An external dosimetry audit programme to credential static and rotational IMRT delivery for clinical trials quality assurance

Study of PRESAGE® dosimeter for end-to-end 3D radiotherapy verification using an anthropomorphic phantom with bespoke dosimeter insert

Modern radiotherapy techniques have advanced and become more sophisticated. End-to-end 3D verification of the complex radiotherapy dose distribution in an anthropomorphic phantom can ensure the accuracy of the treatment delivery. The phantoms commonly used for dosimetry are homogeneous solid water phantom which lacks the capability to measure the 3D dose distribution for heterogeneous tissues necessary for advanced radiotherapy techniques. Therefore, we developed an end-to-end 3D radiotherapy dose verification system based on MAX-HD anthropomorphic phantom (Integrated Medical Technologies Inc., Troy, New York) with bespoke intracranial insert for PRESAGE® dosimeter. In this study, several advanced radiotherapy treatment techniques of various levels of complexity; 3D-CRT, IMRT and VMAT treatment, were planned for a 20 mm diameter of a spherical target in the brain region and delivered to the phantom. The dosimeters were read out using an in-house developed optical computed tomography (OCT) imaging system known as 3DmicroHD-OCT. It was found that the measured dose distribution of the PRESAGE® when compared with the measured dose distribution of EBT film and Monaco TPS has a maximum difference of less than 3% for 3D-CRT, IMRT and VMAT treatment plans. The gamma analysis results of PRESAGE® in comparison to EBT film and Monaco TPS show pass rates of more than 95% for the criteria of 3% dose difference and 3 mm distance-to-agreement. This study proves the capability of PRESAGE® and bespoke MAX-HD phantom in conjunction with the 3DmicroHD-OCT system to measure 3D dose distribution for end-to-end dosimetry verification.

Quantified difference of the collapsed cone convolution (CCC) and Monte Carlo (MC) algorithms based on DVH and gamma analysis for cervical cancer radiation therapy

OBJECTIVE

To quantify the difference between the (collapsed cone convolution) CCC algorithm and the (Monte Carlo) MC algorithm and remind that the planners should pay attention to some possible uncertainties of the two algorithms when employing the two algorithms.

METHODS

Thirty patients' cervical cancer VMAT plans were designed with a Pinnacle TPS (Philips) and divided equally into two groups: the simple group (SG, target volume was only the PTV) and the complex group (CG, target volume included the PTV and PGTV). The plans from the Pinnacle TPS were transferred to the Monaco TPS (Elekta). The plans' parameters all remained unchanged, and the dose was recalculated. Gamma passing rates (GPRs) obtained from dose distribution from Pinnacle TPS compared with that from Monaco TPS with SNC software based on three triaxial planes (transverse, sagittal and coronal). GPRs and DVH were used to quantify the difference between the CCC algorithm in pinnacle TPS and the MC algorithm in Monaco TPS.

RESULTS

Among the statistical dose indexes in DVHs from the Pinnacle and Monaco TPSs, there were 7(7/15) dose indexes difference with statistically significant differences in the SG, and 10(10/18) dose indexes difference with statistically significant differences in the CG. With 3%/3 mm criterion, the most (5/6) GPRs were greater than 95% from the SG and CG. But with 2%/2 mm criterion, the most (5/6) GPRs were less than 90% from the two groups. In addition, we found that GPRs were also related to the selected triaxial planes and the complexity of the plan (GPRs varied with the SG and CG).

CONCLUSIONS

Obvious difference between the CCC and MC algorithms from Pinnacle and Monaco TPS. DVH maybe better than 2D gamma analysis on quantifying difference of the CCC and MC algorithms. Some attention should be paid to the uncertainty of the TPS algorithm, especially when the indicator on the DVH is at the critical point of the threshold value, because the algorithm used may overestimate or underestimate the DVH indicator.

End-to-end test for lung SBRT: An Italian multicentric pilot experience

PURPOSE

Set up a lung SBRT end-to-end (e2e) test and perform a multicentre validation.

MATERIAL AND METHODS

A group of medical physicists from four hospitals and the Italian Institute of Ionizing Radiation Metrology designed the present e2e test. One sub-group set up the test, while another tested its feasibility and ease of use. A satisfaction questionnaire was used to collect user feedback. Each participating centre (PC) received the ADAM breathing phantom, a microDiamond detector and radiochromic films. Following the e2e protocol, each PC performed its standard internal procedure for simulating, planning, and irradiating the phantom. Each PC uploaded its planning and treatment delivery data in a shared Google Drive. A single centre analyzed all the data.

RESULTS

The e2e test was successfully performed by all PCs. Participants' comments indicated that ADAM was well suited to the purpose and the protocol well described. All PCs performed the test in static and dynamic modes. The ratio between measured and planned point dose obtained by PC1, PC2, PC3, PC4 was: 0.99, 0.96, 1.01 and 1.01 (static track) and 0.99, 1.02, 1.01 and 0.94 (dynamic track). The gamma passing rates (3 % global, 3 mm) between planned and measured dose maps were 98.5 %, 94.0 %, 99.1 % and 94.0 % (static track) and 99.5 %, 96.5 %, 86.0 % and 94.5 % (dynamic track) for PC1, PC2, PC3 and PC4, respectively.

CONCLUSIONS

An e2e test for lung SBRT has been proposed and tested in a multicentre framework. The results and user feedback prove the validity of the proposed e2e test.

An overview of the medical-physics-related verification system for radiotherapy multicenter clinical trials by the Medical Physics Working Group in the Japan Clinical Oncology Group-Radiation Therapy Study Group

The Japan Clinical Oncology Group-Radiation Therapy Study Group (JCOG-RTSG) has initiated several multicenter clinical trials for high-precision radiotherapy, which are presently ongoing. When conducting multi-center clinical trials, a large difference in physical quantities, such as the absolute doses to the target and the organ at risk, as well as the irradiation localization accuracy, affects the treatment outcome. Therefore, the differences in the various physical quantities used in different institutions must be within an acceptable range for conducting multicenter clinical trials, and this must be verified with medical physics consideration. In 2011, Japan's first Medical Physics Working Group (MPWG) in the JCOG-RTSG was established to perform this medical-physics-related verification for multicenter clinical trials. We have developed an auditing method to verify the accuracy of the absolute dose and the irradiation localization. Subsequently, we credentialed the participating institutions in the JCOG multicenter clinical trials that were using stereotactic body radiotherapy (SBRT) for lungs, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) for several disease sites, and proton beam therapy (PT) for the liver. From the verification results, accuracies of the absolute dose and the irradiation localization among the participating institutions of the multicenter clinical trial were assured, and the JCOG clinical trials could be initiated.

Results of a multicentre dosimetry audit using a respiratory phantom within the EORTC LungTech trial

INTRODUCTION

The EORTC 22113-08113 LungTech trial assesses the safety and efficacy of SBRT for centrally located NSCLC. To insure protocol compliance an extensive RTQA procedure was implemented.

METHODS

Twelve centres were audited using a CIRS008A phantom. The phantom was scanned using target inserts of 7.5 mm and 12.5 mm radius in static condition. For the 7.5 mm insert a 4DCT was acquired while moving according to a cos⁶ function. Treatment plans were measured using film and an ionization chamber. Wilcoxon's signed-rank tests were performed to compare the three plans across institutions. A Spearman correlation was calculated to evaluate the influence of factors such as PTV, slice thickness and total number of monitor units on the dosimetric results.

RESULTS

The reference output dose median [min, max] variation was 0.5% [-1.1, +1.5]. The median deviations between chamber doses and point-planned doses were 1.8% [-0.1; 6.7] for the 7.5 mm and 1.1% [-2.8; 5.0] for the 12.5 mm sphere in static situation and 3.2% [-3.2; 15.7] for the dynamic situation. Film gamma median pass rates were 92.0% [68.0, 99.0] for 7.5 mm static, 96.2% [73.0, 99.0] for 12.5 mm static and 71.0% [40.0, 99.0] for 7.5 mm dynamic. Wilcoxon's signed-rank tests showed that the dynamic irradiations resulted in significantly lower gamma pass rates compared to the 12.5 mm static plan (p = 0.001). The total number of MUs per plan was correlated to both film and IC results.

CONCLUSION

An end-to-end audit was successfully performed, revealing important variations between institutions especially in dynamic irradiations. This shows the importance of dosimetry audits and the potentials for further technique and methodology improvements.

Driving developments in UK oesophageal radiotherapy through the SCOPE trials

BACKGROUND

The SCOPE trials (SCOPE 1, NeoSCOPE and SCOPE 2) have been the backbone of oesophageal RT trials in the UK. Many changes in oesophageal RT techniques have taken place in this time. The SCOPE trials have, in addition to adopting these new techniques, been influential in aiding centres with their implementation. We discuss the progress made through the SCOPE trials and include details of a questionnaire sent to participating centres. to establish the role that trial participation played in RT changes in their centre.

METHODS

Questionnaires were sent to 47 centres, 27 were returned.

RESULTS

100% of centres stated their departmental protocol for TVD was based on the relevant SCOPE trial protocol. 4DCT use has increased from 42 to 71%. Type B planning algorithms, mandated in the NeoSCOPE trial, were used in 79.9% pre NeoSCOPE and now in 83.3%. 12.5% of centres were using a stomach filling protocol pre NeoSCOPE, now risen to 50%. CBCT was mandated for IGRT in the NeoSCOPE trial. 66.7% used this routinely pre NeoSCOPE/SCOPE 2 which has risen to 87.5% in the survey.

CONCLUSION

The results of the questionnaires show how participation in national oesophageal RT trials has led to the adoption of newer RT techniques in UK centres, leading to better patient care.

Remote dosimetric auditing of clinical trials: The need for vendor specific models to convert images to dose

INTRODUCTION

A previous pilot study has demonstrated the feasibility of a novel image-based approach for remote dosimetric auditing of clinical trials. The approach uses a model to convert in-air acquired intensity modulated radiotherapy (IMRT) images to delivered dose inside a virtual phantom. The model was developed using images from an electronic portal imaging device (EPID) on a Varian linear accelerator. It was tuned using beam profiles and field size factors (FSFs) of a series of square fields measured in water tank. This work investigates the need for vendor specific conversion models for image-based auditing. The EPID measured profile and FSF data for Varian (vendor 1) and Elekta (vendor 2) systems are compared along with the performance of the existing Varian model (VM) and a new Elekta model (EM) for a series of audit IMRT fields measured on vendor 2 systems.

MATERIALS AND METHODS

The EPID measured beam profile and FSF data were studied for the two vendors to quantify and understand their relevant dosimetric differences. Then, an EM was developed converting EPID to dose in the virtual water phantom using a vendor 2 water tank data and images from corresponding EPID. The VM and EM were compared for predicting vendor 2 measured dose in water tank. Then, the performance of the new EM was compared to the VM for auditing of 54 IMRT fields from four vendor 2 facilities. Statistical significance of using vendor specific models was determined.

RESULTS

Observed dosimetry differences between the two vendors suggested developing an EM would be beneficial. The EM performed better than VM for vendor 2 square and IMRT fields. The IMRT audit gamma pass rates were (99.8 ± 0.5)%, (98.6 ± 2.3)% and (97.0 ± 3.0)% at respectively 3%/3 mm, 3%/2 mm and 2%/2 mm with improvements at most fields compared with using the VM. For the pilot audit, the difference between gamma results of the two vendors was reduced when using vendor specific models (VM: P < 0.0001, vendor specific models: P = 0.0025).

CONCLUSION

A new model was derived to convert images from vendor 2 EPIDs to dose for remote auditing vendor 2 deliveries. Using vendor specific models is recommended to remotely audit systems from different vendors, however, the improvements found were not major.

Multi-institutional evaluation using the end-to-end test for implementation of dynamic techniques of radiation therapy in Thailand

AIM

In this study, an accuracy survey of intensity-modulated radiation therapy (IMRT) and volumetric arc radiation therapy (VMAT) implementation in radiotherapy centers in Thailand was conducted.

BACKGROUND

It is well recognized that there is a need for radiotherapy centers to evaluate the accuracy levels of their current practices, and use the related information to identify opportunities for future development.

MATERIALS AND METHODS

An end-to-end test using a CIRS thorax phantom was carried out at 8 participating centers. Based on each center's protocol for simulation and planning, linac-based IMRT or VMAT plans were generated following the IAEA (CRP E24017) guidelines. Point doses in the region of PTVs and OARs were obtained from 5 ionization chamber readings and the dose distribution from the radiochromic films. The global gamma indices of the measurement doses and the treatment planning system calculation doses were compared.

RESULTS

The large majority of the RT centers (6/8) fulfilled the dosimetric goals, with the measured and calculated doses at the specification points agreeing within ±3% for PTV and ±5% for OARS. At 2 centers, TPS underestimated the lung doses by about 6% and spinal cord doses by 8%. The mean percentage gamma pass rates for the 8 centers were 98.29 ± 0.67% (for the 3%/3 mm criterion) and 96.72 ± 0.84% (for the 2%/2 mm criterion).

CONCLUSIONS

The 8 participating RT centers achieved a satisfactory quality level of IMRT/VMAT clinical implementation.

A remote EPID-based dosimetric TPS-planned audit of centers for clinical trials: outcomes and analysis of contributing factors

Background

A novel remote method for external dosimetric TPS-planned auditing of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for clinical trials using electronic portal imaging device (EPID) has been developed. The audit has been applied to multiple centers across Australia and New Zealand. This work aims to assess the audit outcomes and explores the variables that contributed to the audit results.

Methods

Thirty audits were performed of 21 radiotherapy facilities, 17 facilities underwent IMRT audits and 13 underwent VMAT audits. The assessment was based on comparisons between the delivered doses derived from images acquired with EPIDs and planned doses from the local treatment planning systems (TPS). Gamma pass-rate (GPR) and gamma mean value (GMV) were calculated for each IMRT field and VMAT arc (total 268 comparisons). A multiple variable linear model was applied to the GMV results (3%/3 mm criteria) to assess the influence and significance of explanatory variables. The explanatory variables were Linac-TPS combination, TPS grid resolution, IMRT/VMAT delivery, age of EPID, treatment site, record and verification system (R&V) type and dose-rate. Finally, the audit results were compared with other recent audits by calculating the incidence ratio (IR) as a ratio of the observed mean/median GPRs for the remote audit to the other audits.

Results

The average (± 1 SD) of the centers’ GPRs were: 99.3 ± 1.9%, 98.6 ± 2.7% & 96.2 ± 5.5% at 3%, 3 mm, 3%, 2 mm and 2%, 2 mm criteria respectively. The most determinative variables on the GMVs were Linac-TPS combination, TPS grid resolution and IMRT/VMAT delivery type. The IR values were 1 for seven comparisons, indicating similar GPRs of the remote audit with the reference audits and > 1 for four comparisons, indicating higher GPRs of the remote audit than the reference audits.

Conclusion

The remote dosimetry audit method for clinical trials demonstrated high GPRs and provided results comparable to established more resource-intensive audit methods. Several factors were found to influence the results including some effect of Linac-TPS combination.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1125-8) contains supplementary material, which is available to authorized users.

A virtual dosimetry audit - Towards transferability of gamma index analysis between clinical trial QA groups

PURPOSE

Quality assurance (QA) for clinical trials is important. Lack of compliance can affect trial outcome. Clinical trial QA groups have different methods of dose distribution verification and analysis, all with the ultimate aim of ensuring trial compliance. The aim of this study was to gain a better understanding of different processes to inform future dosimetry audit reciprocity.

MATERIALS

Six clinical trial QA groups participated. Intensity modulated treatment plans were generated for three different cases. A range of 17 virtual 'measurements' were generated by introducing a variety of simulated perturbations (such as MLC position deviations, dose differences, gantry rotation errors, Gaussian noise) to three different treatment plan cases. Participants were blinded to the 'measured' data details. Each group analysed the datasets using their own gamma index (γ) technique and using standardised parameters for passing criteria, lower dose threshold, γ normalisation and global γ.

RESULTS

For the same virtual 'measured' datasets, different results were observed using local techniques. For the standardised γ, differences in the percentage of points passing with γ < 1 were also found, however these differences were less pronounced than for each clinical trial QA group's analysis. These variations may be due to different software implementations of γ.

CONCLUSIONS

This virtual dosimetry audit has been an informative step in understanding differences in the verification of measured dose distributions between different clinical trial QA groups. This work lays the foundations for audit reciprocity between groups, particularly with more clinical trials being open to international recruitment.

Auditing local methods for quality assurance in radiotherapy using the same set of predefined treatment plans

BACKGROUND AND PURPOSE

Local implementation of plan-specific quality assurance (QA) methods for intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment plans may vary because of dissimilarities in procedures, equipment and software. The purpose of this work is detecting possible differences between local QA findings and those of an audit, using the same set of treatment plans.

METHODS

A pre-defined set of clinical plans was devised and imported in the participating institute's treatment planning system for dose computation. The dose distribution was measured using an ionisation chamber, radiochromic film and an ionisation chamber array. The centres performed their own QA, which was compared to the audit findings. The agreement/disagreement between the audit and the institute QA results were assessed along with the differences between the dose distributions measured by the audit team and computed by the institute.

RESULTS

For the majority of the cases the results of the audit were in agreement with the institute QA findings: ionisation chamber: 92%, array: 88%, film: 76% of the total measurements. In only a few of these cases the evaluated measurements failed for both: ionisation chamber: 2%, array: 4%, film: 0% of the total measurements.

CONCLUSION

Using predefined treatment plans, we found that in approximately 80% of the evaluated measurements the results of local QA of IMRT and VMAT plans were in line with the findings of the audit. However, the percentage of agreement/disagreement depended on the characteristics of the measurement equipment used and on the analysis metric.

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

PURPOSE

To conduct patient-specific geometric and dosimetric quality assurance (QA) for the Dynamic WaveArc (DWA) using logfiles and ArcCHECK (Sun Nuclear Inc., Melbourne, FL, USA).

METHODS

Twenty 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.

RESULTS

The 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%.

CONCLUSIONS

We 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.