ArcCheck bulk density
David Eaton
Can I ask other Pinnacle and ArcCheck users: do you all use the scaled electron density (1.15g/cc) to model ArcCheck in the TPS, including the MultiPlug or CavityPlug inserts, which are also PMMA.
If so, does anyone know what is the underlying reason for this? In a Sun Nuclear document (appl note 1220029), it discusses the difficulties of modelling PMMA, but for Pinnacle just refers to a publication who used 1.15 (by chance?) and got good results, even though for most materials it is the physical density which is entered into Pinnacle. Am I missing something?
Best regards,
David Eaton
Mount Vernon Hospital
London, UK
Feygelman, Vladimir
Here is the underlying reason:
Radiological properties in the radiotherapy MV energy range are controlled by electron density. For most materials, relative densities track. PMMA is one of those, where relative electron and physical densities diverge more than in other commonly encountered media. We verified that for a Pinnacle system that models PDD in water well, the best results for “heavy water” representation of the ArcCHECK PMMA is with 1.147 rel density. Verification was based on the exit to entrance dose measurements with an ion chamber in a homogeneous PMMA cylinder of ArcCHECK dimensions.
VF
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