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

IntroductionPencil beam scanning technique used at CNAO requires beam characteristics to be carefully assessed and periodically checked to guarantee patient safety. This study aimed at characterizing the Lynx® detector (IBA Dosimetry) for commissioning and periodic quality assurance (QA) for proton and carbon ion beams, as compared to EBT3 films, currently used for QA checks.Methods and materialsThe Lynx® is a 2-D high-resolution dosimetry system consisting of a scintillating screen coupled with a CCD camera, in a compact light-tight box. The scintillator was preliminarily characterized in terms of short-term stability, linearity with number of particles, image quality and response dependence on iris setting and beam current; Lynx® was then systematically tested against EBT3 films. The detector response dependence on radiation LET was also assessed.ResultsPreliminary results have shown that Lynx is suitable to be used for commissioning and QA checks for proton and carbon ion scanning beams; the cross-check with EBT3 films showed a good agreement between the two detectors, for both single spot and scanned field measurements. The strong LET dependence of the scintillator due to quenching effect makes Lynx® suitable only for relative 2-D dosimetry measurements.ConclusionLynx® appears as a promising tool for commissioning and periodic QA checks for both protons and carbon ion beams. This detector can be used as an alternative of EBT3 films, allowing real-time measurements and analysis, with a significant time sparing.     

Sensitivity of the IQM and MatriXX detectors in megavolt photon beams

AimThis study focused on evaluating the sensitivity of integral quality monitoring (IQM^®) system and MatriXX detectors. These two detectors are recommended for radiotherapy pre-treatment quality assurance (QA).BackgroundIQM is a large wedged-shaped ionisation chamber mounted to the linear accelerator (linac) head in practice. MatriXX consists of an array of ionisation chambers also attached to the linac head.Materials and methodsIn this study, the dosimetric performance and sensitivity of MatriXX and IQM detectors were evaluated using the following characteristics: reproducibility, linearity, error detection capability and three-dimensional conformal radiotherapy (3D-CRT) plans of the head and neck, thorax and pelvic regions.ResultsThis study indicates that the signal responses of the large ionisation chamber device (IQM) and the small pixel array of ionisation chambers device (MatriXX) are reproducible, linear and sensitive to MLC positional errors, backup jaw positional errors and dose errors. The local percentage differences for dose errors of 1%, 2%, and 3% were, respectively, within 0.35–8.23%, 0.78–16.21%, and 1.10–24.41% for the IQM device. While for the MatriXX detector, the ranges were between 0.24–3.19, 0.57–6.43 and 0.81–12.95, respectively. Since IQM is essentially a double wedge-shaped large ionisation chamber, its reproducibility and detection capability are competitive to that of MatriXX. In addition, the sensitivity of the two QA systems increases with an increase in escalation percentage, and the signal responses are patient plan specific.ConclusionsThe two detectors response signals have good correlations and they are accurate for pre-treatment QA. Statistically, (P < 0.05) there is a significant difference between the IQM and MatriXX response to dose errors.     

Quality assurance of isocentres for passive proton beam nozzles using motion capture cameras

PurposeThe objective of this work is to determine mechanical, radiation, and imaging isocentres in three-dimensional (3D) coordinates and verifying coincidence of isocentres of passively scattered proton beam using a visual tracking system (VTS) and an in-house developed phantom named the Eagle.MethodsThe Eagle phantom consists of two modules: The first, named Eagle-head, is used for determining 3D mechanical isocentre of gantry rotation. The second, named Eagle-body, is used for determining 3D radiation and imaging isocentres. The Eagle-body has four slots wherein radiochromic films were inserted for measuring the 3D radiation isocentre and a metal bead was embedded in the centre of one cube to determine the imaging isocentre; this was determined by analysing cone-beam computed tomography images of the cube. Infrared reflective markers that can be tracked by VTS were attached to the Eagle at predetermined locations. The tracked data were converted into 3D treatment room coordinates. The developed method was compared with other methods to assess accuracy.ResultsThe isocentres were determined in mm with respect to the laser isocentre. The mechanical, radiation, and imaging isocentres were (−0.289, 0.189, 0.096), (−0.436, −0.217, 0.009), and (0.134, 0.142, 0.103), respectively. When compared with other methods, the difference in coordinates was (−0.033, −0.107, 0.014) and (0.003, 0.067, 0.039) for radiation and imaging isocentres, respectively.ConclusionThe developed system was found to be useful in providing fast and accurate measurements of the three isocentres in the 3D treatment room coordinate system.     

Geometric and dosimetric quality assurance using logfiles and a 3D helical diode detector for Dynamic WaveArc

PurposeTo conduct patient-specific geometric and dosimetric quality assurance (QA) for the Dynamic WaveArc (DWA) using logfiles and ArcCHECK (Sun Nuclear Inc., Melbourne, FL, USA).MethodsTwenty DWA plans, 10 for pituitary adenoma and 10 for prostate cancer, were created using RayStation version 4.7 (RaySearch Laboratories, Stockholm, Sweden). Root mean square errors (RMSEs) between the actual and planned values in the logfiles were evaluated. Next, the dose distributions were reconstructed based on the logfiles. The differences between dose-volumetric parameters in the reconstructed plans and those in the original plans were calculated. Finally, dose distributions were assessed using ArcCHECK. In addition, the reconstructed dose distributions were compared with planned ones.ResultsThe means of RMSEs for the gantry, O-ring, MLC position, and MU for all plans were 0.2°, 0.1°, 0.1 mm, and 0.4 MU, respectively. Absolute means of the change in PTV D_99% were 0.4 ± 0.4% and 0.1 ± 0.1% points between the original and reconstructed plans for pituitary adenoma and prostate cancer, respectively. The mean of the gamma passing rate (3%/3 mm) between the measured and planned dose distributions was 97.7%. In addition, that between the reconstructed and planned dose distributions was 99.6%.ConclusionsWe have demonstrated that the geometric accuracy and gamma passing rates were within AAPM 119 and 142 criteria during DWA. Dose differences in the dose-volumetric parameters using the logfile-based dose reconstruction method were also clinically acceptable in DWA.     

Evaluations of a flat-panel based compact daily quality assurance device for proton pencil beam scanning (PBS) system

PurposeTo evaluate the flat-panel detector quenching effect and clinical usability of a flat-panel based compact QA device for PBS daily constancy measurements.Materials & MethodThe QA device, named Sphinx Compact, is composed of a 20x20 cm² flat-panel imager mounted on a portable frame with removable plastic modules for constancy checks of proton energy (100 MeV, 150 MeV, 200 MeV), Spread-Out-Bragg-Peak (SOBP) profile, and machine output. The potential quenching effect of the flat-panel detector was evaluated. Daily PBS QA tests of X-ray/proton isocenter coincidence, the constancy of proton spot position and sigma as well as the energy of pristine proton beam, and the flatness of SOBP proton beam through the 'transformed' profile were performed and analyzed. Furthermore, the sensitivity of detecting energy changes of pristine proton beam was also evaluated.ResultsThe quenching effect was observed at depths near the pristine peak regions. The flat-panel measured range of the distal 80% is within 0.9 mm to the defined ranges of the delivered proton beams. X-ray/proton isocenter coincidence tests demonstrated maximum mismatch of 0.3 mm between the two isocenters. The device can detect 0.1 mm change of spot position and 0.1 MeV energy changes of pristine proton beams. The measured transformed SOBP beam profile through the wedge module rendered as flat.ConclusionsEven though the flat-panel detector exhibited quenching effect at the Bragg peak region, the proton range can still be accurately measured. The device can fulfill the requirements of the daily QA tests recommended by the AAPM TG224 Report.     

Experimental assessment of proton dose calculation accuracy in inhomogeneous media

PurposeProton therapy with Pencil Beam Scanning (PBS) has the potential to improve radiotherapy treatments. Unfortunately, its promises are jeopardized by the sensitivity of the dose distributions to uncertainties, including dose calculation accuracy in inhomogeneous media. Monte Carlo dose engines (MC) are expected to handle heterogeneities better than analytical algorithms like the pencil-beam convolution algorithm (PBA). In this study, an experimental phantom has been devised to maximize the effect of heterogeneities and to quantify the capability of several dose engines (MC and PBA) to handle these.MethodsAn inhomogeneous phantom made of water surrounding a long insert of bone tissue substitute (1 × 10 × 10 cm³) was irradiated with a mono-energetic PBS field (10 × 10 cm²). A 2D ion chamber array (MatriXX, IBA Dosimetry GmbH) lied right behind the bone. The beam energy was such that the expected range of the protons exceeded the detector position in water and did not attain it in bone. The measurement was compared to the following engines: Geant4.9.5, PENH, MCsquare, as well as the MC and PBA algorithms of RayStation (RaySearch Laboratories AB).ResultsFor a γ-index criteria of 2%/2 mm, the passing rates are 93.8% for Geant4.9.5, 97.4% for PENH, 93.4% for MCsquare, 95.9% for RayStation MC, and 44.7% for PBA. The differences in γ-index passing rates between MC and RayStation PBA calculations can exceed 50%.ConclusionThe performance of dose calculation algorithms in highly inhomogeneous media was evaluated in a dedicated experiment. MC dose engines performed overall satisfactorily while large deviations were observed with PBA as expected.     

Optimization of an ultra-fast silicon detector for proton and carbon beams using GEANT4 Monte Carlo toolkit

AimThe purpose of this study was to investigate the crosstalk effects between adjacent pixels in a thin silicon detector with 50 um thickness.BackgroundThere are some limitations in the applications of detectors in hadron therapy. So it is necessary to have a detector with concurrent excellent time and resolution. In this work, the GEANT4 toolkit was applied to estimate the best value for energy cutoff in the thin silicon detector in order to optimize the detector.Materials and MethodsGEANT4 toolkit was applied to simulate the transport and interactions of particles. Calculations were performed for a thin silicon detector (2 cm × 2 cm×0.005 cm) irradiated by proton and carbon ion beams. A two-dimensional array of silicon pixels in the x-y plane with 100 um × 100 um × 50 um dimensions build the whole detector. In the end, the ROOT package is used to interpret and analyze the resultsResultsIt is seen that by the presence of energy cutoff, pixels with small deposited energy are ignored. The best values for energy cutoff are 0.01 MeV and 0.7 MeV for proton and carbon ion beams, respectively. By applying these energy cutoff values, efficiency and purity values are maximized and also minimum output errors are achieved.ConclusionsThe results are reasonable, good and useful to optimize the geometry of future silicon detectors in order to be used as beam monitoring in hadron therapy applications.     

Instrumentation for diagnostics and control of laser-accelerated proton (ion) beams

Suitable instrumentation for laser-accelerated proton (ion) beams is critical for development of integrated, laser-driven ion accelerator systems. Instrumentation aimed at beam diagnostics and control must be applied to the driving laser pulse, the laser–plasma that forms at the target and the emergent proton (ion) bunch in a correlated way to develop these novel accelerators. This report is a brief overview of established diagnostic techniques and new developments based on material presented at the first workshop on ‘Instrumentation for Diagnostics and Control of Laser-accelerated Proton (Ion) Beams’ in Abingdon, UK. It includes radiochromic film (RCF), image plates (IP), micro-channel plates (MCP), Thomson spectrometers, prompt inline scintillators, time and space-resolved interferometry (TASRI) and nuclear activation schemes. Repetition-rated instrumentati on requirements for target metrology are also addressed.     

A machine learning-based framework for delivery error prediction in proton pencil beam scanning using irradiation log-files

PurposeThis study aims to investigate the use of machine learning models for delivery error prediction in proton pencil beam scanning (PBS) delivery.MethodsA dataset of planned and delivered PBS spot parameters was generated from a set of 20 prostate patient treatments. Planned spot parameters (spot position, MU and energy) were extracted from the treatment planning system (TPS) for each beam. Delivered spot parameters were extracted from irradiation log-files for each beam delivery following treatment. The dataset was used as a training dataset for three machine learning models which were trained to predict delivered spot parameters based on planned parameters. K-fold cross validation was employed for hyper-parameter tuning and model selection where the mean absolute error (MAE) was used as the model evaluation metric. The model with lowest MAE was then selected to generate a predicted dose distribution for a test prostate patient within a commercial TPS.ResultsAnalysis of the spot position delivery error between planned and delivered values resulted in standard deviations of 0.39 mm and 0.44 mm for x and y spot positions respectively. Prediction error standard deviation values of spot positions using the selected model were 0.22 mm and 0.11 mm for x and y spot positions respectively. Finally, a three-way comparison of dose distributions and DVH values for select OARs indicates that the random-forest-predicted dose distribution within the test prostate patient was in closer agreement to the delivered dose distribution than the planned distribution.ConclusionsPBS delivery error can be accurately predicted using machine learning techniques.     

Quality assurance of canine vaginal cytology: A preliminary study

Regulatory controls of quality assurance in veterinary laboratories are less common than in human reproduction laboratories and the intra- and inter-technician variation in the assessment of canine vaginal cytology has not been reported. This study was designed to determine whether variation in classification of vaginal epithelial cells and interpretation of vaginal cytology smears existed within and between technicians in a canine reproductive laboratory.Sixteen vaginal cytology smears representing different known stages of the oestrous cycle were examined twice by one experienced technician and three inexperienced technicians in a blinded random order study design. Seven assessments were made; counting and classifying one hundred vaginal epithelial cells into four morphological classifications and assessment of three cellular categories. Technicians also interpreted their results and reported the stage of the cycle they thought each slide represented. In addition, selected samples were sent to four external commercial laboratories for interpretation.For the experienced technician, intra-technician variation was low for the morphological classifications and cellular assessments (r = 0.69-0.95). There was more intra-technician variation between results from Examination One and Examination Two for the inexperienced technicians (r = 0.53-0.92 where correlations were found). When inexperienced technicians' results were compared to results from the experienced technician, the inter-technician variation was low; results were correlated for 17 of the 21 observations (four morphological classifications and three cellular assessments across the three technicians) (r = 0.38-0.87). When technician interpretations of stage of the oestrous cycle were compared to the known stage of the cycle for each smear, the experienced technician correctly interpreted 19 of the 32 smears, whilst the three inexperienced technicians correctly interpreted 14, 16, and 18 of the 32 smears. The interpretation of vaginal smears by external laboratories was varied and sometimes inconclusive; 50% of laboratories incorrectly identified metoestrus smears as proestrus and 25% of the laboratories incorrectly identified an oestrus smear as proestrus.The results of this study are highly important for clinicians undertaking canine reproductive assessments since they demonstrate the potential for variability of results. While the greatest precision was found when vaginal smears were examined by an experienced technician (who, on a daily basis, examines many smears), more variability in both the reporting of different cell types and interpretation of the smears was observed by inexperienced technicians and when samples were sent to external commercial laboratories. These findings suggest that suitable quality control programmes should be implemented for laboratories that are undertaking routine assessments of canine reproductive function.     

Commissioning of the 4-D treatment delivery system for organ motion management in synchrotron-based scanning ion beams

PurposeThe aim of this work was the commissioning of delivery procedures for the treatment of moving targets in scanning pencil beam hadrontherapy.MethodsEBT3 films fixed to the Anzai Respiratory Phantom were exposed to carbon ion scanned homogeneous fields (E = 332 MeV/u). To evaluate the interplay effect, field size and flatness for 3 different scenarios were compared to static condition: gated irradiation or repainting alone and combination of both. Respiratory signal was provided by Anzai pressure sensor or optical tracking system (OTS). End-exhale phase and 1 s gating window were chosen (2.5 mm residual motion). Dose measurements were performed using a PinPoint ionization chamber inserted into the Brainlab ET Gating Phantom. A sub-set of tests was also performed using proton beams.ResultsThe combination of gating technique and repainting (N = 5) showed excellent results (6.1% vs 4.3% flatness, identical field size and dose deviation within 1.3%). Treatment delivery time was acceptable. Dose homogeneity for gated irradiation alone was poor. Both Anzai sensor and OTS appeared suitable for providing respiratory signal. Comparisons between protons and carbon ions showed that larger beam spot sizes represent more favorable condition for minimizing motion effect.ConclusionResults of measurements performed on different phantoms showed that the combination of gating and layered repainting is suitable to treat moving targets using scanning ion beams. Abdominal compression using thermoplastic masks, together with multi-field planning approach and multi-fractionation, have also been assessed as additional strategies to mitigate the effect of patient respiration in the clinical practice.     

Visualization of air and metal inhomogeneities in phantoms irradiated by carbon ion beams using prompt secondary ions

PurposeNon-invasive methods for monitoring of the therapeutic ion beam extension in the patient are desired in order to handle deteriorations of the dose distribution related to changes of the patient geometry. In carbon ion radiotherapy, secondary light ions represent one of potential sources of information about the dose distribution in the irradiated target. The capability to detect range-changing inhomogeneities inside of an otherwise homogeneous phantom, based on single track measurements, is addressed in this paper.MethodsAir and stainless steel inhomogeneities, with PMMA equivalent thickness of 10 mm and 4.8 mm respectively, were inserted into a PMMA-phantom at different positions in depth. Irradiations of the phantom with therapeutic carbon ion pencil beams were performed at the Heidelberg Ion Beam Therapy Center. Tracks of single secondary ions escaping the phantom under irradiation were detected with a pixelized semiconductor detector Timepix. The statistical relevance of the found differences between the track distributions with and without inhomogeneities was evaluated.ResultsMeasured shifts of the distal edge and changes in the fragmentation probability make the presence of inhomogeneities inserted into the traversed medium detectable for both, 10 mm air cavities and 1 mm thick stainless steel. Moreover, the method was shown to be sensitive also on their position in the observed body, even when localized behind the Bragg-peak.ConclusionsThe presented results demonstrate experimentally, that the method using distributions of single secondary ion tracks is sensitive to the changes of homogeneity of the traversed material for the studied geometries of the target.     

A modular dose delivery system for treating moving targets with scanned ion beams: Performance and safety characteristics,and preliminary tests

PurposeThe purpose of this study was to develop a modular dose-delivery system (DDS) for scanned-ion radiotherapy that mitigates against organ motion artifacts by synchronizing the motion of the beam with that of the moving anatomy.MethodsWe integrated a new motion synchronization system and an existing DDS into two centers. The modular approach to integration utilized an adaptive layer of software and hardware interfaces. The method of synchronization comprised three major tasks, namely, the creation of 3D treatment plans (each representing one phase of respiratory motion and together comprising a 4D plan), monitoring anatomic motion during treatment, and synchronization of the beam to anatomic motion. The synchronization was accomplished in real time by repeatedly selecting and delivering a 3D plan, i.e., the one that most closely corresponded to the current anatomic state, until all plans were delivered. The performance characteristics of the motion mitigation system were tested by delivering 4D treatment plans to a moving phantom and comparing planned and measured dose distributions. Dosimetric performance was considered acceptable when the gamma-index pass rate was >90%, homogeneity-index value was >95%, and conformity-index value was >60%. Selected safety characteristics were tested by introducing errors during treatment and testing DDS response.ResultsAcceptable dosimetric performance and safety characteristics were observed for all treatment plans.ConclusionsWe demonstrated, for the first time, that a modular prototype system, synchronizing scanned ion beams with moving targets can deliver conformal, motion-compensated dose distributions. The prototype system was implemented and characterized at GSI and CNAO.     

High resolution ion chamber array delivery quality assurance for robotic radiosurgery: Commissioning and validation

PurposeHigh precision radiosurgery demands comprehensive delivery-quality-assurance techniques. The use of a liquid-filled ion-chamber-array for robotic-radiosurgery delivery-quality-assurance was investigated and validated using several test scenarios and routine patient plans.Methods and materialPreliminary evaluation consisted of beam profile validation and analysis of source–detector-distance and beam-incidence-angle response dependence. The delivery-quality-assurance analysis is performed in four steps: (1) Array-to-plan registration, (2) Evaluation with standard Gamma-Index criteria (local-dose-difference ⩽ 2%, distance-to-agreement ⩽ 2 mm, pass-rate ⩾ 90%), (3) Dose profile alignment and dose distribution shift until maximum pass-rate is found, and (4) Final evaluation with 1 mm distance-to-agreement criterion. Test scenarios consisted of intended phantom misalignments, dose miscalibrations, and undelivered Monitor Units. Preliminary method validation was performed on 55 clinical plans in five institutions.ResultsThe 1000SRS profile measurements showed sufficient agreement compared with a microDiamond detector for all collimator sizes. The relative response changes can be up to 2.2% per 10 cm source–detector-distance change, but remains within 1% for the clinically relevant source–detector-distance range. Planned and measured dose under different beam-incidence-angles showed deviations below 1% for angles between 0° and 80°. Small-intended errors were detected by 1 mm distance-to-agreement criterion while 2 mm criteria failed to reveal some of these deviations. All analyzed delivery-quality-assurance clinical patient plans were within our tight tolerance criteria.ConclusionWe demonstrated that a high-resolution liquid-filled ion-chamber-array can be suitable for robotic radiosurgery delivery-quality-assurance and that small errors can be detected with tight distance-to-agreement criterion. Further improvement may come from beam specific correction for incidence angle and source–detector-distance response.     

Determination of the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams

PurposeTo determine the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams.MethodsAn AGMS-DM+ semiconductor detector was calibrated in terms of air kerma measured with an ionization chamber. Air kerma was measured for 20 x-ray beams with tube voltages of 50–140 kVp and a half-value layer (HVL) of 2.2–9.7 mm Al for given quality index (QI) values of 0.4, 0.5, and 0.6, and converted to the surface dose. Finally, the air kerma and HVL measured by the AGMS-DM+ detector were expressed as a ratio of the surface dose for 10 × 10 and 20 × 20 cm² fields. The ratio of both was represented as a function of HVL for the given QI values and verified by comparing it with that calculated using the Monte Carlo method.ResultsThe air kerma calibration factor, CF, for the AGMS-DM+ detector ranged from 0.986 to 1.016 (0.9% in k = 1). The CF values were almost independent of the x-ray fluence spectra for the given QI values. The ratio of the surface dose to the air kerma determined by the PTW 30,013 chamber and the AGMS-DM+ detector was less than 1.8% for the values calculated using the Monte Carlo method, and showed a good correlation with the HVL for the given QI values.ConclusionIt is possible to determine the surface dose of a water phantom from the air kerma and HVL measured by a semiconductor detector for given QI values.     

A systematic quality assurance framework for the upgrade of radiation oncology information systems

In spite of its importance, no systematic and comprehensive quality assurance (QA) program for radiation oncology information systems (ROIS) to verify clinical and treatment data integrity and mitigate against data errors/corruption and/or data loss risks is available. Based on data organization, format and purpose, data in ROISs falls into five different categories: (1) the ROIS relational database and associated files; (2) the ROIS DICOM data stream; (3) treatment machine beam data and machine configuration data; (4) electronic medical record (EMR) documents; and (5) user-generated clinical and treatment reports from the ROIS. For each data category, this framework proposes a corresponding data QA strategy to very data integrity. This approach verified every bit of data in the ROIS, including billions of data records in the ROIS SQL database, tens of millions of ROIS database-associated files, tens of thousands of DICOM data files for a group of selected patients, almost half a million EMR documents, and tens of thousands of machine configuration files and beam data files. The framework has been validated through intentional modifications with test patient data. Despite the ‘big data’ nature of ROIS, the multiprocess and multithread nature of our QA tools enabled the whole ROIS data QA process to be completed within hours without clinical interruptions. The QA framework suggested in this study proved to be robust, efficient and comprehensive without labor-intensive manual checks and has been implemented for our routine ROIS QA and ROIS upgrades.     

A study on dosimetric properties of electronic portal imaging device and its use as a quality assurance tool in Volumetric Modulated Arc Therapy

Aim

In this study, the dosimetric properties of the electronic portal imaging device were examined and the quality assurance testing of Volumetric Modulated Arc Therapy was performed.

Background

RapidArc involves the variable dose rate, leaf speed and the gantry rotation. The imager was studied for the effects like dose, dose rate, field size, leaf speed and sag during gantry rotation.

Materials and methods

A Varian RapidArc machine equipped with 120 multileaf collimator and amorphous silicon detector was used for the study. The characteristics that are variable in RapidArc treatment were studied for the portal imager. The accuracy of a dynamic multileaf collimator position at different gantry angles and during gantry rotation was examined using the picket fence test. The control of the dose rate and gantry speed was verified using a test field irradiating seven strips of the same dose with different dose rate and gantry speeds. The control over leaf speed during arc was verified by irradiating four strips of different leaf speeds with the same dose in each strip. To verify the results, the RapidArc test procedure was compared with the X-Omat film and verified for a period of 6 weeks using EPID.

Results

The effect of gantry rotation on leaf accuracy was minimal. The dose in segments showed good agreement with mean deviation of 0.8% for dose rate control and 1.09% for leaf speed control over different gantry speeds.

Conclusion

The results provided a precise control of gantry speed, dose rate and leaf speeds during RapidArc delivery and were consistent over 6 weeks.