Monitoring pencil beam scanned proton radiotherapy using a large format CMOS detector

Flynn, Samuel; Manolopoulos, S.; Rompokos, V.; Poynter, A.; Toltz, A.; Beck, L.; Ballisat, Laura; Velthuis, J. J.; Allport, P. P.; Green, Stuart; Thomas, R.; Price, Tony

doi:10.1016/j.nima.2022.166703

Cited by 5 publications

(6 citation statements)

References 16 publications

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“…The linearisation of the vM2428 detector can be seen in figure 5, where a linear response was observed up to 34 nA current in the ionisation chamber. This observed response is consistent with the prior CMOS measurements [24].…”

Section: Linearity Studysupporting

confidence: 92%

“…Unlike prior measurements with the vM2428 detector carried out at other proton beam facilities [24], it was found that the IBA Cyclotron was very stable at a variety of beam currents. This is shown in figure 4, although the beam stability is observed to decrease at higher beam current.…”

Section: Linearity Studycontrasting

confidence: 81%

“…The vM2428 detector, also referred to as Athena or LASSENA [23], is a large-format Complementary Metal-Oxide-Semiconductor (CMOS) sensor designed for scientific and medical x-ray imaging. Although it was not designed for pMBRT, previous investigations at University College Hospitals London NHS Foundation Trust (UCLH) [24] have demonstrated that the detector was a viable candidate for use with proton beams, whilst the precursor to the vM2428 detector, the vM1212 detector, was found to be able to measure static and dynamic x-ray microbeams in a Small Animal Radiation Research Platform (SARRP) [25,26]. The vM2428 detector's specifications are described further in table 1.…”

Section: Cmos Detectormentioning

confidence: 99%

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Development of CMOS dosimetry in proton minibeams for enhanced QA and primary standard absorbed dose calorimetry

et al. 2023

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Performing accurate and reliable dosimetry in spatially fractionated beams remains a significant challenge due to the steep dose gradients and microscopic scale of features. This results in many conventional detectors and instrumentation being unsuitable for online dosimetry, necessitating frequent offline validation using radiochromic film. In this study, the use of a Complementary Metal-Oxide-Semiconductor (CMOS) detector for evaluation of relative real-time dosimetry of proton minibeam radiation therapy (pMBRT) was investigated. The linearity of the CMOS detector was investigated by varying the proton beam current, with a comparison to a PTW 34001 Roos ionisation chamber used to carry out an independent check. It was found that the relative peaks and valleys of the pMBRT beam could be measured, with results comparable to EBT3XD film. The high sensitivity of the CMOS detector meant it was able to measure dose profiles from peak to valley regions, something not possible with the EBT3XD. The CMOS detector was compared to the treatment delivery log files, with correlation in beam position seen as the beam is scanned along each slit, but not across; and agreement in beam intensity, with the CMOS detector able to observe beam interruptions. Lastly, the CMOS detector was used in conjunction with the NPL primary-standard proton calorimeter (NPL PSPC) for a preliminary study on combining the NPL PSPC with high resolution temporal information about the incident pMBRT beam. The ultimate aim of this approach is to facilitate detailed thermal modelling to reduce the overall uncertainty in the absolute dose measured from the calorimeter. In these experiments, saturation in the CMOS pixels prevented further thermal modelling of the radiation induced heat flow, however the instantaneous dose rate was observed to be comparable with the predicted NPL PSPC response obtained by masking the CMOS detector.

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Section: Linearity Studysupporting

confidence: 92%

Section: Linearity Studycontrasting

confidence: 81%

Section: Cmos Detectormentioning

confidence: 99%

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Development of CMOS dosimetry in proton minibeams for enhanced QA and primary standard absorbed dose calorimetry

et al. 2023

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“…To avoid the interconnection step, reduce material and bring the first signal amplification stage close to the generated signal, monolithic detector chips have been developed. In [23], a commercial large-scale CMOS detector for X-ray imaging was evaluated as a proton beam monitor. The determination of the beam profile was shown to reproduce measurements with films with minor deviations as long as saturation was not reached.…”

Section: Alternative Beam Monitoring Concepts and Devicesmentioning

confidence: 99%

A Beam Monitor for Ion Beam Therapy Based on HV-CMOS Pixel Detectors

et al. 2023

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Particle therapy is a well established clinical treatment of tumors. More than one hundred particle therapy centers are in operation world-wide. The advantage of using hadrons like protons or carbon ions as particles for tumor irradiation is the distinct peak in the depth-dependent energy deposition, which can be exploited to accurately deposit doses in the tumor cells. To guarantee this, high accuracy in monitoring and control of the particle beam is of the utmost importance. Before the particle beam enters the patient, it traverses a monitoring system which has to give fast feedback to the beam control system on position and dose rate of the beam while minimally interacting with the beam. The multi-wire chambers mostly used as beam position monitors have their limitations when a fast response time is required (drift time). Future developments such as MRI-guided ion beam therapy pose additional challenges for the beam monitoring system, such as tolerance of magnetic fields and acoustic noise (vibrations). Solid-state detectors promise to overcome these limitations and the higher resolution they offer can create additional benefits. This article presents the evaluation of an HV-CMOS detector for beam monitoring, provides results from feasibility studies in a therapeutic beam, and summarizes the concepts towards the final large-scale assembly and readout system.

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“…Silicon detectors based on flat panels developed for x-ray imaging and depleted monolithic active pixel sensors (DMAPS) were tested with proton beams in charge integration modality (Martišíková et al 2011, Flynn et al 2022, Dierlamm et al 2023. Direct particle counting of proton beams was investigated using the Medipix3 hybrid pixel detector (Yap et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Performance of LGAD strip detectors for particle counting of therapeutic proton beams

Monaco,

Ali,

Bersani

et al. 2023

Phys. Med. Biol.

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Objective: The performance of silicon detectors with moderate internal gain, named Low-Gain Avalanche Diodes (LGADs), was studied to investigate their capability to discriminate and count single beam particles at high fluxes, in view of future applications for beam characterization and on-line beam monitoring in proton therapy.Approach: Dedicated LGAD detectors with an active thickness of 55 μm and segmented in 2 mm2 strips were characterized at two Italian proton-therapy facilities, CNAO in Pavia and the Proton Therapy Center of Trento, with proton beams provided by a synchrotron and a cyclotron, respectively. Signals from single beam particles were discriminated against a threshold and counted. The number of proton pulses for fixed energies and different particle fluxes was compared with the charge collected by a compact ionization chamber, to infer the input particle rates.Main results: The counting inefficiency due to the overlap of nearby signals was less than 1 % up to particle rates in one strip of 1 MHz, corresponding to a mean fluence rate on the strip of about 5⸱107 p/(cm2⸱s). Count-loss correction algorithms based on the logic combination of signals from two neighboring strips allow to extend the maximum counting rate by one order of magnitude. The same algorithms give additional information on the fine time structure of the beam. Significance. The direct counting of the number of beam protons with segmented silicon detectors allows to overcome some limitations of gas detectors typically employed for beam characterization and beam monitoring in particle therapy, providing faster response times, higher sensitivity, and independence of the counts from the particle energy. 

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Monitoring pencil beam scanned proton radiotherapy using a large format CMOS detector

Cited by 5 publications

References 16 publications

Development of CMOS dosimetry in proton minibeams for enhanced QA and primary standard absorbed dose calorimetry

Development of CMOS dosimetry in proton minibeams for enhanced QA and primary standard absorbed dose calorimetry

A Beam Monitor for Ion Beam Therapy Based on HV-CMOS Pixel Detectors

Performance of LGAD strip detectors for particle counting of therapeutic proton beams

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