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Commissioning of An Equinox-100 Cobalt-60 Radiotherapy Unit in the Eclipse Treatment Planning System

L Schreiner

C Jechel1 , T Bulenga2 , C Joshi1,2 , G Salomons1,2 , L J Schreiner1,2*, (1) Cancer Center of Southeastern Ontario, Kingston, ON (2) Queen's University, Kingston, ON


SU-I-GPD-T-446 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Recent efforts to deliver modern conformal treatments using cobalt-60 teletherapy equipment have highlighted the need for treatment planning software specific to cobalt-60 radiotherapy. Open beam treatments delivered by an Equinox-100 cobalt-60 teletherapy unit upgraded from a T780c (Best Theratronics, Kanata, ON, Canada) were commissioned within the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA, USA) which has a seldom-used cobalt-60 dose calculation module.

Methods: Open beam commissioning data were measured using a 0.13 cm³ ion chamber in a water tank. The commissioning beam data were imported into the Eclipse treatment planning system (TPS). A primary calibration was also carried out to establish the reference dose rate. Numerous experiments were performed to test the performance of the Eclipse TPS when calculating dose for cobalt-60 beams under various conditions. For example, dose profiles were measured downstream of lung and bone equivalent cylinders in a water tank to compare to dose calculations in heterogeneous media. Treatment plans were validated against delivery using a water-equivalent phantom housing a 0.6 cm³ ion chamber and radiochromic film.

Results: Measured and calculated percent depth-dose profiles and historical cobalt-60 reference data from the British Journal of Radiology Supplement 25 show excellent agreement. Dose measurements downstream of tissue-equivalent cylinders agree within 2% suggesting Eclipse can effectively model the cobalt-60 beam in heterogeneous media. Ion chamber measurements for 4-field box treatment techniques agree with calculated dose within 1.5% for individual fields and 0.2% for entire treatments, while film measurements indicate that Eclipse is able to accurately calculate dose at the field edges.

Conclusion: Cobalt-60 treatment planning in the Eclipse treatment planning system is appropriate for forward planning of simple open beam treatments. Our next steps will involve the installation and modelling of a multi-leaf collimator to study cobalt-60 3D conformal radiotherapy and intensity modulated radiotherapy.

Funding Support, Disclosures, and Conflict of Interest: We acknowledge and appreciate support from OCAIRO (through the Ontario Research Excellence Fund, with an industrial partnership with Best Theratronics) and CIHR (Canadian Institutes for Health Research).

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