Proton Calorimetry/Meetings/2017/05/24

Minutes for UCL Proton Calorimetry Meeting, 24th May 2017 (D17, Physics & Astronomy, UCL)

Present

Simon Jolly, Laurent Kelleter, Anastasia Basharina-Freshville, Jordan Silverman

ABF:

• Full data acquisition now running completely over the network:
  • Single 50m cat6a cable runs into treatment room.
  • Network hub in treatment room connects to DAQ PC/laptop and scope.
  • DAQ PC connects to Caen digitiser, HV and detector emulator.
  • Connect to scope and DAQ PC via Windows Remote Desktop.
• Looking at effect of splitting signals for remote testing:
  • Need to split signal from PMT to Caen digitiser and scope with 50 Ω splitter.

LK:

• Looking at dose build-up effect in proton therapy and secondary particles:
  • Electron contribution to dose increases with smaller range cut: more short-range electrons produced.
  • Threshold at ~1 micron: for shorter range cuts, no difference in dose. Probably due to 990 eV "safety threshold" for ionisation in Geant4.
• Fun facts about Geant4:
  • Deposited energy ignores energy of secondary particles.
  • Energy loss records energy of tracked particle and its secondaries BUT in the place where they are produced! (not where the secondaries deposit their energy).
  • Range cut: Only secondaries which are expected to travel further then the range cut will be tracked BUT this theoretically only applies to secondary electrons, positron, gammas and protons.
  • To be more clear: exotic secondaries as neutrons will always be produced and tracked, independently from the range cut. No influence of the range cut on the number of secondary protons seen.
  • There is a safety energy threshold for the production of secondary particles of 990 eV since otherwise Geant4 models might fail.
• LET-weighted results show much higher contribution from hadronic secondaries, particularly at high energy.
• Range cut effects not clearly understood: ABF suggests contacting Ben Morgan at Warwick.

SJ:

• SJ and ABF visiting Nuvia a.s. on Monday 29th May. SJ needs to pull his finger out and book his flights...
• SJ talking at UCL Medical Physics PART Group meeting; LK may be press-ganged into joining.
• During 3-day trip to PSI, discussed collaboration with Ros Perrin, Tony Lomax and Sairos Safai to look at effect of lung motion interplay during PBT dose delivery:
  • LuCa lung phantom is tissue equivalent with air-driven breathing cycle: photos and movies can be found here.
  • Plastic scintillator disc would be inserted into phantom and irradiated during treatment: light emission imaged by camera.
  • PSI would look after camera, mounting and optics.
  • UCL (ie. LK) would write the code to reconstruct the dose distribution in each slice from camera movie by fitting to quenched light output.
  • Approximately 3 months total work for LK: would include time spent at PSI as part of OMA placement.
  • ABF also interested in spending time at PSI.