Gafchromic Film Research Articles

Development of patient-specific pre-treatment verification procedure for FLASH proton therapy based on time resolved film dosimetry.

Pre-clinical studies demonstrate that delivering a high dose at a high dose rate result in less toxicity while maintaining tumor control, known as the FLASH effect. In proton therapy, clinical trials have started using 250MeV transmission beams and more trials are foreseen. A novel aspect of FLASH treatments, compared to conventional radiotherapy, is the importance of dose rate next to dose and geometry. Therefore, to ensure the safety and quality of FLASH treatments, patient-specific dose-rate verification before treatment is an important additional prerequisite. Various definitions of dose rate have been reported, however, the scanning proton beam (PBS) dose rate definition of Folkerts 2020 is currently the most used. It is the ratio between delta dose (ΔD) and delta time (Δt), subject to a predefined threshold, for a given position. Gafchromic film is a widely available detector used to perform relative and absolute integrated dose measurements. Since the response time of film is in the order of micro seconds it could also be suitable for pre-treatment verification of FLASH proton therapy. Development of a patient-specific pre-treatment verification procedure for FLASH proton therapy based on time resolved film dosimetry. The detector design is presented and validated using three tests. A dedicated setup was built that holds a Gafchromic film and a high-speed camera to record the film during the irradiations. The red color channel of the camera's readings was converted into optical density (OD) and an OD-to-dose calibration curve was applied to determine the relative dose accumulation over time. To undo the film measurement (film response) of the post-irradiation coloration process, it is assumed that each dose deposit (pulse) results in a similar film response function. The convolution of the film response function over the pulse provides the film response. First the film response function was obtained by fitting this parameter onto a known film response and corresponding pulse. Post-irradiation coloration correction was performed by deconvoluting all film measurement by the obtained film response function. From the integral of each measured pulse, the Δt was obtained. Several validation tests were conducted: compare the Δt film measurement to a reference detector, exclude that revisiting spots result in an unwanted artefact on the dose accumulation measurement and thereby Δt, and compare Δt distributions of film measurement and simulation (local gamma evaluation, criteria 10%/2 mm) for nine QA fields (dose values; 12, 15, and 20Gy, and, nozzle currents; 25, 120, and 215nA). A similar analysis was performed for three dose optimized treatment beams, with and without scan patterns optimized on local dose rate. Good agreement was found for Δt comparing film to the reference detector, but for Δt values smaller than ∼20ms the error becomes larger (≥15%). Dose accumulation measured with film over time from a single spot is independent of whether the dose is delivered at once, twice or thrice. All gamma evaluations resulted in a gamma pass rate of ≥90%. Time resolved film dosimetry to perform patient-specific pre-treatment verification in FLASH proton therapy is feasible.

GAFchromic EBT film lateral resolution and contrast reproduction in the UV-blue range

The sensitivity of radiochromic films to UV-blue light is increasingly considered for light dosimetry purposes, owing to their bidimensional detection capabilities and ease of use. While film response to radiation intensity has been widely investigated by commercial scanners, spatial resolution studies remain scarce, especially for small field-of-view applications. These are of growing interest due to the antimicrobial or photo-bio-stimulating effects of UV-blue light sources in in vitro, ex vivo and in vivo models, where precise knowledge of irradiation conditions with adequate spatial resolution is crucial. In this study, we report the spatial lateral resolution and contrast reproduction of GAFchromic EBT2 and EBT3 models. Upon film irradiation by a 405 nm laser source or 365 nm LED, a confocal microscope setup was employed to read the film response at 405, 470, 488, 532 and 570 nm wavelengths, with radiant exposure of 10–70 J/cm2. The measured lateral resolution ranged from 8 to 33 μm. The film capability to reproduce contrast across various spatial frequencies (4–14 lines/mm) was evaluated using modulation transfer function analysis with irradiation performed at 365 nm and 405 nm, revealing a pronounced dependency on both radiant exposure and reading wavelength. These results confirm the film capacity to detect and resolve light intensity variability with a ~ 10 μm resolution, with notable applications in micro-beam profiling and light dosimetry.

A quantification of the electron return effect using Monte Carlo simulations and experimental measurements for the MRI-linac

The integration of magnetic resonance (MR) imaging and linear accelerators into hybrid treatment systems has made MR-guided radiation therapy a clinical reality. This work aims to evaluate the influence of the Electron Return Effect (ERE) on the dose distributions. This study was conducted using MRIdian (ViewRay, Cleveland, Ohio) system. Monte-Carlo simulations (MCs) and experimental measurements with EBT3 Gafchromic films were performed to investigate the dose distribution in a slab water phantom with and without a 2-cm air gap. Plus, MCs took into account different field sizes and a lung gap. A gamma analysis compared calculated versus measured dose distributions. The MCs have shown an increase of the ERE with the radiation field size both in Percent Depth Dose (PDD) and crossline direction. As concerns to the PDD direction, the smallest field for which there was a significant dose accumulation was 4.15×4.15 cm2both for air-gap (13.5%) and lung-gap (3.3%). The largest field for which there was a significant dose accumulation was 24.07×24.07 cm2both for air-gap (39.7%) and lung-gap (4.9%). Instead for the crossline direction, the smallest field for which there was a significant dose accumulation was 2.49×2.49 cm2both for air-gap (8.6% ) and lung-gap (0.5%). The largest field for which there was a significant dose accumulation was 24.07×24.07 cm2both for air-gap (46.2%) and lung-gap (4.2%). PDD and crossline profiles showed good agreement with a gamma-passing rate higher than 91.15% for 2%/2 mm. The ERE can be adequately calculated by MC dose calculation platform available in the MRIdian Treatment Planning System. The MCs show an increase of the ERE directly proportional with the radiation field size. Good agreement was observed between the experimental measurements and calculated dose distributions.

RBIO-03. A SMALL ANIMAL RADIATION RESEARCH PLATFORM (FLASH-SARRP) TO MEASURE IMMUNOLOGICAL EFFECT OF ULTRA HIGH DOSE RATE (FLASH) RADIOTHERAPY

Abstract Patients who undergo radiation therapy (RT), particularly fractionated courses, often develop lymphopenia. Clinical outcome for various cancer types, including brain tumors, identifies lymphopenia as a negative prognostic factor. The mechanism for RT induced lymphopenia is unclear. Simulated models suggest the volume of blood flowing through a radiation field could play a crucial role in death of radiosensitive lymphocytes. FLASH RT is ultrahigh dose rate administration of RT, >100 times faster dose rate than standard RT that has been observed to improve the therapeutic ratio in preclinical models by preferential normal tissue sparing. Hypothesized mechanisms include chemical reactions depleting oxygen in well oxygenated normal cells creating radioresistance, differing pro-inflammatory signaling impacting tumor and normal tissue, and less impact on circulating immune cells consequent to decreased proportion exposed during a treatment session which may enhance antineoplastic response. We designed the novel FLASH kV x-ray cabinet system for preclinical laboratory research (FLASH-SARRP) to deliver ultra-high dose rates up to 100 Gy/s as well as conventional dose rates of 1.0 Gy/s to facilitate comparative studies. A custom designed docking system was developed to reproducibly position and immobilize mouse for stereotactic radiation of the brain. Dose and dose rate measurements were performed with calibrated Gafchromic EBT3 film in solid water with 0.025 mm additional copper filter. FLASH-SARRP system delivered kV x-rays at an average dose-rate of 79.2±2.1Gy/s corresponding to 10 mm depth in the immobilized mouse brain. For the delivery of 15 Gy, treatment duration was 0.2 seconds for FLASH RT administration whereas it was 244 seconds for conventional dose rate. We successfully designed a high-precision platform to study partial brain x-ray FLASH effects in mice and studies are ongoing to assess differential impact on normal brain tissue, circulating cytokines, and immune cell populations for single dose and fractionated administration of FLASH and standard radiotherapy.

Characterization of novel 3D-printed metal shielding for brachytherapy applicators.

To characterize 3D-printed stainless steel metal samples in the presence of an Iridium-192 source for organ-at-risk sparing in gynecologic brachytherapy. Samples of 3D-printed stainless steel (5.5×5.5 cm2, thickness range 1-5mm) were embedded in a solid water phantom at varying distances from source catheters. An Ir-192 brachytherapy source was passed through the phantom and the dose was measured using EBT3 Gafchromic film. The film was initially positioned in the sagittal plane 2cm away from the catheters, with the metal directly below and then 1cm from the film. A uniform dose was delivered at the film plane. A second setup measured a depth dose curve in solid water with film in the transverse plane directly above the metal samples. This setup was recreated using Monte Carlo simulations (EGSnrc egs_brachy). Validation between methods was performed with unshielded (solid water only) measurements. The planar dose passing through the metal samples (thickness 1-5mm) at the midpoint between the film and catheters, decreased compared to solid water by 7.4%±6.9% to 26.5%±5.5%. Dose enhancement on the order of 5% was noted when metal was directly adjacent to the film. The average decrease in depth dose from a single dwell position ranged from 10.0%±5.9% (1mm) to 21.1%±5.3% (5mm) as measured with film, and from 3.8%±0.9% (1mm) to 16.3%±0.9% (5mm) using MC simulation. The average depth dose values were measured using a line width of 2.5mm for film, and 3mm for MC simulation, and the measurements generally agree within standard error. The 3D-printed metal samples show potential for personalized applicators. Maximum dose reduction of 26.5%±5.5% compared to solid water was measured at 2cm from the source using the 5mm sample. An outer layer of solid water could potentially be used to reduce dose enhancement due to increased scatter near the metal.

Development and international multicentre pilot testing of a postal dosimetry audit methodology for high dose rate brachytherapy

Background and PurposeDosimetry audits are essential for reducing errors in brachytherapy. A postal dosimetry audit methodology was developed and tested in an international multicentre pilot, to assess the accuracy of the Reference Air Kerma Rate of 192Ir and 60Co brachytherapy sources. Materials and MethodsA compact phantom made of polymethyl methacrylate was developed to accommodate two catheters, a radiophotoluminescence dosimeter (RPLD) for dose measurements and a Gafchromic (RTQA2) film strip for source position verification. Deviations of the audit setup from TG-43 conditions were quantified experimentally and compared to previous Monte Carlo (MC) simulations. A measurement uncertainty budget was estimated for the RPLD analysis. The methodology was tested in an international pilot study consisting of 59 dosimeter sets among 48 centres from 11 countries. ResultsThe experimental correction factors showed good agreement with previous MC simulations, and the total correction factor accounting for non-water equivalence, lack of scatter and beam quality was found to be 1.029 ± 0.009 for 192Ir and 1.059 ± 0.007 for 60Co sources, to be employed in audit measurement. The total uncertainty budget was estimated to be 2.24 % (k = 1). In the multicentre study, the ratio between measured and reported user dose ranged from 0.968 to 1.049, with all irradiated dosimeter sets within ± 5 %, and 54 out of 59 within ± 3 %. ConclusionsThe methodology was tested in an international multicentre pilot study and has shown good performance validating the uncertainty budget.

Development of a 3D-printed phantom for total skin electron therapy dose assessment.

Total skin electron therapy (TSET) is a complex radiotherapy technique, posing challenges in commissioning and quality assurance (QA), especially due to significant variability in patient body shapes. Previous studies have correlated dose with factors such as obesity index, height, and gender. However, current treatment planning systems cannot simulate TSET plans, necessitating heavy reliance on QA methods using standardized anthropomorphic phantoms and in-vivo dosimetry. Given the relatively few studies on rotational techniques, comprehensive data in commissioning could streamline the process. Developing a full-body phantom would enable a more thorough TSET commissioning process, including testing for position-specific dose distributions and comprehensive measurements across all body surfaces, unlike the typical torso-only phantoms. This was created using digital modeling software, fabricated using 3D-printing FDM technology, and filled with tissue-equivalent gelatine. The phantom was positioned at an SSD of 340cm and irradiated with a standard rotational TSET plan using the 6E HDTSE mode on a Varian TrueBeam linac at gantry angles of±18° from the horizontal. The dose was measured at over 50 points across the surface using Gafchromic EBT3 film. Dose distributions were generally consistent with existing literature values from in-vivo dosimetry, with several position-specific differences identified, including the hands and scalp compared to conventional positions. Hotspots were observed for the mid-dorsum of the foot and nose, with areas under 80% of the dose identified as the soles of the feet, perineum, vertex of the scalp, top of the shoulder, and palm of the hand. Additionally, analysis using an interpolated dose heatmap found that 90% of the pixel area received a dose within 10% of the prescribed dose, indicating good uniformity with the commissioned technique. With high agreement with the current literature, a 3D-printed phantom proves effective for measuring doses in areas typically unmeasurable in TSET commissioning.

Monte Carlo calculated absorbed-dose energy dependence of EBT3 and EBT4 films for 5-200 MeV electrons and 100 keV-15 MeV photons.

To use Monte Carlo simulations to study the absorbed-dose energy dependence of GAFChromic EBT3 and EBT4 films for 5-200MeV electron beams and 100keV-15MeV photon beams considering two film compositions: a previous EBT3 composition (Bekerat etal.) and the final composition of EBT3/current composition of EBT4 (Palmer etal.). A water phantom was simulated with films at 5-50mm depth in 5mm intervals. The water phantom was irradiated with flat, monoenergetic 5-200MeV electron beams and 100 and 150keV kilovoltage and 1-15MeV megavoltage photon beams and the dose to the active layer of the films was scored. Simulations were rerun with the films defined as water to compare the absorbed-dose response of film to water, . For electrons, the Bekerat etal. composition had variations in of up to from 5to200MeV. Similarly, the Palmer etal. composition had differences in up to from 5to200MeV. For photons, varied up to and from 100keV to 15MeV for the Bekerat etal. and Palmer etal. compositions, respectively. The depth of films did not appear to significantly affect for photons at any energy and for electrons at energies 50MeV. However, for 5 and 10MeV electrons, decreases of up to in were seen due to stacked films and increased beam attenuation in films compared to water. The up to and variations in for electrons and photons, respectively, across the energies considered in this study indicate the importance of calibrating films with the energy intended for measurement. Additionally, this work emphasizes potential issues with stacking films to measure depth dose curves, particularly for electron beams with energies 10MeV.

Characterization of a new low-dose and low-energy Gafchromic film LD-V1.

To characterize the dose-response, energy dependence, postexposure changes, orientation dependence, and spatial capabilities of LD-V1, a new low-dose Gafchromic film for low-energy x-ray dosimetry. A single sheet of LD-V1 Gafchromic film was cut into 15 × 20mm2 rectangles with a notch to track orientation. Eight different doses between 5 and 320mGy were delivered by an MXR-160/22 x-ray tube using x-ray beams of 90, 100, and 120kVp filtered with 3mm of Al and 2mm of Ti. The 120kVp films were scanned at 1, 1.5, 2, 3, 12, 24, 48, 72, and 168h postexposure in portrait orientation and additionally scanned in landscape orientation at 24h. The 90 and 100kVp films were scanned at 24h postexposure in portrait orientation. Lastly, a 20 × 200mm2 strip of film was irradiated using a thin-slit imaging collimator and scanned 24h postexposure to test the film performance in an x-ray imaging application. Of the three color channels, the red channel was found to produce a dose-response curve with a large range of net optical density (netOD) values across the considered dose range. A prominent energy dependence was discovered, resulting in dose discrepancies on the scale of 17mGy between 90 and 120kVp for a dose of 80mGy. The measured postexposure changes suggest that the calibration irradiation-to-scan time should be longer than 12h with a±4h scanning time window for dose errors of<0.5%. An average dose difference of 3.4% was found between the two scanning orientations. Lastly, noise of 4% was measured in the thin slit collimator film for a dose of 30mGy. We have characterized the LD-V1 film for low-energy, low-dose x-ray dosimetry. Energy, scan-time, and orientation dependencies should be considered when using this film.

Optimum delineation of skin structure for dose calculation with the linear Boltzmann transport equation algorithm in radiotherapy treatment planning.

This study investigated the effectiveness of placing skin-ring structures to enhance the precision of skin dose calculations in patients who had undergone head and neck volumetric modulated arc therapy using the Acuros XB algorithm. The skin-ring structures in question were positioned 2mm below the skin surface (skin A) and 1mm above and below the skin surface (skin B) within the treatment-planning system. These structures were then tested on both acrylic cylindrical and anthropomorphic phantoms and compared with the Gafchromic EBT3 film (EBT3). The results revealed that the maximum dose differences between skins A and B for the cylindrical and anthropomorphic phantoms were approximately 12% and 2%, respectively. In patients 1 and 2, the dose differences between skins A and B were 9.2% and 8.2%, respectively. Ultimately, demonstrated that the skin-dose calculation accuracy of skin B was within 2% and did not impact the deep organs.

Evaluation of the usefulness of small detectors made of Gafchromic EBT3 film for measurements in areas with high dose gradient and without charged-particle equilibrium (CPE)

Evaluation of the usefulness of small detectors made of Gafchromic EBT3 film for measurements in areas with high dose gradient and without charged-particle equilibrium (CPE)

704: Dose response and energy dependence of the new EBT4 GafChromic film model

704: Dose response and energy dependence of the new EBT4 GafChromic film model

Characterization of a Modified Clinical Linear Accelerator for Ultra-High Dose Rate Beam Delivery

Irradiations at Ultra-High Dose Rate (UHDR) regimes, exceeding 40 Gy/s in single fractions lasting less than 200 ms, have shown an equivalent antitumor effect compared to conventional radiotherapy with reduced harm to normal tissues. This work details the hardware and software modifications implemented to deliver 10 MeV UHDR electron beams with a linear accelerator Elekta SL 18 MV and the beam characteristics obtained. GafChromic EBT XD films and an Advanced Markus chamber were used for dosimetry characterization, while a silicon sensor assessed the machine’s beam pulses stability and repeatability. The dose per pulse, average dose rate and instantaneous dose rate in the pulse were evaluated for four experimental settings, varying the source-to-surface distance and the beam collimation, i.e., with and without the use of a cylindrical applicator. The results showed a dose per pulse from 0.6 Gy to a few tens of Gy and an average dose rate up to 300 Gy/s. The obtained results demonstrate the possibility to perform in vitro radiobiology experiments and test new technologies for beam monitoring and dosimetry at the upgraded LINAC, thus contributing to the electron UHDR research field.

Multi-institutional experimental validation of online adaptive proton therapy workflows

Objective. To experimentally validate two online adaptive proton therapy (APT) workflows using Gafchromic EBT3 films and optically stimulated luminescent dosimeters (OSLDs) in an anthropomorphic head-and-neck phantom. Approach. A three-field proton plan was optimized on the planning CT of the head-and-neck phantom with 2.0 Gy(RBE) per fraction prescribed to the clinical target volume. Four fractions were simulated by varying the internal anatomy of the phantom. Three distinct methods were delivered: daily APT researched by the Paul Scherrer Institute (DAPTPSI), online adaptation researched by the Massachusetts General Hospital (OAMGH), and a non-adaptive (NA) workflow. All methods were implemented and measured at PSI. DAPTPSI performed full online replanning based on analytical dose calculation, optimizing to the same objectives as the initial treatment plan. OAMGH performed Monte-Carlo-based online plan adaptation by only changing the fluences of a subset of proton beamlets, mimicking the planned dose distribution. NA delivered the initial plan with a couch-shift correction based on in-room imaging. For all 12 deliveries, two films and two sets of OSLDs were placed at different locations in the phantom. Main results. Both adaptive methods showed improved dosimetric results compared to NA. For film measurements in the presence of anatomical variations, the [min-max] gamma pass rates (3%/3 mm) between measured and clinically approved doses were [91.5%–96.1%], [94.0%–95.8%], and [67.2%–93.1%] for DAPTPSI, OAMGH, and NA, respectively. The OSLDs confirmed the dose calculations in terms of absolute dosimetry. Between the two adaptive workflows, OAMGH showed improved target coverage, while DAPTPSI showed improved normal tissue sparing, particularly relevant for the brainstem. Significance. This is the first multi-institutional study to experimentally validate two different concepts with respect to online APT workflows. It highlights their respective dosimetric advantages, particularly in managing interfractional variations in patient anatomy that cannot be addressed by non-adaptive methods, such as internal anatomy changes.

Reading of gafchromic EBT-3 film using an overhead scanner

Gafchromic film, a commercially available radiochromic film, has been developed and widely used as an effective tool for radiation dose verification and quality assurance in radiotherapy. However, the orientation effect in scanning a film remains a concern for practical application in beam profile monitoring. To resolve this issue, the authors introduced a novel method using an overhead scanner (OHS) coupled with a tracing light board instead of a conventional flatbed scanner (FBS) to read Gafchromic EBT3 films. We investigated the orientation effect of the EBT3 film with a regular hexagonal shape after irradiation with 5 Gy x-rays (160 kV, 6.3 mA) and compared the digitized images acquired using a commercially available OHS (CZUR Aura) and a conventional FBS (EPSON GT-X980). As a result, RGB color intensities acquired from the OHS showed significantly lower orientation effect of the color intensities of RGB components than those from FBS. This finding indicates the high potential of the proposed method for achieving more precise two-dimensional dosimetry. Further studies are required to confirm the effectiveness of this method under different irradiation conditions over a wider dose range.

Preclinical photon minibeam radiotherapy using a custom collimator: Dosimetry characterization and preliminary in-vivo results on a glioma model

PurposeThe purpose of this study is to investigate the dosimetric characteristics of a collimator for minibeam radiotherapy (MBRT) with film dosimetry and Monte Carlo (MC) simulations. The outcome of MBRT with respect to conventional RT using a glioma preclinical model was also evaluated. MethodsA multi-slit collimator was designed to be used with commercial small animal irradiator. The collimator was built by aligning 0.6 mm wide and 5 mm thick parallel lead leaves at 0.4 mm intervals. Dosimetry characteristics were evaluated by Gafchromic (CG) films and TOPAS Monte Carlo (MC) code.An in vivo experiment was performed using a glioma preclinical model by injecting two million GL261cells subcutaneously and treating with 25 Gy, single fraction, with MBRT and conventional RT. Survival curves and acute radiation damage were measured to compare both treatments. ResultsA satisfactory agreement between experimental results and MC simulations were obtained, the measured FWHM and distance between the peaks were respectively 0.431 and 1.098 mm.In vivo results show that MBRT can provide local tumor control for three weeks after RT treatment and a similar survival fraction of open beam radiotherapy. No severe acute effects were seen for the MBRT group. ConclusionsWe developed a minibeam collimator and presented its dosimetric features. Satisfactory agreement between MC and GC films was found with differences consistent with uncertainties due to fabrication and set-up errors. The survival curves of MBRT and open field RT are similar while atoxicity is dramatically lower with MBRT, preliminarily confirming the expected effect.

Dosimetry and Monte Carlo modelling of the Papillon+ contact X-ray brachytherapy device

PurposeThis study aimed to develop and validate a Monte Carlo (MC) model for the Papillon+ contact x-ray brachytherapy (CXB) device, producing 50 kilovolt (kV) x-rays, specifically focusing on its application with a 25 mm diameter rectal applicator for contact therapy. Material and methodsThe validation process involved depth dose and transverse dose profile measurements using EBT3 gafchromic films positioned in a Plastic Water Low Energy Range phantom. The half-value layer (HVL) was further measured and derived from the simulated x-ray spectra. ResultsExcellent agreement within ± 2 % was achieved between the measured and simulated on-axis depth dose curves for the 25 mm rectal applicator. Transverse dose profile measurements showed a high level of agreement between the simulation and measurements, on average 3.1 % in contact with the applicator at the surface of the phantom and on average 1.7 % at 10 mm depth. A close agreement within 5.5 % was noticed concerning the HVL between the measurement and simulation. The simulated gamma spectra and 2D-dose distribution demonstrated a soft x-ray energy spectrum and a uniform dose distribution in contact with the applicator. ConclusionsAn MC model was successfully developed for the Papillon+ eBT device with a 25 mm diameter rectal applicator. The validated model, with its demonstrated accuracy in depth dose and transverse dose profile simulations, is a valuable tool for quality assurance and patient safety and, in a later phase, may be used for treatment planning, dose calculations and tissue inhomogeneity corrections.

Radiochromic film EBT3 calibration for linear accelerator in 10 MV

Radiochromic film is used to applications in dosimetry have become increasingly significant for studies on radiotherapy. Due to sensitivity to exposure to ionizing radiation, radiochromic films are commonly used to obtain dose distribution maps and for calibration curves. The calibration curves in the radiochromic films can be use radiochromic films as a dosimetry method and then seek the generation of images with lower dose deposition and higher diagnostic quality. When ionizing radiation interacts with matter it generates energy deposition. Radiation dosimetry is important for medical applications of ionizing radiation due to the increasing demand for diagnostic radiology and radiotherapy. The film is a dose measurement method that records the energy deposition by the darkening of its emulsion. Radiochromic films have a little visible light sensitivity and respond better to ionizing radiation exposure. The aim of this study is to obtain the resulting calibration curve by the irradiation of radiochromic film strips, making it possible to relate the darkening of the film with the absorbed dose, to measure doses in experiments with X-ray beam of 10 MeV in Linear Accelerator. The objective of this study is to obtain the calibration curves of the radiographic film for exposure with X-ray beam in Linear Accelerator scanner for realize measures of typical doses found in radiotherapy. It was used Gafchromic EBT Radiochromic Film, which shows little sensitivity to visible light and a response in the range of 0.1 to 10 Gy for X-ray beam. In the experiments, a Solid Water Phantom, with a 30x30x2.0 cm³. The strips were scanned and processed using the ImageJ software to obtain the intensity values resulting from the absorbed radiation by grayscale. The darkening responses on film strips according to the doses were observed and they allowed obtaining the corresponding numeric values to the darkening for each specific dose value. From the numerical values of darkening, a calibration curve was obtained.

First in vitro cell co-culture experiments using laser-induced high-energy electron FLASH irradiation for the development of anti-cancer therapeutic strategies

Radiation delivery at ultrahigh dose rates (UHDRs) has potential for use as a new anticancer therapeutic strategy. The FLASH effect induced by UHDR irradiation has been shown to maintain antitumour efficacy with a reduction in normal tissue toxicity; however, the FLASH effect has been difficult to demonstrate in vitro. The objective to demonstrate the FLASH effect in vitro is challenging, aiming to reveal a differential response between cancer and normal cells to further identify cell molecular mechanisms. New high-intensity petawatt laser-driven accelerators can deliver very high-energy electrons (VHEEs) at dose rates as high as 1013 Gy/s in very short pulses (10–13 s). Here, we present the first in vitro experiments carried out on cancer cells and normal non-transformed cells concurrently exposed to laser-plasma accelerated (LPA) electrons. Specifically, melanoma cancer cells and normal melanocyte co-cultures grown on chamber slides were simultaneously irradiated with LPA electrons. A non-uniform dose distribution on the cell cultures was revealed by Gafchromic films placed behind the chamber slide supporting the cells. In parallel experiments, cell co-cultures were exposed to pulsed X-ray irradiation, which served as positive controls for radiation-induced nuclear DNA double-strand breaks. By measuring the impact on discrete areas of the cell monolayers, the greatest proportion of the damaged DNA-containing nuclei was attained by the LPA electrons at a cumulative dose one order of magnitude lower than the dose obtained by pulsed X-ray irradiation. Interestingly, in certain discrete areas, we observed that LPA electron exposure had a different effect on the DNA damage in healthy normal human epidermal melanocyte (NHEM) cells than in A375 melanoma cells; here, the normal cells were less affected by the LPA exposure than cancer cells. This result is the first in vitro demonstration of a differential response of tumour and normal cells exposed to FLASH irradiation and may contribute to the development of new cell culture strategies to explore fundamental understanding of FLASH-induced cell effect.

Proton beam spot size and position measurements using a multi-strip ionization chamber

PurposeTo develop and characterize a large-area multi-strip ionization chamber (MSIC) for efficient measurement of proton beam spot size and position at a synchrotron-based proton therapy facility. Methods and MaterialsA 420 mm x 320 mm MSIC was designed with 240 vertical strips and 180 horizontal strips at 1.75 mm pitch. The MSIC was characterized by irradiating a grid of proton spots across 17 energies from 73.5 MeV to 235 MeV and comparing to simultaneous measurements made with a reference Gafchromic EBT3 film. Beam profiles, spot sizes, and positions were analyzed. Short term measurement stability and sensitivity were evaluated. ResultsExcellent agreement was demonstrated between the MSIC and EBT3 film for both spot size and position measurements. Spot sizes agreed within ± 0.18 mm for all energies tested. Measured beam spot positions agreed within ± 0.17 mm. The detector showed good short term measurement stability and low noise performance. ConclusionThe large-area MSIC enables efficient and accurate proton beam spot characterization across the clinical energy range. The results indicate the MSIC is suitable for pencil beam scanning proton therapy commissioning and quality assurance applications requiring fast spot size and position quantification.