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

Virtual pretreatment patient-specific quality assurance of volumetric modulated arc therapy using deep learning

BACKGROUND

Automatic patient-specific quality assurance (PSQA) is recently explored using artificial intelligence approaches, and several studies reported the development of machine learning models for predicting the gamma pass rate (GPR) index only.

PURPOSE

To develop a novel deep learning approach using a generative adversarial network (GAN) to predict the synthetic measured fluence.

METHODS AND MATERIALS

A novel training method called "dual training," which involves the training of the encoder and decoder separately, was proposed and evaluated for cycle GAN (cycle-GAN) and conditional GAN (c-GAN). A total of 164 VMAT treatment plans, including 344 arcs (training data: 262, validation data: 30, and testing data: 52) from various treatment sites, were selected for prediction model development. For each patient, portal-dose-image-prediction fluence from TPS was used as input, and measured fluence from EPID was used as output/response for model training. Predicted GPR was derived by comparing the TPS fluence with the synthetic measured fluence generated by the DL models using gamma evaluation of criteria 2%/2 mm. The performance of dual training was compared against the traditional single-training approach. In addition, we also developed a separate classification model specifically designed to detect automatically three types of errors (rotational, translational, and MU-scale) in the synthetic EPID-measured fluence.

RESULTS

Overall, the dual training improved the prediction accuracy of both cycle-GAN and c-GAN. Predicted GPR results of single training were within 3% for 71.2% and 78.8% of test cases for cycle-GAN and c-GAN, respectively. Moreover, similar results for dual training were 82.7% and 88.5% for cycle-GAN and c-GAN, respectively. The error detection model showed high classification accuracy (>98%) for detecting errors related to rotational and translational errors. However, it struggled to differentiate the fluences with "MU scale error" from "error-free" fluences.

CONCLUSION

We developed a method to automatically generate the synthetic measured fluence and identify errors within them. The proposed dual training improved the PSQA prediction accuracy of both the GAN models, with c-GAN demonstrating superior performance over the cycle-GAN. Our results indicate that the c-GAN with dual training approach combined with error detection model, can accurately generate the synthetic measured fluence for VMAT PSQA and identify the errors. This approach has the potential to pave the way for virtual patient-specific QA of VMAT treatments.

Testing the methodology for a dosimetric end-to-end audit of IMRT/VMAT: results of IAEA multicentre and national studies

Introduction: Within an International Atomic Energy Agency (IAEA) co-ordinated research project (CRP), a remote end-to-end dosimetric quality audit for intensity modulated radiation therapy (IMRT)/ volumetric arc therapy (VMAT) was developed to verify the radiotherapy chain including imaging, treatment planning and dose delivery. The methodology as well as the results obtained in a multicentre pilot study and national trial runs conducted in close cooperation with dosimetry audit networks (DANs) of IAEA Member States are presented.Material and methods: A solid polystyrene phantom containing a dosimetry insert with an irregular solid water planning target volume (PTV) and organ at risk (OAR) was designed for this audit. The insert can be preloaded with radiochromic film and four thermoluminescent dosimeters (TLDs). For the audit, radiotherapy centres were asked to scan the phantom, contour the structures, create an IMRT/VMAT treatment plan and irradiate the phantom. The dose prescription was to deliver 4 Gy to the PTV in two fractions and to limit the OAR dose to a maximum of 2.8 Gy. The TLD measured doses and film measured dose distributions were compared with the TPS calculations.Results: Sixteen hospitals from 13 countries and 64 hospitals from 6 countries participated in the multicenter pilot study and in the national runs, respectively. The TLD results for the PTV were all within ±5% acceptance limit for the multicentre pilot study, whereas for national runs, 17 participants failed to meet this criterion. All measured doses in the OAR were below the treatment planning constraint. The film analysis identified seven plans in national runs below the 90% passing rate gamma criteria.Conclusion: The results proved that the methodology of the IMRT/VMAT dosimetric end-to-end audit was feasible for its intended purpose, i.e., the phantom design and materials were suitable; the phantom was easy to use and it was robust enough for shipment. Most importantly the audit methodology was capable of identifying suboptimal IMRT/VMAT delivery.

Radiotherapy Quality Assurance for the CHHiP Trial: Conventional Versus Hypofractionated High-Dose Intensity-Modulated Radiotherapy in Prostate Cancer

AIMS

The CHHiP trial investigated the use of moderate hypofractionation for the treatment of localised prostate cancer using intensity-modulated radiotherapy (IMRT). A radiotherapy quality assurance programme was developed to assess compliance with treatment protocol and to audit treatment planning and dosimetry of IMRT. This paper considers the outcome and effectiveness of the programme.

MATERIALS AND METHODS

Quality assurance exercises included a pre-trial process document and planning benchmark cases, prospective case reviews and a dosimetry site visit on-trial and a post-trial feedback questionnaire.

RESULTS

In total, 41 centres completed the quality assurance programme (37 UK, four international) between 2005 and 2010. Centres used either forward-planned (field-in-field single phase) or inverse-planned IMRT (25 versus 17). For pre-trial quality assurance exercises, 7/41 (17%) centres had minor deviations in their radiotherapy processes; 45/82 (55%) benchmark plans had minor variations and 17/82 (21%) had major variations. One hundred prospective case reviews were completed for 38 centres. Seventy-one per cent required changes to clinical outlining pre-treatment (primarily prostate apex and base, seminal vesicles and penile bulb). Errors in treatment planning were reduced relative to pre-trial quality assurance results (49% minor and 6% major variations). Dosimetry audits were conducted for 32 centres. Ion chamber dose point measurements were within ±2.5% in the planning target volume and ±8% in the rectum. 28/36 films for combined fields passed gamma criterion 3%/3 mm and 11/15 of IMRT fluence film sets passed gamma criterion 4%/4 mm using a 98% tolerance. Post-trial feedback showed that trial participation was beneficial in evolving clinical practice and that the quality assurance programme helped some centres to implement and audit prostate IMRT.

CONCLUSION

Overall, quality assurance results were satisfactory and the CHHiP quality assurance programme contributed to the success of the trial by auditing radiotherapy treatment planning and protocol compliance. Quality assurance supported the introduction of IMRT in UK centres, giving additional confidence and external review of IMRT where it was a newly adopted technique.

IMRT national audit in Portugal

PURPOSE

The IAEA newly developed "end-to-end" audit methodology for on-site verification of IMRT dose delivery has been carried out in Portugal in 2018. The main goal was to evaluate the physical aspects of the head and neck (H&N) cancer IMRT treatments. This paper presents the national results.

METHODS

All institutions performing IMRT treatments in Portugal, 20 out of 24, have voluntarily participated in this audit. Following the adopted methodology, a Shoulder, Head and Neck End-to-End phantom (SHANE) - that mimics an H&N region, underwent all steps of an IMRT treatment, according to the local practices. The measurements using an ionization chamber placed inside the SHANE phantom at four reference locations (three in PTVs and one in the spinal cord) and an EBT3 film positioned in a coronal plane were compared with calculated doses. FilmQA Pro software was used for film analysis.

RESULTS

For ionization chamber measurements, the percent difference was within the specified tolerances of ±5% for PTVs and ±7% for the spinal cord in all participating institutions. Considering film analysis, gamma passing rates were on average 96.9%±2.9% for a criterion of 3%/3 mm, 20% threshold, all above the acceptance limit of 90%.

CONCLUSIONS

The national results of the H&N IMRT audit showed a compliance between the planned and the delivered doses within the specified tolerances, confirming no major reasons for concern. At the same time the audit identified factors that contributed to increased uncertainties in the IMRT dose delivery in some institutions resulting in recommendations for quality improvement.

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.

Novel methodologies for dosimetry audits: Adapting to advanced radiotherapy techniques

With new radiotherapy techniques, treatment delivery is becoming more complex and accordingly, these treatment techniques require dosimetry audits to test advanced aspects of the delivery to ensure best practice and safe patient treatment. This review of novel methodologies for dosimetry audits for advanced radiotherapy techniques includes recent developments and future techniques to be applied in dosimetry audits. Phantom-based methods (i.e. phantom-detector combinations) including independent audit equipment and local measurement equipment as well as phantom-less methods (i.e. portal dosimetry, transmission detectors and log files) are presented and discussed. Methodologies for both conventional linear accelerator (linacs) and new types of delivery units, i.e. Tomotherapy, stereotactic devices and MR-linacs, are reviewed. Novel dosimetry audit techniques such as portal dosimetry or log file evaluation have the potential to allow parallel auditing (i.e. performing an audit at multiple institutions at the same time), automation of data analysis and evaluation of multiple steps of the radiotherapy treatment chain. These methods could also significantly reduce the time needed for audit and increase the information gained. However, to maximise the potential, further development and harmonisation of dosimetry audit techniques are required before these novel methodologies can be applied.