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Shortcomings of current verification techniques – Part 2

by / Monday, 14 July 2014 / Published in iRT Blog

The following article contains the same information as the video above.

Our previous presentations outlined the increasing complexity of modern treatment techniques and listed the verification tools currently available to manage these modern treatment approaches.

Our last presentation highlighted the following shortcomings of current verification techniques:

  • Pre-Treatment Plan Verification requires many staff and machine hours, making it relatively expensive
  • Pre-Treatment Plan Verification involves conventional tools and methods, which are partially insensitive to clinically relevant errors
  • LinAc Quality Assurance focuses exclusively on static fields
  • Current verification technologies typically involve separate independent processes
  • Current techniques do not include a computerized plausibility check of treatment plans
  • Pre-Treatment Plan Verification is done once before a multi-fraction treatment that takes place over a period of multiple weeks
  • Post Verification error sources like
    • Data corruption
    • Hardware / software malfunction
    • Upgrade to new software version or hardware
    • Human error
    • Other unknown influences are not covered
  • Current techniques don’t cover the time during actual patient treatment
  • Current techniques are insufficient for Adaptive Radiotherapy

 

Today’s presentation focuses on the two major “Shortcomings of current verification techniques, which are both based on the fact that none of the current verification tools monitor the time of the actual patient treatment in real-time.

 

Pre-Treatment QA is typically done once before the actual patient treatment, with 2D and 3D Arrays as well as with Portal Dosimetry. Plan Verification and patient treatment are separate functions in the radiotherapy process. Plan Verification is done once, while a typical fractionized patient treatment is applied over a period of up to 6 weeks.

Any changes to the treatment plan due to post verification error sources like data corruption, system malfunction, errors introduced due to new software versions or hardware upgrades, but most importantly due to human errors are not covered by the pre-treatment Plan Verification process.

There is currently no verification tool available that independently monitors the treatment beam in real-time during the actual patient treatment.

All other Radiotherapy processes are typically verified or monitored by independent means. The one process that matters most – the BEAM ON time during the patient treatment – is not. This process is solely monitored by the internal control processes of the Linear Accelerator and the regular Linear Accelerator Quality Assurance.

 

Since none of the available verification tools monitors the treatment delivery in real-time they are also not sufficient to support Adaptive Radiotherapy.
The increased availability of On-Board Imaging Tools at modern Linear Accelerators allow online corrections of treatment plans (plan adaption) in response to target variations.
Adaptive Radiotherapy (ART) methods like

  • Replanning through direct beam aperture optimization, which is based on the direct optimization of the leaf positions and aperture weights for intensity modulated radiation therapy (IMRT) plans
  • Fluence map optimization, which modifies MLC positions directly based on the geometric relationship between the anatomical deformation and MLC leaves

promise significant improvements in both target conformity and healthy tissue sparing.
Despite these dosimetric improvements, a practical clinical implementation of such an online ART would require the timely dosimetric validation of the adapted treatment fields. This is especially the case if ART is applied in combination with complex treatment methods such as IMRT and volumetric modulated arc therapy (VMAT).
ART requires a dosimetric validation of the modified treatment fields in a very short time, preferably online, which is not possible with the currently available verification tools.

Thank you very much for your attention.

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