Shielding measurements for a proton therapy facility
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Shielding Measurements For A Proton Therapy Facility. S. Avery, K. P. Risolo, M. Bartels, C. Ainsley, J McDonough, R. L. Maughan University of Pennsylvania. Introduction I/II. Penn’s Roberts Proton Therapy Center 5 Treatment rooms

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Shielding measurements for a proton therapy facility

Shielding Measurements For A Proton Therapy Facility

S. Avery, K. P. Risolo, M. Bartels, C. Ainsley, J McDonough, R. L. Maughan

University of Pennsylvania


Introduction i ii
Introduction I/II

  • Penn’s Roberts Proton Therapy Center

    • 5 Treatment rooms

    • Single Scattering, Double Scattering, Uniform Scanning, Modulated Scanning

  • Double scatting beam line components

    • First and second scatters

    • Modulator wheel

    • Primary jaws

    • Collimator (MLCs)

    • Compensator


Introduction ii ii
Introduction II/II

  • Shielding calculations performed using analytical methods including neutron spectra

  • Calculations performed for IBA double scattering mode

    • Max beam current

    • At any particular energy

    • Usage factors

    • Beam direction

    • Occupancy factors

    • Workload




Methods and materials iii v
Methods and Materials III/V

  • Both photon sensitive and neutron sensitive detectors required

    • Total instantaneous dose equivalent obtained from their sum

  • Neutron detection

    • Prescila detector for up to 100MeV

  • Photon detection

    • Ludum ion chamber


Methods and materials iv v
Methods and Materials IV/V

  • Integrated dose equivalent readings

    • Neutrak Dosimeters inside a Luxel plastic blister pack

      • Two types of detectors used:

        • Those sensitive to 40 keV to 40 MeV with a dose range of 0.2 mSv to 250 mSv

        • Those sensitive to fast, intermediate, and thermal neutrons with a dose range of 0.1 mSv to 250 mSv


Methods and materials v v
Methods and Materials V/V

  • Detectors placed at various locations around facility

    • Primarily around treatment rooms 1 and 5

    • Fast neutron detectors left in for one month

    • Fast, intermediate, and thermal neutrons left in place for an additional month

    • Control detectors for each type


Results i v
Results I/V

  • A modified form of NCRP Report No. 51 equation used to calculate instantaneous dose equivalent index rate

  • Φp derived from Monte Carlo using GEANT4

  • Np is proton beam intensity at the neutron source, related to beam current

  • Measurements normalized to a beam current of 6 nA emerging from the nozzle


Results ii v
Results II/V

  • Points outside the cyclotron and ESS showed shielding to be more than adequate with only one reading above background

    • Reading 4-5 times below the calculated value

  • Points outside TR1 showed 2 readings below background, with 6 other readings found below their calculated values

  • Measurements with the dose badges showed only photon irrdatiation


Results iii v
Results III/V

  • Neutron dose equivalent transmission data from NCRP Report 144 used with the analytic method

  • Measurements made under identical gantry angle and proton energy conditions for both neutron and gamma ray dose

  • The instantaneous and integrated two month dose equivalent data allows for calculate of annual dose equivalents




Conclusions
Conclusions

  • Shielding in place at Roberts Proton Center is more than adequate

    • Conservative shielding calculations

      • Measured vs. Analytic

  • Film dosimeters questionable

    • Only saw photon component


Concluding remarks
Concluding Remarks

  • Thanks to the authors Dr. Avery, Dr. Maughan, Dr. McDonough, Dr. Ainsley, and Mr. Bartels

  • Thanks to the HPS


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