Presenter of 3 Presentations
LIAC FLASH: a life changing device
A PRELIMINARY STUDY ON RADIATION PROTECTION REQUIREMENTS FOR A FLASH IOERT LINAC
Q&A Session
Author Of 11 Presentations
A PRELIMINARY STUDY ON RADIATION PROTECTION REQUIREMENTS FOR A FLASH IOERT LINAC
Q&A Session
LIAC FLASH: a life changing device
MONITORING A FLASH BEAM: FOR PRECLINICAL STUDIES AND TOWARDS CLINICAL APPLICATIONS
Abstract
Background and Aims
With medical linear accelerators, the dose is delivered in approximately a thousand of low-dose radiation pulses and is regulated by monitoring ionization chambers, which turn off the beam once the preset number of Monitor Units (MU) is reached. In FLASH electron beams, on the contrary, the dose-per-pulse is much higher (> 1 Gy/pulse), which, a) prevent the use of conventional monitoring systems, and b) implies that the complete treatment is delivered with a very limited number of pulses, sometimes only one. To guarantee that the planned dose is delivered as intended, new methodologies for monitoring must be elaborated for FLASH beam delivery.
Methods
In preclinical studies with ElectronFLASH4000 (SIT), we have defined FLASH-MU as a fraction of the pulse’s temporal profile integral, which is recorded with a non-destructive monitoring toroid. For the control experiments performed at conventional dose-rate, MU measured by classical monitor chambers have been cross-referenced with FLASH-MU, through calibration by film dosimetry.
Results
FLASH electron beams can be effectively monitored by toroidal current transformers, provided they have adequate performances. Prescribed doses have been translated in MU with different pulse length, pulse amplitude and/or number of pulses. Heterogeneous pulse sequences including decreasing doses-per-pulse allowed a smaller cut-off step.
Conclusions
This opens the discussion on techniques for FLASH monitoring and on beam cut-off strategies for radiotherapy treatments delivered with very few ultra-high-dose pulses. At least some of them can already be tested for dose accuracy and biological effectiveness.
Acknowledgement: This work is part of 18HLT04-UHDpulse project, which received funding from the EMPIR program.
CHARACTERIZE THE ELF: THE NOVEL ELECTRON FLASH IRRADIATION SYSTEM UNVEILED WITH STANDARD DOSIMETRIC TOOLS_
Abstract
Background and Aims
As the development of suitable detectors in ultra high Dose Per Pulse (DPP) beams is on-going, temporary protocols solving limitations with standard tools are required for the acceptance of new dedicated machines. We present a protocol for system commissioning using clinically available dosimeters, optimizing the use of the detectors. Extra attention was given to beam characterization when varying the DPP.
Methods
Measurements were performed on the ELF, a dedicated research linac for Flash radiotherapy with electrons (ElectronFlash, SIT, Italy) at 7 and 9 MeV using standard dosimetric tools: a PTW Advanced Markus (AM) plane-parallel ion chamber, Gafchromic EBT-XD films, and alanine pellets. The system is highly tunable for pulse length, pulse repetition frequency and number of pulses. Collaboration with the developer allowed further tuning. The DPP was varied using pulse length, distance from the linac and e-gun current.
Results
Performance tests assessing dose, dose stability, PDD, profiles, and output linearity to system settings were measured cross-referencing at least two detectors (comparable within 5%). Energy and dose outputs, monitored with films and AM, were stable within 5% in several months. The AM was used for daily QA for doses up to 0.5 Gy/pulse (model proposed in abstract #211). Changing the DPP using the above-mentioned parameters resulted in a linear output change and minimal variation (<1 MeV) of the spectrum.
Conclusions
We characterized the ELF using standard dosimetric tools. We propose the combination of alanine and Gafchromic films as absolute dosimetric standard. The AM can be employed as real-time tool for daily QA.
FASTER THAN LIGHT: CAN SCINTILLATORS GUIDE ELECTRON FLASH EXPERIMENTS?
Abstract
Background and Aims
The radiobiological study of the FLASH effect requires accurate and reliable dosimetry. As scintillators are promising candidates, this work presents a first characterization of their response at UHDR, suggesting solutions to account for possible saturating effects.
Methods
Five scintillating fibers, one clinical and two experimental Y2O3:Eu-based scintillators (DoseVue N.V., Belgium) and two experimental Al2O3:C-based scintillators (SCK CEN, Belgium), were irradiated using the ElectronFlash system (SIT, Italy). Linearity with dose was validated by varying the number of pulses for both experimental Y2O3:Eu-based scintillators. Dose per pulse (DPP) linearity was investigated in all scintillators by varying pulse duration and the distance from the linac exit window (SSD). Pulse scheme stability was investigated by changing of the pulse repetition frequency (PRF).
Results
Good linearity with dose (R²>0.99) was observed in both experimental Y2O3:Eu-based scintillators. Linearity with increasing pulse duration (R²>0.95) and an inverse squared relation between DPP and SSD (R²>0.95) were observed in 4 out of 5 scintillators. However, a concave curvature in response, suggesting saturation, was observed for all scintillators. This effect was more pronounced for the smaller applicator diameter. Our results showed reduced saturation effects when increasing integration time as well as when reducing signal intensity. All scintillators showed a decreasing response with increasing PRF.
Conclusions
The promising characteristics of scintillators as on-line dosimeters for UHDR were validated and possible solutions to reduce saturation effects have been evaluated. Further research on the response by varying PRF is needed.
This work is part of the 18HLT04 UHDpulse project which received funding from the EMPIR programme.
OVERVIEW AND CURRENT STATUS OF THE JOINT RESEARCH PROJECT UHDPULSE - “METROLOGY FOR ADVANCED RADIOTHERAPY USING PARTICLE BEAMS WITH ULTRA-HIGH PULSE DOSE RATES”
Abstract
Background and Aims
Dosimetry for FLASH radiotherapy, VHEE radiotherapy as well as for laser-driven beams cause significant metrological challenges due to the ultra-high dose rates and pulsed structure of these beams, in particular for real time measurements with active dosimeters. It is not possible to simply apply existing Codes of Practice available for dosimetry in conventional external radiotherapy here. However, reliable standardized dosimetry is necessary for accurate comparisons in radiobiological experiments, to compare the efficacy of these new radiotherapy techniques and to enable safe clinical application. UHDpulse aims to develop the metrological tools needed for reliable real-time absorbed dose measurements of electron and proton beams with ultra-high dose rate, ultra-high dose per pulse or ultra-short pulse duration.
Methods
Within UHDpulse, primary and secondary absorbed dose standards and reference dosimetry methods are developed, the responses of available state-of-the-art detector systems are characterised, novel and custom-built active dosimetric systems and beam monitoring systems are designed, and methods for relative dosimetry and for the characterization of stray radiation are investigated.
Results
Prototypes of different active dosimetry systems show promising results for real-time dosimetry for particle beams with ultra-high pulse dose rates. The results of the UHDpulse project will be the input data for future Codes of Practice.
Conclusions
A brief overview of the progress in the UHDpulse project and the involved institutions will be given.
Acknowledgement: This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
ULTRA THIN PLANE-PARALLEL IONIZATION CHAMBERS: EXPANDING THE RANGE OF AIR IONIZATION CHAMBERS INTO ULTRA-HIGH DOSE RATE.
Abstract
Background and Aims
Ionization chambers (IC) have been and remain the secondary standard of choice in the vast majority of hospitals all over the world. When an IC is irradiated at dose rates that exceed the conventional limits the ion recombination correction factor of these chambers starts to increase. Working in these regimes is unfeasible as the required correction factors exceed dosimetry standards. Analytical theories describing ion recombination effect fail to actually describe their behavior in the ultra high dose rate (UHDR).
Methods
Ultra-thin gap plane-parallel ionization chambers exhibit a submillimetric electrode distance. This geometry enhances the collection of the charge carriers by increasing the electric field strength inside the chamber and reducing the charge carrier densities between electrodes. The free electron fraction is much higher than in a conventional chamber, decreasing the amount of ion-recombination. The experimental measurements have been performed in UHDR electron beams (7 MeV and 9 MeV) at SIT ElectronFLASH accelerator.
Results
Figure 1: Response of an ultra-thin plane parallel ionization chamber prototype with a 0.27 mm gap polarized at -250 V in an electron beam from a SIT ElectronFLASH accelerator without application of any ion recombination correction.
Conclusions
Ultra thin gap plane-parallel ionization chambers are a promising option as secondary standard dosimeters for the FLASH radiotherapy quality assurance.
Acknowledgement
This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
A FEASIBILITY STUDY OF IORT-FLASH USING A GPU-BASED FAST MONTE CARLO
Abstract
Background and Aims
Intra Operative Radiation Therapy (IORT) may represent one of the first clinical modalities of a Flash clinical treatment. Within IORT, whenever needed and possible, temporarily beam modifiers (such as the protection disc for breast carcinoma treatment) are used to protect the underlying healthy tissues during the irradiation. In this contribution we investigate the efficiency achievable in IORT-FLASH treatment using a GPU-based fast Monte Carlo called FRED (Fast particle thErapy Dose evaluator), as a tool for dose calculation and treatment optimization.
Methods
The FRED MC has been developed to allow a fast optimization of the Treatment Planning System in Particle Therapy (simulation time reduced by a factor of 1000), while keeping the dose release accuracy typical of a MC tool. We have simulated in detail the geometry and the material of the applicator coupled with the linac, provided by the SIT company (Aprilia, Italy). We have then combined the FRED simulation with a simple modelling of the FLASH effect and compared it with a conventional IORT treatment.
Results
The tumour coverage and the dose absorbed by the organs at risk have been compared, carrying out a quantitative analysis comparing the obtained Dose Volume Histograms, with a standard IORT treatment.
Conclusions
The results demonstrate the potential of FLASH effect in IORT and of FRED as a tool for treatment planning and dose-report calculations.
REALIZATION AND CHARACTERIZATION OF NOVEL DIAMOND DETECTOR PROTOTYPES FOR FLASH THERAPY APPLICATIONS
Abstract
Background and Aims
Commercially available real time response dosimetric systems were shown to be unsuitable for Flash therapy, in which ultra-high Dose Per Pulse (DPP) is of interest. There is a need for novel, reliable and fast response detectors for such an application. In the present work, a comprehensive investigation is reported on the properties of diamond-based detectors specifically designed for Flash therapy.
Methods
Several diamond Schottky diode prototypes were produced at Rome Tor Vergata University, in cooperation with PTW Freiburg. Quite a few relevant design and electronical parameters were systematically varied, tuning the device’s overall performance and meet the stringent requirements of ultra-high DPP irradiation. The resulting prototypes were tested by using an ElectronFllsh linac (SIT S.P.A.), by using a 9 MeV electron beam and DPPs up to 12.5 Gy/pulse.
Results
The performance of the prototypes, investigated under a wide range of irradiation parameters, was found to depend on their specific structural properties and designs, showing a response linearity up to a DPP of 12.5 Gy/pulse in the best case.
Conclusions
First results of this systematic investigation, clearly demonstrate the feasibility of a diamond based detector for Flash therapy applications. The analysis of the obtained experimental results will be used as an input for further development and optimization procedure of the investigated prototypes.
The present work is part of the 18HLT04 UHDpulse project which has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
A NOVEL METHOD FOR DETERMINING IC SATURATION FACTOR (UP TO 0.5 GY/P FOR ADV. MARKUS)
Abstract
Background and Aims
Ionization chambers (IC) represent the standard for performing the commissioning of medical linacs. Nevertheless, their use in the UHDR range is not currently possible, due to the amount of charge produced by each pulse.
For dose-per-pulse (dpp) above 0.5 cGy/p, the approach implemented by international protocols for modelling ion recombination failed, because the free electron fraction p contribution must be considered. We modify the approach of Di Martino (2005) in order to obtain p by means of ionometric measurements only.
Methods
According to the proposed model:
where
qcol is the charge collected by IC;
V is the voltage applied to IC;
qgen is the charge generated by the pulse;
A and λ are parameters depending on the IC..
By varying the voltage applied V, such function can be determined versus the unknown parameters (qgen, A and λ ); then, such parameters can be determined by means of the non-linear regression method.
Once all parameters are known, p is calculated and and then ksat is determined as:
being α = A / V .
Results
The method has been adopted for estimating ksat for the Adv. Markus, both with the beam produced by ElectronFlash and by LIAC HWL.The fit provided an agreement better than 1% within IORT range and better than 5% with 0.6 Gy/p.
Conclusions
Once ksat is known, ionometric measurements at the larger distance might become the central element of a reliable Quality Assurance program for any Flash linac.