Proton Calorimetry/Meetings/2025/02/04

Minutes for UCL Proton Beam Therapy Group Meetings, 4th February

Present

Joe Bateman, Sonia Escribano, Simon Jolly, Raffaella Radogna (via Teams), Kirsty Hall (from Hamamatsu)

• Discussion with Kirsty Hall from Hamamatsu about photodiode arrays for scintillating fibre array to allow for better integration with QuARC.
• Kirsty to investigate two possible routes for going forward:
  • Possibility of having on board DDC or way of connecting S13885-128 photodiode array to DDC board.
  • Possibility of having surface mounted photodiodes (such as S12859-021) shrunk to a smaller size so that pixel pitch is comparable with 0.5mm fibre diameter.
• Also will look into questions Raffy has a about current experience with S13885-128 photodiode array, i.e.:
  • If observed response at saturation (e.g., decreasing signal rather than plateau or charge sharing among neighbours) is expected
  • How response of individual photodiodes within array vary and how to characterise this.

Raffaella Radogna

• Discussed with Bari mech eng Producing second prototype with resin material harry suggested - use inventor files (should be able to open fusion) will share with them once harry has finished with the fusion file
• Produce 2 new prototypes (frame + fibres + screws etc) and have one sent here
• Beam test in Trento
  • ~5s per beam
  • 10 beam deliveries each for CONV and UHDR calibrations (but may only need 8)
  • Background measurement at FSR for 12.5pC acquisition and for for FLASH
  • Happy to cut out as many pristine Bragg peaks as necessary to keep within FLASH time limits at Trento
  • I.e. 1 minute = 12 Bragg peaks at ~5s per measurements
  • Or Bragg peaks at lower measurement time per FLASH Bragg peak (i.e. <5 s)
  • Spot scanning at CONV dose rates
  • Potentially WET measurement of fibres at next UCLH if using giraffe on new QuARC electronics

Sonia Escribano

• Looking at new calibration method - now works with txt file that is generated with calibration values
• Problem with calibration
  • Need calibRMS - need separate file with these values?
    • Important for the fit
    • Include rms beneath calibration coefficients
  • How do we save name of header file for calibration file
  • Include in header file which files were used to generate calibration coefficients

• In new file structure maybe have new file directory for background data, i.e. calibration, background, date
  • For now do it manually
• New calibration and fitting procedure
  • generate calibration txt files using shoot throughs
  • Apply calibration values generates calibrated txt with every single measurement
  • Fit data averaged at 25 Hz -read calibrated data and fit at desired frequency (default 25hz)
• Things for new experiment
  • Raw data = 160*8 (hex length and 8 modules)
  • Calibration: 4 calibration_i files
  • Calibrate data
  • Initially split the raw data in two files for each Bragg peak
• Messaged harry about scintillators waiting to hear from John and Wayne but still hasn't sent them scintillator sheets yet
• Simon and Sonia to check final design on fusion

• How do you ensure consistency between modules if there's difference in coupling etc
  • Take Manchester data and do shoot-through calibration in current way then apply it to one of the shoot-through calibration files and see how it looks for each module (i.e. treat each module independently)
  • Need to find a way to scale to dose in each of the modules

Joe Bateman

• Re-did simulations in TOPAS (ongoing) and FRED with adjusted input beam size from DICOM for 3x3 and 5x5 cm box fields
  • Calculated new input beam size as: σ_P = (σ_iso × (SAD - d)) / SAD Where:
    • σ_P is spot size at position P
    • σ_iso is spot size from DICOM (at isocenter)
    • SAD is virtual source-axis distance
    • d is distance from isocenter to position P
  • Using d as 10 cm upstream from phantom surface

• Resulting shape looks more characteristic of TPS distribution.