kV Beam Research Articles

Finite element analysis of beam optics, gun envelope and magnetic of megawatt electron gun of microwave power source

We present the beam & gun envelopes, and magnet system design, simulation, and test of a 5.5-MW electron gun of microwave power source for the use of proton accelerator in neutron spallation source. The maximum surface gradient of the beam and gun envelopes are 5.8 kV/mm & 1.65 kV/mm, respectively. The beam perveance is 1.39 AV-3/2(μP) at 110 kV beam voltage. The magnet system transports the beam with low scalloping parameter of 2.7% with laminar flow downstream. The gun faced no structural change under the operational temperature of 970 Co. The simulations (2D & 3D), and test results are in good agreement. The beam characteristics fully matches the interaction parameters of the power source of a proton accelerator.

Design, simulation and analysis of beam optics and solenoid of high-power gun for RF power source

A 5.5-Megawatt thermionic electron gun and solenoid have been designed, simulated and analyzed for the use of ultra-high radio frequency (P-band) amplifier for proton beam acceleration. The gun produced space charge limited current more than 50 A at 110 kV (beam perveance, 1.37 μP) acceleration potential. The maximum surface gradient less than 61 kV/cm has been achieved to avoid any breakdown due to high voltage operation. An average cathode loading of 1.30 A/cm 2 has been achieved that is agreeable with the theoretical limitations. Beam optics has been designed in EGUN & DGUN (2-dimensional) codes respectively, for fast parametrization and optimization of the electrodes and then cross verified in CST (3-dimensional) software that are found in good agreement. A solenoid has been designed in POISSON (2-dimensional) software and then also in CST for a constant flow and transmission of the beam downstream. A laminar beam with ripple rate 3.5% (on average) has successfully been achieved with beam fill factor less than 0.660. Simulations results show that a triple code design scheme is effective and has an excellent beam transport characteristic. The results anticipate enhanced life and stability of the gun due to low surface gradient and cathode loading.

A technique for external beam radiotherapy to the eyelid without the need for an internal eye shield

Cancer of the eyelids is difficult to treat. Surgery can lead to tissue loss. Superficial radiotherapy (SXRT) can be used in this scenario, but each fraction requires topical ophthalmic local anaesthetic and the insertion of an internal eye shield (IES) to protect the radiation sensitive anterior structures from the incident beam during beam-on time. The use of an IES comes with challenges. A technique was developed to avoid the IES based on the ability of selected cooperative patients to move the anterior structures out of the incident beam during beam-on time. We present two cases in which this technique was used. Case 1 involves the lower eyelid and case 2 the upper eyelid. Case 1 was a 69-year old, immunosuppressed woman needing definitive SXRT for lentigo maligna (LM) of the lower eye lid. She was treated using the new non-IES technique to a total dose of 50 Gy in 25 fractions using a 100 kV beam from a superficial Xstrahl 300 radiotherapy unit (Xstrahl, Surrey, UK). In vivo dosimetry (IVD) measured during a fraction on the posterior of the external eye shield located above the anterior structures showed that the transmitted dose through the external eye shield was less than ten percent of the dose applied. The patient developed conjunctivitis during SXRT that responded to topical antibiotics. Ophthalmology review five months post SXRT showed no change in eye function from baseline. Reflectance confocal microscopy (RCM) eight months after SXRT showed no LM. Case 2 was a 72-year old woman needing post-operative radiotherapy (PORT) for sebaceous cell carcinoma (SebC) of the upper eyelid. She was treated with 60 Gy in 30 fractions at 5 fractions per week with 100kV SXRT using the new non-IES technique. All the treatment was delivered on time. As per Case 1, IVD under the external eye shield showed the transmitted dose was ten percent of the dose applied. Ophthalmology review pre- and post-RT showed no change in eye function. She remains in complete remission six months after the end of PORT. The new non-IES technique is safer and quicker and simplifies the workflow. This has become the standard technique in our department for treating eyelids with SXRT. Multidisciplinary care involving an ophthalmologist pre- and post-SXRT is advised.

Optimal Beam Quality in Chest Radiography Using CsI-flat Panel Detector for Detection of Pulmonary Nodules

Optimal beam quality for detection of pulmonary nodules in digital chest radiography using CsI-flat panel detector (FPD) was investigated in consideration of image quality and patient dose. The human chest phantom with inserted imitated nodules (diameter: 10 mm, CT value: +30 Hounsfield unit (HU), -375 HU, -620 HU) was used for the measurement of contrast-to-noise ratio (CNR) of imitated nodules by twenty beams arranged by five tube voltages and four filters. The CNR varies with X-ray tube voltage and added filter. CNR correlates weakly to the tube voltage, fairly to the effective energy in second-order polynomial and strongly to the quality index (effective energy divided X-ray tube voltage). In order to improve the CNR, the effective energy and the quality index are kept about 50 keV and more than 0.5, respectively, using an 80-100 kV beam with a copper filter. A 90 kV (2.5 mm Al inherent filtration) beam with a 0.15 mm copper filter and a 90 kV or 100 kV (2.5 mm Al inherent filtration) beam with a 0.2 mm copper filter are appropriate for chest radiography using CsI-FPD.

Multiple-beam and double-mode staggered double vane travelling wave tube with ultra-wide band

This paper presents design, fabrication and cold test of an ultra-wide band travelling wave tube (TWT) with planar alignment multiple pencil beams. The fundamental double-mode of staggered double vane slow wave structure (SDV-SWS) rather than the only one mode are put forward and adopted to match with the same electron beam to increase the bandwidth greatly. Simultaneous planar alignment multiple pencil beam tunnels are designed to improve interaction impedance and then to enhance output power, gain, efficiency, growth rate. The transmission performance of a two-stage 51-period SDV-TWT in G-band with structure attenuator between two sections shows that it indeed has an ultra-wideband performance from 81 to 110 GHz. By using computer numerical control machining, the SDV-SWS was manufactured and a detailed cold test was conducted. Good agreement is found at the wide band, where S21 is above − 5 dB and S11 is below − 10 dB. 3D PIC simulations with double-mode multiple-beam SDV-TWT within total length of 70 mm show that it can get a nearly 2120 W peak output power, a 42.5 dB corresponding gain and a 10.7% electron efficiency at 94 GHz with a 22.1 kV beam voltage and a 3 × 0.15A beam current. The 3 dB bandwidth of our double-mode SDV-TWT can achieve about 29 GHz.

Image quality evaluation of intra-irradiation cone-beam computed tomography acquired during one- and two-arc prostate volumetric-modulated arc therapy delivery: A phantom study.

PurposeTo evaluate (a) the effects of megavoltage (MV)‐scatter on concurrent kilovoltage (kV) projections (P MVkV) acquired during rotational delivery, and (b) the image quality of intra‐irradiation cone‐beam computed tomography (ii‐CBCT) images acquired during prostate volumetric‐modulated arc therapy (VMAT) delivery.MethodsExperiment (1): P MVkVs were acquired with various MV beam parameters using a cylindrical phantom: field size (FS), MV energy (6 or 15 MV), dose rate (DR), and gantry speed. The average pixel values were calculated in a region on each P MVkV which were extracted at eight equally spaced gantry angles. Experiment (2): 11 one‐arc and seven two‐arc 15 MV prostate VMAT plans were used along with a pelvis phantom. One plan was selected from each of arc plans and its MV energy was changed to 6 MV. After P MVkVs were acquired, projections consisting of MV‐scatter only (P MVS) were acquired with closing kV blades and subtracted from P MVkV (P MVScorr). Projections by kV beams only were acquired (P kV). The corresponding CBCT images were reconstructed (CBCTMVkV, CBCTMVScorr, and CBCTkV). The root‐mean‐square errors (RMSEs) were calculated in prostate region and 3D gamma analysis was conducted, in which the CBCT‐number was used instead of doses between ii‐CBCT images and CBCTkV (30 HU/1 mm).ResultsExperiment (1): The MV‐scatters were dependent on the FSs, MV energies, and DRs. Experiment (2): The median RMSEs for CBCTMVScorr were decreased by 107.5 HU (1‐arc) and 42.9 HU (2‐arc) compared to those for CBCTMVkV. The median GPRs for CBCTMVScorr were 94.7% (1‐arc) and 93.4% (2‐arc), while those for CBCTMVkV were 61.1% and 79.9%, respectively. GPRs for 6 MV plans were smaller than those for 15 MV plans.ConclusionsThe number of MV‐scatters increased with larger FSs and DRs, and smaller MV energy. The MV‐scatters were corrected on the CBCTMVScorr regardless of the number of arcs.

Systematic Design Study of the Elliptical Sheet Beam Electron Gun for Terahertz TWT Applications

The design methodology of a sheet beam electron gun has been discussed and, subsequently, used for the design of a gun intended for use in a 0.3 THz traveling wave tube amplifier. The initial gun design parameters have been calculated analytically using a theoretical approach. Then, starting with these calculated parameters, the designed gun is then simulated using a commercial 3-D simulation code “CST Particle Studio” and optimized to get the target beam parameters. The circular-shaped cathode with an elliptically shaped beam-focusing electrode and elliptically shaped anode has been used to produce the good laminar elliptical sheet beam. The effect of varying the several parameters, such as height, width, and distance of focusing electrode, cathode-anode distance, and anode height have been studied to investigate their sensitivity on the target beam parameters. The simulation results predict that the designed sheet beam electron gun produces an elliptical beam with a desired beam cross section of 0.33 mm × 0.066 mm at a beam-waist position of 6.61 mm from the curved cathode emission surface corresponding to the beam parameters of 12 kV beam voltage and 55 mA beam current.

Enhanced efficiency of C‐band sheet beam driven backward wave oscillator guided by periodic magnetic field

AbstractIn this article we present the effect of periodic magnetic field on the efficiency of a sheet beam driven C‐band backward wave oscillator (operational in Megawatt power regime) through MAGIC3D PIC simulation. At 90 kV beam energy, 200 A beam current, and 0.6 T average magnetic field, our results depict an efficiency of nearly 70% due to improved electron beam confinement and electron bunching. A qualitative comparison is shown for efficiency through the same slow wave structure, guided by a uniform axial magnetic and the proposed periodic magnetic field. Efficiency enhancement of nearly 20% is observed in case of periodic magnetic field.

In operando investigation of GaN PIN device characteristics under electron irradiation energies comparable to Pm-147 source for betavoltaic application

Here, we report on the application of an electron source with high accelerating voltage (62 kV–200 kV) to simulate betavoltaic power generation capabilities of a planar GaN PIN (p-GaN/i-GaN/n-GaN) device. The in situ electrical characterization reported here enables detailed performance comparison of new device designs to conventional device configurations. In operando investigation of a GaN PIN device under irradiation by a modified transmission electron microscope is being reported here. A large-area planar GaN PIN (0.04 cm2, 17.8 nA/cm2 at 5 V reverse bias) device was irradiated with an electron beam of approximately equivalent spot size. At an approximate input current density of 5 nA/cm2, the maximum power produced (MPP) decreases from 2.45 µW/cm2 to 0.45 µW/cm2 with an increase in the beam voltage from 62 kV to 200 kV. This reduction in power corresponds to reduced electron–hole pair generation and capture within the active region of the device. The inverse relation of MPP to beam voltage is modeled by CASINO2 Monte Carlo simulations of energy absorption and is found to be in good agreement with the experimental measurement. At a constant 62 kV beam voltage, MPP is shown to increase with beam current density up to 48.2 µW/cm2 at 177 nA/cm2. Repeated device dark current measurements following the irradiation indicate no degradation of the device. An irradiation dose of ∼1016 cm−2, equivalent to exposure from a 10 mCi radioisotope source for 1 yr, was performed at an energy of 200 kV, with no appreciable deterioration in device performance.

Direct measurement and correction of both megavoltage and kilovoltage scattered x-rays for orthogonal kilovoltage imaging subsystems with dual flat panel detectors.

PurposeTo measure the scattered x‐rays of megavoltage (MV) and kilovoltage (kV) beams (MV scatter and kV scatter, respectively) on the orthogonal kV imaging subsystems of Vero4DRT.MethodsImages containing MV‐ and kV‐scatter from another source only (i.e., MV‐ and kV‐scatter maps) were acquired for each investigated flat panel detector. The reference scatterer was a water‐equivalent cuboid phantom. The maps were acquired by changing one of the following parameters from the reference conditions while keeping the others fixed: field size: 10.0 × 10.0 cm2; dose rate: 400 MU/min; gantry and ring angles: 0°; kV collimator aperture size at isocenter: 10.0 × 10.0 cm2: tube voltage: 110 kV; and exposure: 0.8 mAs. The average pixel values of MV‐ and kV‐scatter (i.e., the MV‐ and kV‐scatter values) at the center of each map were calculated and normalized to the MV‐scatter value under the reference conditions (MV‐ and kV‐scatter value factor, respectively). In addition, an MV‐ and kV‐scatter correction experiment with intensity‐modulated beams was performed using a phantom with four gold markers (GMs). The ratios between the intensities of the GMs and those of their surroundings were calculated.ResultsThe measurements showed a strong dependency of the MV‐scatter on the field size and dose rate. The maximum MV‐scatter value factors were 2.0 at a field size of 15.0 × 15.0 cm2 and 2.5 at a dose rate of 500 MU/min. The maximum kV‐scatter value was 0.48 with a fully open kV collimator aperture. In the phantom experiment, the intensity ratios of kV images with MV‐ and kV‐scatter were decreased from the reference ones. After correction of kV‐scatter only, MV‐scatter only, and both MV‐ and kV‐scatter, the intensity ratios gradually improved.ConclusionsMV‐ and kV‐scatter could be corrected by subtracting the scatter maps from the projections, and the correction improved the intensity ratios of the GMs.

A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds.

The purpose of this study was to investigate the feasibility of using fused deposition modeling (FDM) three-dimensional (3D) printer to generate radiation compensators for high-resolution (~1mm) intensity-modulated radiation therapy (IMRT) for small animal radiation treatment. We propose a novel method incorporating 3D-printed compensator molds filled with NaI powder. The inverse planning module of the computational environment for radiotherapy research (CERR) software was adapted to simulate the XRAD-225Cx irradiator, both geometry and kV beam quality (the latter using a phase space file provided for XRAD-225Cx). A nine-field IMRT treatment was created for a scaled-down version of the imaging and radiation oncology core (IROC) Head and Neck IMRT credentialing test, recreated on a 2.2-cm-diameter cylindrical phantom. Optimized fluence maps comprising nine fields and a total of 2564 beamlets were calculated at resolution of 1.25×1.25mm2 . A hollow compensator mold was created (using in-house software and algorithm) for each field using 3D printing with polylactic acid (PLA) filaments. The molds were then packed with sodium iodide powder (NaI, measured density ρNaI =2.062g/cm3 ). The mounted compensator mold thickness was limited to 13.8mm due to clearance issues with couch collision. At treatment delivery, each compensator was manually mounted to a customized block tray attached to the reference 40×40mm2 collimator. Compensator reproducibility among three repeated 3D-printed molds was measured with Radiochromic EBT2 film. The two-dimensional (2D) dose distributions of the nine fields were compared to calculated 2D doses from CERR using gamma comparisons with distance-to-agreement criteria of 0.5-0.25mm and dose difference criteria of 3-5%. Good reproducibility of 3D-printed compensator manufacture was observed with mean error of ±0.024Gy and relative dose error of ±4.2% within the modulated part of the beam. Within the limit of 13.8mm compensator height, a maximum radiation blocking efficiency of 91.5% was achieved. Per field, about 45.5g of NaI powder was used. Gamma analysis on each of the nine delivered IMRT fields using radiochromic films resulted in eight of nine treatment fields with >90% pass rate with 5%/0.5mm tolerances. However, low gamma passing rate of 49-66% (3%/0.25mm to 5%/0.5mm) was noted in one field, attributed to fabrication errors resulting in over-filling the mold. The nine-field treatment plan was delivered in under 30min with no mechanical or collisional issues. We show the feasibility of high spatial resolution IMRT treatment on a small animal irradiator utilizing 3D-printed compensator shells packed with NaI powder. Using the PLA mold with NaI powder was attractive due to the ease of 3D printing a PLA mold at high geometric resolution and the well-balanced attenuation properties of NaI powders that prevented the mold from becoming too bulky. IMRT fields with 1.25-mm resolution are capable with significant fluence modulation with relative dose accuracy of ±4.2%.

Dose indicator for CyberKnife image-guided radiation therapy.

The purpose of this study was to calculate dose distributions from CyberKnife image-guided radiation therapy (IGRT) for brain, H&N, lung, and pelvis treatment regions and use them to extract the corresponding effective dose and estimate-related risk. We developed a CyberKnife IGRT kV beam model in a standard treatment planning system and validated it against measurements in heterogeneous phantoms. Five brain, five head and neck, five thorax, and 10 (five male and five female) pelvis patient computed tomographies (CTs) were contoured. The dose distribution resulting from different CyberKnife IGRT protocols was calculated. From them, the effective dose was calculated according to ICRP publication Nr 103, using the average dose to contoured organs. The corresponding risk factors were calculated. Entrance surface dose (ESD) was also calculated and compared with existing data. The maximum effective dose produced by CyberKnife IGRT protocols was 0.8mSv (brain), 1.9mSv (H&N), 20.2 (pelvis), and 42.4mSv (thorax) per fraction for a risk estimate of 0.004% (brain), 0.01% (H&N), 0.1% (pelvis), and 0.2% (thorax). Calculated ESD were compatible with existing data. Dose calculation models for CyberKnife IGRT kV beams were implemented in a clinical treatment planning system and validated in water and heterogeneous phantoms. We determined the effective dose and the related risk estimate resulting from CyberKnife IGRT protocols for brain, head and neck, thorax, and pelvis cases. The effective doses calculated for CyberKnife IGRT protocols were similar to those obtained for cone beam CT protocols on conventional C-arm linear accelerators, except for extreme irradiation conditions for thorax cases (140kV X-ray tube tension).

Investigation of a synthetic diamond detector response in kilovoltage photon beams.

An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbed-dose and intrinsic energy responses. The former can be characterized using Monte Carlo (MC) simulations, whereas the latter (i.e., detector signal per absorbed dose to detector) is extracted from experimental data. Such a characterization is especially relevant when detectors are used in nonrelative measurements at a beam quality that differs from the calibration beam quality. Having in mind the possible application of synthetic diamond detectors (microDiamond PTW 60019, Freiburg, Germany) for nonrelative dosimetry of low-energy brachytherapy (BT) beams, we determined their intrinsic and absorbed-dose energy responses in 25-250kV beams relative to a 60 Co beam, which is usually the reference beam quality for detector calibration in radiotherapy. Three microDiamond detectors and, for comparison, two silicon diodes (PTW 60017) were calibrated in terms of air-kerma free in air in six x-ray beam qualities (from 25 to 250kV) and in terms of absorbed dose to water in a 60 Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbed-dose energy response of the detectors (modeled based on blueprints) relative to air and water depending on calibration conditions. The MC results were used to extract the relative intrinsic energy response of the detectors from the overall energy response. Measurements using an independent setup with a single ophthalmic BEBIG I25.S16 125 I BT seed (effective photon energy of 28keV) were used as a qualitative check of the extracted intrinsic energy response correction factors. Additionally, the impact of the thickness of the active volume as well as the presence of extra-cameral components on the absorbed-dose energy response of a microDiamond detector was studied using MC simulations. The relative intrinsic energy response of the microDiamond detectors was higher by a factor of 2 in 25 and 50kV beams compared to the 60 Co beam. The variation in the relative intrinsic energy response of silicon diodes was within 10% over the investigated photon energy range. The use of relative intrinsic energy response correction factors improved the agreement among the absorbed dose to water values determined using microDiamond detectors and silicon diodes, as well as with the TG-43 formalism-based calculations for the 125 I seed. MC study of microDiamond detector design features provided a possible explanation for inter-detector response variation at low-energy photon beams by differences in the effective thickness of the active volume. MicroDiamond detectors had a non-negligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbed-dose energy response relative to water at low-energy photon beams. Silicon diodes, in contrast, had an absorbed-dose energy dependence on photon energy that varied by a factor of 6, whereas the intrinsic energy dependence on beam quality was within 10%. It is important to decouple these two responses for a full characterization of detector energy response especially when the user and reference beam qualities differ significantly, and MC alone is not enough.

Evaluation of 90 kV Beam with 0.15 mm Cu Filter in Chest Radiography Using CsI-flat Panel Detector

To compare the visibility of anatomic structure in chest radiography acquired with different beam quality (120 kV beam and 90 kV beam with 0.15 mmCu) using CsI-flat panel detector. Pair image obtained by different beam quality of 100 person's chest radiographies which were taken periodical health examination were compared with the visibility of normal structures (pulmonary vessels) and abnormal opacities by two pulmonologists and four radiological technologists. Moreover, the spectrum of the two beam quality were calculated using Monte Carlo simulation. Dominant observers gave high score significantly (p<0.01) to the 90 kV beam's image in spite of 20% less dose. Monte Carlo simulation showed that 90 kV beam with 0.15 mmCu were much absorbed primary photon than 120 kV beam to CsI detector, and less absorbed secondary photon. The visibility of anatomic structure and abnormal opacities in FPD chest radiography was improved by using the 90 kV beam with 0.15 mmCu than traditional 120 kV beam's chest radiography.

Quantifying Imaging Radiation to Patient from Optimized Procedures with LIVE System during SBRT Lung Treatment

Tumor control and normal tissue complication probabilities are known to be highly correlated to the target localization accuracy in radiation therapy. The Limited-angle Intra-fractional Verification (LIVE) system was developed to track tumor movement for patient positioning verification during SBRT. However, the 4D MV/kV imaging involved results in additional radiation dose to patients. As such, the purpose of this study is to evaluate the additional imaging radiation dose from optimized MV/kV image acquisition in the LIVE system and to determine if it exceeds the AAPM TG-180 report image dose threshold. A medical linear accelerator with a fully integrated system for image guidance was assessed. Monte Carlo simulated kV and MV beams were calibrated and then used as incident sources in an EGSnrc Monte Carlo dose calculation in a CT-image-based patient model. In three representative lung SBRT treatments evaluated in this study, tumors were located in the patient’s posterior-left lung, mid-left lung and right upper lung. The optimized imaging sequence comprised of arcs ranging from 2-7, acquired between adjacent 3D/VMAT beams, with multiple simultaneous kV (125 kVp) and MV (6 MV) image projections in each arc, for different optimization scenarios. The MV imaging fields were generally confined to the treatment target, while kV images were acquired with a normal open field size and full bow-tie filter. In a 7-arc image acquisition case (highest imaging dose scenario), the maximum kV doses to 50% of the tissue volume (D50 from DVH’s), for spinal cord, right lung, heart, left lung and the target, were 0.4 cGy, 0.4 cGy, 0.6 cGy, 0.7 cGy and 1.4 cGy, respectively. The corresponding MV imaging doses were 0.1 cGy to the spinal cord, right lung, heart and left lung, and 11 cGy to the target. In contrast, the maximum radiation dose from two cases treated with two field VMAT and 2-arc image acquisitions, is approximately 30% of that of the 7-arc acquisition. We have evaluated the additional radiation dose resulting from optimized LIVE system MV/kV image acquisitions in two best (least imaging dose) and one worst (highest imaging dose) lung SBRT treatment scenarios. The results show that these MV/kV imaging doses are comparable to those resulting from current imaging procedures used in IGRT and are within the dose threshold of 5% target dose as recommended by the AAPM TG-180 report.

Dose to water versus dose to medium from cavity theory applied to small animal irradiation with kilovolt x-rays

Dose reporting is a matter of concern in the preclinical field as the different dose descriptors dose-to-water-in-medium and dose-to-medium-in-medium coexist. For kV photons differences between both quantities are expected to be amplified due to photon energy absorption coefficients differences for different media, and could represent a limiting factor for accurate translation of pre-clinical research into clinical trials. The main goal of this study was to analyse the relationship between and for kV irradiation of small animals, using different flavours of the intermediate cavity theory (ICT).Irradiations of mathematical phantoms and a mouse CT scan, both with different voxel sizes and materials, were investigated. A modified version of the Monte Carlo code DOSXYZnrc was used to derive and convert to using ICT. Local photon spectra were generated in different regions of the mouse.Depending on energy and cavity size, which we equate to the voxel size, ranged from 0.68 to 4.37 times . Higher kV energy combined with very small cavity sizes yielded decreased in comparison to ; this behaviour was reversed for larger cavities combined with lower kV energies. Hence, the impact of the cavity dimensions on estimated is significant on pre-clinical kV beams. and in the ex vivo male mouse were found to differ by −29% to 286%. Caution is advised when using the ICT due to a lack of consensus on weighting factor (d-parameter) deriving methods; for the same irradiation conditions, different d-values affected up to 20%. Pre-clinically, such divergence between dose descriptors could enable biological damage.The abiding debate over which quantity to favour is foreseen to linger while it is unclear which quantity correlates better with the biological effects of ionizing irradiation: preclinical radiotherapy might represent an ideal platform for measurement-based studies to settle this fundamental question. Finally, dose distribution comparisons require caution and should use the same reporting quantity.

Dosimetric properties of colloidal quantum dot-based systems for scintillation dosimetry

Colloidal quantum dots (cQDs) are starting to be used in radiation detection, either combined with an organic fluorophore or used as a sole luminescent material. In the latter case, only few studies report on cQD-based detectors for medical applications, especially for scintillation dosimetry in radiation therapy. Moreover, most of these studies focus on the effects of radiation on cQD photoluminescence but do not look into the properties of the scintillation signal itself. The present article provides a study of those cQD scintillation properties not previously investigated including the linearity of the signal as a function of dose, the signal dose rate and beam energy dependencies. The latter was also characterized for the commercially available scintillating fiber BCF-60 and liquid scintillator Ultima Gold. CdSe multishell cQDs in two physical forms were used as a sensitive dosimeter volume: a cQD powder to constitute a fiber optic based dosimeter and cQD liquid dispersions to be volumetric dosimeters. The signal linearity was assessed with a R2 coefficient >0.999 over a clinically relevant dose range at kV and MV beam energies. The cQDs had a good overall dose rate independence, with a change from the relative dose of 1% at MV energies and 2% at kV energies, of their scintillation output when irradiated with an orthovoltage device and a linear accelerator. Regarding the beam energy dependence, the cQD powder had the highest dependence amongst all the scintillators compared, the 120 kVp light output being up to almost 4 times that of the 6 MV beam. The smallest effect of the beam energy was reported for the cQD alkylbenzene liquid dispersion, having a variation of light signal normalized to 6 MV of 15% that is even less than for BCF-60 and Ultima Gold.

Technical Note: Imaging dose resulting from optimized procedures with limited-angle intrafractional verification system during stereotactic body radiation therapy lung treatment.

The limited-angle intrafractional verification (LIVE) system was developed to track tumor movement during stereotactic body radiation therapy (SBRT). However, the four-dimensional (4D) MV/kV imaging procedure results in additional radiation dose to patients. This study is to quantify imaging radiation dose from optimized MV/kV image acquisition in the LIVE system and to determine if it exceeds the American Association of Physicists in Medicine Task Group Report 180 image dose threshold. TrueBeam™ platform with a fully integrated system for image guidance was studied. Monte Carlo-simulated kV and MV beams were calibrated and then used as incident sources in an EGSnrc Monte Carlo dose calculation in a CT image-based patient model. In three representative lung SBRT treatments evaluated in this study, tumors were located in the patient's posterior left lung, mid-left lung, and right upper lung. The optimized imaging sequence comprised of arcs ranging from 2 to 7, acquired between adjacent three-dimensional (3D)/IMRT beams, with multiple simultaneous kV (125kVp) and MV (6MV) image projections in each arc, for different optimization scenarios. The MV imaging fields were generally confined to the treatment target while kV images were acquired with a normal open field size with a full bow-tie filter. In a seven-arc acquisitions case (highest imaging dose scenario), the maximum kV imaging doses to 50% of the tissue volume (D50 from DVHs), for spinal cord, right lung, heart, left lung, and the target, were 0.4, 0.4, 0.6, 0.7, and 1.4cGy, respectively. The corresponding MV imaging doses were 0.1cGy to spinal cord, right lung, heart, and left lung, and 11cGy to target. In contrast, the maximum radiation dose from two cases treated with two Volumetric-Modulated Arc Therapy (VMAT) fields and two-arc image acquisitions is approximately 30% of that of the seven-arc acquisition. We have evaluated the additional radiation dose resulting from optimized LIVE system MV/kV image acquisitions in two best (least imaging dose) and one worst (highest imaging dose) lung SBRT treatment scenarios. The results show that these MV/kV imaging doses are comparable to those resulting from current imaging procedures used in Image-Guided Radiation Therapy (IGRT) and are within the dose threshold of 5% target dose as recommended by the AAPM TG-180 report.

Positioning errors of metal localization devices with motion artifacts on kV and MV cone beam CT.

Objective:To investigate motion artifacts on kV CBCT and MV CBCT images with metal localization devices for image-guided radiation therapy.Methods:The 8 μ pelvis CBCT template for the Siemens Artiste MVision and Pelvis template for the Varian IX on-board Exact Arms kV were used to acquire CBCT images in this study. Images from both CBCT modalities were compared in CNRs, metal landmark absolute positions, and image volume distortion on three different planes of view. The images were taken on a breathing-simulated thoracic phantom in which several typical metal localization devices were implanted, including clips and wires for breast patients, gold seeds for prostate patients, and BBs as skin markers. To magnify the artifacts, a 4 cm diameter metal ball was also implanted into the thoracic phantom to mimic the metal artifacts.Results:For MV CBCT, the CNR at a 4 sec breathing cycle with 1 cm breathing amplitude was 5.0, 3.4 and 4.6 for clips, gold seeds and BBs, respectively while it was 1.5, 2.0 and 1.6 for the kV CBCT. On the images, the kV CBCT showed symmetric streaking artifacts both in the transverse and longitudinal directions relative to the motion direction. The kV CBCT images predicted 89 % of the expected volume, while the MV CBCT images predicted 95 % of the expected volume. The simulated soft tissue observed in the MVCT could not be detected in the kV CBCT.Conclusion:The MV CBCT images showed better volume prediction, less streaking effects and better CNRs of a moving metal target, i.e. clips, BBs, gold seeds and metal balls than on the kV CBCT images. The MV CBCT was more advantageous compared to the kV CBCT with less motion artifacts for metal localization devices.Advances in knowledge:This study would benefit clinicians to prescribe MV CBCT as localization modality for radiation treatment with moving target when metal markers are implanted.

Development and commissioning of a full-size prototype fixed-beam radiotherapy system with horizontal patient rotation.

Compared to conventional linacs with rotating gantries, a fixed-beam radiotherapy system could be smaller, more robust and more cost-effective. In this work, we developed and commissioned a prototype x-ray radiotherapy system utilizing a fixed vertical radiation beam and horizontal patient rotation. The prototype system consists of an Elekta Synergy linac with gantry fixed at 0° and a custom-built patient rotation system (PRS). The PRS was designed to immobilize patients and safely rotate them about the horizontal axis. The interlocks and emergency stops of the linac and PRS were connected. Custom software was developed to monitor the system status, control the motion of the PRS and modify treatment plans for the fixed-beam configuration. Following installation, the prototype system was commissioned for three-dimensional (3D) conformal therapy based on guidelines specified in AAPM TG-45 and TG-142, with modifications for the fixed-beam geometry made where necessary. The system and control software was tested in a variety of machine states and executed motion, stop and beam gating commands as expected. Interlocks and emergency stops of the linac and PRS were found to correctly stop PRS motion and both kV and MV radiation beams when triggered. For 3D conformal treatments, the prototype system metall AAPM TG-45 and TG-142 specifications for geometric and dosimetric accuracy. Motion of the PRS was within 0.6±0.3mm and 0.10°±0.07° of input values for translation and rotation respectively. The axis of rotation of the PRS was coincident with the radiation beam axis to less than 1mm. End-to-end treatment verification for 6MV conformal treatments showed less than 2% difference between planned and delivered dose for all fields. In this work, we have developed and commissioned a radiotherapy system that utilizes a fixed vertical radiation beam and horizontal patient rotation. This system is a proof-of-concept prototype for a fixed-beam treatment system without a rotating gantry. Fixed-beam systems that are smaller and more cost-effective could help in improving global access to radiotherapy.