in radiotherapy beam delivery using a head-mounted detector A beta - - PowerPoint PPT Presentation

Real-time detection of deviations in radiotherapy beam delivery using a head-mounted detector

Martijn Kusters PhD, Richard Canters PhD, Radboudumc, Nijmegen, The Netherlands A beta test of the IQM system in cooperation with

Outline

• Current practice of treatment monitoring
• The IQM system
• Testing the IQM system
• Discussion & Conclusions

Current practice

Prescription Patient Dose

Current practice

Errors in Delta 4 pre treatment QA Prescription



TPS



R&V



Linac

• - Not always treatment linac

Transfer

• - Not always treatment linac

Absolute dosimetry

• - Not always treatment linac

Delivered beam



Dose in patient



Solutions to monitor the delivered beam (and patient)

Monitor fluence from linac head Epid dosimetry

• Relatively easy
• Checks your linacs
• Actual patient is

not monitored

• Harder to implement and

more labour intensive

• Actual delivered dose to the patient

can be made visible

Error detection with in vivo monitoring

Errors in Delta 4 pre treatment QA Epid dosimetry Linac head monitor Prescription

  

TPS

  

R&V

  

Linac

• - Not always treatment linac

 

Transfer

• - Not always treatment linac

 

Absolute dosimetry

• - Not always treatment linac

 

Delivered patient beam

  

Dose in patient

  

Error detection with in vivo monitoring

Errors in Delta 4 pre treatment QA Prescription



TPS



R&V



Linac

• - Not always treatment linac

Transfer

• - Not always treatment linac

Absolute dosimetry

• - Not always treatment linac

Delivered beam



Dose in patient



The IQM system

Integral Quality Monitor Wedge shaped ionization chamber Signal dependent on:

• Field/segment position
• Field size and shape
• Monitor units

Checksum

• ne number, sensitive for

many parameters



   

Area field IQM

y x S I y x AOF MU C ) , ( ) , (

Intended use of the IQM system

• In vivo treatment monitoring
• Realtime monitoring of beam delivery
• Increased patient safety
• Insight in the linac behaviour per

segment/control point

• Pre-treatment QA
• Can be run in between regular

treatments or whenever there is free time.

• RTT’s can run the tests
• Reduces a substantial effort in pre-

treatment QA

• Possible to measure plans during 1st

fraction if not critical.

Tests:error detection sensitivity

How well does IQM perform in intra-fractional detection?

• Various IMRT and VMAT clinical beams,
• Same beams with induced errors
• One segment/control point retraction of leaves by 10, 5 and 2 mm
• One segment increase of 10, 5 or 2 MU
• Comparison to Delta4

5000 10000 15000 20000 25000 5 10 15 20 25 30

Checksum Segment Per segment checksum

50000 100000 150000 200000 250000 300000 5 10 15 20 25 30

Checksum Segment Cumulative checksum

Testing the IQM system – detecting errors: one segment different MU

• 10MU
• 5MU
• 2MU

10 10

1

10

2

10

• 1

10 10

1

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical VMAT modified 10 10

1

10

2

10

• 1

10 10

1

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical IMRT clinical VMAT modified IMRT modified 10 10

1

10

2

10

• 1

10 10

1

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical IMRT clinical VMAT modified IMRT modified VMAT clinical IMRT clinical VMAT modified IMRT modified

Testing the IQM system – detecting errors: one segment leaf retraction

• 10mm
• 5mm
• 2mm

10 10

1

10

2

10

• 1

10 10

1

10

2

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical IMRT clinical VMAT modified IMRT modified 10 10

1

10

2

10

• 1

10 10

1

10

2

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical IMRT clinical VMAT modified IMRT modified 10 10

1

10

2

10

• 1

10 10

1

10

2

Maximum difference in segment signal [%] Maximum difference in cumulative signal [%]

IQM VMAT clinical IMRT clinical VMAT modified IMRT modified

The ROC-curve

10 10

1

10

2

10

• 1

10

Maximum difference in segment signal [%] Maximum difference in cumulative

VMAT modified IMRT modified

10090 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity 10090 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity 10090 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity

Testing the IQM system – detecting errors

• 10mm leaf retraction, 10MU
• 2 mm, 2 MU

100 90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity IQM Delta4 100 90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity IQM Delta4 100 90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 90 100 Specificity [%] Sensitivity [%] Sensitivity/specificity IQM Delta4

• 5mm, 5MU

Discussion & Conclusions

• IQM enables realtime, intrafraction monitoring of beam delivery
• Sensitivity and specificity can be expected to be sufficient for clinical

practice, and at least equal to our current equipment

• Pre-treatment QA with IQM has the potential to save a lot of time, but has

yet to be tested

Conclusions

Realtime monitoring with almost no user interaction

Prescription Patient Dose Calculate plan Checksum

Compare with measured checksum

Error detection well below clinically relevant limits