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Clinical implementation of 3D EPID-based in vivo dose verification of IMRT/VMAT treatments

Clinical implementation of 3D EPID-based in vivo dose verification of IMRT/VMAT treatments. Ben Mijnheer. Disclosure.

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Clinical implementation of 3D EPID-based in vivo dose verification of IMRT/VMAT treatments

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  1. Clinical implementation of 3D EPID-based in vivo dose verification of IMRT/VMAT treatments Ben Mijnheer

  2. Disclosure The Netherlands Cancer Institute – Antoni van Leeuwenhoek Hospital has a research cooperation with Elekta concerning the development of cone-beam CT and EPID dosimetry software

  3. EPID-based in vivo 3D dose verification using a back-projection model 1) Calculate plan 2) Measure EPID dose 3) Reconstruct dose in multiple planes Patient CT 4) Compare planned and reconstructed 3D dose distribution

  4. Clinical use of 3D EPID-based in vivo dosimetry

  5. Clinical use of 3D EPID-based in vivo dosimetry • New software tools were clinically introduced to allow automated image acquisition, to periodically inspect the record-and-verify database, and to automatically run the EPID dosimetry software

  6. Clinical use of 3D EPID-based in vivo dosimetry • New software tools were clinically introduced to allow automated image acquisition, to periodically inspect the record-and-verify database, and to automatically run the EPID dosimetry software • The comparison of the EPID-reconstructed and planned 3D dose distribution is done offlineand data are available a few minutes afterdelivery • Alerts are immediately raised, without any human intervention, when deviations are outside clinical criteria, and actions scheduled

  7. Clinical use of 3D EPID-based in vivo dosimetry • New software tools were clinically introduced to allow automated image acquisition, to periodically inspect the record-and-verify database, and to automatically run the EPID dosimetry software • The comparison of the EPID-reconstructed and planned 3D dose distribution is done offlineand data are available a few minutesafterdelivery • Alerts are immediately raised, without any human intervention, when deviations are outside clinical criteria, and actions are scheduled

  8. 3D in vivo dose verification of prostate VMAT g automatic classification g-analysis statistics isoc dose (all arcs) 3D g-evaluation in the volume enclosed by the 50% isodose surface isoc dose

  9. Clinical results of 3D EPID-based in vivo dosimetry (2012) 82% of the verified plans were within tolerance level (automatically approved)

  10. Clinical results of 3D EPID-based in vivo dosimetry (2012) 82% of the verified plans were within tolerance level (automatically approved) 18% of the verified plans had at least one of the alert criteria outside tolerance level (limitation of transit dosimetry,

  11. Breast IMRT: influence of setup error The problem The cause: 1.6 cm shift The solution: shift the measured images

  12. Clinical results of 3D EPID-based in vivo dosimetry (2012) 82% of the verified plans were within tolerance level (automatically approved) 18% of the verified plans had at least one of the alert criteria outside tolerance level (limitation of transit dosimetry, tumor regression,

  13. Head–and-neck VMAT: tumor regression After adding bolus, in vivo dosimetry showed that the dose was OK planning CT cone-beam CT

  14. Clinical results of 3D EPID-based in vivo dosimetry (2012) 82% of the verified plans were within tolerance level (automatically approved) 18% of the verified plans had at least one of the alert criteria outside tolerance level (limitation of transit dosimetry, tumor regression, anatomical changes ….)

  15. Lung step & shoot IMRT: recovery from atelectasis

  16. Lung step & shoot IMRT: recovery from atelectasis Based on the in vivo dosimetry and CBCT results it was decided to replan te patient

  17. Clinical results of 3D EPID-based in vivo dosimetry (2012) 82% of the verified plans were within tolerance level (automatically approved) 18% of the verified plans had at least one of the alert criteria outside tolerance level (limitation of transit dosimetry, tumor regression, anatomical changes ….) 1/300 of the verified plans required immediate action (errors in the procedure in the clinic)

  18. Head-and-neck VMAT: bolus not present during planning CT scan

  19. Head-and-neck VMAT: bolus not present during planning CT scan New CT scan and plan: in vivo dosimetry OK!

  20. Breast non-IMRT field: incorrect positioning of jaws “Something is wrong with the first field”

  21. Breast non-IMRT fields: incorrect positioning of jaws “Something is wrong with the first field” Problem: A button “asymmetric beam” was accidentally ticked just before treatment, resulting in a symmetric adjustment of the backup jaws for one beam Action: Extra field for the remaining fractions

  22. Online EPID-based 3D dose verification • By optimizing the dose reconstruction algorithm and the I/O performance, the delivered 3D dose distribution is verified in less than 200 ms per portal image, which includes the comparison between the reconstructed and planned dose distribution.

  23. Online EPID-based 3D dose verification • By optimizing the dose reconstruction algorithm and the I/O performance, the delivered 3D dose distribution is verified in less than 200 ms per portal image, which includes the comparison between the reconstructed and planned dose distribution. • The RMS of the difference between the cumulative planned and reconstructed 3D dose distribution is used to generate a trigger that can stop the irradiation

  24. Online EPID-based 3D dose verification • By optimizing the dose reconstruction algorithm and the I/O performance, the delivered 3D dose distribution is verified in less than 200 ms per portal image, which includes the comparison between the reconstructed and planned dose distribution. • The RMS of the difference between the cumulative planned and reconstructed 3D dose distribution is used to generate a trigger that can stop the irradiation • Irradiation of a polystyrene slab phantom with a 10 MV single arc VMAT prostate treatment when a serious error, the leaves were wide open, was introduced.

  25. The next step: on-line treatment verification

  26. Conclusions • Our automatic offline EPID-based dosimetry tool facilitated the large scale clinical implementation of 3D in vivo dose verification of IMRT/VMAT treatments, and was able to trace clinically relevant errors

  27. Conclusions • Our automatic offlineEPID-based dosimetry tool facilitated the large scale clinical implementation of 3D in vivo dose verification of IMRT/VMAT treatments, and was able to trace clinically relevant errors • It replaced pre-treatment verification, except for single fraction and large field treatments, and may safe resources for other purposes

  28. Conclusions • Our automatic offline EPID-based dosimetry tool facilitated the large scale clinical implementation of 3D in vivo dose verification of IMRT/VMAT treatments, and was able to trace clinically relevant errors • It replaced pre-treatment verification, except for single fraction and large field treatments, and may safe resources for other purposes • Our online 3D in vivo dose verification approach can be used to halt the treatment machine in case of severe errors

  29. Conclusions • Our automatic offline EPID-based dosimetry tool facilitated the large scale clinical implementation of 3D in vivo dose verification of IMRT/VMAT treatments, and was able to trace clinically relevant errors • It replaced pre-treatment verification, except for single fraction and large field treatments, and may safe resources for other purposes • Our online 3D in vivo dose verification approach can be used to halt the treatment machine in case of severe errors • 3D EPID-based in vivo dosimetry is a major step forward towards optimal quality and safety in radiation oncology practice

  30. Many thanks for your attention!

  31. ….. and special thanks to the EPID dosimetry group at NKI-AVL: • Anton Mans • Hanno Spreeuw • Igor Olaciregui-Ruiz • Jan-Jakob Sonke • Marcel van Herk • Patrick Gonzalez • René Tielenburg • Roel Rozendaal • Ron Vijlbrief

  32. Future developments • To use deformable image registration algorithms to automate registration of CBCT scans to planning CT contours, calculate a new plan and compare the new 3D dose distribution with the measured 3D in vivo dosimetry results

  33. Future developments • To use deformable image registration algorithms to automate registration of CBCT scans to planning CT contours, calculate a new plan and compare the new 3D dose distribution with the measured 3D in vivo dosimetry results • Preliminary results of the variation in plan characteristics during a series of VMAT treatments of 20 H&N patients showed only small changes in the D50 of the PTV

  34. Future developments Incorporate setup deviations in the analysis Implement alert criteria based on DVH analysis (currently manual evaluation)

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