Comparison of dose evaluation using difference voxel sizes in Stereotactic Radiotherapy Planning
PO-1866
Abstract
Comparison of dose evaluation using difference voxel sizes in Stereotactic Radiotherapy Planning
Authors: LAI|, Tin Lok(1)*[tinloklai@hotmail.com];Tsang|, Edna(2);
(1)GensisCare Australia, WROC, Melbourne, Australia;(2)GensisCare Australia, Epping ROC, Melbourne, Australia;
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Purpose or Objective
Genesis Care (GC) Australia has developed a national stereotactic team responsible for planning stereotactic brain radiotherapy using Monaco TPS for all Elekta based centres across Australia. All reporting for through Monaco is done using a 0.1cc volumetric matrix. GC Victoria provides stereotactic radiotherapy (SRT) across all sites using Pinnacle TPS and Varian Truebeam linear accelerators. Pinnacle TPS allow dose volume to be reported to as small as 0.01cc. Many international clinical trial report doses to 0.03cc whilst the AAPM Task Group 101 (2010) defined “point” as 0.035cc or less. This study aims to evaluate whether there are major differences in OARs dose reporting between voxel resolution sizes of 0.1cc Vs 0.03cc
Material and Methods
22 SRT brain patients planned using Pinnacle TPS were reviewed retrospectively. A script was created to report OAR using dose to 0.1cc (D0.1cc), dose to 0.03cc (D0.03cc) and maximum point dose (DMax). DMax in this case is defined as the maximum dose reported on the dose volume histogram in Pinnacle. The OARs reported include the left and right optic nerves, optic chiasm, left and right lens and brainstem. Data are entered onto spreadsheet for comparison.
Results
Out of 22 samples, 5 (22.7%) showed 1 to 2Gy discrepancy for at least one OAR and 3 (13.6%) showed larger than 2Gy difference between values obtained using D0.1cc and D0.03cc voxels. The reminder of the cohort showed less than 1Gy discrepancy. DMax figures were provided as a supplementary comparison
Conclusion
There are concerning factors when evaluating DVH data using larger voxels. This study demonstrated over 20% of the studied population have recorded higher dose received by an OAR by up 2Gy using a finer voxel resolution. This translates to a 1 in 5 chances of potential misinterpretation. A possible explanation to this observation could be related to the proximity of the OAR/s to the target volume where smaller voxels will be required to confidently evaluate dose within or near the high gradient zone. Clinicians should exercise higher degree of caution when evaluating DVH data in situation where the target is near any OAR.