azienda ospedaliera universitaria pisana
Fisica sanitaria
Fabio Di Martino Health Physics Unit (Pisa Hospital), National Institute of nuclear Physics (INFN)-section of Pisa, Pisa Center for Research and clinical implementation of Flash Radiotherapy (CPFR@CISUP) , Pisa(Italy) I am a Physicist with a specialization in Health Physics, obtained at the University of Pisa. I have been working as a health physicist at the University-Hospital of Pisa since 2002. I am affiliated with the National Institute of Nuclear Physics(INFN), section of Pisa (Italy). I have been involved in Nuclear Medicine (diagnostics and therapy), Radiotherapy, Laser safety (I am the laser safety responsible for my hospital) and radiation protection (radiation protection expert of degree III). In particular, I have a long experience in the field of dosimetry and radiobiology of high dose-per-pulse electron beams generated by linac dedicated to IOeRT (Intra-Operative-Electrons-Radiation-Therapy). I am the creator and the responsible for the Linac of the newly established Pisa Center for Research and clinical implementation of Flash Radiotherapy (CPFR@CISUP), a multi-disciplinary scientific center born through a grant from the Pisa Foundation as a special project of the Center for Instrument Sharing of the University of Pisa (CISUP), and composed of Radiotherapists, Medical Physicists, Biophysicists, Biologists and theoretical-computational Physicists, from the Hospital of Pisa, the University of Pisa, the National Research Center (CNR) and the INFN-section of Pisa. CPFR will be equipped, starting from April 2022, with a Linac dedicated for Flash research and suitably designed for our center (ELECTRONFLASH equipped with a triode gun), and a laboratory for radiobiology.

Presenter of 2 Presentations

A NEW MODEL OF GAS CHAMBER FOR UHDR RANGE

Session Type
Live E-Poster Discussions
Date
Thu, 02.12.2021
Session Time
17:20 - 18:20
Room
Station 01
Lecture Time
17:20 - 17:25

A NOVEL METHOD FOR DETERMINING IC SATURATION FACTOR (UP TO 0.5 GY/P FOR ADV. MARKUS)

Session Type
FLASH in the Clinic Track (Oral Presentations)
Date
Thu, 02.12.2021
Session Time
11:00 - 12:00
Room
Room 2.31
Lecture Time
11:40 - 11:50

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:

equation1.png

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:

equation2.png

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.

fig1.png

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.

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Author Of 5 Presentations

A NEW MODEL OF GAS CHAMBER FOR UHDR RANGE

Session Type
Live E-Poster Discussions
Date
Thu, 02.12.2021
Session Time
17:20 - 18:20
Room
Station 01
Lecture Time
17:20 - 17:25

CHARACTERIZE THE ELF: THE NOVEL ELECTRON FLASH IRRADIATION SYSTEM UNVEILED WITH STANDARD DOSIMETRIC TOOLS_

Session Type
FLASH Modalities Track (Oral Presentations)
Date
Wed, 01.12.2021
Session Time
10:20 - 11:30
Room
Room 2.31
Lecture Time
10:40 - 10:50

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.

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A FEASIBILITY STUDY OF IORT-FLASH USING A GPU-BASED FAST MONTE CARLO

Session Name
Session Type
FLASH Mechanisms Track (Oral Presentations)
Date
Thu, 02.12.2021
Session Time
11:00 - 12:00
Room
Room 2.15
Lecture Time
11:00 - 11:10

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.

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INORGANIC SCINTILLATORS FOR FLASH-IORT DOSIMETRY: DEVELOPMENT AND TEST OF A LYSO DETECTOR PROTOTYPE

Session Type
FLASH in the Clinic Track (Oral Presentations)
Date
Thu, 02.12.2021
Session Time
11:00 - 12:00
Room
Room 2.31
Lecture Time
11:10 - 11:20

Abstract

Background and Aims

Fast and accurate active dosimeters are the key component to perform quantitative measurements in FLASH radiotherapy. No reference active dosimeters are currently available since most detectors show non recoverable saturation effects for dose-per-pulse (DPP) values typical of FLASH (1Gy/p or higher). Aim of this study is to develop and test a detector prototype based on inorganic scintillators for FLASH-IORT active dosimetry.

Methods

The detector prototype is composed of a LYSO scintillating crystal (2x2x10 mm^3) wrapped in 5 Teflon layers and coupled to an optical fiber 1.2 m long (0.980 mm diameter, PMMA core). The other end of the fiber is connected to a Photodiode (PD, Thorlabs - SM05PD7A) read out by a multimeter (Keithley 617) that integrates the PD photocurrent. The detector was placed in a PMMA support and covered with solid water slabs. The phantom was irradiated with a 7 MeV IORT electron LINAC (NOVAC7 from SIT, Aprilia, Italy) at different SSDs and depths in solid water to vary DPP at the detector position. The DPP spanned from conventional (3 cGy/pulse) to FLASH values (250 cGy/pulse). The DPP was evaluated by means of calibrated Gafchromic films.

lyso.jpg

iort.png

Results

The PD integrated charge was linear in the whole range of DPP values explored and 0.46 nC/Gy in sensitivity was measured.

sensitivity.png

Conclusions

Further measurements are planned to fully characterize the detector such as extend the DPP upper limit and investigate the dependency on the instantaneous DPP, but these first results indicate LYSO based detectors as promising candidates for FLASH-IORT active dosimetry.

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A NOVEL METHOD FOR DETERMINING IC SATURATION FACTOR (UP TO 0.5 GY/P FOR ADV. MARKUS)

Session Type
FLASH in the Clinic Track (Oral Presentations)
Date
Thu, 02.12.2021
Session Time
11:00 - 12:00
Room
Room 2.31
Lecture Time
11:40 - 11:50

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:

equation1.png

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:

equation2.png

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.

fig1.png

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.

Hide