Po‐Thur Eve General‐06: Experimental Validation of the Eclipse AAA Algorithm

Abstract

The Medical Physics departments of the Tom Baker Cancer Center (TBCC) and the Cross Cancer Institute (CCI) independently performed preliminary evaluation of the new Analytical Anisotropic Algorithm (AAA) implemented in Varian's Eclispe (v. 6.0) treatment planning system (TPS). The TPS was pre‐commissioned with “Golden Beam Data” from the vendor. We measured central and off‐axis profiles in several beam configurations including: open square, rectangular and asymmetric (half‐blocked) beams; wedged square and half‐blocked beams; square fields at three SSDs; open and wedged oblique beams; irregular field defined by MLC and cerrobend blocks. All measurements were performed on Varian 2100EX linear accelerators. Measurements were made to assess the dose in heterogeneous media at both the CCI (CIRS Thorax IMRT phantom) and at the TBCC (TLDs in a Rando phantom). Profiles were evaluated in the buildup, penumbra, inner and outer beam regions as per AAPM Task Group 53. Measured and calculated profiles agreement was very good in all regions except for the inner beam region at the CCI, attributed a difference in interpolation schemes at the two institutions and the large volume ion chamber used for measurements. The AAA penumbra was also found to be steeper than measured penumbra since AAA was pre‐commissioned using diode measurements. Total scatter factors for most measurements differed by less than 2% from the calculated ones except for the hard wedges where differences up to 4% were found. Anthropomorphic phantoms measurements differed from AAA by as much as 5.6%. Funding provided by Varian.

Accuracy of out-of-field dose calculations by a commercial treatment planning system

“…Numerous previous studies have demonstrated that the Eclipse AAA accurately calculates the dose inside the treatment field and within the penumbra region in both water and heterogeneous media (Aspradakis et al 2003, Sievinen et al 2005, Fogliata et al 2006, 2008, Huyskens et al 2006, Murray et al 2006, Van Esch et al 2006, Breitman et al 2007, Tillikainen et al 2008). In general, the inaccuracies reported in this study are for low dose regions at large distances outside the irradiation target and are of modest significance when considering acute toxicities.…”

Dose‐shaping using targeted sparse optimization

“…All clinical plans were optimized using Varian's Eclipse treatment planning system by an experienced dose planner, and clinical dose maps were calculated using the AAA algorithm. 29 We utilized CERR's QIB algorithm 30 for dose calculation, because it was not possible to obtain the pertinent dose deposition matrices from Eclipse. As such, algorithmic dissimilarity between Eclipse AAA and CERR QIB was a potential issue.…”