The radiotherapy with proton beams is rapidly becoming the gold standard for eye and cephalo-pediatric tumour treatments. Since the eye includes several critical tissues in a tiny volume (less than 7 cm3), the correct clinical range assessment is crucial for the treatment safety and effectiveness: it is essential that the QA procedures can rely on devices with excellent spatial resolution in the beam direction. The medical device industry is indeed working in the direction of offering on the market new detectors to quickly and precisely measure the beam energy deposition in the exposed tissues, with the aim of providing non-invasive treatments preserving the healthy tissues around the tumour region.
- Treating the eye with accelerated ions allows to optimise the dose delivered to the tumour in terms of both, beam position and beam energy.
- The main improvement of particle therapy (right picture) respect to conventional radiotherapy (left picture) is the better results in terms of sparing surrounding healthy tissues.
A product is the results of multiple design phases.
In DE.TEC.TOR. we bet on the importance of collaboration
which includes scientific and technology partners into the product development.
Let’s take a look into the QEye case
starting form the role-play
- MLFC proof of concept
- Lab prototype
- Feasibility study
- DAQ SW
- Design transfer
- Product compliance
- Project Management
- Mechanical design
- Manufacturing & Testing
- Medical device
- Client (and partner)
Technology transfer with the HZB research center
QEye is the result of a technology transfer activity that origins from the Multi-Leaf Faraday Cup (MLFC) prototype developed by the research group of the Helmholtz Zentrum für Materialien und Energie GmbH in Berlino (HZB), composed of a stack of thin planar conductors connected to ground through an ammeter, alternated to insulating leaves.
HZB MLFC R&D activity
- started in 2003
- 47 DAQ channels: 10 !m copper + 25 !m kapton
- 4.6 mm WE
- Electrometer for sensor readout – iThemba Labs Rabbit Box
HZB Cyclotron: 68 MeV, 500 pA 16.68 Al as pre-absorber
à50 !m relative spatial resolution (100 !m clinical requirement)
In a MLFC device each incident proton stops on a single foil, according to its initial energy, and the differential fluence between adjacent channels can be measured as the charge deposited in each layer.
The research prototype included a limited number of channels manually piled up, not enough to cover with a single beam shot the whole energy range of interest in ocular treatments (30-70 MeV), so that passive absorbers to degrade the incident beam energy and focus the measurement on the energy deposition peak region. Moreover, the read-out electronics and the control unit were external and set far from the sensors, in a fragile and mechanically unstable setup.
Critical aspects of HZB prototype
- Sensor production cost and quality
- Mechanical and size limits
- Clinical energy range not totally covered
- Low readout current limit
- Channel-to-channel crosstalk
- Large background noise signal (external ELM)
- Poor repeatability
First feasibility study with DeTecTor readout electronics
First test with accelerated ions
DE.TEC.TOR. performed a feasibility test with accelerated protons at the HZB experimental room, in September 2019.
During this activity the HZR research prototype has been coupled with DE.TEC.TOR. front-end readout electronics. At this phase we studied the impedance matching and the related electronics pick-up noise and the system behaviour during the data transmission. This test was crucial to identify the limits of the developed sensor and all the feasible aspects related to the incoming re-design.
Helmholtz-Zentrum Berlin, Experimental room 16.09.2019
TORET Devices focused on the HZB prototype re-design by mainly investigating a new manufacturing method for the multi-layer sensors, in order to ensure the performance reproducibility in a serial production, primarily concerning the spatial resolution, with reasonable production time and cost. The solution was the design of 4 multi-layer sensor stacks, 128-channel each, for a total water equivalent range of 60 mm (enough to fully absorb the 30-70 MeV energy range) with a sub-millimeter spatial resolution (0.12 mm/ch average range pitch), easily integrated in a modular mechanical support designed to host also the front-end electronics and the control unit, and ensure the minimisation of the electronic noise.
The complete design has been then transferred to DE.TEC.TOR. srl for the realisation of the related medical device, QEYE, hosted in an eye-shaped spherical shell.
- 512 sensor layers guarantee more than 60 mm of water equivalent path length and the signal full absorption for the entire clinical proton energy range.
- the 512 sensors are arranged in 4 stacked modules 128 layers each
- 1 sensor module is readout by 1 TERA board integrating 2 TERA08 ASIC
- the device integrates a large number of heating source in a compact volume therefore, a dedicated cooling-system based on fans and thermal conduction contacts has been designed and tested. Temperature sensors collect the system status showed on the software GUI.
A new raw data acquisition software has been implemented and equipped with a collected charge reconstruction algorithm in order to convert the raw charge counts into dose/energy distributions.
Preliminary test @ CNAO
DE.TEC.TOR. carried out the planned verification and validation tests, including a preliminary test with clinical protons at the Centro Nazionale per l’Adroterapia Oncologica (CNAO) in Pavia, Italy.
In the field of particle therapy detector development, it is in fact crucial the phase when the new device faces accelerated ions, which is something that a manufacturer company could not provide itself. This step allows to identify the last operation issues that have to be solved thus to complete the product development.
Applied technical solutions
- stack module cross-talk and air interface minimisation introducing additional Al-Mylar shielding leaves
- implementation (software-level) of geometry-weighted calibration factors
- the stacked module interfaces were noisy
- presence of soldering imperfections introducing capacitive effects
- the sensor-air interfaces were facing ionization effects
Extensive test @ HZB
The complete device characterisation was performed during the 17-18 September 2020 test campaign at the HZB accelerator facility.
During this activity, QEye was exposed to accelerated protons provided by the HZB cylotron at both, the clinical and the experimental room.
The device was shipped from the DE.TEC.TOR. headquarter in Turin to the HZB accelerator facility in Berlin. Once completed the test activity, QEye became an actual product then shipped to the Holland Particle Therapy Center in Delft.
- DAQ period scan: 10 -1000 ms
- Background recording
- Online background subtraction
- HW behaviour at stacked module interfaces
- Proton energy scan 1-70 MeV
- Beam current delivered 300 pA – 5.8 nA
QEye test at the HZB clinical room
The HZB clinical room provides a beam extraction with proton up to 61 MeV.
Although this test has the intrinsic importance of representing the real operating scenario for a QA ocular detector, a more dynamic tuning is accessible at the experimental room, where beam attenuation techniques are performed with a larger extracted-particle beam intensities. The maximum proton energy is larger too.
QEye test at the HZB experimental room
EMAX = 69 MeV
The software has been successfully tested and validated on the fixed-energy HZB cyclotron, with protons down to few MeV energies.
Example of 68.6MeV delivered protons with FWHM = 2.6cm, current intensity i = 5.8nA.
The first QEye has been delivered in September 2020 at the Holland Proton Therapy Center in Delft, Netherlands.
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