Acceptance Test Results - IQM - Integral Quality Monitor

Signal reproducibility test (short-term)

10 consecutive applications of a 6MV photon beam with the reference field size of 10cm x 10cm

The results of the short term reproducibility test show
a very high signal reproducibility of average 0,06%
when the linear accelerator operates under the same conditions

Signal reproducibility test (long-term)The long-term reproducibility test takes the linear accelerator variations into account when treating on different days.

Our clinical reference centers measured the QA Test Field multiple times on different days for a total of 54 measurements.

The QA Test Field was specifically designed to verify unique capabilities of the IQM System and is used during every system acceptance. It consists of 18 IMRT beam segments: one 10cm x 10cm beam segment at central axis and 17 4cm x 4cm beam segments equally distributed over the entire detector area.

These linear accelerator induced variations
increased the measured standard deviation
from average 0,06% short-term
to
0,684% long-term.

Signal linearity testDose Output Test

The signal linearity test verifies that the detector measures a signal that is directly proportional to the dose output.

All tests show that the IQM signal varies linear with the applied dose output.
Any change in the dose output proportionally changes the IQM signal.

Dose rate dependence test

The dose rate dependence test verifies that the IQM system measures the same signal for the same dose independent from the dose rate in which the dose is delivered.

A 10cm x 10cm x06 beam is delivered with a constant dose output of 100MU and the following dose rates

20MU/min / 50MU/min / 100MU/min
200MU/min / 400MU/min / 600MU/min
(for FFF beams the highest dose rate is also measured)

All measurements performed show a high independence of the IQM signal from the dose rate with an average variation of 0.2%

Beam location / position test

Tests how much the signal changes when an identical beam segment is delivered at a different position.

The QA test field consisting of 17 4cm x 4cm beam segments each delivering a dose output of 100MU with a 6MV photon beam and a constant dose rate of 600MU/min

The following segments are compared to Field 1

Field 7
(7cm in heel direction of the gradient)

Field 8
(14cm in heel direction of the gradient)

Field 15
(7cm in toe direction of the gradient)

Field 16
(14cm in toe direction of the gradient)

All signal changes measured during this test are significant.

Even the smallest relative variation of 13% over a movement of 7cm indicates variation of 1.75% per centimeter.
This is still a significant variation (>0.5%) for a movement of 3mm, which is more than double the resolution of the 2D array with the highest resolution currently available on the market.

Field size test

The field size test verifies the chambers sensitivity to different square field sizes.

The field size test uses a 6MV photon beam with a dose output of each 50MU applied at a constant dose rate.
The field size test compares the following field sizes with each other:

1cm x 1cm vs. 2cm x 2cm

2cm x 2cm vs. 4cm x 4cm

3cm x 3cm vs. 6cm x 6cm

5cm x 5cm vs. 10cm x 10cm

10cm x 10cm vs. 20cm x 20cm

The signal comparison for different field sizes show a significant signal variation when changing the field size.

Field shape test

The field shape test compares those rectangular fields with each other where the length of the first field matches the width of the second field and the width of the first field matches the length of the second field.

The field shape test uses a 6MV photon beam with a dose output of each 50MU applied at a constant dose rate.
The field shape test compares the following field sizes with each other:

4cm x 12cm vs. 12cm x 4cm
4cm x 8cm vs. 8cm x 4cm‘
8cm x 12cm vs. 12cm x 8cm
8cm x 20cm vs. 20cm x 8cm
10cm x 30cm vs. 30cm x 15cm
15cm x 40cm vs. 40cm x 15cm
25cm x 35cm vs. 35cm x 25cm
25cm x 40cm vs. 40cm x 25cm

IQM is capable of differentiating between fields that cover the same area,
but are different in length and width

Signal reproducibility test (short-term)

Signal reproducibility test (long-term)The long-term reproducibility test takes the linear accelerator variations into account when treating on different days.

Signal linearity testDose Output Test

Dose rate dependence test

Beam location / position test

Field size test

Field shape test

An intriguing device...

"This allows everyone to stay ahead of the game of QA."

"IQM constitutes a paradigm shift in treatment verification..."

"The best idea I have seen in years..."

"A physics tool for the independent verification of the final beam product."

"Measuring with IQM is a piece of cake..."

"I see endless possibilities..."

"The IQM System is a highly sensitive dose monitoring device.”

"IQM is an especially good candidate for monitoring small fields due to its unique detector design"

"Why didn't anybody think of this before?"

"Our study demonstrates clinically negligible changesin beam quality and surface dose for all investigated beams.”

"The results of our study demonstrate the clear and consistent correlation of the IQM signal with DVH metrics.”

"IQM is a key component of our automated treatment quality control and allows us to fully comply with the requirements defined in the 2013/59/EURATOM directive."

"The quick setup and fully automated handling of all clinical data significantly reduces the time we need for Plan QA. Our clinical evaluation has shown that the error detection capability of the IQM System is at least as good, and in many cases even better, than with conventional 3D phantoms."