Proton Calorimetry/Meetings/2017/04/28

Minutes for UCL Proton Dose Build-up Meeting, 28th April 2017 (Skype)

Present

Richard Amos, Adam Gibson, Jenny Griffiths, Simon Jolly, Laurent Kelleter

We have graph of amount of buildup against energy. Can we get a graph of depth of buildup (perhaps depth at which buildup reaches 95% of expected value) or something? For electron and proton buildup? That’s probably reanalysing existing Bragg peaks.

Verify the results showing the effect of air — it’s surprising that air appears to have no effect. Perhaps try 1m of air, and look for heavy particles hitting skin as a result of interactions with air.

Energy spectrum of electrons/secondary protons as a function of depth for 60, 150, 230 MeV beams. Identify particles which are generated. Find LET for each type. Give contribution to dose from each particle.

Can we predict RBE given LET? Literature is unclear, but probably for electrons and protons, not for other particles without a lot of work.

For clinical relevance, can we calculate:

• Buildup for SOBP (say choose 50% modulation at different energies and plot buildup against maximum energy of SOBP)
• Buildup for SOBP (say choose a single energy and for different modulations from 0-100% or depth, plot graph of buildup v % modulation)

(By modulation, I mean the depth of the SOBP as a percentage of the total depth, ie a SOBP giving maximum dose at depths from 5cm to 10cm would have a modulation of 50%)

Laurent's presentation: Effect of air on electron build-up, influence of range cut on electron dose and quantization of build-up versus energy from 40MeV to 300MeV.

Relevant References

• Gottschalk B, E W Cascio, J Daartz, and M S Wagner (2015), "On the nuclear halo of a proton pencil beam stopping in water" Physics in Medicine and Biology 60(14) p.5627.
• Newhauser W D and R Zhang (2015), "The physics of proton therapy" Physics in Medicine and Biology 60(8) R155-
• Apipunyasopon L, S Srisatit, and N Phaisangittisakul (2013), "An investigation of the depth dose in the build-up region, and surface dose for a 6-MV therapeutic photon beam: Monte Carlo simulation and measurements" Journal of Radiation Research 54(2) 374-382.
• Carlsson C A and G A Carlsson (1977), "Proton dosimetry with 185 MeV protons. Dose buildup from secondary protons and recoil electrons" Health Phys. 33(57) 481-484.
• Kry S F, S A Smith, R Weathers, and M Stovall (2012), "Skin dose during radiotherapy: a summary and general estimation technique" Journal of Applied Clinical Medical Physics; Vol 13, No 3 (2012)
• Paganetti H (2011), "Proton therapy physics" Proton Therapy Physics. Series: Series in Medical Physics and Biomedical Engineering, ISBN: 978-1-4398-3644-6. CRC Press, Edited by Harald Paganetti 1
• Penoncello G P and G X Ding (2016), "Skin dose differences between intensity-modulated radiation therapy and volumetric-modulated arc therapy and between boost and integrated treatment regimens for treating head and neck and other cancer sites in patients" Medical Dosimetry 41(1) 80-86.

Laurent's meeting presentations

• 22/03/2017: Reproduction of Ben Tham's build-up results and new definition of build-up.
• 29/03/2017: Differentiation between electron and nuclear build-up, reproduction of Ben's secondary particle species plot.
• 27/04/2017: Effect of air on electron build-up, influence of range cut on electron dose and quantization of build-up versus energy from 40MeV to 300MeV.
• 10/05/2017: Abstract of Geant4 fun facts, detailed analysis of secondary particles, LET-weighted energy deposition, air effect on electron and nuclear build-up, introduction of 95% threshold.