Delivery Quality Assurance Research Articles

A rare instance of latent systematic error in volumetric-modulated arc therapy with field-extended multi-isocentre irradiation leading to a serious dose-delivery accident.

Volumetric-modulated arc therapy (VMAT) with field-extended multi-isocentre irradiation (VMAT-FEMII) is an effective irradiation technique, particularly for large planning target volumes in the craniocaudal direction. A variety of treatment planning techniques have been reported to reduce the dosimetric impact. However, there is no guarantee that unexpected latent systematic errors would not occur. Herein, we report the experience with a rare case that could have led to a serious VMAT-FEMII-related accident. A patient with uterine cervical carcinoma was scheduled for VMAT-FEMII to the whole pelvis and the para-aortic lymph node region. A combination of the two sets of field groups with different isocentres was planned: one to cover the para-aortic lymph nodes and the other to cover the whole pelvis. Measurements based on the pretreatment dose delivery quality assurance (QA) revealed an unexpected overdose of >20% in the field overlap region. This overdose phenomenon is not reflected in the calculated dose distribution in the radiotherapy treatment planning system. Therefore, the plan was altered; a homogeneous dose distribution inside the dose junction was achieved. Several analyses were performed to elucidate the overdosing phenomenon. However, no conclusive answer was found to why non-reflection at the calculated dose distribution was found. The limitations to VMAT-FEMII are primarily related to systematic errors in the positional setup from patient-derived and/or mechanical sources. However, this report highlights a rare case of overdosing caused by inverse optimization and dose calculation. We recommend checking the aperture status of the jaw and multi-leaf collimator at each control point of the treatment plan and using a high-resolution image measurement system on a VMAT-FEMII QA to confirm the dose junction status.

Analysis on the delivery quality assurance using SunCHECK for the VMAT in halcyon linear accelerator

Analysis on the delivery quality assurance using SunCHECK for the VMAT in halcyon linear accelerator

Influence of the Planning Parameters of a New Algorithm on the Dosimetric Quality, Beam-on Time and Delivery Accuracy of Tomotherapy Plans

Background: This work aimed to determine the optimum VOLOTM Ultra algorithm parameters for tomotherapy treatments. Methods: 1056 treatment plans were generated with VOLOTM Ultra for 36 patients and six anatomical locations. The impact of varying four parameters was studied: the accelerated treatment (AT), leaf open/close time (LOT) cutoff, normal tissue objective (NTO) weight, and number of iterations. The beam-on time and dosimetric metrics were quantified for the target volumes and organs at risk (OARs). Delivery quality assurance measurements were obtained for 36 plans to assess the delivery accuracy. Results: The mean beam-on time for the helical tomotherapy and TomoDirect (TD) plans decreased by 26.6 ± 2.8% and 17.4 ± 4.3%, respectively, when the accelerated treatment parameter was increased from 0 to 10, at the expense of the planning target volume (PTV) coverage (2% lower D98%) and OAR dose (up to 15% increase). For TD plans, it seems preferable to systematically use an AT value of 10. Increasing the number of iterations beyond six seems unnecessary. In this study, an NTO weight of approximately 10 appears to be ideal and eliminates the need to use rings in the treatment plan. Finally, no correlation was found between the leaf open/close time cutoff and the delivery accuracy, while a leaf open/close cutoff of 60 ms seemed to degrade dosimetry quality. Conclusion: Optimal values for the AT, LOT cutoff, NTO weight, and number of optimization rounds were identified and should help improve the management of patients whose tomotherapy treatments are planned with VOLOTM Ultra.

Development of a 3D printed phantom for commissioning and quality assurance of multiple brain targets stereotactic radiosurgery

Single plan techniques for multiple brain targets (MBT) stereotactic radiosurgery (SRS) are now routine. Patient specific quality assurance (QA) for MBT poses challenges due to the limited capabilities of existing QA tools which necessitates several plan redeliveries. This study sought to develop an SRS QA phantom that enables flexible MBT patient specific QA in a single delivery, along with complex SRS commissioning. PLA marble and PLA StoneFil materials were selected based on the literature and previous research conducted in our department. The HU numbers were investigated to determine the appropriate percentage infill for skull and soft-tissue equivalence. A Prusa MK3S printer in conjunction with the above-mentioned filaments were used to print the SRS QA phantom. Quality control (QC) was performed on the printed skull, film inserts and plugs for point dose measurements. EBT3 film and point dose measurements were performed using a CC04 ionisation chamber. QC demonstrated that the SRS QA phantom transverse, coronal and sagittal film planes were orthogonal within 0.5°. HU numbers for the skull, film inserts and plugs were 858 ± 20 and 35 ± 12 respectively. Point and EBT3 film dose measurements were within 2.5% and 3%/2 mm 95% gamma pass rate, respectively except one Gross Tumour Volume (GTV) that had a slightly lower gamma pass rate. Dose distributions to five GTVs were measured with EBT3 film in a single plan delivery on CyberKnife. In conclusion, an SRS QA phantom was designed, and 3D printed and its use for performing complex MBT patient specific QA in a single delivery was demonstrated.

2V-CBCT: Two-Orthogonal-Projection based CBCT Reconstruction and Dose Calculation for Radiation Therapy using Real Projection Data.

This work demonstrates the feasibility of two-orthogonal-projection-based CBCT (2V-CBCT) reconstruction and dose calculation for radiation therapy (RT) using real projection data, which is the first 2V-CBCT feasibility study with real projection data, to the best of our knowledge. RT treatments are often delivered in multiple fractions, for which on-board CBCT is desirable to calculate the delivered dose per fraction for the purpose of RT delivery quality assurance and adaptive RT. However, not all RT treatments/fractions have CBCT acquired, but two orthogonal projections are always available. The question to be addressed in this work is the feasibility of 2V-CBCT for the purpose of RT dose calculation. 2V-CBCT is a severely ill-posed inverse problem for which we propose a coarse-to-fine learning strategy. First, a 3D deep neural network that can extract and exploit the inter-slice and intra-slice information is adopted to predict the initial 3D volumes. Then, a 2D deep neural network is utilized to fine-tune the initial 3D volumes slice-by-slice. During the fine-tuning stage, a perceptual loss based on multi-frequency features is employed to enhance the image reconstruction. Dose calculation results from both photon and proton RT demonstrate that 2V-CBCT provides comparable accuracy with full-view CBCT based on real projection data.

Development of a novel delivery quality assurance system based on simultaneous verification of dose distribution and binary multi-leaf collimator opening in helical tomotherapy

BackgroundIntensity-modulated radiation therapy (IMRT) requires delivery quality assurance (DQA) to ensure treatment accuracy and safety. Irradiation techniques such as helical tomotherapy (HT) have become increasingly complex, rendering conventional verification methods insufficient. This study aims to develop a novel DQA system to simultaneously verify dose distribution and multi-leaf collimator (MLC) opening during HT.MethodsWe developed a prototype detector consisting of a cylindrical plastic scintillator (PS) and a cooled charge-coupled device (CCD) camera. Scintillation light was recorded using a CCD camera. A TomoHDA (Accuray Inc.) was used as the irradiation device. The characteristics of the developed system were evaluated based on the light intensity. The IMRT plan was irradiated onto the PS to record a moving image of the scintillation light. MLC opening and light distribution were obtained from the recorded images. To detect MLC opening, we placed a region of interest (ROI) on the image, corresponding to the leaf position, and analyzed the temporal change in the light intensity within each ROI. Corrections were made for light changes due to differences in the PS shape and irradiation position. The corrected light intensity was converted into the leaf opening time (LOT), and an MLC sinogram was constructed. The reconstructed MLC sinogram was compared with that calculated using the treatment planning system (TPS). Light distribution was obtained by integrating all frames obtained during IMRT irradiation. The light distribution was compared with the dose distribution calculated using the TPS.ResultsThe LOT and the light intensity followed a linear relationship. Owing to MLC movements, the sensitivity and specificity of the reconstructed sinogram exceeded 97%, with an LOT error of − 3.9 ± 7.8%. The light distribution pattern closely resembled that of the dose distribution. The average dose difference and the pass rate of gamma analysis with 3%/3 mm were 1.4 ± 0.2% and 99%, respectively.ConclusionWe developed a DQA system for simultaneous and accurate verification of both dose distribution and MLC opening during HT.

A Comparison of Patient-specific Delivery Quality Assurance (DQA) Devices in Radiation Therapy

A Comparison of Patient-specific Delivery Quality Assurance (DQA) Devices in Radiation Therapy

Radiomics Breakthrough Could Spark the Head and Neck Cancer Radiotherapy Revolution

Radiomics, the method by which digital images could be transformed into mineable data, opens new horizons for biomedical research and in particular in oncology, for diagnostic, predictive and prognostic purposes. The use of artificial intelligence (AI) algorithms in the radiomics algorithm makes radiomics and AI two inseparable, intricate domains. AI defined as machine capability of imitating human intelligence, has already been implemented on a large scale in oncology and radiotherapy. One of the two main branches (the virtual one) of machine learning depending on the application, artificial intelligence is involved both in the diagnostics processes as well as treatment planning, – dose delivery and radiotherapy quality assurance (QA). Head and neck cancer (HNC), although it is the 6th malignancy in incidence worldwide, is redoubtable due to the high rate of therapeutic failures, especially of loco-regional recurrence. Although intensity-modulated treatment techniques have brought benefits especially in limiting the toxicities associated with irradiation, AI and especially radiomics, due the possibility to extract data from high-resolution medical imaging in order to build predictive diagnostic and prognostic models, could upgrade the technological revolution in HNC radiotherapy at a higher level. Beyond the already intensively studied diagnostic applications, radiomics could be useful for predicting the response to radio-chemotherapy, anticipating treatment related toxicities and for pre-therapeutic evaluation of the need for adaptive radiotherapy (ART). Clinical-radiomic models have superior predictive power and the delta variation of radiomic features could be a biomarker still less evaluated. Due to characteristics of modern radiotherapy which includes as standard the image guided radiotherapy (IGRT) concept using the computer tomography (CT) simulator and Cone Beam CT (CBCT) to ensure the accuracy of the patient’s positioning during the treatment, radiomics in radiotherapy could be the spearhead of the translation radiomics in daily clinical routine and of the HNC RGRT concept development.

Development of Automated Delivery Quality Assurance Analysis Software for Helical Tomotherapy.

To develop a fully automated in-house gamma analysis software for the "Cheese" phantom-based delivery quality assurance (QA) of helical tomotherapy plans. The developed in-house software was designed to automate several procedures, which need to be manually performed using commercial software packages. The region of interest for the analysis was automatically selected by cropping out film edges and thresholding dose values (>10% of the maximum dose). The film-measured dose was automatically aligned to the computed dose using an image registration algorithm. An optimal film scaling factor was determined to maximize the percentage of pixels passing gamma (gamma passing rate) between the measured and computed doses (3%/3 mm criteria). This gamma analysis was repeated by introducing setup uncertainties in the anterior-posterior direction. For 73 tomotherapy plans, the gamma analysis results using the developed software were compared to those analyzed by medical physicists using a commercial software package. The developed software successfully automated the gamma analysis for the tomotherapy delivery quality assurance. The gamma passing rate (GPR) calculated by the developed software was higher than that by the clinically used software by 3.0%, on average. While, for 1 of the 73 plans, the GPR by the manual gamma analysis was higher than 90% (pass/fail criteria), the gamma analysis using the developed software resulted in fail (GPR < 90%). The use of automated and standardized gamma analysis software can improve both the clinical efficiency and veracity of the analysis results. Furthermore, the gamma analyses with various film scaling factors and setup uncertainties will provide clinically useful information for further investigations.

Development and Evaluation of Multipurpose Phantom for Delivery Quality Assurance of Intensity-modulated Radiation Therapy

Treatments demanding high accuracy, such as intensity-modulated radiation therapy (IMRT), should provide the optimal dose distribution and correct intervention. Otherwise, they may become unsafe and cause adverse effects to patients. Delivery quality assurance (DQA) for treatment verification can be performed considering the absolute dose using an ionization chamber and relative dose using a film. However, a film imposes a long waiting time for measurement and is sensitive to temperature and humidity, development conditions, and noise. We aim to evaluate the usefulness of a multipurpose phantom for fast and simple IMRT DQA. The multipurpose phantom is made of poly (methyl methacrylate)-based resin. The phantom allows the insertion of a 2D array detector and an ionization chamber. Therefore, the relative and absolute doses can be measured simultaneously. The IMRT DQA evaluation provided absolute dose of 0.35 ± 1.74% and relative dose of 99.03 ± 0.6 % in 3 mm/3% gamma evaluation for a linear accelerator. In addition, the absolute and relative doses were 1.37 ± 1.05% and 98.7 ± 0.78% in helical tomotherapy, respectively. Therefore, the dose measurements were within acceptable error limits of 3%. The results demonstrate the multipurpose capabilities of the proposed phantom for evaluating dose distribution and absolute dosimetry.

Feasibility on Statistical Process Control Analysis of Delivery Quality Assurance in Helical Tomotherapy

Feasibility on Statistical Process Control Analysis of Delivery Quality Assurance in Helical Tomotherapy

Machine performance and stability of the first clinical self-shielded stereotactic radiosurgery system: Initial 2-year experience.

This study provides insight into the overall system performance, stability, and delivery accuracy of the first clinical self-shielded stereotactic radiosurgery (SRS) system. Quality assurance procedures specifically developed for this unit are discussed, and trends and variations over the course of 2-years for beam constancy, targeting and dose delivery are presented. Absolute dose calibration for this 2.7MV unit is performed to deliver 1 cGy/MU at dmax =7mm at a source-to-axis-distance (SAD) of 450mm for a 25mm collimator. Output measurements were made with 2-setups: a device that attaches to a fixed position on the couch (daily) and a spherical phantom that attaches to the collimating wheel (monthly). Beam energy was measured using a cylindrical acrylic phantom at depths of 100 (D10 ) and 200 (D20 )mm. Beam profiles were evaluated using Gafchromic film and compared with TPS beam data. Accuracy in beam targeting was quantified with the Winston-Lutz (WL) and end-to-end (E2E) tests. Delivery quality assurance (DQA) was performed prior to clinical treatments using Gafchromic EBT3/XD film. Net cumulative output adjustments of 15% (pre-clinical), 9% (1st year) and 3% (2nd year) were made. The mean output was 0.997±0.010 cGy/MU (range: 0.960-1.046cGy/MU) and 0.993±0.029 cGy/MU (range: 0.884-1.065cGy/MU) for measurements with the daily and monthly setups, respectively. The mean relative beam energy (D10 /D20 ) was 0.998±0.004 (range: 0.991-1.006). The mean total targeting error was 0.46±0.17mm (range: 0.06-0.98mm) for the WL and 0.52±0.28mm (range: 0.11-1.27mm) for the E2E tests. The average gamma pass rates for DQA measurements were 99.0% and 90.5% for 2%/2mm and 2%/1mm gamma criteria, respectively. This SRS unit meets tolerance limits recommended by TG-135, MPPG 9a., and TG-142 with a treatment delivery accuracy similar to what is achieved by other SRS systems.

Association between radiotherapy protocol variations and outcome in the CONVERT trial

BackgroundRadiotherapy quality assurance (QA) is integral to radiotherapy delivery. Here we report comprehensive contouring, dosimetry, and treatment delivery QA, describe protocol compliance, and detail the impact of protocol variations on acute grade ≥3 toxicity, progression free survival (PFS), and overall survival (OS) in the phase III CONVERT trial. Materials/MethodsRadiotherapy planning data from one hundred randomly selected patients were requested. Members of the CONVERT Trial Management Group (TMG) recontoured the heart, lung, and spinal cord organs at risk (OAR) according to the trial guideline. The existing radiotherapy plan were re-applied to the new structures and the new dosimetric data were recollected. Compliance with radiotherapy QA components were recorded and radiotherapy QA components were pooled into protocol variations: acceptable, acceptable variation, and unacceptable variation. Univariable analysis with a Cox proportional hazards model established the relationship between protocol variations and patient outcome. ResultsNinety-three cases were submitted for retrospective radiotherapy QA review. Demographics of the radiotherapy QA cohort (n=93) matched the non-QA (n=450) cohort. 97.8% of gross tumour volume (GTV) contours were protocol compliant. OAR contours were non-compliant in 79.6% instances of the heart, 37.6% lung, and 75.3% spinal cord. Of the non-compliant heart contours, 86.5% and 2.7% had contours caudal and cranial to the protocol-defined heart borders. 10.8% did not include the pericardial sac and 2.7% did not include the anterior aspect of the pericardium. Eleven (11.8%) submissions exceeded protocol-defined dosimetric heart constraints; six of which were only noted on the application of protocol-compliant contours. Unacceptable variations were not associated with an increase in grade 3 toxicity (p=0.808), PFS (p=0.232), or OS (p=0.743). ConclusionNon-protocol compliant heart contours were associated with increased dose delivered to the heart OAR, with 11.8 % of submitted heart structures exceeding protocol-defined constraints. In this QA cohort of patients with small cell lung cancer, unacceptable variations were not associated with acute grade ≥3 toxicity, PFS, or OS. Radiotherapy QA remains the cornerstone of high-quality radiotherapy delivery and should be embedded into clinical trial and non-clinical trial practice; clinical trials should report standardised radiotherapy QA parameters alongside trial outcomes.

OGC O05 Does Minimally Invasive Transthoracic Esophagectomy Reduce Postoperative Pulmonary Complications? An International Cohort Study from the Oesophagogastric Anastomosis Audit (OGAA)

Abstract Background Ongoing debate exists around optimum surgical approach to esophageal cancers, with limited data characterizing the external validity of randomised trials on MIE for esophageal cancers. This study aimed to report the postoperative pulmonary outcomes of transthoracic minimally invasive esophagectomy (MIE) in esophageal cancers patients from an international, multicenter cohort. Methods Patients undergoing open (OE, n=744), hybrid (HE, n=500), and totally MIE (TMIE, n=540) for esophageal cancers were identified from the Oesophagogastric Anastomosis Audit (OGAA). Results PPC rates were lower after MIE compared to OE and HE (31% vs 38% vs 39%, p=0.002), even on adjusted analyses compared to OE (odds ratio (OR): 0.57, CI95%: 0.44–0.74). MIE was associated with higher rates of AL (16% vs 11% vs. 11%, p=0.026), but not overall complications (60% vs 65% vs. 62%, p=0.2) and 90-day mortality compared to OE and HE (3% vs 4% vs. 3%, p=0.6). On adjusted analyses, MIE was associated with lower overall complications (OR: 0.67, CI95%: 0.51–0.87), but not AL (OR: 1.39, CI95%: 0.96–2.01) and 90-day mortality (OR: 0.49, CI95%: 0.22–1.04) compared to OE. Conclusions In contrast to previous reports, this study provides real-world data that TMIE was associated with lower 90-day PPC 90- than OE and HE, especially in patients with higher ASA grades and underlying respiratory disease. These warrant a further review into causes and mechanisms in selected patients, and that quality assurance in delivery of TMIE is probably of major importance. Finally, the proxies of oncologic impact, such as R0 rates and extend of lymphadenectomy, are superior with the TMIE approach. The ideal surgical approach remains unclear, and may be context dependent, and ongoing trials such as ROBOT-II will provide a large body of randomized data within a few years that may clarify the optimum approach to locally advanced esophageal cancers.

Treatment Planning Guideline of EBT Film-based Delivery Quality Assurance Using Statistical Process Control in Helical Tomotherapy

Treatment Planning Guideline of EBT Film-based Delivery Quality Assurance Using Statistical Process Control in Helical Tomotherapy

Characterization of Tissue Equivalent Materials Using 3D Printing for Patient-Specific DQA in Radiation Therapy

Three-dimensional printing technology has the advantage of facilitating the construction of complex three-dimensional shapes. For this reason, it is widely used in medical and radiological fields. However, few materials with high electron density similar to that of bone exist for fabricating a human phantom. In this study, commercially available filament materials were used with an FDM 3D printer to perform delivery quality assurance (DQA) and were evaluated for medical use. For the bone filament material, BaSO4 was synthesized in five ratios of 2%, 4%, 6%, 8%, and 10% with 40% PBAT and 50~58% PLA. The electron density for the 3D printing material fabricated was obtained using kV energy CT and compared with the electron density of human organs and bones. The radiation beam properties of the 3D printed structures were analyzed as films for treatment using a linear accelerator. As a result, by changing the infill density of the material, it was possible to produce a material similar to the density of human organs, and a homogeneous bone material with HU values ranging from 371 ± 9 to 1013 ± 28 was produced. The 3D printing material developed in this study is expected to be usefully applied to the development of a patient-specific phantom to evaluate the accuracy of radiotherapy.

IBA myQA SRS Detector for CyberKnife Robotic Radiosurgery Quality Assurance

The IBA myQA® SRS high-resolution solid-state detector was evaluated in the context of robotic radiosurgery delivered using CyberKnife®. The performance was investigated for periodic machine delivery quality assurance (DQA) and patient-specific treatment verification. myQA® SRS is a 140 × 120 mm CMOS matrix with 400 µm resolution, allocated in a cylindrical ABS phantom topped by a hemispheric cap. Evaluations included: periodic DQA tests, angular response, dose-rate dependence and Iris variable aperture collimator field size measurements. For patient-specific QA various intracranial targets were studied (Gamma Index, 3%/1 mm agreement criteria), taking into account also the detector’s angular response. Results for periodic DQA were in accordance with the machine commissioning data. Dose-rate dependence was confirmed, and angular response tests resulted in a signal decay &gt;5% when beams were delivered outside a ±50° amplitude cone with respect to the vertical direction. Concerning patient-specific QA, &gt;50° angled beams elimination led to a Gamma Index passing rates improvement ranging between +3% and +115%. IBA myQA® SRS proved to be a suitable device for many CyberKnife® constancy DQA checks, providing high-resolution real-time results. Patient-specific Gamma tests showed high passing rates once angular dependence corrections were performed, even in high complexity treatments such as those for trigeminal neuralgia targets.

Multi-Institutional Study of End-to-End Dose Delivery Quality Assurance Testing for Image-Guided Brachytherapy Using a Gel Dosimeter

To quantify dose delivery errors for high-dose-rate image-guided brachytherapy (HDR-IGBT) using an independent end-to-end dose delivery quality assurance test at multiple institutions. The novelty of our study is that this is the first multi-institutional end-to-end dose delivery study in the world. The postal audit used a polymer gel dosimeter in a cylindrical acrylic container for the afterloading system. Image acquisition using computed tomography, treatment planning, and irradiation were performed at each institution. Dose distribution comparison between the plan and gel measurement was performed. The percentage of pixels satisfying the absolute-dose gamma criterion was reviewed. Thirty-five institutions participated in this study. The dose uncertainty was 3.6% ± 2.3% (mean ± 1.96σ). The geometric uncertainty with a coverage factor of k = 2 was 3.5 mm. The tolerance level was set to the gamma passing rate of 95% with the agreement criterion of 5% (global)/3 mm, which was determined from the uncertainty estimation. The percentage of pixels satisfying the gamma criterion was 90.4% ± 32.2% (mean ± 1.96σ). Sixty-six percent (23/35) of the institutions passed the verification. Of the institutions that failed the verification, 75% (9/12) had incorrect inputs of the offset between the catheter tip and indexer length in treatment planning and 17% (2/12) had incorrect catheter reconstruction in treatment planning. The methodology should be useful for comprehensively checking the accuracy of HDR-IGBT dose delivery and credentialing clinical studies. The results of our study highlight the high risk of large source positional errors while delivering dose for HDR-IGBT in clinical practices.

Development of Automated Delivery Quality Assurance Analysis Software for Helical Tomotherapy

Development of Automated Delivery Quality Assurance Analysis Software for Helical Tomotherapy

P120 - Deep learning method for tomotherapy delivery quality assurance: prediction of three-dimensional dose distribution and performance evaluation on phantom

P120 - Deep learning method for tomotherapy delivery quality assurance: prediction of three-dimensional dose distribution and performance evaluation on phantom