Output Calibration Research Articles

Suppressing simulation bias in multi-modal data using transfer learning

Many problems in science and engineering require making predictions based on few observations. To build a robust predictive model, these sparse data may need to be augmented with simulated data, especially when the design space is multi-dimensional. Simulations, however, often suffer from an inherent bias. Estimation of this bias may be poorly constrained not only because of data sparsity, but also because traditional predictive models fit only one type of observed outputs, such as scalars or images, instead of all available output data modalities, which might have been acquired and simulated at great cost. To break this limitation and open up the path for multi-modal calibration, we propose to combine a novel, transfer learning technique for suppressing the bias with recent developments in deep learning, which allow building predictive models with multi-modal outputs. First, we train an initial neural network model on simulated data to learn important correlations between different output modalities and between simulation inputs and outputs. Then, the model is partially retrained, or transfer learned, to fit the experiments; a method that has never been implemented in this type of architecture. Using fewer than 10 inertial confinement fusion experiments for training, transfer learning systematically improves the simulation predictions while a simple output calibration, which we design as a baseline, makes the predictions worse. We also offer extensive cross-validation with real and carefully designed synthetic data. The method described in this paper can be applied to a wide range of problems that require transferring knowledge from simulations to the domain of experiments.

Modified electron beam output calibration based on IAEA Technical Report Series 398.

PurposeThe recently worldwide standard measurement of electron beam reference dosimetry include the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)‐398 and Association of Physicists in Medicine (AAPM) Task Group (TG)‐51 protocols. Muir et al. have modified calibration methods for electron beam calibration based on AAPM TG‐51. They found that the use of cylindrical chambers at low energy gave acceptable results. In this study, we propose and report a modified calibration for electron beam based on IAEA TRS‐398, the standard reference dosimetry protocol worldwide.MethodsThis work was carried out with energies of 6, 8, 10, 12, and 15 MeV. The electron beam is generated from Elektra Synergy Platform and Versa HD linear accelerator. The charge readings were measured with PTW 30013, IBA CC13, Exradin A1Sl, and Exradin A11 chambers connected to the electrometer. The dose calculation uses an equation of modified calibration for electron beam using the updated kQ factor in previous work. The absorbed dose to water for electron beam is expressed in dose per monitor unit (cGy/MU). Thus, we compared dose per monitor unit (D/MU) calculation using a modified calibration to TRS‐398.ResultsIn this work, we have succeeded in implementing the modified calibration of electron beam based on TRS‐398 by applying a cylindrical chamber in all energy beams and using the updated kQ factor. The ratio of the absorbed dose to water between original and modified calibration protocols of TRS‐398 (D w) for the cylindrical chamber was 1.002 on the Elekta Synergy Platform and 1.000 on the Versa HD while for the parallel‐plate chamber it was 1.013 on the Elekta Synergy Platform and 1.014 on the Versa HD. Based on these results, both the cylindrical and parallel‐plate chambers are still within the tolerance limit allowed by the TRS‐398 protocol, which is ±2%. Therefore, modified calibration based on TRS‐398 gives acceptable results and is simpler to use clinically.

Confidence-Calibrated Human Activity Recognition.

Wearable sensors are widely used in activity recognition (AR) tasks with broad applicability in health and well-being, sports, geriatric care, etc. Deep learning (DL) has been at the forefront of progress in activity classification with wearable sensors. However, most state-of-the-art DL models used for AR are trained to discriminate different activity classes at high accuracy, not considering the confidence calibration of predictive output of those models. This results in probabilistic estimates that might not capture the true likelihood and is thus unreliable. In practice, it tends to produce overconfident estimates. In this paper, the problem is addressed by proposing deep time ensembles, a novel ensembling method capable of producing calibrated confidence estimates from neural network architectures. In particular, the method trains an ensemble of network models with temporal sequences extracted by varying the window size over the input time series and averaging the predictive output. The method is evaluated on four different benchmark HAR datasets and three different neural network architectures. Across all the datasets and architectures, our method shows an improvement in calibration by reducing the expected calibration error (ECE)by at least 40%, thereby providing superior likelihood estimates. In addition to providing reliable predictions our method also outperforms the state-of-the-art classification results in the WISDM, UCI HAR, and PAMAP2 datasets and performs as good as the state-of-the-art in the Skoda dataset.

Investigation of absolute dose calibration accuracy for TomoTherapy using real water.

A systematic bias in TomoTherapy output calibration was reported by the Imaging and Radiation Oncology Core Houston (IROC‐H) after analyzing intensity‐modulated radiation therapy (IMRT) credentialing results from hundreds of TomoTherapy units. Multiple theories were developed to explain this observation. One theory was that the use of a solid water “cheese” phantom instead of real water in the calibration measurement was the culprit. A phantom filled with distilled water was built to investigate whether our TomoTherapy was miscalibrated due to the use of a solid water phantom. A miscalibration of −1.47% was detected on our TomoTherapy unit. It is found that despite following the vendor's updated recommendation on computed tomography (CT) number to density calibration, the cheese phantom was still mapped to a density of 1.028 g/cm3, rather than the 1.01 g/cm3 value reported in literature. When the density of the cheese phantom was modified to 1.01 g/cm3 in the treatment planning system, the measurement also indicated that our TomoTherapy machine was miscalibrated by −1.52%, agreeing with the real water phantom findings. Our single‐institution finding showed that the cheese phantom density assignment can introduce greater than 1% errors in the TomoTherapy absolute dose calibration. It is recommended that the absolute dose calibration for TomoTherapy be performed either in real water or in the cheese phantom with the density in TPS overridden as 1.01 g/cm3.

A four-channel air pressure cooperative control system for 3-D bio-printing device

In recent years, the research and development of 3D bioprinting device for artificial blood vessels has attracted great attention of researchers. In this paper, the research object is the control system of 3D bioprinting device for artificial blood vessel and the four-channel air pressure cooperative control technology for 3D bioprinting device double nozzles printing is mainly studied. Through the scheme design, working principle innovation, hardware selection and air pressure output calibration experiment of four-way air pressure cooperative control system, the hardware platform of 3D bioprinting device air pressure control system is built. Then, by using the embedded TwinCAT NC PTP software platform based on EtherCAT Ethernet bus protocol, the four-channel air pressure cooperative control is programmed and field experiments are carried out, which realizes the printing process of uniform liquid output and good continuity, and meets the requirements of 3D bioprinting for printing continuity and forming quality. The study of four-channel air pressure cooperative control system in this course is a worthy of application and promotion control method.

Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check.

Accurate radiation dosimetry in radiobiological experiments is crucial for preclinical research in advancement of cancer treatment. Vendors of cell irradiators often perform calibration for end-users. However, calibration accuracy remains unclear due to missing detailed information on calibration equipment and procedures. In this study, we report our findings of a vender miscalibration of the radiation output and our investigation on the root cause of the discrepancy. Independent calibration verification for a commercial preclinical orthovoltage irradiator was conducted. Initially, in the absence of ionization chambers calibrated at kV energy, radiochromic films (EBT3) was first calibrated at MV energy. Energy correction factors from literature were used to create an in-house kV dosimetry system. The miscalibration identified with the in-house kV EBT3 dosimetry was later confirmed by ADCL calibrated ionization chambers (Exradin A1SL and PTW 30013) at kV energy. Ionization chambers were suspended in-air following TG-61 recommendation for output calibration. To investigate the root cause of the miscalibration, additional measurements were performed with ionization chambers placed on the shelf. A validated Monte Carlo simulation code was also used to investigate the impact of placing the ionization chamber on the shelf instead of suspending it in air during the vendor-performed calibration process. Up to a 6% dosimetry error was observed when comparing the vendor calibrated output of the preclinical irradiator with our independent calibration check. Further investigation showed incorrect setups in the vendor's calibration procedure which may result in dose errors up to 11% from the backscatter of the shelf board during calibration, and up to 5% from omitting temperature and pressure corrections to ionization chamber readings. Our study revealed large dose calibration errors caused by incorrect setup and the omission of temperature/pressure correction in the vendor's calibration procedure. The findings also highlighted the importance of performing an independent check of the dose calibration for preclinical kV irradiators. More absolute dosimetry training is needed for both vendors and end users for establishing accurate absolute dosimetry.

Filmless quality assurance of a Leksell Gamma Knife® Icon™

PurposeThe annual quality assurance (QA) of Leksell Gamma Knife® (LGK) systems are typically performed using films. Film is a good candidate for small field dosimetry due to its high spatial resolution and availability. However, there are multiple challenges with using film; film does not provide real‐time measurement and requires batch‐specific calibration. Our findings show that active detector‐based QA can simplify the procedure and save time without loss of accuracy.MethodsAnnual QA tests for a LGK Icon™ system were performed using both film‐based and filmless techniques. Output calibration, relative output factors (ROF), radiation profiles, sector uniformity/source counting, and verification of the unit center point (UCP) and radiation focal point (RFP) coincidence tests were performed. Radiochromic films, two ionization chambers, and a synthetic diamond detector were used for the measurements. Results were compared and verified with the treatment planning system (TPS).ResultsThe measured dose rate of the LGK Icon was within 0.4% of the TPS value set at the time of commissioning using an ionization chamber. ROF for the 8 and 4‐mm collimators were found to be 0.3% and 1.8% different from TPS values using the MicroDiamond detector and 2.6% and 1.9% different for film, respectively. Excellent agreement was found between TPS and measured dose profiles using the MicroDiamond detector which was within 1%/1 mm vs 2%/1 mm for film. Sector uniformity was found to be within 1% for all eight sectors measured using an ionization chamber. Verification of UCP and RFP coincidence using the MicroDiamond detector and pinprick film test was within 0.3 mm at isocenter for both.ConclusionThe annual QA of a LGK Icon was successfully performed by employing filmless techniques. Comparable results were obtained using radiochromic films. Utilizing active detectors instead of films simplifies the QA process and saves time without loss of accuracy.

Investigation of LED-based photodynamic therapy efficiency on breast cancer cells.

Photodynamic therapy (PDT) is based on special light source, photosensitizer (PS), and in the presence of oxygen. Different light sources have been used for PDT applications. Recent studies have focused on LED light sources for PDT applications due to reducing the cost of laser-based PDT and providing easy access for research laboratory or clinic facilities. LED-mediated PDT applications have shown promising results for the treatment of different types of disease. However, few studies have determined the effects of LED-based PDT on cancer cells. For the first time, the aim of this study was to explore the therapeutic effects of 5-aminolevulinic acid (5-ALA)-mediated PDT after LED irradiation on two sub-types (a poorly aggressive MCF-7 and a highly aggressive MDA-MB-231) of breast cancer cell lines. The effectiveness of 5-ALA PDT treatment was evaluated by WST-1, annexin V, and acridine orange staining with different energy levels. The LED system was specially developed with optical power and wavelength stability techniques. The system consists of user interface and embedded LED controller with real-time optic power output calibration by photodiode feedback. Our results demonstrated that the cell viability of breast cancer cells was considerably decreased a LED dose-dependent manner (P < 0.05). Additionally, a significant increase in the percentage of apoptotic cells was detected in breast cancer cells after irradiation with LED at a density of 18 and 30 J/cm2 energy. Consequently, the LED system could be effectively used for irradiation of 5-ALA in the treatment of breast cancer cells.

Percentage depth dose measurement in high energy photons and electrons by using the Al2O3 optically stimulated luminescent (OSL) dosimeter

The study focused on the measurement of percentage depth dose (PDD) in high energy photons and electrons by using the optically stimulated luminescent (OSL) dosimeters. The beam output calibration was performed on 6 MV photons and 6 MeV electrons and compared to that in the ionization chamber. The PDD was measured in 6 MV photons and 6 MeV electrons and the PDD curves were plotted by using the OSL dosimeters. The PDD curves were compared to that in other common dosimeters including ionization chamber, Gafchromic® EBT2 film dosimeter and the treatment planning software (TPS). The results showed that the beam output calibration measured by using the OSL dosimeters was in good agreement to the ionization chamber within 1.6 and 5.9% percentage of discrepancy for both 6 MV photons and 6 MeV electrons respectively. The measured PDD by using the OSL dosimeters were also in in good agreement to the ionization chamber, EBT2 film and TPS software within percentage 13.4 and 10.4% of discrepancies for 6 MV photons and 6 MeV electrons respectively. The overall results indicated the suitability of OSL dosimeters to be used for direct dosimetry measurements in high energy photons and electrons.

A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration.

To present and demonstrate the accuracy of a modified formalism for electron beam reference dosimetry using updated Monte Carlo calculated beam quality conversion factors. The proposed, simplified formalism allows the use of cylindrical ionization chambers in all electron beams (even those with low beam energies) and does not require a measured gradient correction factor. Data from a previous publication are used for beam quality conversion factors. The formalism is tested and compared to the present formalism in the AAPM TG-51 protocol with measurements made in Elekta Precise electron beams with energies between 4MeV and 22MeV and with fields shaped with a 10×10cm2 clinical applicator as well as a 20×20cm2 clinical applicator for the 18MeV and 22MeV beams. A set of six ionization chambers are used for measurements (two cylindical reference-class chambers, two scanning-type chambers and two parallel-plate chambers). Dose per monitor unit is derived using the data and formalism provided in the TG-51 protocol and with the proposed formalism and data and compared to that obtained using ionization chambers calibrated directly against primary standards for absorbed dose in electron beams. The standard deviation of results using different chambers when TG-51 is followed strictly is on the order of 0.4% when parallel-plate chambers are cross-calibrated against cylindrical chambers. However, if parallel-plate chambers are directly calibrated in a cobalt-60 beam, the difference between results for these chambers is up to 2.2%. Using the proposed formalism and either directly calibrated or cross-calibrated parallel-plate chambers gives a standard deviation using different chambers of 0.4%. The difference between results that use TG-51 and the primary standard measurements are on the order of 0.6% with a maximum difference in the 4MeV beam of 2.8%. Comparing the results obtained with the proposed formalism and the primary standard measurements are on the order of 0.4% with a maximum difference of 1.0% in the 4MeV beam. The proposed formalism and the use of updated data for beam quality conversion factors improves the consistency of results obtained with different chamber types and improves the accuracy of reference dosimetry measurements. Moreover, it is simpler than the present formalism and will be straightforward to implement clinically.

Novel PCS Output Calibration Technique

Many issues like large size, poor response time and accuracy which were plaguing the performance of the conventional Photo Catalytic Processes were overcome by PCS (Photo Catalytic Sensor). The continuing advancements in the field of sensor interface development are to calibrate and correct the inherent non-idealities present in transducers forced us to work in this area. The varieties of different parameters inside PCS subject to the transfer characteristics of PCS results because of Photo-catalytic oxidation of organic compounds has been done by Whig and Ahmad in 2015 and it is found that the major contributors to non-idealness are typically the nonlinear response to stimulus (gain), the temperature, and the offset dependence of either of these elements. Expectedly the calibration of the sensor has been done physically in the research facility available in laboratory before the genuine deployment in the system. This requires a great deal of manual calculation very high skilled manpower. To make this tedious procedure easy and to make PCS sensor more accurate, a novel sensor calibration with built-in calibration registers using FPGAs is proposed.

Evaluation of Delta4DVH Anatomy in 3D Patient-Specific IMRT Quality Assurance.

Purpose:To evaluate the performance of Delta4DVH Anatomy in patient-specific intensity-modulated radiotherapy quality assurance.Materials and Methods:Dose comparisons were performed between Anatomy doses calculated with treatment plan dose measured modification and pencil beam algorithms, treatment planning system doses, film doses, and ion chamber measured doses in homogeneous and inhomogeneous geometries. The sensitivity of Anatomy doses to machine errors and output calibration errors was also investigated.Results:For a Volumetric Modulated Arc Therapy (VMAT) plan evaluated on the Delta4 geometry, the conventional gamma passing rate was 99.6%. For a water-equivalent slab geometry, good agreements were found between dose profiles in film, treatment planning system, and Anatomy treatment plan dose measured modification and pencil beam calculations. Gamma passing rate for Anatomy treatment plan dose measured modification and pencil beam doses versus treatment planning system doses was 100%. However, gamma passing rate dropped to 97.2% and 96% for treatment plan dose measured modification and pencil beam calculations in inhomogeneous head & neck phantom, respectively. For the 10 patients’ quality assurance plans, good agreements were found between ion chamber measured doses and the planned ones (deviation: 0.09% ± 1.17%). The averaged gamma passing rate for conventional and Anatomy treatment plan dose measured modification and pencil beam gamma analyses in Delta4 geometry was 99.6% ± 0.89%, 98.54% ± 1.60%, and 98.95% ± 1.27%, respectively, higher than averaged gamma passing rate of 97.75% ± 1.23% and 93.04% ± 2.69% for treatment plan dose measured modification and pencil beam in patients’ geometries, respectively. Anatomy treatment plan dose measured modification dose profiles agreed well with those in treatment planning system for both Delta4 and patients’ geometries, while pencil beam doses demonstrated substantial disagreement in patients’ geometries when compared to treatment planning system doses. Both treatment planning system doses are sensitive to multileaf collimator and monitor unit (MU) errors for high and medium dose metrics but not sensitive to the gantry and collimator rotation error smaller than 3°.Conclusions:The new Delta4DVH Anatomy with treatment plan dose measured modification algorithm is a useful tool for the anatomy-based patient-specific quality assurance. Cautions should be taken when using pencil beam algorithm due to its limitations in handling heterogeneity and in high-dose gradient regions.

Understanding nutrient throughput of operational RAS farm effluents to support semi-commercial aquaponics: Easy upgrade possible beyond controversies.

The present research attempted to address a key industry-level question amidst Recirculating Aquaculture System (RAS) waste throughput and aquaponics limitations controversies. Nutrient throughput of three operational RAS farms with progressive size proportions (16, 130, 1400 m3), aquaculture intensity (24, 62, 86 kg stock m-3) were studied. Results suggest - daily total efflux and potency of nutrients in effluents should not be generalized, extreme variability exists. Consistencies of nutrients in wastewater (except N, Ca and Na) are higher than in sludge. Asynchrony between patterns of nutrient loading and effluent nutrient concentrations exist for secondary macronutrients and micronutrients (S, Mg, Fe, Cu, Zn, B, Mo). Macronutrient output generally increases with increasing farm size and culture intensity but same cannot be said for micronutrients. Deficiency in wastewater can be completely masked using raw or mineralized sludge, usually containing 3-17 times higher nutrient concentrations. RAS effluents (wastewater and sludge combined) contain adequate N, P, Mg, Ca, S, Fe, Zn, Cu, Ni to meet most aquaponic crop needs. K is generally deficient requiring a full-fledged fertilization. Micronutrients B, Mo are partly sufficient and can be easily ameliorated by increasing sludge release. The presumption surrounding 'definite' phyto-toxic Na levels in RAS effluents should be reconsidered - practical solutions available too. No threat of heavy metal accumulation or discharge was observed. Most of the 'well-known' operational influences failed to show any significant predictable power in deciding nutrient throughput from RAS systems. Calibration of nutrient output from operational RAS farms may be primarily focused around six predictors we identified. Despite inherent complexity of effluents, the conversion of RAS farms to semi-commercial aquaponics should not be deterred by nutrient insufficiency or nutrient safety arguments. Incentivizing RAS farm wastes through semi-commercial aquaponics should be encouraged - sufficient and safe nutrients are available.

Influence of light output calibration on neutron energy spectrum unfolding up to 300 MeV using liquid organic scintillator

The influence from uncertainty on light output calibration was studied experimentally for neutron energy spectra up to 300 MeV obtained by an unfolding method using a liquid organic scintillator. The neutrons were generated from the interactions of 100 and 290 MeV/u 28Si ion beams on thick silicon targets at a 75° direction with respect to the beam axis. The light output calibration determined by using Compton edges of γ-rays from 60Co and 241Am-Be sources was used for the unfolding method. The uncertainty of the calibration points at the Compton edges was estimated to be within 3%. Two calibration lines which connected the 3% larger light output point of the Compton edge of the γ-ray from 60Co and that the 3% lower light output point of that from 241Am-Be and vice versa were examined for influence on variation of calibration line. The unfolded spectra using the two calibration lines were compared with one using the calibration line connecting light output points of Compton edges from both γ-ray sources. The comparison indicates the uncertainty of calibration line influences the neutron light output spectrum within order of several %. The all unfolded spectra generally reproduced one by the time-of-flight (TOF) method in the same experiment. The difference between TOF and unfolded spectra were 17 and 8% for 100 and 290 MeV/u data, at maximum.

A history matching approach for calibrating hydrological models

Calibration of hydrological time-series models is a challenging task since these models give a wide spectrum of output series and calibration procedures require significant amount of time. From a statistical standpoint, this model parameter estimation problem simplifies to finding an inverse solution of a computer model that generates pre-specified time-series output (i.e., realistic output series). In this paper, we propose a modified history matching approach for calibrating the time-series rainfall-runoff models with respect to the real data collected from the state of Georgia, USA. We present the methodology and illustrate the application of the algorithm by carrying a simulation study and the two case studies. Several goodness-of-fit statistics were calculated to assess the model performance. The results showed that the proposed history matching algorithm led to a significant improvement, of 30% and 14% (in terms of root mean squared error) and 26% and 118% (in terms of peak percent threshold statistics), for the two case-studies with Matlab-Simulink and SWAT models, respectively.

A novel risk analysis of clinical reference dosimetry based on failure modes and effects analysis

PurposeThe output of a linear accelerator (linac) is one of the most important quality assurance (QA) factors in radiotherapy. However, there is no quantitative rationale for frequency and tolerance. The purpose of this study is to develop a novel risk analysis of clinical reference dosimetry based on failure modes and effects analysis (FMEA). MethodsClinical reference dosimetry data and the daily output data of two linacs (Clinac iX and Clinac 6EX) at Hiroshima University Hospital were analyzed. The analysis involved the number of patients per year for five types of fractionations. Risk priority number (RPN) is defined as the product of occurrence (O), severity (S), and detectability (D) in standard FMEA. In addition, we introduced “severity due to output drifting” (mean output change per day) (S′) and the number of patients per year for five types of fractionations (W). We calculated the RPN = O × S × D × S′ × W and quantitatively evaluated the risk for clinical reference dosimetry. ResultsFewer fractions and less output calibration frequency resulted in higher RPN. Since clinical reference dosimetry data has a drift effect, which is missing in human processes, it was essential to use S′ in addition to standard FMEA. Moreover, the parameter W was important in evaluating interinstitutional QA for clinical reference dosimetry. The relative risk of Clinac 6EX to Clinac iX was different approximately by twofold. ConclusionsWe developed a novel index that can quantitatively evaluate risk for clinical reference dosimetry of each facility and machines in common on the basis of FMEA.

English

English

A Multi-Model Consensus Forecast Technique for Tropical Cyclone Intensity Based on Model Output Calibration

ABSTRACT We analyzed the errors associated with forecasts of tropical cyclone (TC) intensity from 2010-2012 in the western North Pacific region made by seven operational numerical weather prediction models. The results show that the forecast error is significantly related to the initial error as well as the initial TC intensity, size, and translation speed. Other factors highly related to the forecast error include the environmental sea surface pressure, vertical wind shear and maximum potential intensity. We used stepwise regression to set up model forecast error estimation equations, which were used to calibrate the model output. Independent experiments showed that the calibrated model forecasts have significant skill compared to the original model output. Finally, a multimodel consensus forecast technique for TC intensity was developed based on the calibrated model output; this technique has 28% (15-20%) skill at 12 h (24-72 h) compared to the climatology and persistence forecasts of TC intensity. This consensus technique has greater skill than the consensus forecast based on the original model output and therefore it has the potential to be applied in operation.

A novel calibration device for quality assurance of therapeutic ultrasound

Photosensitive acrylate polymers can be spatially patterned to produce layers of alternating optical contrast using multi-beam interference patterns of laser light. This technology is widely used for the fabrication of photonic devices including optical sensors and holographic elements [1] , [2] . Here, the use of photonic Bragg structures fabricated in a pressure-sensitive photopolymer [3] for the calibration of therapeutic ultrasound pressure output is presented. On exposure to ultrasound pressure waves, the Bragg structure is compressed, inducing a change in the spacing of the periodic layers of varying optical contrast and, thus, changing the devices readout wavelength i.e. colour. The device colour change due to pressure can either be visually assessed or spectroscopically interrogated for more accurate pressure quantification. This technology offers a fast, straight-forward and low-cost method for regular mapping and calibration of ultrasound pressure output. This is crucial for quality assurance of therapeutic ultrasound scanners used in Extracorporeal Shock Wave Lithotripsy and High Intensity Focused Ultrasound. To date, the photopolymer composition and Bragg device structure has been optimised for MPa range pressures. Results from the optimisation and characterisation of the pressure-sensitive devices are presented.

Moving from Clinac to TrueBeam for Total Skin Electron Therapy (TSET): Beam characteristics and commissioning

The TSET beam characteristics for two Varian TrueBeam accelerators were acquired and compared with existing Varian Clinac TSET data. The 6 MeV high dose rate total skin electron (HDTSe) mode is employed for the modified Stanford dual angle rotational TSET treatments. After the optimal gantry angle pair was determined, the following measurements were made: (a) a percentage depth ionization curve at the central axis and off axis (b) lateral and vertical beam profiles (c) composite PDDs with both GafchromicTM EBT3 film and thermoluminescent dosimeters (TLD) (e) monitor chamber linearity and reproducibility and (f) calibration of beam output. The PDDs measured on the central axis and off-axis were in agreement to better than 1%. The dose profile uniformity and PDD characteristics were in line with the European Organization for Research and Treatment of Cancer (EORTC) guidelines. The monitor linearity and reproducibility were found to be within 0.4% and 0.1% respectively. It was found that to deliver the same dose (78 cGy at dmax) requires 750 MU for the Clinac and 2112 MU for the TrueBeam. This is due to the difference in sensitivity of the monitor chambers between the two machines. Verification of the technique on the new linacs was provided by TLD measurements. A good level of agreement was found for the fundamental beam data, with the main difference being the sensitivity of the monitor chambers by a factor of 2.8. The baseline values were established and quality control tests implemented.