggests that the Eclipse TPS is appropriate for forward planning of Co 60 3D conformal radiation therapy for large fields. Further investigations for small fields are required.