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BELdART Belgian dosimetry Audits in RadioTherapy

B. Schaeken, R. Cuypers, S. Lelie, W. Schroeyers, F. Sergent, S. Vynckier, A. Rijnders, D. Verellen, H. Janssens

IAEA-IDOS - Vienna, nov. 2010

Organisation: national audit

“Basic”

mechanical

checks: isocentrum; lasers; telemeter; light field correspondence

“Basic”

dosimetry

checks: dose measurements in water on beam axisat pre-defined depths

-

photon beams: 11 dose measurements all types-

electron beams: 2 dose measurements in reference conditions

-

31 locations-

79 linac’s

-

126 photon beams-

113 electron

beams

“Visited”

audits / 3 y time span; all Belgian clinical beams


BELdART• first large-scale audit based on alanine/ EPR dosimetry

• requested dose: 4 Gy, 4 pellets: uc

(Dw

) = 1.1 % (k =1)• MU should be calculated with TPS as would be done for patients

• δ ≡ (Dmeas

-Dcenter

)/ Dcenterwithin optimal level:

|

δ | ≤

3%

• dose determined with “individual base functions”Anton: Appl.Rad.Isot

62, 2005; Phys.Med.Biol

51, 2006

• measured dose expressed as “dose normalized amplitudes”

10 cm x 10 cm

ssdsad

dref

dref

ssd set-upsad set-up

alanine


BELdART

sleevebfading

fadingbT

TQQ

M

jj

M

jj

bbmD k

kk

kkkkwithkDm

mA

⋅⋅⋅=⋅⋅⋅=Α ∏∏==

0,11


PTB-traceable

BELdARTDosimetry

audits: photon beams

Exp. Nr

Experiment Depth(cm)

Irradiationdistance

Field size Accessory Nr det Requested 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 wedged beam

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“symm/irreg”

8 ssd or sad circular no 11 4 Gy 3.9

10 MLC 2 “asymm/irreg”

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

11 MLC 3“asymm/irreg.+

wedge”

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


BELdARTDosimetry

audits: electron

beams

Exp Nr

Experiment Depth(cm)

Irradiationdistance

Field size accesso ry

Nr det Requested dose

ref

12 Ref. field_MeV1

dref ssd or clinical practice

10cm x 10cm no 14 4 Gy 4.13

13 Ref. field_MeV2(R50 > 7 cm)

dref ssd or clinical practice

10cm x 10cm no 15 4 Gy 4.14

involving 68 alanine pellets


1. Actual status:

• 36 linacs: Varian: 11; Siemens: 7; Elekta: 16; Novalis: 1; BrainLabAB/MHI “Vero”: 1

• Dosimetry

was checked in • 64 photon beams: 4x 4MV; 1x 5MV; 32x 6MV; 1x 10MV; 17x 15MV; 9x 18MV• 54 electron beams: 2x 4MeV; 1x 5MeV; 18x 6MeV; 1x 7MeV;

3x 8MeV; 2x 9MeV; 3x 12MeV; 1x 14MeV; 9x 15MeV; 12x 18MeV; 1x 20MeV; 1x 25MeV

• For 1st

and 2nd

run measurements in photon beams: – Dmeas

/ Dstated

= 0.999 , σ

= 0.013 (#803)– Dalanine

/ Dionometry

= 1.001 , σ

= 0.008 (#98)


BELdART2. Traceability:

N = 17mean = 0,998σ = 0,005range = 0,016

Alanine vs. ionisation chamber: ref. beams

0 ,9 0 0 ,9 2 0 ,9 4 0 ,9 6 0 ,9 8 1 ,0 0 1 ,0 2 1 ,0 4 1 ,0 6 1 ,0 8 1 ,1 00

5

1 0

1 5

2 0

2 5

3 0

Num

ber o

f bea

ms

D w , a la n in e /D w , io n c h a m b e r

N = 9 8m e a n = 1 , 0 0 1σ = 0 , 0 0 6ra n g e = 0 , 0 3 1

A l a n i n e v s . i o n i s a t i o n c h a m b e r : r e f e re n c e a n d n o n ‐ r e f e re n c e b e a m s


3.Results MV:

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

10

12

14

16

18

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 56mean = 1,000σ = 0,010range = 0,061

Photon ref beam output

BELdART


0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

10

12

14

16

Num

ber o

f bea

ms

QImeas/QIcenter (TPR20/10)

N = 62mean = 0,997σ = 0,010range = 0,042

Quality Index

3.Results MV:

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

5

10

15

20

25

30

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 120mean = 0,998σ = 0,017range = 0,088

Photon wedged beam output

BELdART


0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

20

40

60

80

100

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 372mean = 1,000σ = 0,015range = 0,085

Photon beam output with collimator opening

3.Results MV:

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

10

12

14

16

18

20

22

Num

ber o

f bea

ms

Dw, meas/Dw, center

MLC1 MLC2 MLC3

Photon irr. Field output MLC1 MLC2 MLC3N = 61 59 56mean = 1,000 0,998 0,993σ = 0,016 0,015 0,017range = 0,071 0,077 0,072

BELdART


BELdART

MeV kQ,Q0

4 1.031 1.0256 1.017 1.0138 1.018 1.017

10 1.01612 1.00515 0.99718 1.002 1.00220 0.99322 0.962

kQ,Q0

in high-energy electron beams:

• SL25: 4, 6, 8, 10, 12, 15, 18, 20, 22 MeV• ROOS chamber cross calibrated vs. Farmer at 18 MeV / NCS-18 protocol

• Roos/Farmer = 1.0180• Alanine (8 Gy): ur

(Dw

) = 0.3%; Roos/Farmer: ur

(Dw

) = 1.8% (NCS-18/pp69)

• Two types of holder


3.Results MeV:

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

10

12

14

16

18

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 57mean = 0,994σ = 0,025range = 0,133

All electron beams

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

10

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 29mean = 0,996σ = 0,021range = 0,094

Low energy electron beams

0,90 0,92 0,94 0,96 0,98 1,00 1,02 1,04 1,06 1,08 1,100

2

4

6

8

Num

ber o

f bea

ms

Dw, meas/Dw, center

N = 28mean = 0,992σ = 0,028range = 0,133

High energy electron beams

BELdART


3.Results summary (latest):

BELdART

output measurements Dmeas/ Dcenter 1sd R(min‐max) #

photon ref beam 1.000 0.012 0.061 56

QI (open beam) 0.997 0.010 0.042 62

wedged photon beam 0.998 0.017 0.088 120

regular field sizes 1.000 0.015 0.085 375

MLC 1‐3 1.000 0.016 0.071 61

0.988 0.015 0.077 59

0.993 0.017 0.072 56

electron beams 0.994 0.025 0.133 57

Results are incl. 2nd and 3th run measurementsIf deviations are observed, it’s likely that they are systematic, even within optimal level…Finding explanations for a deviation needs a detailed look-up…Out of tolerance situations disappear in a 2nd run, although a clear explanation is difficult to find…


BELdART


4. Conclusion:

• alanine/EPR was successfully used as transfer dosimetry

system

• allowing sufficient accurate dose measurements

• results into accordance with (reference) ionometry

• beam data are well modeled in TPS for the visited centers

• suits well for mailed dosimetry

(practicalities)

• but…

the true benefit of alanine/EPR lays in complex dose deliveries (helical, IMRT, SRS, brachytherapy...)

BELdART

Acknowledgments: Hilde Beutjens

(lab ass) and Mathias Anton (PTB);fully supported by FANC-AFCN

Visit us at www.nutec.beInfo

[email protected]


BELdART - Human Health Campus - Home · ssd. sad. dref. dref. sad set-up. ssd set-up. alanine....

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