Measurements of the Time Spread of Proton Pencil Beams at a Clinical Therapy Facility


Measurements of the Time Spread of Proton Pencil Beams at a Clinical Therapy Facility

Petzoldt, J.; Roemer, K. E.; Kormoll, T.; Enghardt, W.; Fiedler, F.; Helmbrecht, S.; Hueso-González, F.; Golnik, C.; Rohling, H.; Werner, T.; Pausch, G.

In proton therapy, high dose conformality and the finite range of the projectiles are exploited to reduce the dosage to healthy tissue while increasing the dose inside the tumor volume compared to conventional radiotherapy. However, those benefits can be diminished by range uncertainties. An online range verification and in-vivo dosimetry is therefore highly desired.
The prompt gamma ray timing (PGT) method utilizes the detection time of high energetic photons emitted during treatment. The time distribution of the gamma rays contains essential information about the range of the protons. However, PGT spectra are smeared by the time spread of the proton bunches. Knowledge about this time spread would help to disentangle the PGT data and to give better input parameters to simulation procedures.
At the UniversitaetsProtonenTherapieDresden (Dresden, Germany), a dedicated experiment was realized to measure the time spread of a clinical proton pencil beam created by a Cyclone 230 fixed energy cyclotron from Ion Beam Applications. Two phoswich detectors each made out of plastic scintillator and BGO were placed under 90 degrees to detect coincident protons originating from elastic pp-scattering at a thin slice of PMMA. The time spread was measured for incident proton energies between 70 MeV and 225 MeV as well as for several positions of the momentum limiting slits of the energy selection system. Additionally, the absolute transmission of protons from point of extraction to beam exit was determined.
Summarizing, the measured data will help to create reasonable range verification procedures using the PGT method in clinical routine.

Keywords: proton therapy; prompt gamma ray timing

  • Lecture (Conference)
    2015 IEEE Nuclear Science Symposium & Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA

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Publ.-Id: 23140