beldart -2 · belgian dosimetry audits in radiotherapy (beldart) 2009-2011: final report. 50 fig....

BELdART-2:

Moving towards safer radiotherapy

Steven Lelie1,2, Wouter Schroeyers1, Brigitte Reniers1, Sonja Schreurs1

1 Nucleair Technologisch Centrum (XIOS/Uhasselt), Wetenschapspark 27, 3590 Diepenbeek 2 BEFY (Vrije Universiteit Brussel), Laarbeeklaan 101, 1090 Jette

International Symposium 50 years BVS-ABR, April 10th, Brussels

TOC

• Introduction

• BELdART-1

• BELdART-2

• The future

• Conclusions

Introduction

• Succes/Failure absorbed doses

– Centers do QA

– What if:

• Wrong calibration

• Faulty equipment

• …

• Need for an external audit

Introduction (2)

• What was/is available? (not free of charge)

– IAEA & WHO: TLD audit (since 1969)

• World wide TLD audits

• Postal audit for photon beams

• Focus on developing countries

– ESTRO-QUALity assurance network (since 1998)

• European postal audit with TLD

• Photon & Electron beams

– RPC-MD Anderson (1968)

• World wide TLD audits

• Moving towards OSL

Introduction (3)

• Starting from 2009

– FANC asked for a national audit program for reference and non reference conditions via public tender

– NuTeC was selected to perform a national audit

– BELdART was born (feb 2009)

– No cost for center

– A total of 34 centers

• 91 clinical machines

BELdART-1

• Visited audit of all centers (+ satellites)

• Auditing of

– Basic mechanical parameters

– Photon beams

– Electron beams

• Equipment independent of hospital

BELdART-1 (2)

• BELdART was unique:

– Visited national audit including all centers

– All centers participated with at least 1 accelerator

– Used the L-α-alanine dosimetry system

The alanine system

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Base function using reference dosimeters of 0 Gy and 20 Gy Calibration using dosimeters in the range 2 Gy – 25 Gy

The alanine system

• Measurement uncertainties

– Part of continuous internal QA procedure

– 5 measurements of calibration set over several months

The alanine system Uncertainty budget (4 Harwell detectors; 5 rotations, 4 Gy):

Base function detectors (20 Gy):

Dose (primary standard) 0.20%

Amplitude: (AbD) 0.15%

Mass: (≈ 50mg) 0.04%

Field detector (4 Gy):

Amplitude: (AD; 30 mGy = worst case) 0.75% Mass:(≈ 50mg) 0.04%

Experimental conditions:

Fading: 0.02%

Irr temp: 0.03%

Beam quality: 0.27%

Positioning 0.05%

Combined standard uncertainty 0.84%

Audit protocol

• Mechanical parameters

– Position of the isocenter

– Optical distance indicator

– Position of the laser lines

– Correspondence light-radiation field

Audit protocol (2)

• Dosimetrical tests (reference and non-reference) Exp Experiment Depth

(cm) Irradiation distance

Field size accessory Det. Dose ref

1 Ref. field dref ssd or sad 10cm x 10cm no 1 4 Gy 3.1

2 Tray factor Dref ssd or sad 10cm x 10cm tray 2 4 Gy 3.2

3 Energy open beam

10&20 ssd or sad 10cm x 10cm no 3,4 4 Gy 3.3

4 Energy beam with wedge

10&20 ssd or sad 10cm x 10cm wedge 5,6 4 Gy 3.4

5 Output factor1 8 ssd or sad 6cm x 6cm no 7 4 Gy 3.5



8 Output factor4 8 sad or ssd 20cm x 20cm no 10 4 Gy 3.8

9 MLC 1 “Circular”

8 ssd or sad 5.6cm circular

no 11 4 Gy 3.9

10 MLC 2 “inverted Y”

8 ssd or sad 15cm x 12cm no 12 4 Gy 3.10

11 MLC 3 “irreg.+ wedge”

8 ssd or sad 12cm x 8 cm wedge 13 4 Gy 3.11

Audit protocol (3) Exp Experiment Depth

(cm) Irradiation distance

Field size accessory Nr det Delivered dose

ref

12 Ref. field_ MeV1

dref ssd or clinical practice

10cm x 10cm no 15 4 Gy 4.13

13 Ref. field_ MeV2 (R50 > 7 cm)

dref ssd or clinical practice

10cm x 10cm no 16 4 Gy 4.14

The relative deviation is classified in 4 levels:

The relative deviation d º Dmeasured - Dcenter Dcenter is classified into 4 levels:

· "within optimal level": d £ 3%

· "out of optimal level but within tolerance": 3% < d £ 5%

· "out of tolerance level": 5% < d £ 10%

· "alarm level": d > 10%

BELdART-1 results

• All centers were audited for at least 1 unit

• A total of 61 out of 91 machines

• Total number of 212 beams

• Not audited:

– Tomotherapy

– Cyberknife

– Gammeknife

– Mobetron

BELdART-1 results

• Mechanical parameters

BELdART-1 results • Dosimetric parameters

Belgian Dosimetry Audits in Radiotherapy (BELdART) 2009-2011: final report. 49

3.3. Dosimetry verification

3.3.1. 1st and 2nd run measurements

Upon availability of the test results obtained in a 1st run measurement campaign for high-energy

photon beams, a second run was organised if at least one of the measurements resulted in a

deviation δ larger than the tolerance level, that is the observed deviation is in the range 5% < δ ≤

10%. However, when a systematic and significant (> 3%) shift in the measurement results was found,

a second run was initiated for this specific linac, as systematic deviations should not be expected and

its underlying cause should be understood. Even in the case when systematic deviations were

observed within tolerance level (≤ 3%) we contacted the local physicist on this matter, but no 2nd run

was initiated. Depending on the number of measurements outside the 5% level, the entire audit was

repeated in a 2nd run, or just the tests for which the outcome deviated > 5% were repeated.

From a total of 61 linacs audited in the BELdART project, 13 linacs (22%) divided over 11 sites were

involved in a second run measurement campaign. Evaluating the results more in detail, 11 linacs

divided over 10 sites needed a second run because of observed deviations in the measurements of

the photon beams and 9 linacs divided over 8 sites needed a second run because of observed

deviations ( > 5%) in the measurements of electron beams.

Fig. 3.6 shows the relative and absolute number of measurements falling into the four categories :

“optimal”, “within tolerance”, “out of tolerance” and “alarm” for all high-energy photon beams as

registered in the 1st runs measurement campaign. The deviation in “emergency” level was connected

to test D2 but appeared to be non significant, as the second run check of this beam was within

“tolerance” level. No explanation could be found a posteriori.

Fig. 3.6: Relative and absolute frequencies for the four levels in deviation for the dosimetrical tests as a result of 1

st run measurements in high-energy photon beams.

0% 0%

6%

94%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%

δ # %

δ > 10% 1 0,1

10% ≥ δ > 5% 4 0,3

5% ≥ δ > 3% 80 5,9

δ ≤ 3% 1270 93,7


Fig. 3.7: Relative and absolute frequencies for the four levels in deviation for the dosimetrical tests as a

result of 2nd

run measurements in high-energy photon beams.

Eighty second run measurements (6%) were completed versus 1375 first run measurements. After

completing the 2nd run measuring campaign, all test measurements are “within tolerance level” or

better (Fig. 3.7) that is: 96.7% of all measurements in high-energy photon beams are “within optimal

level” and only 3.3% of the measurements remain in the “tolerance level”. For the latter, the local

physicist was asked to take a close look at these measurements.

Fig. 3.8: Percentages and absolute values of 1st

run measurements in electron beams regarding to their deviations.

0% 0%

3%

97%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%

δ # %

δ > 10% 0 0,0

10% ≥ δ > 5% 0 0,0

5% ≥ δ > 3% 44 3,3

δ ≤ 3% 1296 96,7

1% 4%

13%

82%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%δ # %

δ > 10% 1 1,0

10% ≥ δ > 5% 4 4,1

5% ≥ δ > 3% 13 13,3

δ ≤ 3% 80 81,6

BELdART-1 results • Dosimetric parameters


Fig. 3.7: Relative and absolute frequencies for the four levels in deviation for the dosimetrical tests as a result of 2

nd run measurements in high-energy photon beams.

Eighty second run measurements (6%) were completed versus 1375 first run measurements. After

completing the 2nd run measuring campaign, all test measurements are “within tolerance level” or

better (Fig. 3.7) that is: 96.7% of all measurements in high-energy photon beams are “within optimal

level” and only 3.3% of the measurements remain in the “tolerance level”. For the latter, the local

physicist was asked to take a close look at these measurements.

Fig. 3.8: Percentages and absolute values of 1st

run measurements in electron beams regarding to their deviations.

0% 0%

3%

97%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%

δ # %

δ > 10% 0 0,0

10% ≥ δ > 5% 0 0,0

5% ≥ δ > 3% 44 3,3

δ ≤ 3% 1296 96,7

1% 4%

13%

82%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%δ # %

δ > 10% 1 1,0

10% ≥ δ > 5% 4 4,1

5% ≥ δ > 3% 13 13,3

δ ≤ 3% 80 81,6


Fig. 3.9: Percentage and absolute values after the 2nd

run measurements in electron beams regarding to

their deviations.

Regarding measurements in high-energy electron beams, we can make an analogous analysis. Fig. 3.8

shows the relative and absolute number of measurements falling into the four classes: “optimal”,

“within tolerance”, “out of tolerance” and “alarm” for all high-energy electron beams as registered in

the 1st runs measurement campaign. Twenty three (23%) second run measurements were

undertaken versus 98 first run measurements.

After completing the 2nd run measuring campaign, all test measurements are “within tolerance

level” or better (Fig. 3.9) that is: 87.3% of all measurements in high-energy electron beams are

“within optimal level” however, about 13% of the measurements remain catalogued as “within

tolerance”. The larger spread in the results for high-energy electron beams is also observed in other

audits [Ferreira, 2000] and a clear explanation is difficult to find. No bias in the results was found

with respect to nominal energy (low energy electron beams show a more delicate dosimetry, in

particular for the 4 MeV beam). Dividing the audited electron beams in “low” and “high” energy

however, reveal no explanation as seven low energy electron beams needed a 2nd run versus six high

energy electron beams.

In the following paragraphs the presented results will always be connected with the second run

measurement campaign, unless otherwise stated.

0% 0%

13%

87%

δ > 10%

10% ≥ δ > 5%

5% ≥ δ > 3%

δ ≤ 3%δ # %

δ > 10% 0 0,0

10% ≥ δ > 5% 0 0,0

5% ≥ δ > 3% 14 12,7

δ ≤ 3% 96 87,3

Audited centers


for the “Vero” system which could be included in the audit, as the beam collimation is quite similar to

a standard linac.

Considering the year of installation, we observe that 76 % of the linacs present in Belgium are

installed within the last 10 years and 47% linacs were installed during the last 5 years. The median

value for the “year of installation” is 2006. From these data, we may conclude that Belgium is

equipped with modern and up-to-date radiation facilities.

Fig. 3.3: Geographical dispersal of radiotherapy centres where BELdART activities were developed . All

radiotherapy centres were visited. For some centres, not all available clinical beams were submitted

to an audit because the BELdART program provides a limited number of audits (208 beams).

BELdART-2

Courtesy of Varian Medical Systems

BELdART-2

• Advanced and dynamic radiotherapy

– IMRT

– RapidARC

– Tomotherapy

– Cyberknife

– …

Protocol

• A combination of

– L-α-alanine dosimetry

• 2 pellets per point instead of 4

• Both in high and low dose points

• Used for absolute dosimetry

– EBT-3 film dosimetry

• 3-channel algorithm

• 2D dose distributions

• In plane of alanine pellets (relating to absolute dose)

3-channel

BELdART-2 planning

• Devided in 2 phases

– Phase 1 (6 months)

• Getting some feeling with EBT3

• What could we expect in Belgium

• Homogeneous phantom with selected centers

– Phase 2

• Open for all radiotherapy centers

• Heterogeneous phantom

Phase 1: what did we check?

Beam configuration

Delivery of the modulation

BELdART-2: Phase 1

• Use of easy-cube phantom

• Because of the shape:

– Prostate case with dosimeters @

• Prostate

• Rectum

• Bladder

– Film through all 3 structures (sagittal plane)

BELdART-2: Phase 1

Phase 2:

heterogeneities

Delivery of the modulation

Phase 2:

• Heterogeneous phantom:

– Lung or head & neck phantom

– Including

• Heterogeneities

• Imaging

• Tumor definition (using a description provided)

• Radiotherapy planning

• Image guided positioning (if applicable)

• Treatment

Dosimeters

• For both phases:

– Dosimeters are inserted by the BELdART-2 team

– Phantom delivered including dosimeters

– No visit of the auditor in the center during treatment/planning

– Phantom has to be treated as if a patient

• Audit is free of charge for all Belgian radiotherapy centers!

What is checked by the end?

BELdART-3?

• New technologies are being implemented

Conclusion

• Radiotherapy is in constant movement

• A rigid, independent auditing system is necessary to ensure safe radiotherapy

• BELdART-1 showed that all radiotherapy center work within tolerance levels

• BELdART-2 is the first national audit investigating the implementation of advanced radiotherapy techniques

• Within 3 years we will know how good we work in Belgium

A word of thanks to

• The scientific IMRT committee – Michael Duchateau, UZBrussel

– Wouter Crijns, UZLeuven

– Yassine Boucours, Centre Hospitalier Peltzer-La Tourelle

– Antoine Delor, UCL

– Michel Mathot, University of Liege

• The steering committee – François Sergent; Clinique et Maternité Ste-Elisabeth

– Stefaan Vynckier; UCL

– Dirk Verellen; UZBrussel

– Alex Rijnders; Cliniques de l’Europe

– Karen Feyen; AZ St. Maarten

Thank you

Symposium: “Radiation protection for medical doctors”

Date: Saterday April 27th 2013 Location: Klein Auditorium, Uhasselt campus “Oude gevangenis”, Hasselt Target audience: Surgeons, intervention cardiologists, reumatologists, dentists, …

More info?

www.nutec.be [email protected]

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beldart -2 · belgian dosimetry audits in radiotherapy (beldart) 2009-2011: final report. 50 fig....

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