ESTRO 37 Abstract book

S923

ESTRO 37

Oncology, Lund, Sweden 5 Fox Chase Cancer Center, Radiation Oncology, Philadelphia, USA 6 Wayne State University, Radiation Oncology, Detroit, USA 7 Ackerman Cancer Center, Radiation Oncology, Fernandina Beach, USA Purpose or Objective The AAPM convened a working group to define the media for TPS reference dose specification. We review the best practice for obtaining dose-to-tissue as the final result of dose calculations with commercial algorithms, following the requirement by the cooperative clinical trial groups. Material and Methods Different algorithms were analyzed one-by-one, based on the available peer-reviewed literature, manufacturer user guides and white papers, interviews with vendors, and comparisons with the Monte Carlo (MC) simulations done for this work. The output is a table specifying whether a multiplicative manual correction (0.99) to the TPS reference dose-to-water is necessary to obtain dose- to-tissue for each algorithm. Results For the photons, MC- and Boltzmann equation solver- based algorithms, as a rule, organically report dose to tissue and no manual correction is necessary, except for one system where the patient is inherently treated as water of varying density in MC simulations. Pencil beam (PB) algorithms, including AAA, report dose to water and require a manual correction. Superposition/Convolution (S/C) algorithms are most complicated in terms of dose reporting. Many, but not all, use tissue-specific mass attenuation coefficients for TERMA calculations and in theory report dose-to-tissue, although numerically this is not exact. For consistency we do not recommend a manual correction for S/C, except when final dose is unequivocally reported in water. A sample of recommendations for the correction application is listed in the Table.

Dose report ed by TPS Primari ly dose- to- water

Correcti on

Vendor System Algorithm

Primari ly dose- to- tissue

Elekta Monaco XVMC

X

1.0

Monaco Collapsed Cone

X

1.0

Conclusion The performance of an angular independent silicon detector (edgeless) developed by CMRP was investigated in two different Cyberknife machines (G4 and M6) with both collimator types (fixed cones and Iris). It has been found that the results obtained by edgeless detectors were in close agreement with the data obtained by common commercial detectors employed in Cyberknife QA and with TPS calculations, proving its suitability to be the candidate for dosimetric verification in non-isocentric SRS modalities. EP-1726 Implementation of AAPM recommendations on medium for TPS reference dose specification V. Feygelman 1 , S. Kry 2 , P. Balter 3 , T. Knöös 4 , C. Ma 5 , M. Snyder 6 , B. Tonner 7 , O. Vassiliev 3 1 H. Lee Moffit Cancer Center, Department of Radiation Oncology, Tampa, USA 2 M.D.Anderson Cancer Center, IROC, Houston, USA 3 M.D.Anderson Cancer Center, Radiation Oncology, Houston, USA 4 Skåne University Hospital and Lund University, Radiation

Monaco Pencil Beam

X

0.99

Oncentr a

Collapsed Cone Multi-Grid Superposit ion

X

1.0

XiO

X

0.99

Philips Pinnacl e

CCC

X

1.0

RaySear ch

RaySear ch

Collapsed Cone

X

0.99

Varian Eclipse Acuros XB

X

1.0

Eclipse AAA

X

0.99 0.99

Eclipse PBC,CDC X

X

0.99

ViewRay ViewRay Monte Carlo