Original paper| Volume 77, P181-186, September 2020

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Clinical application of a gantry-attachable plastic scintillating plate dosimetry system in pencil beam scanning proton therapy beam monitoring

Published:August 29, 2020DOI:


      • Pioneering treatment beam monitoring system for intensity modulated proton therapy.
      • Gantry attachable plastic scintillating plate dosimetry monitoring beam fluences.
      • Cost-effective dosimetry system for pencil beam scanning proton therapy.
      • Possible solution for an independent verification of individual energy layers.



      The entrance beam fluence of therapeutic proton scanning beams can be monitored using a gantry-attachable plastic scintillating plate (GAPSP). This study evaluated the clinical application of the GAPSP using a method that measures intensity modulated proton therapy (IMPT) beams for patient treatment.


      IMPT beams for the treatment of nine patients, at sites that included the spine, head and neck, pelvis, and lung, were measured using the GAPSP, composed of an EJ-212 plastic scintillator and a CMOS camera. All energy layers distinguished by the GAPSP were accumulated to determine the dose distribution of the treatment field. The evaluated fields were compared with reference dose maps verified by quality assurance.


      Comparison of dose distributions of evaluation treatment fields with reference dose distributions showed that the 3%/1 mm average gamma passing rate was 96.4%, independent of the treatment site, energy range and field size. When dose distributions were evaluated using the same criteria for each energy layer, the average gamma passing rate was 91.7%.


      The GAPSP is a suitable, low-cost method for monitoring pencil beam scanning proton therapy, especially for non-spot scanning or additional collimation. The GAPSP can also estimate the treatment beam by the energy layer, a feature not common to other proton dosimetry tools.



      GAPSP (Gantry attachable plastic scintillating plate), PBS (Pencil beam scanning), QA (Quality assurance), CT (Computed tomography), EPID (Electronic portal imaging device), IMPT (Intensity modulated proton therapy), CMOS (Complementary metal-oxide semiconductor), fps (Frames per second), AVF (Azimuthally varying field), PTC (Proton therapy center), ESS (Energy selection system), SOBP (Spread-out Bragg peak), TPS (Treatment planning system), H&N (Head and neck)
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