Chamber Film Research Articles

Sensitivity characteristics of a wave height sensor based on a MEMS piezoresistive cantilever and waterproof film

Abstract This paper presents the frequency characteristics of a barometric pressure-sensing wave height sensor employing a microelectromechanical system (MEMS) piezoresistive cantilever and a micromesh waterproof film. The proposed sensor exhibited mechanical bandpass filter characteristics owing to air leakage around the cantilever and film. Consequently, high robustness can be achieved if the frequency is designed to match the wave range. We theoretically and experimentally verified that the frequency response is influenced by the film's chamber volume and permeability constant. We demonstrated that the proposed frequency-response model helps design a waterproof wave height sensor using a cantilever-type differential pressure sensor.

A Simple Method for Fabricating Ink Chamber of Inkjet Printheads.

The process of fabricating chambers is becoming more important for inkjet printheads. However, there are some problems with the majority of present fabrication methods, such as nozzle structural deformation, blocked chambers, and collapsed chambers. In this paper, we propose a new process for preparing printhead chips by bonding tantalum nitride thin-film heaters and SU-8 chamber film using UV curing optical adhesive. This process simplifies the preparation process of printhead chips and overcomes the limitations of the traditional adhesive bonding process. Firstly, a chamber film was prepared by the molding lithography process based on a PDMS mold. The chamber film was then bonded with the membrane heater by the adhesive bonding process based on film transfer to form a thermal bubble printhead chip. Finally, the chip was integrated with other components to form a thermal inkjet printhead. The results show that the overflow width of bonding interface of 3.10 μm and bonding strength of 3.3 MPa were achieved. In addition, the printhead could stably eject polyvinyl pyrrolidone binder droplets, which are expected to be used for binder-jetting printing of powder such as ceramics, metals, and sand molds. These results might provide new clues to better understand the adhesive bonding process based on film transfer and the new applications of inkjet printheads.

Monte Carlo Dose Calculation - A QA Method for SRT and SBRT Plans in Treating Multiple and Small Metastatic Lesions.

To provide accurate and fast 3-D dose verification for hypofractionated stereotactic radiotherapy (SRT/SBRT) of small and multi targets calculated with a Varian Eclipse treatment planning system (TPS) delivered on a Varian accelerator. Ten brain and lung hypofractionated SRT/SBRT linac-based and CyberKnife plans were generated by the Eclipse system for delivery on the accelerator with the Millenium-120 leaf multileaf collimator (MLC) and Multiplan for the CyberKnife machine. These clinical SRT/SBRT plans required accurate quality assurance measurements to obtain absolute point dose and 3-D dose distributions due to the low number of fractions and high fraction doses. For small-field and multi-target plans, the EGS4/MCSIM code was used to calculate the dose distribution. A 0.125 cc ion chamber, a 0.016 cc pin-point chamber and Kodak EDR2 film were used for the measurements and the results were compared with Monte Carlo (MC) calculations. The dosimetry for small-field and multi-target treatment plans is challenging due to the comparable range of secondary electrons and the field sizes defined by SRT/SBRT MLC segments. Our MC simulations can accurately reproduce the linac dose distributions (within 1%/1 mm) three dimensionally. For the clinical SRT/SBRT plans investigated in this work, the MC doses agreed within 3% with ion chamber measurements and within 2%/2 mm with film measurements. The doses calculated by the Eclipse AAA algorithm and Multiplan differed by no more than 5% from MC calculations for small (4–40 cc) Planning Target Volumes (PTVs). MC dose calculation provides accurate and fast 3-D dose verification for hypofractionated SRT for small and multi-target treatment plans generated by a Varian Eclipse TPS on a Varian accelerator and Multiplan treatment planning on the CyberKnife System.

Surface dose and build-up region depth dose measurements in non-standard beams of Cyberknife and tomotherapy systems.

The purpose of this study was to measure the surface dose and build-up region depth dose characteristics of 6 MV photon beams in Cyberknife and helical tomotherapy (HT) systems for non-standard small fields using parallel plate chambers (Roos and Markus), Gafchromic EBT3 films, and nanoDot optically stimulated luminescence dosimeters (OSLDs), as well as to investigate the effect of oblique incidence on the surface dose of the beam. All measurements were conducted in a virtual water phantom under machine-specific reference conditions. The Roos and OSLDs overestimated the surface dose when compared with the Markus chamber and EBT3 films by 20%. We applied water equivalent thickness (WET) correction to account for the intrinsic build-up thickness of the detectors from their effective point of measurement (EPOM). With WET correction, a reasonably close surface dose estimate was obtained for all detectors, within 1.9% agreement for the 60mm collimator of Cyberknife and 3.1% agreement for the HT system, with a 5 × 10 cm2 field size. The surface dose increased from the normally incident Cyberknife and HT fields with increasing angle of incidence. The surface dose increased to twice its value at normal incidence for highly oblique angles of incidence above 55°. For the tested fields, a reasonable surface dose estimate could be measured with the detectors if the correction for intrinsic buildup thickness was applied. Nevertheless, the use of Roos chambers with large dimensions and nanoDot OSLDs is not recommended for estimating the surface dose for small fields.

A High-Precision Method for In Vitro Proton Irradiation.

PurposeAlthough proton therapy has become a well-established radiation modality, continued efforts are needed to improve our understanding of the molecular and cellular mechanisms occurring during treatment. Such studies are challenging, requiring many resources. The purpose of this study was to create a phantom that would allow multiple in vitro experiments to be irradiated simultaneously with a spot-scanning proton beam.Materials and MethodsThe setup included a modified patient-couch top coupled with a high-precision robotic arm for positioning. An acrylic phantom was created to hold 4 6-well cell-culture plates at 2 different positions along the Bragg curve in a reproducible manner. The proton treatment plan consisted of 1 large field encompassing all 4 plates with a monoenergetic 76.8-MeV posterior beam. For robust delivery, a mini pyramid filter was used to broaden the Bragg peak (BP) in the depth direction. Both a Markus ionization chamber and EBT3 radiochromic film measurements were used to verify absolute dose.ResultsA treatment plan for the simultaneous irradiation of 2 plates irradiated with high linear energy transfer protons (BP, 7 keV/μm) and 2 plates irradiated with low linear energy transfer protons (entrance, 2.2 keV/μm) was created. Dose uncertainty was larger across the setup for cell plates positioned at the BP because of beam divergence and, subsequently, variable proton-path lengths. Markus chamber measurements resulted in uncertainty values of ±1.8% from the mean dose. Negligible differences were seen in the entrance region (<0.3%).ConclusionThe proposed proton irradiation setup allows 4 plates to be simultaneously irradiated with 2 different portions (entrance and BP) of a 76.8-MeV beam. Dosimetric uncertainties across the setup are within ±1.8% of the mean dose.

Dosimetric Comparison of Four Commercial Patient-Specific Quality Assurance Devices for Helical Tomotherapy

In this study, the delivery quality assurance (DQA) results of commercially available dosimetric systems (ionization chamber and EBT film, MapCHECK, ArcCHECK, and dosimetry check (DC) software) for helical tomotherapy (HT) were compared, and the feasibility of performing pretreatment using MapCHECK, ArcCHECK, and DC for HT, instead of ionization chambers and EBT films, was assessed. Sixty-five HT-treated patients were considered. Point dose differences, dose profiles, and gamma passing rates were used to evaluate the agreement between the calculated and the measured data, and the outcomes of the four DQA devices were compared in various clinical cases. The calculated and the measured point doses were within ±5% of each other. In terms of the root-mean-square error (RMSE), the point dose differences were within 2.9 for the four tested devices in all of the studied cases. Gamma analysis was performed based on the 3%/3 mm and 2%/2 mm passing rate criteria. In terms of the average RMSE, the gamma passing rates of the four tested DQA devices were within 2.85 (3%/3 mm) and 7.30 (2%/2 mm). These DQA systems could be used interchangeably for routine DQA pretreatment in HT cases.

Dose verification for liver target volumes undergoing respiratory motion.

Respiratory motion has a significant impact on dose delivered to abdominal targets during radiotherapy treatment. Accurate treatment of liver tumours adjacent to the diaphragm is complicated by large respiratory movement, as well as differing tissue densities at the lung-liver interface. This study aims to evaluate the accuracy of dose delivered to superior liver tumours using passive respiratory monitoring, in the absence of gating technology, for a range of treatment techniques. An in-house respiratory phantom was designed and constructed to simulate the lung and liver anatomy. The phantom consisted of adjacent slabs of lung and liver equivalent materials and a cam drive system to emulate respiratory motion. A CC04 ionisation chamber and Gafchromic EBT3 film were used to perform point dose and dose plane measurements respectively. Plans were calculated using an Elekta Monaco treatment planning system (TPS) on exhale phase study sets for conformal, volume modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) techniques, with breathing rates of 8, 14 and 23bpm. Analysis confirmed the conformal delivery protocol currently used for this site within the department is suitable. The experiments also determined that VMAT is a viable alternative technique for treatment of superior liver lesions undergoing respiratory motion and was superior to IMRT. Furthermore, the measurements highlighted the need for respiratory management in these cases. Displacements due to respiration exceeding planned margins could result in reduced coverage of the clinical target volume and much higher doses to the lung than anticipated.

Klondike on the Moskva: Lev Kuleshov, the Jack London short story, and the chamber film

ABSTRACTThis article seeks to re-contextualize Lev Kuleshov’s By the Law (Po zakonu, 1926) as a chamber film, a genre mostly associated with Weimar-era German cinema (the Kammerspielfilm) that uses naturalist settings and characters; expressive, chiaroscuro lighting; and slow, ponderous acting that critique lower-middle-class lives. By the Law is the result of Kuleshov’s montage experiments and theoretical reworking of chamber film dynamics, all of which were undertaken in a climate of material and financial scarcity. In order to understand how Kuleshov both adopted and reinvigorated chamber aesthetics, we need to examine Kuleshov’s process of adapting two naturalist Jack London short stories, ‘Just Meat’ (1906) and ‘The Unexpected’ (1905). After developing a process of making études, or films without film, with material like ‘Just Meat’, Kuleshov would extend his experimentation to shooting and editing By the Law deliberately as a chamber film. In particular, his use of expressive American montage represents an important evolution away from the German Kammer tradition.

The Perpetrator's mise-en-scene: Language, Body, and Memory in the Cambodian Genocide

Rithy Panh's film S-21. The Khmer Rouge Killing Machine (2003) was the result of a three-year shooting period in the Khmer Rouge centre of torture where perpetrators and victims exchanged experiences and re-enacted scenes from the past under the gaze of the filmmaker's camera. Yet, a crucial testimony was missing in that puzzle: the voice of the prison's director, Kaing Guek Eav, comrade Duch. When the Extraordinary Chambers in the Courts of Cambodia (ECCC) were finally established in Phnom Penh to judge the master criminals of Democratic Kampuchea, the first to be indicted was this desk criminal. The film Duch, Master of the Forges of Hell (R. Panh, 2011) deploys a new confrontation – an agon, in the terminology of tragedy ¬– between a former perpetrator and a former victim, seen through cinema language. The audiovisual document registers Duch's words and body as he develops his narrative, playing cunningly with contrition and deceit. The construction of this narrative and its deconstruction by Panh can be more fully understood by comparing some film scenes with other footage shot before, during and after the hearings. In sum, this 'chamber film' permits us to analyse two voices: the one of the perpetrator, including his narrative and body language; and the invisible voice of the survivor that expresses itself through editing, sound effects, and montage.

188 Orthovoltage rotational breast radiotherapy: A Monte Carlo and experimental study

Purpose To investigate depth-dose characteristics of a new technique for orthovoltage rotational breast radiotherapy (RT) via Monte Carlo (MC) simulations and experimental phantom study, following the initial work by Boone [1] . Methods Geant4 MC simulations were developed to calculate dose distributions generated by an orthovoltage (320 kVp, 4 mm Cu filtration) or kilovoltage (150 kV, 1 mm Cu) X-ray beams rotating 360° around a cylindrical phantom (polyethylene or PMMA) placed at isocentre to simulate prone patient’s breast. Horizontal beam collimation was 1–14 cm. Radial and longitudinal depth-dose distributions were performed for homogeneous phantoms (with or without lesions simulated for different depths in phantom). Experimental validation was performed on the same geometry with the 150 kV beam. Farmer-type air ionization chamber and radiochromic films are used to measure radial dose profiles. Results MC simulations at 320 kVp show that rotational kilovoltage radiotherapy assures sufficient skin sparing during breast RT. Centre to periphery dose ratio is less than 20:1 (1 cm collimation in the horizontal plane at 320 kVp). The vertical dose spread profile shows limited influence of the scatter dose at distance of 10 mm from the irradiated slice. MC simulations will be compared to laboratory measurements at 150 kV. Conclusions We showed the potential of orthovoltage external beam rotational RT for breast cancer with satisfactory skin sparing, though using a kilovoltage beam.

A simple method for determining dosimetric leaf gap with cross-field dose width for rounded leaf-end multileaf collimator systems

PurposeThe dosimetric leaf gap (DLG) and multileaf collimator (MLC) transmission are two important systematic parameters used to model the rounded MLC leaf ends effect when commissioning an Eclipse treatment planning system (TPS). Determining the optimal DLG is a time consuming process. This study develops a simple and reliable method for determining the DLG using the cross-field dose width.Methods and materialsA Varian TrueBeam linac with 6 MV, 10 MV, 6 MV flattening filter free (FFF) and 10 MV FFF photon beams and equipped with the 120 Millennium MLC and the Eclipse™ TPS was used in this study. Integral sliding fields and static slit MLC field doses with different gap widths were measured with an ionization chamber and GAFCHROMIC EBT3 films, respectively. Measurements were performed for different beam energies and at depths of 5 and 10 cm. DLGs were derived from a linear extrapolation to zero dose and intercepting at the gap width axis. In the ion chamber measurements method, the average MLC leaf transmission to the gap reading for each gap (RgT) were calculated with nominal and cross-field dose widths, respectively. The cross-field dose widths were determined according to the dose profile measured with EBT3 films. Additionally, the optimal DLG values were determined using plan dose measurements, as the value that produced the closest agreement between the planned and measured doses. DLGs derived from the nominal and cross-field dose width, the film measurements, and the optimal process, were obtained and compared.ResultsThe DLG values are insensitive to the variations in depth (within 0.07 mm). DLGs derived from nominal gap widths showed a significantly lower values (with difference about 0.5 mm) than that from cross-field dose widths and from film measurements and from plan optimal values. The method in deriving DLGs by correcting the nominal gap widths to the cross-field dose widths has shown good agreements to the plan optimal values (with difference within 0.21 mm).ConclusionsThe DLG values derived from the cross-field dose width method were consistent with the values derived from film measurements and from the plan optimal process. A simple and reliable method to determine DLG for rounded leaf-end MLC systems was established. This method provides a referable DLG value required during TPS commissioning.

Experimental validatıon of peripheral dose distribution of electron beams for eclipse electron Monte Carlo algorithm

AbstractAimThe accuracy of two calculation algorithms of the Varian Eclipse treatment planning system (TPS), the electron Monte Carlo algorithm (eMC) and general Gaussian pencil beam algorithm (GGPB) for calculating peripheral dose distribution of electron beams was investigated.MethodsPeripheral dose measurements were carried out for 6, 9, 12, 15, 18 and 22 MeV electron beams using parallel plate ionisation chamber and EBT3 film in the slab phantom. Measurements were performed for 6×6, 10×10 and 25×25 cm2 cone sizes at dmax of each energy up to 20 cm beyond the field edges. The measured and TPS calculated data were compared.ResultsThe TPS underestimated the out-of-field doses. The difference between measured and calculated doses increase with the cone size. For ionisation chamber measurement, the largest deviation between calculated and measured doses is &lt;4·29% using the eMC, but can increase up to 8·72% of the distribution using GGPB. For film measurement, the minimum gamma analysis passing rates between measured and calculated dose distributions for all field sizes and energies used in this study were 91·2 and 74·7% for eMC and GGPB, respectively.FindingsThe use of GGPB for planning large field treatments with 6 MeV could lead to inaccuracies of clinical significance.

Influence of Backscatter Radiation on Cranial Bone Fixation Devices

Postoperative radiation can cause ulcer formation, leading to the denudation of skin over alloplastic materials. The influence of backscatter radiation from fixation devices has not been investigated. The aim of this study is to evaluate backscatter dose variations for different cranial bone fixation devices in an experimental model designed to simulate postoperative radiotherapy. The authors assessed the radiation backscatter doses associated with resorbable (PLLA-PGA) and titanium plates. The samples were irradiated with 6 and 10 MV photon beams from a linear accelerator. Measurements were obtained using an ionization chamber and radiochromic films cut from the same batch. As a result, the backscatter radiation of water and PLLA-PGA proportionally decreased as the depth increased. However, the backscatter radiation of the titanium plate increased just above the plate. This depth lies in the region of the scalp. Each material showed a dose of radioactivity that was higher at 10 MV than that at 6 MV. These devices showed a significant difference, which suggested that these materials amplified the dose compared with water at 6 MV. In conclusion, it is supposed that PLLA-PGA should be used to fix the cranium to decrease the potential for radiation ulcers.

OC-0406: Validation of the INTRABEAM system dosimetry with ionization chamber and EBT3 film measurements

OC-0406: Validation of the INTRABEAM system dosimetry with ionization chamber and EBT3 film measurements

Evaluation on dose distribution of longitudinal profile on helical tomotherapy Gha-Jung Kim

In this study is aimed to evaluate the accuracy of longitudinal dose distribution during helical tomotherapy slice treatment using ion chamber and EBT film, and measure the flatness in the longitudinal profile for each radiation field width. As the experiment condition, the radiation field widths were set to 10 mm, 25 mm, and 50 mm, respectively, to acquire and evaluate a longitudinal beam profile. A slab phantom and A1SL ion chamber was used to evaluate the accuracy of longitudinal dose distribution in helical tomotherapy. Also, solid phantom and EBT film was used to measurement of dose flatness in the longitudinal axis (Y axis). The difference between reference and measured data values of FWHM at the radiation field width of 10 mm was 0.546 ± 0.186% on average, and the maximum γ-index was 0.522 ± 0.056. The difference between reference and measured data values of FWHM at the radiation field width of 25 mm was 0.133 ± 0.113% on average, and the maximum γ-index was 0.417 ± 0.102. The difference between reference and measured data values of FWHM at the radiation field width of 50 mm was 0.120 ± 0.072% on average, and the maximum γ-index was 0.467 ± 0.077. The dose flatness within a range of 250 mm longitudinal axis (Y axis) for each radiation field width was 1.71 ± 0.46% on average, which was a value within 3%. The results exhibited that the dose flatness became more even as the radiation field width became wider. The above study results will contribute to clarifying the accuracy of radiation dose delivered to real patients, or the DQA, which is an important QA item in the IMRT using tomotherapy.

31. Impact of Pinnacle model calculation on the dynamic arc-therapy dose delivered by a linac, and the need to cross-check control tools

Introduction Volumetric modulated arc-therapy (VMAT) is a fast treatment technique allowing the delivery of good quality radiotherapy. TPS are used for treatment planning and need to perform precise calculations. It is thus important to affine and validate the models created before starting treatments. Our study demonstrates the need to do quality assurance adapted to the model. It is necessary to cross-check the measurements from at least two detectors before proceeding to pretreatment controls. Methods Photon beams of 6MV, delivered by an Elekta Synergy linac equipped with an Agility multi-leaf collimator, were modeled in Pinnacle TPS V9.8. Two models were created and compared: M1 and M2. M1 focuses on border and out-of-field parameters while M2 focuses on output factors agreement between models and measurements. Both models were evaluated using several tests found in the literature used as quality assurance. On the other hand, 20 treatment cases were controlled with the ArcCHECK device, the PTW TM31010 ionization chamber as well as EBT3 gafchromic films. Results M1 exhibits good agreement with measurements when performing tests from the literature, while M2 performs poorly in the “strip pattern” test. However, M1 calculation/measurement ratio goes up to 4.0% when comparing the dose in atypical fields, while M2 ratio stays below 1.3%. ArcCHECK gamma-test pass rates are similar between both models with 98.2% and 97.6% for M1 and M2, respectively (3%, 3 mm, local). Single point calculations differences with ionization chamber measurements are 2.5% and 1.0% in average, and reach a maximum of 3.6% and 2.0% for the M1 and M2 models, respectively. Gafchromic films analysis confirm the significant differences found with the ionization chamber for the M1 model and exhibit much better agreement for the M2 model. Conclusions The results demonstrate the importance to cross-check control tools. The significant gaps found with the M1 model were neither detected with quality assurance tests, neither with ArcCHECK measurements. It was necessary to implement home-made ionization chamber and gafchromic films test. This defect is preponderant with respect to the dose delivered on the target volume but is not prevalent in the zones of low doses where the diodes of the ArcCHECK are located.

Abstract ID: 198 Monte Carlo simulation and simple model of dose distribution in synchrotron radiation rotational radiotherapy of breast cancer: An experimental phantom study

External beam rotational radiotherapy of breast cancer with kilovoltage photons (kV-EBRT), with the patient in prone position, has been proposed [1] as a possible alternative to conventional radiotherapy with two tangential 6-MV X-ray beams produced by a medical linac with a supine patient. kV-EBRT uses a dedicated setup initially developed for breast CT, with a 320-kVp beam from an orthovoltage X-ray tube rotating in full circles around the breast; CT for tumour localization can be performed by using the same setup. Though dose build-up is not present, rotational summation of dose delivery allows a skin sparing comparable to conventional radiotherapy. We proposed the use of a monoenergetic synchrotron radiation (SR) collimated beam for image-guided rotational radiotherapy for the pendant breast (SR3T) [2] . The high flux of SR permits dose rates even greater to that of conventional radiotherapy, while the optimal photon energy can be selected for the treatment. In this work, we present Monte Carlo simulation and a simple model for evaluation of the 3D dose distribution in SR3T. The MC code was based on GEANT4 toolkit ver.10.00. We validated these simulations via measurements on breast phantoms performed at the Imaging and Medical Beamline of the Australian Synchrotron. We measured the dose distribution in cylindrical PMMA and polyethylene phantoms at 60 keV, using an ionization chamber, thermoluminescent dosimeters and radiochromic films. This study indicated that for a tumour localized at the centre of a mid-sized breast (14-cm diameter at chest wall), a ”skin-to-tumour” dose ratio of 14% can be reached at 60 keV with a collimated SR beam. Non uniform dose distribution to the target (dose painting) can be performed with multiple rotations around the organ. Kilovoltage SR3T with suitable radiosensitizers may exploit the dose enhancement factor due to increased photoelectric absorption, at SR beam energies in the 60–110 keV range.

A preliminary study of test and clinical application of a physical model based on the three-dimensional dose verification system using electronic portal imaging device

Objective To establish a physical model and optimize its physical parameters using the electronic portable imaging device (EPID) three-dimensional dose verification system, and to prepare it for clinical application. Methods EPID was used to acquire images of 3, 5, 10, 15, 20, and 25 cm square fields for construction of a physical model. The parameters of the physical model were optimized based on the percentage depth dose, total scatter factor, and off-axis ratio at a depth of 10 cm in a homogeneous water phantom. A thimble ionization chamber and radiochromic films were used to measure the point and planar doses for single fields, combined fields, and IMRT plans in a homogenous phantom and a human phantom. The results were compared with those in the three-dimensional reconstruction. In the human phantom and 10 intensity-modulated radiotherapy (IMRT) plans for tumors in different sites, the passing rates under the criteria of 5%/3 mm and 3%/3 mm were compared between three-dimensional reconstruction and treatment planning system (TPS) calculation. The dose and volume analyses were performed on target volume and organs at risk (OARs) in patients. Results For the single fields, combined fields, and IMRT plans, the mean deviations of point dose were less than 0.5% between three-dimensional reconstruction and ionization chamber measurement, and less than 2.0% between three-dimensional reconstruction and TPS calculation. In the homogenous phantom, the human phantom, and patients, the mean passing rates of both two-and three-dimensional doses were higher than 95% under the criteria of 5%/3 mm and 3%/3 mm. In patients, however, OARs with small volume had relatively large dose deviations. Conclusions A series of pre-clinical tests show that the three-dimensional dose verification system is an effective approach for clinical dose verification and holds promise for clinical application. Key words: Electronic portal imaging device; Three-dimensional dose verification; Physical model; Intensity modulated radiation therapy

Dosimetry for low energy protons with ionization chambers and EBT3 films in the BRAGG peak region

Introduction Protons beams are largely used for tumor therapy thanks to their property of delivering dose in a small localized area (Bragg peak). The 3 MV Tandem accelerator at CNA allows to perform measurements with low energy protons. By degrading passively the beam energy, we can study the dosimetry at the end of the range in tissue of therapeutic proton beams. Purpose Study of dosimetry in the Bragg peak region, in order to establish a dosimetry protocol in such region. Materials and methods A special device was used to degrade passively the energy of the beam. It mainly consists of a precise positioning system and a holder designed to house a ionization chamber (IC) and radiochromic films, which allowed to perform dosimetry studies at different distances in air. Results We present an experimental study of the Bragg peak in air using two ICs, the dosimetry with radiochromic films in the Bragg peak region and the comparison of data with Geant4 Monte Carlo simulations. Moreover, we expect to give a characterization of the radiochromic film dosimetry for the Bragg peak region where effects of saturation are occurring comparing Geant4 simulations with experimental data. Conclusion Few studies have been conducted until now to quantify the dose deposition in the Bragg peak, and by means of such measurements we are trying to establish a dosimetry protocol in such region, using Monte Carlo simulations and measurements with ICs and radiochromic films. Disclosure The authors have no conflicts of interest.

Betatron with variable energy for IORT

Introduction Since 2014 years in Tomsk Polytechnic University a new generation of betatrons for intraoperative radiation therapy (IORT) has been developing which has typical diameter approx. 70 cm at 6 MeV energy. The main advantages of the betatrons are that they operate at large frequency (400 Hz) at rather low pulse current, they have low energy spread and the relatively low cost of a device (typically $200,000). Purpose The purpose of the project is to develop and test the compact betatron with adjustable energy of the extracted electron beam. Materials and methods The depth dose distribution was measured along axis using plane-parallel Marcus ionization chamber and Gafchromic EBT-3 polymer film. Dosimetry was carried out following TG-51 and TRS-398 international protocols. The polymer films were calibrated using 10 MeV electron beam of Electa Axcess accelerator and 6 MeV electron beam of previous generation IORT betatron with constant energy. All measurements were performed in tissue-equivalent phantom with zero air gap. Results The investigation of 3D dose distributions generated by new type of IORT source based on betatron was carried out in the energy range 2–6 MeV with 500 keV steps. In addition the radiation background distribution near the betatron was measured and it would be used for design of biological protection. Conclusion According to the measured data it was proved that the extracted electron beam has designed energy that could be changed. The dose distributions allow assume that the compact IORT source based on betatron could be developed in the nearest future.