EBT3 Radiochromic Films Research Articles

P14.16.A IS A LINAC WITH A 5MM MLC WIDTH REALLY A BARRIER TO IMPLEMENTING A HIGH-QUALITY COMPLEX SRS SERVICE?

Abstract BACKGROUND Stereotactic Radiosurgery (SRS) for patients with intracranial disease is increasing, especially for smaller and more numerous metastases. In England, Varian HyperArc using a Truebeam linac is nationally commissioned via benchmarking. HyperArc contains SRS-specific optimisation and non-coplanar VMAT delivery and is an attractive option due to its cost effectiveness compared with competing specialised platforms such as Elekta GammaKnife and Accuray CyberKnife. Depsite these benefits, the treatment of small targets or those with highly complex shapes is dominated by specialised platforms with a largely stated reason being perceived concern over delivered dosimetric certainty. This work assesses achievable dosimetric accuracy for complex SRS using Varian HyperArc suing a standard 120-leaf 5mm width MLC. MATERIAL AND METHODS Four patients with small and/or complex PTVs previously treated with CyberKnife at our institution were identified:26 metastases 24Gy/1f (PTV min. volume 0.01cc);5 metastases 24 Gy/1f (PTV min. volume 0.11cc);Pituitary adenoma 25Gy/1f (PTV width min. 5 mm near optics);Acoustic neuroma 21 Gy/3f (PTV width min. 3 mm near cochlea). Patients were re-planned with HyperArc using 4 arcs at 6FFF, emulating the prescription dose spillage (PDS) & modified gradient index (mGI) achieved in the CyberKnife plans. Plans were produced in Eclipse v17.1, calculated using the AAA algorithm (v 17.1.0.1) on a 1mm calculation grid. The plan was then transferred to a CT scan of an in-house water equivalent phantom containing radiochromic EBT3 film in clinically meaningful coronal and sagittal dose planes and re-calculated. All plans were delivered under image guidance and the 2D film dosimetry was compared with the calculated dose from Eclipse using a global 5%/1mm (TH 20%) gamma test using well-established absolute dose film methodology in Sun Nuclear SNC Patient (v 8.2). RESULTS In all cases, HyperArc had very similar plan quality to CyberKnife, with maximum dose gradients between 20-23% of prescription dose per mm beyond the PTV (up to 5.8Gy/mm). Up to 1mm geometric offset was permitted to allow for imaging localization & film registration uncertainty in the analysis. Mean gamma pass rates were 93.3% pre-alignment and 98.5% post-alignment. CONCLUSION The very high gamma pass rates achieved in this novel work illustrate excellent delivered dose accuracy for high-quality SRS plans. The use of a radiochromic film dosimetry allows for the demonstration of such accuracy using a standard Truebeam linac without the use of a high-definition MLC even for the smallest and most complex SRS targets. This work enables us to re-think previously held beliefs around perceived dosimetric limitations of multi-arc VMAT with a 5 mm MLC width for the delivery of high-quality SRS. Removing this barrier could start to bridge the existing gap in worldwide SRS service provision for patients.

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.

Experimental and Monte Carlo based dosimetric investigation of a novel 3mm radiosurgery 3MV beam using the microSilicon detector.

The ZAP-X system is a novel gyroscopic radiosurgical system based on a 3MV linear accelerator and collimator cones with a diameter between 4 and 25mm. Advances in imaging modalities to detect small and early-stage pathologies allow for an early and less invasive treatment, where a smaller collimator matching the anatomical target could provide better sparing of surrounding healthy tissue. A novel 3mm collimator cone for the ZAP-X was developed. This study aims to investigate the usability of a commercial diode detector (microSilicon) for the dosimetric characterization of this small collimator cone; and to investigate the underlying small field perturbation effects. Profile measurements in five depths as well as PDD and output ratio measurements were performed with a microSilicon detector and radiochromic EBT3 films. In addition, comprehensive Monte Carlo simulations were performed to validate the measurement observations and to quantify the perturbation effects of the microSilicon detector in these extremely small field conditions. It is shown that the microSilicon detector enables an accurate dosimetric characterization of the 3mm beam. The profile parameters, such as the FWHM and 20%-80% penumbra width, agree within 0.1 to 0.2mm between film and detector measurements. The output ratios agree within the measurement uncertainty between microSilicon detector and films, whereas the comparisons of the PDD results show good agreement with the Monte Carlo simulations. The analysis of the perturbation factors of the microSilicon detector reveals a small field correction factor of approximately 3% for the 3mm circular beam and a correction factor smaller than 1.5% for field diameters above 3mm. It could be shown that the microSilicon detector is well-suitable for the characterization of the new 3mm circular beam of the ZAP-X system.

Depth dose measurement by using Al2O3 OSL dosimeters in high energy photons in the presence of air cavity and density inhomogeneity

Air cavities and tissue density inhomogeneity significantly affects the distribution of radiation doses, potentially resulting in adverse consequences such as cancer recurrence. This research aims to assess the accuracy of Al2O3 optically stimulated luminescence (OSL) dosimeters in measuring doses within varying thicknesses of air cavities (3, 5, and 8 cm) and tissue inhomogeneity of low and high density simulated by the lung and bone phantoms. An expanded polystyrene (EPS) was employed in homogeneous solid water® phantoms to simulate the air cavity. The percentage depth-dose (PDD) curves at 6 MV photons were obtained in both presence of air cavity and density inhomogeneity and compared to that in the EBT3 radiochromic film dosimeters and treatment planning system (TPS). The results indicated that the presence of an air cavity and tissue inhomogeneity affected the depth dose measured in OSL dosimeters, EBT3 films and TPS. OSLD and TPS showed good agreement at the centre of the cavity, which is within ±5% but could not estimate scattered radiation to the distal and proximal surfaces of the air cavity. The obtained p-values showed no significant differences of dose measured in OSL dosimeters compared to those in EBT3 films and TPS. The Kruskal Wallis test and Mann-Whitney showed no significant difference between OSL dosimeters, EBT3 film and TPS in the measurement of depth doses in the presence of density inhomogeneity. The overall results indicated the suitability of OSL dosimeters as indirect dosimeters for the measurements of depth dose in the presence of air cavity and tissue density inhomogeneity

MR compatible detectors assessment for a 0.35 T MR-linac commissioning

PurposeTo assess a large panel of MR compatible detectors on the full range of measurements required for a 0.35 T MR-linac commissioning by using a specific statistical method represented as a continuum of comparison with the Monte Carlo (MC) TPS calculations. This study also describes the commissioning tests and the secondary MC dose calculation validation.Material and methodsPlans were created on the Viewray TPS to generate MC reference data. Absolute dose points, PDD, profiles and output factors were extracted and compared to measurements performed with ten different detectors: PTW 31010, 31021, 31022, Markus 34045 and Exradin A28 MR ionization chambers, SN Edge shielded diode, PTW 60019 microdiamond, PTW 60023 unshielded diode, EBT3 radiochromic films and LiF µcubes. Three commissioning steps consisted in comparison between calculated and measured dose: the beam model validation, the output calibration verification in four different phantoms and the commissioning tests recommended by the IAEA-TECDOC-1583.Main resultsThe symmetry for the high resolution detectors was higher than the TPS data of about 1%. The angular responses of the PTW 60023 and the SN Edge were − 6.6 and − 11.9% compared to the PTW 31010 at 60°. The X/Y-left and the Y-right penumbras measured by the high resolution detectors were in good agreement with the TPS values except for the PTW 60023 for large field sizes. For the 0.84 × 0.83 cm2 field size, the mean deviation to the TPS of the uncorrected OF was − 1.7 ± 1.6% against − 4.0 ± 0.6% for the corrected OF whereas we found − 4.8 ± 0.8% for passive dosimeters. The mean absolute dose deviations to the TPS in different phantoms were 0 ± 0.4%, − 1.2 ± 0.6% and 0.5 ± 1.1% for the PTW 31010, PTW 31021 and Exradin A28 MR respectively.ConclusionsThe magnetic field effects on the measurements are considerably reduced at low magnetic field. The PTW 31010 ionization chamber can be used with confidence in different phantoms for commissioning and QA tests requiring absolute dose verifications. For relative measurements, the PTW 60019 presented the best agreement for the full range of field size. For the profile assessment, shielded diodes had a behaviour similar to the PTW 60019 and 60023 while the ionization chambers were the most suitable detectors for the symmetry. The output correction factors published by the IAEA TRS 483 seem to be applicable at low magnetic field pending the publication of new MR specific values.

Rapid calibration curve generation using single-sheet radiochromic film for proton-based stereotactic radiosurgery verification

Proton-based stereotactic radiosurgery (PSRS) holds promise for treating benign tumours, with patient-specific quality assurance (PSQA) playing a crucial role in ensuring high-quality clinical services. EBT3 films are a perfect tool for PSQA, particularly owing to their compatibility with small-field dosimetry. However, a successful absolute EBT3 dosimetry relies on detailed dose calibration, consuming much time and films. A novel approach has been developed in this study and tested to establish a calibration curve using a single sheet of EBT3 radiochromic films exposed to six multi-leaf collimator (MLC) fields. Notably, this method allows for the completion of a calibration curve in just 15 min, enabling the practical generation of new EBT3 calibrations daily. This single-sheet approach can generate a dose calibration curve with an error of less than 1.5% across the entire dose range and is well agreed to by traditional multi-film calibrations involving large fields, with a discrepancy of less than 0.8%.

In vivo dosimetry using EBT3 and EBT-XD radiochromic films for high-energy electron beam in hypofractionation keloid radiotherapy

Radiochromic film is commonly used for in vivo dose verification in radiotherapy. The aim of this study was to investigate the difference in the in vivo dose of high-energy electron beam with single hypofractionation radiotherapy between EBT3 and EBT-XD films in keloid patients. Thirty patients who received postoperative keloid radiotherapy were enrolled in the study (ethics approval: FEMH-IRB-108165). Gafchromic EBT3 and EBT-XD films in the form of 2 × 3 cm2 sheets were used to measure the surface dose to the postoperative keloid scars. The research compared the measurement dose and prescribed dose as well as the difference between EBT3 and EBT-XD radiochromic films. The surface dose in the EBT3 group was 85.5–104.7 % of the prescribed dose and that in the EBT-XD group was 88∼106.6 % of the prescribed dose. The mean percentage differences for thirty measurements were −4.9 % and −2.5 % for the EBT3 and EBT-XD films, respectively. The maximum variation for both film types was −15.3 % and −12.4 % for Patient #6 with a scapula keloid lesion. This investigation also demonstrated that, for 40 % of the patients in the EBT3 group, good agreement (within 5 % variation) was obtained between the dose measurements and the prescribed dose. In contrast, 73 % of the patients in the EBT-XD group agreed well with the expected dose. Moreover, for 10 % of the patients, high agreement (within 1 % variation) was demonstrated for the EBT3 film, and 23 % of the patients were consistent with the EBT-XD film. This study also revealed significant differences between the EBT3 and EBT-XD gafchromic films (p = 0.002). This was not only the first study to perform in vivo dosimetry using EBT-XD film, but also to survey the difference in surface dose between EBT3 and EBT-XD films under the same treatment conditions for clinical patients. For in vivo dosimetry in electron beam radiotherapy, compared with the EBT3 radiochromic film, the EBT-XD film is more suitable for hypofractionation surface dose verification.

On the color channel's effect on the dose-response of Gafchromic EBT2 and EBT3 radiochromic films to 6 MeV electron beam

The color channel's effect on the dose-response of Gafchromic™ EBT2 and EBT3 radiochromic films irradiated with a 6 MeV electron beam in the range from 0 to 1000 cGy was investigated and compared. A Canon flatbed scanner was used to scan the irradiated Gafchromic™ EBT2 and EBT3 films, while ultraviolet-visible (UV-Vis) absorption spectra were analyzed with a spectrophotometer. Triple RGB channel, weighted and unweighted grey images were analyzed using the free software ImageJ. As the 6 MeV electron beam dose increases, the pixel values of the red, green, weighted, and unweighted grey images decrease exponentially for both Gafchromic™ EBT2 and EBT3 films. The blue channel fluctuates with the increase of 6 MeV electron beam dose for both EBT2 and EBT3 films and decreases the unweighted grey image more than the weighted greyscale image. The characteristic peaks at 582 ± 2 nm and 632 ± 2 nm of Gafchromic™ EBT2 and EBT3 films are correlated with the absorbed 6 MeV electron beam dose. The sensitivity deterioration constant b3 (is a free parameter of fitting in units of (cGy−1)) of EBT2 film is higher than EBT3 at both characteristic peaks at 582 ± 2 nm, and 632 ± 2 nm, indicating that EBT2 has better sensitivity at the expense of dynamic range, whilst EBT3 has lower sensitivity but a higher dynamic range. In comparison to the red and green channels, UV-Vis absorption in the blue channel range between 450 nm and 490 nm has a weak response and a small dynamic range. The Gafchromic™ EBT2 and EBT3 films scan with monochromatic red or green channels resulting in increased sensitivity and a wider dynamic range.

Response of the modified GAFCHROMIC EBT2 radiochromic film to DC glow discharge plasma

The response of the modified GAFCHROMIC EBT2 radiochromic film to DC Oxygen glow discharge plasma was investigated using a flatbed scanner and an UV–Vis spectrophotometer. The film was modified by removing the polyester overlaminate, adhesive, and topcoat layers with a total thickness of 80 µm, and is now referred to as EBT2-M. The EBT2-M films were exposed to DC Oxygen plasma for different durations: 0, 0.5, 1, 2, 3, 4, 7, and 10 min. The exposed films exhibit coloration homogeneity with an average variation of (1.6 ± 0.3) × 10−4 pixel values/µm, irrespective of the applied exposure time. The pixel values of the red-and-green channels and weighted grayscale images decreased exponentially with different sensitivity amounts to ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} 39.67, 49.69, and 42.11 min−1, respectively, as the exposure time increased. The two absorption peaks at 580 ± 4 nm and 632 ± 4 nm in the UV–Vis absorption spectra of the exposed GAFCHROMIC EBT2-M radiochromic films are increasing with increasing exposure time up to 4 min, thereafter saturated for prolonged exposure time. The integrated absorbance in the range from 400 to 700 nm is linearly correlated with the exposure time. The indirect and direct optical energy band gaps and Urbach energy of the modified GAFCHROMIC EBT2 film are weakly correlated with the exposure time. These findings suggest the utilization of the modified GAFCHROMIC EBT2 radiochromic film as a novel and simple technique for plasma diagnostics.

Dose-rate dependence and IMRT QA suitability of EBT3 radiochromic films for pulse reduced dose-rate radiotherapy (PRDR) dosimetry.

Pulsed reduced dose rate (PRDR) is an emerging radiotherapy technique for recurrent diseases. It is pertinent that the linac beam characteristics are evaluated for PRDR dose rates and a suitable dosimeter is employed for IMRT QA. This study sought to investigate the pulse characteristics of a 6 MV photon beam during PRDR irradiations on a commercial linac. The feasibility of using EBT3 radiochromic film for use in IMRT QA was also investigated by comparing its response to a commercial diode array phantom. A plastic scintillator detector was employed to measure the photon pulse characteristics across nominal repetition rates (NRRs) in the 5-600 MU/min range. Film was irradiated with dose rates in the 0.033-4Gy/min range to study the dose rate dependence. Five clinical PRDR treatment plans were selected for IMRT QA with the Delta4 phantom and EBT3 film sheets. The planned and measured dose were compared using gamma analysis with a criterion of 3%/3mm. EBT3 film QA was performed using a cumulative technique and a weighting factor technique. Negligible differences were observed in the pulse width and height data between the investigated NRRs. The pulse width was measured to be 3.15±0.01 and the PRF was calculated to be 3-357Hz for the 5-600 MU/min NRRs. The EBT3 film was found to be dose rate independent within 3%. The gamma pass rates (GPRs) were above 99% and 90% for the Delta4 phantom and the EBT3 film using the cumulative QA method, respectively. GPRs as low as 80% were noted for the weighting factor EBT3 QA method. Altering the NRRs changes the mean dose rate while the instantaneous dose rate remains constant. The EBT3 film was found to be suitable for PRDR dosimetry and IMRT QA with minimal dose rate dependence.

Dose mapping of hard X-ray radiation due to runaway electrons in Alvand tokamak using combination of high-dose and low-dose level dosimeters

Tokamaks are one of the strongest types of hard x-ray (HXR) sources that always generate energetic hard x-rays because of the bremsstrahlung radiation, when energetic runaway electrons are accelerated in the presence of the toroidal electric field. In addition, the characteristics of small-sized tokamaks make them capable of having a considerable population of runaway electrons during discharge time. In this research, the hard x-ray dose distribution of Alvand tokamak is measured and calculated using EBT3 radiochromic film and GR-200 TLD as a high-dose and low-dose dosimeters, respectively. The purpose of this measurement is to obtain a dose distribution map in the Alvand tokamak laboratory (35 m × 13 m) and its environment. It has been determined that the maximum absorbed dose on the equatorial plane of the vacuum chamber is approximately 73 mSv/shot for a 3 ms discharge. According to the observations, the occurrence of Z instability in the vertical position of the plasma leads to the concentration of a substantial amount of radiation in an upward conical shell, which reaches up to 250 mSv/shot at a 60-degree angle above the horizontal line. Calculating the amount of radiation attenuation of the concrete shield installed in the vicinity of Alvand tokamak Laboratory, which is about 99.3 % ± 0.35, is an important result from the radiation protection point of view. This result indicates that the dose limit in public area is about background level and this area is effectively protected from the intense radiation of Alvand tokamak by the concrete shield.

Particular issues to be considered in small field dosimetry for TrueBeam STx commissioning

This study aims to report the relevant issues concerning small fields in the commissioning of a TrueBeam STx for photon energies of 6MV, 10MV, 6FFF, and 10FFF. Percent depth doses, profiles, and field output factors were measured according to the beam model configuration of the treatment planning system. Multiple detectors were used based on the IAEA TRS-483 protocol as well as EBT3 radiochromic film. Analytical Anisotropic and Acuros XB algorithms, were configured and validated through basic dosimetry comparisons and end-to-end clinical tests.

A study on quality control check of dose distribution in blood bags irradiated by 137Cs source blood irradiator by using EBT3 radiochromic film dosimetry

In this study, the dose homogeneity in the blood bags delivered by a137Cs blood irradiator is investigated by using EBT3 radiochromic film dosimetry. The dose delivered to blood bags is an important factor for protection to TA-GVHD patients during transfusion in medicine. To do this, the dose results experimentally determined by EBT3 films were then compared with those of a MCNPX simulation in which the irradiation canister containing the blood bags was irradiated with a MSD Gammacell 3000 Elan. In the simulation, two different irradiation situations were modeled; one is the canister full with blood bags and the other is half-full of blood bags. The simulation dose results showed that when the canister was filled fully with blood bags, a dose of 24.4 ± 0.1 Gy was estimated in the canister center line. When the canister was half-full with the bags, a 28.8 ± 0.1 Gy dose was estimated in the canister center line. Whereas the dose of 31.3 ± 0.6 Gy dose was experimentally determined in the canister center line when the canister was filled (3 blood bags) half full. As a result, the dose homogeneity in the irradiated blood bags can easily checked by means of a two-dimensional EBT3 film dosimetry technique. Hence, this study showed that EBT3 film dosimetry is still powerful method for quality control check of dose homogeneity of any blood bags before it was used in patient.

Dosimetric Investigation of Six Ru-106 Eye Plaques by EBT3 Radiochromic Films and Monte Carlo Simulation.

Ophthalmic brachytherapy using radioactive plaques is an effective technique for the treatment of uveal melanoma. Ru-106 eye plaques are considered as interesting issue due to their steep gradient dose. The pre-planning evaluation of dosimetric parameters is essential for the treatment planning system. The current study aims at providing dose distributions of six Ru-106 eye plaques (CCA, CCB, CGD, CIB, COB and COD) using radiochromic EBT3 film, Geant4 Monte Carlo toolkit and the treatment planning software (Plaque Simulator). In this experimental study, an in-house phantom was employed for depth dose measurements with EBT3 films. Also, Geant4.10.5 scoring mesh was implemented to obtain the 2D dose distribution of the plaques. The results were compared with Plaque Simulator software and the manufacturer's (BEBIG) data. The gamma index criterion (3%/3 mm) was used to evaluate dose distributions obtained by the film measurements and Geant4 simulation. A good agreement was achieved between simulation and experimental results. Gamma index passing rate was 94.2%, 89.3%, 88.2%, 82.2%, 92.2% and 90.1% for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. Absolute dose rate (mGy/min) obtained by EBT3 film at the depth of 2 mm was 79.4 mGy/min, 81.0 mGy/min, 78.6 mGy/min, 62.2 mGy/min, 75.2 mGy/min and 81.2 mGy/min for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. The measured dose distributions and lateral dose profiles may be utilized in the treatment planning system to cover clinical volumes such as the clinical target volume and the gross tumor volume.

Leaf-individual calibration for a double stack multileaf collimator in photon radiotherapy.

In online adaptive stereotactic body radiotherapy treatments, linear accelerator delivery accuracy is essential. Recently introduced double stack multileaf collimators (MLCs) have new facets in their calibration. We established a radiation-based leaf-individual calibration (LIMCA) method for double stack MLCs. MLC leaf positions were evaluated from four cardinal angles with test patterns at measurement positions throughout the radiation field on EBT3 radiochromic film for each single stack. The accuracy of the method and repeatability of the results were assessed. The effect of MLC positioning errors was characterized for a measured output factor curve and a clinical patient plan. All positions in the motor step - position calibration file were optimized in the established LIMCA method. The resulting double stack mean accuracy for all angles was 0.2±0.1 mm for X1 (left bank) and 0.2±0.2 mm for X2 (right bank). The accuracy of the leaf position evaluation was 0.2 mm (95% confidence level). The MLC calibration remained stable over four months. Small MLC leaf position errors (e.g. 1.2 mm field size reduction) resulted in important dose errors (-5.8 %) for small quadratic fields of 0.83×0.83 cm2. Single stack position accuracy was essential for highly modulated treatment plans. LIMCA is a new double stack MLC calibration method that increases treatment accuracy from four angles and for all moving leaves.

Dosimetric comparison and evaluation of two computational algorithms in VMAT treatment plans.

This study aimed to assess the accuracy and dosimetric impact of the Acuros XB (AXB) algorithm compared to the Anisotropic Analytical Algorithm (AAA) in two situations. First, simple phantom geometries were set and analyzed; moreover, volumetric modulated arc therapy (VMAT) clinical plans for Head & Neck and lung cases were calculated and compared. First, a phantom study was performed to compare the algorithms with radiochromic EBT3 film doses using one PMMA slab phantom and two others containing foam or air gap. Subsequently, a clinical study was conducted, including 20 Head & Neck and 15 lung cases irradiated with the VMAT technique. The treatment plans calculated by AXB and AAA were evaluated in terms of planning target volume (PTV) coverage (V95% ), dose received by relevant organs at risk (OARs), and the impact of using AXB with a grid size of 1mm. Finally, patient-specific quality assurance (PSQA) was performed and compared for 17 treatment plans. Phantom dose calculations showed a better agreement of AXB with the film measurements. In the clinical study, AXB plans exhibited lower Conformity Index and PTV V95% , higher maximum PTV dose, and lower mean and minimum PTV doses for all anatomical sites. The most notable differences were detected in regions of intense heterogeneity. AXB predicted lower doses for the OARs, while the calculation time with a grid size of 1mm was remarkably higher. Regarding PSQA, although AAA was found to exhibit slightly higher gamma passing rates, the difference did not affect the AXB treatment plan quality. AXB demonstrated higher accuracy than AAA in dose calculations of both phantom and clinical conditions, specifically in interface regions, making it suitable for sites with large heterogeneities. Hence, such dosimetric differences between the two algorithms should always be considered in clinical practice.

Development of a hydrated electron dosimeter for radiotherapy applications: A proof of concept.

Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent clinical radiation dosimeters. This has been demonstrated in high-dose-per-pulse radiochemistry research, but, owing to the weak absorption signal, its application in existing low-dose-per-pulse radiotherapy provided by clinical linear accelerators (linacs) has yet to beinvestigated. The aims of this study were to measure the optical absorption associated with hydrated electrons produced by clinical linacs and to assess the suitability of the technique for radiotherapy (⩽ 1 cGy per pulse)applications. 40 mW of 660-nm laser light was sent five passes through deionized water contained in a 10 2 cm3 glass-walled cavity by using four broadband dielectric mirrors, two on each side of the cavity. The light was collected with a biased silicon photodetector. The water cavity was then irradiated by a Varian TrueBeam linac with both photon (10 MV FFF, 6 MV FFF, 6 MV) and electron beams (6 MeV) while monitoring the transmitted laser power for absorption transients. Radiochromic EBT3 film measurements were also performed forcomparison. Examination of the absorbance profiles showed clear absorption changes in the water when radiation pulses were delivered. Both the amplitude and the decay time of the signal appeared consistent with the absorbed dose and the characteristics of the hydrated electrons. By using literature value for the hydrated electron radiation chemical yield (3.0±0.3), we inferred doses of 2.1±0.2 mGy (10 MV FFF), 1.3±0.1 mGy (6 MV FFF), 0.45±0.06 mGy (6 MV) for photons, and 0.47±0.05 mGy (6 MeV) for electrons, which differed from EBT3 film measurements by 0.6%, 0.8%, 10%, and 15.7%, respectively. The half-life of the hydrated electrons in the solution was ∼ 24 s. By measuring 660-nm laser light transmitted through a cm-scale, multi-pass water cavity, we observed absorption transients consistent with hydrated electrons generated by clinical linac radiation. The agreement between our inferred dose and EBT3 film measurements suggests this proof-of-concept system represents a viable pathway toward tissue-equivalent dosimeters for clinical radiotherapyapplications.

Development of a 3D printing process of bolus using BolusCM material for radiotherapy with electrons

This work presents the optimized parameters of 3D printing for print bolus using BolusCM material. Printing parameters were selected of the homogeneity and absence of air gaps. The dosimetric features of printed bolus were measured with a plane-parallel ionization chamber and EBT3 radiochromic film. Measured features were compared with those estimated with Monte Carlo methods. BolusCM shows good characteristics to be used as bolus material in radiotherapy with electrons, where the printing process allows personalizing the bolus in function of patient characteristics. The material low-cost, the 3D printing and the dosimetric features are few of the advantages of using BolusCM material in radiotherapy with electrons in skin cancer treatment.

Characterization of a flat-panel detector for 2D dosimetry in scanned proton and carbon ion beams

PurposeTo fully characterize the flat panel detector of the new Sphinx Compact device with scanned proton and carbon ion beams. Materials and methodsThe Sphinx Compact is designed for daily QA in particle therapy. We tested its repeatability and dose rate dependence as well as its proportionality with an increasing number of particles and potential quenching effect. Potential radiation damage was evaluated. Finally, we compared the spot characterization (position and profile FWHM) with our radiochromic EBT3 film baseline. ResultsThe detector showed a repeatability of 1.7% and 0.9% for single spots of protons and carbon ions, respectively, while for small scanned fields it was inferior to 0.2% for both particles. The response was independent from the dose rate (difference from nominal value < 1.5%). We observed an under-response due to quenching effect for both particles, mostly for carbon ions. No radiation damage effects were observed after two months of weekly use and approximately 1350 Gy delivered to the detector. Good agreement was found between the Sphinx and EBT3 films for the spot position (central-axis deviation within 1 mm). The spot size measured with the Sphinx was larger compared to films. For protons, the average and maximum differences over different energies were 0.4 mm (3%) and 1 mm (7%); for carbon ions they were 0.2 mm (4%) and 0.4 mm (6%). ConclusionsDespite the quenching effect the Sphinx Compact fulfills the requirements needed for constancy checks and could represent a time-saving tool for daily QA in scanned particle beams.

Development of a compact linear accelerator to generate ultrahigh dose rate high-energy X-rays for FLASH radiotherapy applications.

In recent years, the FLASH effect, in which ultrahigh dose rate (UHDR) radiotherapy (RT) can significantly reduce toxicity to normal tissue while maintaining antitumor efficacy, has been verified in many studies and even applied in human clinical cases. This work evaluates whether a room-temperature radio-frequency (RF) linear accelerator (linac) system can produce UHDR high-energy X-rays exceeding a dose rate of 40Gy/s at a clinical source-surface distance (SSD), exploring the possibility of a compact and economical clinical FLASH RT machine suitable for most hospital treatmentrooms. A 1.65m long S-band backward-traveling-wave (BTW) electron linac was developed to generate high-current electron beams, supplied by a commercial klystron-based power source. A tungsten-copper electron-to-photon conversion target for UHDR X-rays was designed and optimized with Monte Carlo (MC) simulations using Geant4 and thermal finite element analysis (FEA) simulations using ANSYS. EBT3 and EBT-XD radiochromic films, which were calibrated with a clinical machine Varian VitalBeam, were used for absolute dose measurements. A PTW ionization chamber detector was used to measure the relative total dose and a plane-parallel ionization chamber detector was used to measure the relative normalized dose of each pulse. The BTW linac generated 300-mA-pulse-current 11 MeV electron beams with 29kW mean beam power, and the conversion target could sustain this high beam power within a maximum irradiation duration of 0.75 s. The mean energy of the produced X-rays was 1.66 MeV in the MC simulation. The measured flat-filter-free (FFF) maximum mean dose rate of the room-temperature linac exceeded 80Gy/s at an SSD of 50cm and 45Gy/s at an SSD of 67.9cm, both at a 2.1cm depth of the water phantom. The FFF radiation fields at 50cm and 67.9cm SSD at a 2.1cm depth of the water phantom showed Gaussian-like distributions with 14.3 and 20cm full-width at half-maximum (FWHM) values, respectively. This work demonstrated the feasibility of UHDR X-rays produced by a room-temperature RF linac, and explored the further optimization of system stability. It shows that a simple and compact UHDR X-ray solution can be facilitated for both FLASH-RT scientific research and clinical applications.