LINACwatch

A permanent and very comprehensive Linac QA fully integrated into the patient workflow

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An effective, comprehensive yet simple solution to automatically analyse in real time and running in the background, the beam just delivered by the treatment machines. 

To increase treatment reliability by automatically controlling beams every 25 to 250 ms!

 

THE PERFECT CHOICE

ALL YOU NEED IS HERE!

  • Permanent, batch processing and real-time analysis
  • Immediately alerts therapist of LINAC defects
  • Analysis of thousands of actual measurements
  • Creates RT-plan with out-of-tolerance logfile data to calculate the dose-of-the-day on your TPS
  • Pinpoints the exact origin of errors
  • Extensive range of tested parameters
  • Totally customizable
  • Attractive and adapted pricing

 

WHY include another TPS into a log file analyser?

  • Much higher price
  • No real-time analysis
  • Dilution of the accurate log file data in a pseudo patient and in a poor pencil-beam TPS with gold standard beams
  • Confusion of error origin
  • Overrated importance of log file contents

 

WHY add a hardware to track the collimator output?

  • Expensive purchase and maintenance
  • Tiresome calibrations
  • Risk of breakdown
  • Poor spatial resolution
  • Limited QA parameters
  • Obstacles to collimator exit
  • Loss of light simulation

 

WHY use the EPID during the treatment?

  • Very high hidden cost (EPID degrades 20 to 50 times faster)
  • No real-time analysis
  • Dilution of LINAC defects into patient and dose calculation algorithm: therefore, not really sensible to patient changes
  • Some EPID based QA solutions consider the 1st fraction results as target for the next ones. BUT about 70 % of mistakes are detected during the 1st fraction!

 

A POWERFUL QUALITY ASSURANCE TOOL FOR ROTATIONAL OR NON-ROTATIONALDYNAMIC IMRT

 

Modern LINACs generate machine dynamic log files written in a proprietary format, which corresponds to a copy with a very high frequency (40 Hz for ELEKTA and 20 Hz for VARIAN) of the main parameters characteristic of the irradiation. These temporal tracking files of the real radiation constitute an amazing quality control tool of performed treatments, if they can indeed be rapidly analyzed in a thorough and accurate manner.

 

The LINACWATCH software decrypts these temporal tracking files and automatically analyzes them by comparing them in real time and in background (batch) processing to the planned treatment described in the DICOM RTplan associated with the planned beams.

 

A CRYSTAL CLEAR WORKFLOW! 5 BUTTONS FOR A COMPLETE, PRECISE AND QUICK ANALYSIS

  

Just click on « Import » to download to LINACWATCH the RTplan file which corresponds to your patient's planned teartment.

 

Used in batch processing, LINACWATCH operates in total autonomy, continually scanning the log files associated with the beams of performed treatments as they are generated by the LINAC. The software automatically sends an alert to your email account in the event that the readings fall outside of the tolerances which you have defined. 

 

In the « BATCH journal », the radiographer in the control room views the automatic retrieval and analysis by LINACWATCH, in less than one second, of the log files associated with each beam which treated your patient (Fig. f). By moving the mouse on the session, he has a summary of the session analysis..

 

 

By clicking on « Load session » from the « BATCH journal », the radiographer has at his disposal for the selected beam the details of the analysis of the session divided into the following 6 main tabs:

  • The « Dynamic view » tab (Fig. a) which depicts in the form of a film the temporal evolution of the leaf positions, the percentage of Monitor Units delivered, the gantry angle and the map of the comparison index of fluences calculated at the LINAC’s SAD.

 

 

  • The « Integrated fluence » tab (Fig. c) which presents the integrated fluences, planned and delivered, calculated at the SAD and their comparison in Gamma or Chi index.

 

 

  • The « Leaves » tab (Fig. c) which depicts for all of the MLC leaves, the temporal evolution of the deviations between their planned and treated positions, as well as the statistical analysis of these deviations particularly in terms of a histogram and RMS errors.

 

 

  • The « Jaws » and « Carriage » tabs in which are presented the temporal evolution of the deviations between the prescribed and treated jaw and carriage positions and the statistical analysis of these deviations particularly in terms of  the 95th percentile and RMS errors.
  • The « Gantry » and « Colli » tabs (Fig. d) in which are presented the temporal evolution of the deviations between the prescribed and treated rotation angle and the statistical analysis of these deviations particularly in terms of  the 95th percentile and RMS errors.
  • The « Lags » tab in which are counted in particular the beam extinction lags ordered by the MLC controller.

 

 

By clicking on « Load », the medical physicist can load a complete treatment (all sessions) and see the analysis of all sessions in terms of integrated fluence, jaw and carriage positions, gantry and collimator rotations. He can also follow in the trend curves the evolution of each tested parameter from session to session (Fig. e).

 

 

At any time, by clicking on the corresponding button in the « Summury » tab (Fig. g), the user can print a PDF report of the current analysis or export a DICOM RTplans file generated by LINACWATCH and integrating the “reality” of the irradiation as documented by the machine log files. You can then load this RTplan file onto your TPS to recalculate the “actual” dose delivered during the particular treatment session or the totally of the treatment.

 

 

Specifications

  • Current Released Version            1.0.1b11
  • Operating SystemMS-WINDOWS, 64 bits
  • ProcessorIntel® or AMD®, 2 GHz or greater
  • RAM3Go
  • Hard Drive50 Go or greater
  • Screen Resolution1280 x 800 
  • OthersInternet Access

 

FAQ

UsING LINACWATCH for all treatment sessions delivered with IMRT techniques and for every patients Eliminates the need TO PERFORM machine QA?

NO - in order for pertinent use of LOG files, one must ensure that the data contained in the LOG files is in line with reality. For example, for leaf position and speed, by performing "Picket Fence" tests analysed in parallel; by LINACWATCH for the LOG files and by another software, like QUALIMAGIQ and its MLC-dyn module*, for portal images. However this second software must be capable of detecting deviations of less than 0.1 mm in slit position or width.
In sum, LINACWATCH is a complementary solution to machine QA and pre-treatment QA. It enables effortless checking of the stability of the main irradiation parameters during and between each irradiation session.
(*): MLC-dyn module performs a rapid, precise and comprehensive quality control of the MLC used in dynamic mode.

USING LINACWATCH FOR ALL TREATMENT SESSIONS DELIVERED WITH IMRT TECHNIQUES AND FOR EVERY PATIENTS ELIMINATES the need TO PERFORM pre-treatment QA?

NO - BUT using LINACWATCH for all sessions for every patient allows you to reduce the frequency of pre-treatment QA and to limit it to special cases not statistically studied by previously tested treatments.
By using LINACWATCH you will be more selective about your pre-treatment QA.
Furthermore, by combining the pre-treatment controls with LINACWATCH controls, you can be sure that the performance observed during the pre-treatment QA is stable for the duration of the treatment and not only just before the treatment...

Some dynamic log file analysers introduce a TPS in the control loop. LINACWATCH does not. Can you explain why?

The most important reasons are:
1- To provide analysis results less than 4 seconds after beam end. The therapist* can then easily and rapidly decide to stop the Linac in case of repeated bad results.
2- To be sure that deviations between the prescription and the treatment are attributable only to the Linac and not to the calculation algorithm and other beam data used by the second TPS.
3- To offer an honest solution, i.e. an ON LINE Beam QA integrated into patient workflow. LOG files contain no data concerning the patient. Don't ask LOG files to report more than they contain! A solution which includes a TPS may deceive you into thinking that it is performing a control of the treatment when in fact it performs a beam control diluted into a patient model that is not that of the patient being treated and also diluted into a dose calculation that may be less accurate than the one you do on your TPS. LINACWATCH is very efficient because it doesn't dilute original data contained in the LOG files. LINACWATCH follows the Linac in real time and helps you to efficiently identify the cause of beam defects.
4- To have a low priced solution which allows you to be easily equipped with a solution which strongly contributes to providing secure treatments for all of your patients treated with IMRT techniques.
(*): Another possibility with LINACWATCH, if you refuse to install an additional screen in the Linac control room, is to centralise results from all of your Linacs on one screen, for example in the dosimetry room, and to use audio alerts possibly usable with LINACWATCH, to warn people in the room in the event of non-compliant results.

Dynamic Log files are not measurements and therefore analysing these log files will never be as good as measuring FLUENCE at the exit of the collimator!

NO, this is not true. The dynamic log data contains results from a lot of measurements: chamber signals, encoder signals of each leaf motor rotation confirmed by the potentiometer signal produced by a pin attached to each leaf edge, encoder signals connected to the motor rotation for jaw translation, gantry and collimator rotations. And these measurements are taken every 20, 50 or 250 ms with an accuracy of 0.01 MU, 0.01 mm and 0.01°! 
When you measure the "dose" at the collimator exit, what are the spatial and time resolutions of your detector? 2.5 mm or 8.0 mm for spatial resolution. Worse, some detectors integrate everything to have the Dose.Area Product. But by integrating everything, you see nothing...

Could you compare AN EPID based solution to a LOG FILE BASED SOLUTION?

YES we can!
The main argument of EPID based solutions is to take the patient into account during the treatment.
Two types of EPID based solutions are on the market. The first one is only a gamma index comparison of the integrated EPID image acquired during fraction N with the one acquired during the first fraction. In this case the 1st fraction is the target for the rest of the treatment. As you know, more than 70% of non-conformities occur during the 1st fraction. With this type of solution, you lose the possibility of detecting the most frequent non-conformities definitively! Also please note that some studies show that when patient thickness increases or decreases 20 mm or when the patient is shifted 20 mm, nothing is really detected by the gamma index pass rate... 
The second type of EPID based solution consists in recalculating the dose distribution into the patient from the EPID signal. These solutions dilute beam defects into the patient and into a complex dose calculation algorithm. Moreover this complexity does not allow you to have real time detection of Linac defects.
In sum, all EPID based solutions dilute beam defects and reduce the capability of rapidly detecting a problem on the Linac. 
Another crucial problem is the premature wear of the EPID (20 to 50 times faster!), which will push the Linac manufacturer to significantly increase the cost of your maintenance contract...

Then finally the ideal solution is a dose calculaton based on the beam of the day defined by the DYNAMIC LOG file, applied to the CBCT of the Day?

YES for sure BUT this solution is not yet on the market because it still faces many technological blocks. The first is the ability of your TPS to accurately distort the reference structures based on the comparison of the CBCT of the day with the reference CT scan, especially when tissues disappear or appear which is a very common situation.
Please note that when your TPS will be ready for this adaptive workflow, LINACWATCH can already generate and export RT-Plans containing LOG file data, i.e. defining the beam of the day.

With DYNAMIC LOG FILES analysis, it's impossible to detect a calibration error!

YES, this is true. If you make a mistake, for example you didn't respect the field size requested by the Linac during the calibration, of course LINACWATCH will not detect this error. But this is not the goal of LINACWATCH. Its goal is to control the stability of the field size over time. Normally, following a jaw or a leaf calibration, you need to control the field size with the water tank, film or EPID images to detect a possible calibration error.
In sum, LOG file analysis will never replace a good machine QA, for example performed by QUALIMAGIQ, but a good machine QA and pre-treatment QA will never replace LINACWATCH, which controls the machine between your machine quality controls!

can LINACWATCH document THAT I trEateD a patient correctly during all of the irradiation sessions?

YES of course and in a most pertinent manner.
Indeed LINACWATCH can generate an RT-Plan file including all of the information contained in the dynamic LOG files of all of the sessions. You can then load this RT-Plan representing the entire treatment onto your TPS and, using the many tools available in it, compare in the model patient described by the reference CT scan, the dose distribution delivered and cumulated throughout the treatment relative to the treatment planned by your TPS.
You do not find this documentation very complementary, or more pertinent, than the documentation proposed by the pre-treatment QA? Because in the end the pre-treatment QA only proves that before treating the patient, your Linac and your TPS presented consistent dose distributions in a homogeneous water cylinder, once the beams planned for the patient had irradiated the cylinder.

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