Program Information
Beam Characterization of the GammaBeam 100-80 Cobalt-60 Unit
L Xu*, A Ciresianu , W Kaszuba , Best Theratronics, Ottawa, ON
Presentations
MO-RPM-GePD-T-2 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Lounge
Purpose: Best Theratronics recently brought to market the GammaBeam 100-80, an updated manual Cobalt-60 teletherapy unit. The unit features a touch screen control console, asymmetric collimators , and built-in backup power, which allows up to 4 hours of clinical use during power outages. The source to diaphragm distance (SDD) is kept at 45 cm. The unit is only available in 80 cm source to axis (SAD) configuration. The beam characteristics of this unit is reported.
Methods: Percentage depth doses and dose profiles were collected using an IBA Blue Phantom equipped with a photon diode (PDF3G). Results are compared to published Cobalt-60 beam characteristics such as BJR Supplement 25. Beam flatness, symmetry and penumbra were measured using IEC 976 definitions and prescribed test conditions. PDD's were measured both with and without the electron filter, and these data were used to determine skin dose at an effective depth of 0.5 mm.
Results: Percent depth doses were in good agreement with BJR supplement 25 data. Beam flatness and symmetry showed little change from previous Cobalt-60 units such as THERATRON 780C and the currently available Equinox 80. Measured Penumbras were comparable to previous Cobalt-60 units with 45 cm source to diaphragm distance, but slightly larger than the Equinox 80 unit, which has a source to diaphragm distance of 50 cm. This increased penumbra is an expected trade-off from increased patient clearance. Skin dose measurements suggest that the IEC 60601-2-11 requirement of 90% for the maximum available field size may be exceeded for an open field, but this requirement is met when an electron filter is used.
Conclusion: Our beam physics measurements demonstrate that this unit does not differ significantly from previous Cobalt-60 units. The use of an electron filter is recommended when field sizes greater than 20 x 20 cm^2 are used.
Funding Support, Disclosures, and Conflict of Interest: The authors are employees of Best Theratronics.
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