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LhARA ionacoustic dose profiling meeting: 01Sep21; 09:00 BST
Notes
Ion Acoustic Imaging Meeting
Present: Jeff Bamber, Ben Cox, Ken Long, John Matheson
Discussion To get a handle on the acoustic signal from the LhARA Stage 1 beam Ken is running GEANT simulations. These will be an input for Ben’s acoustic simulations. We need to have a plan for the proof of principle setup, which may partially be based on material to be circulated by Jamie on what has already been shown in the literature. We need something believable on the timescale of a few weeks – Ken and Ben will meet again on Friday to take the simulations forward, hopefully putting some numbers on the acoustic frequencies and pressures of the low energy beam by next meeting (15/09/21). The GEANT simulations use typically 1E4 protons, to give reasonably smooth distributions, whilst the expected LhARA pulse is 1E9 protons. Other facilities where we might test will be considered individually. If there is a threshold on detectability of the acoustic signal, that tells us what minimum beam intensity would be needed to perform a given experiment. Jeff believes he can probably estimate well enough but would like to see the simulation results to confirm.
WRT finishing SmartPhantom, RAL can provide circa £2K which seems reasonable for consumables, etc. Scintillating fibre, carbon fibre supports, tooling for winding all exist at IC and could be shipped back to RAL. Liam Cooper at RAL has previous experience on this – John to talk to Liam. John and Ken to talk at RAL tomorrow. John had received an e-mail from Richard Smith (RAL Manufacturing Facility) and it looks like technical effort could be available if it can be paid for. There is a possibility of some limited money being available via Fergus Wilson (RAL PPD). John to follow up. Jeff asked about the spatial resolution of the fibre planes and whether they offered single photon detection. Ken replied that they were to use 250 micron fibre and were only intended to be a cheap and cheerful way of profiling the beam, to be thrown away in case of radiation damage. Readout is via cheap CMOS camera. Single photon detection is well understood but expensive. Jeff will try to write something for next week’s meeting, to share plans with other WPs. He confirmed that Emma Harris will take on some of his role if needed. Emma’s experience is in image guidance for adaptive radiotherapy and she is already involved in a European project which contains an element of ion acoustic imaging.
Last week there was a discussion about contact with AVO https://www.avoplc.com/en-gb/ and Tony Price will follow up. AVO could give us access to suitable test beams and may have their own interest in ion acoustic imaging.
Actions: KL – circulate long version of GC proposal JG – circulate literature on existing lab ion acoustic imaging setups KL, BC meet to discuss putting the parts of the simulation together to get the acoustic pressure for the low energy beam JM, KL meet at RAL to discuss taking forward the SmartPhantom. JM talk to Liam Cooper, Fergus Wilson. JB to connect KL with Emma Harris and prepare some slides for next week if possible
Present: Jeff Bamber, Ben Cox, Jamie Guggenheim, Ken Long, John Matheson
Apologies: none
- Introduction, notes and actions of previous meeting: KL/All
- None recorded.
- Update on simulation of beam: AMLR, KK, JMcG
- Proposal planning : JB, JM, All
- Next steps--discussion: All
Ken will take over the GEANT simulations as Josie’s placement is coming to an end. The proton-in-water simulations may not include a container so this needs to be added in case it causes reverb of the acoustic signals. Jeff commented that lagging the tank and time gating are among the approaches used to minimise this.
Jeff gave a recap of the last meeting, in which we discussed the GC call; this could be a basis for the current Proposal. A shortened version is on the Wiki, Jeff will circulate the full version.
Jeff suggested that LhARA should aim to address real challenges in the field of ion acoustic imaging:
- How to optimise for weak signals inc. multi-element transducer arrays
- Available transducers most sensitive at high frequency – could tie in with short (10ns) pulses from proton beam
- Utilise the full frequency range of the acoustic signals to get anatomical information and correlate the proton dose maps to anatomy – couple the ion-acoustic imaging to conventional ultrasound imaging techniques
- Microbeams look good for ion acoustic imaging (generate high frequencies) and for radiobiological effectiveness
The ideal transducer array would exploit the max. range of frequencies, from the path of the protons before the Bragg Peak, as well as the peak itself. Ideal arrangement is a sphere with a hole for the beam; this ideally needs a mechanical positioning (translation) capability. A first (cheaper) stage could be a ring array. Similar approaches exist in the literature for breast imaging.
The ultimate development might be a fully conformable array (“ultrasound blanket”).
Ken raised the issue of automation to allow multiple irradiations without intervention, e.g. the robotic arm at Manchester for changing samples. Jeff commented that systems are available commercially but do require intervention – array is split to introduce the experimental animal, suspended in coupling fluid. The animal is supplied with air and anaesthetic via a mask. Not really high throughput yet. https://www.ithera-medical.com/products/preclinical-research/msot-invision/
Plastic isn’t a great material acoustically – for cell culture irradiations a phantom is used which is constructed to give the correct acoustic compatibility.
Ken commented that we need to simulate the signals we have to detect, for the Proposal. Preliminary dose maps from Karis and Anthea are available on the Wiki, which are intended to be an input to Ben’s acoustic simulations. Research/Instrumentation/IonAcoustic/PrelimData – CCAP
Jamie asked where the transducers (which can be sub-mm in size) should be placed for the purposes of Ben’s simulations. After some discussion it was agreed that a physically realistic arrangement could be a sphere of radius 6cm. It is computationally OK to simulate for spheres of 1cm, 3cm, 6cm so this would be done in case smaller radii are found to be better in view of signal size.
Actions:
- JB – circulate long version of GC proposal
- All – read GC proposal in preparation for discussions next week
- KL – simulations of proton beams in water => dose maps
- BC – acoustic simulations from dose maps, aim to demonstrate sufficient acoustic pressures for successful use of available transducers
- AOB: All
