Primary water calorimetry in clinical electron beams, scanned proton

beams, and 192Ir brachytherapy dosimetry

Primary water calorimetry in clinical electron beams, scanned proton

beams, and 192Ir brachytherapy dosimetry

A. Sarfehnia1, K. Stewart1, C. Ross2, M. McEwen2, B. Clasie3, E. Chung1, H. M. Lu3, J. Flanz3, E. Cascio3, M.

Engelsman3, H. Paganetti3, J. Seuntjens1

1 Medical Physics Unit, McGill University, Montreal, Quebec, Canada2 National Research Council of Canada, Ottawa, Ontario, Canada

3 Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA

A. Sarfehnia1, K. Stewart1, C. Ross2, M. McEwen2, B. Clasie3, E. Chung1, H. M. Lu3, J. Flanz3, E. Cascio3, M.

Engelsman3, H. Paganetti3, J. Seuntjens1

1 Medical Physics Unit, McGill University, Montreal, Quebec, Canada2 National Research Council of Canada, Ottawa, Ontario, Canada

3 Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA

International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry

International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry

Water Calorimetry• Calorimetry is the only true primary standard for

absorbed dose to water measurement in radiation dosimetry.

• Advantages: • In principle, energy-independent• Measures Dw to a point

• Currently, implemented only for high energy photon and electron beams.

Dw (vr ) = cw, p ⋅ ΔT (vr ) ⋅ ki∏

Water Calorimetry (experiment)

Water Calorimetry (experiment)

Water Calorimetry (experiment)

Time

Tem

pera

tur e

Ris

e

Predrift Irradiation Postdrift

Water Calorimetry (experiment)

Time

Tem

pera

tur e

Ris

e

Predrift Irradiation Postdrift

Dw (vr ) = cw, p ⋅ ΔT (vr ) ⋅ ki∏

ΔT

Heat transport correction factor

• Comsol Multiphysics software was used to solve the heat transport problem using Finite Element Method (FEM)

ρcp∂T∂t

+ ∇ ⋅ −k∇T + ρcpvuT( )= Q

∇ ⋅ vu = 0

ρ∂vu∂t

−η∇2 vu + ρ vu ⋅∇( )vu + ∇p =vF

kht =ΔTw, ideal

calc

ΔTw, actualcalckht =

ΔTw, idealcalc

ΔTw, actualcalc

AIM

• The aim of our research program is to develop water calorimetry for the following distinct applications

• Clinical high energy electron beams• 192Ir HDR brachytherapy• Scattered/Scanned proton beam

delivery

High Energy Electrons• Varian Clinac 21EX

• 6, 9, 12, 16, 20 MeV

• In 6 MeV, the thermistors are positioned only 13.4 mm below water surface.

High Energy Electrons Dw

Q (vr ) = M ⋅ND,w

60 Co ⋅ kecal ⋅ kR50

' ⋅PgrQ

High Energy ElectronsPresent Work AAPM TG-51 IAEA TRS-398 Mainegra-Hing et

al*

Estimated from the work of Buckley and Rogers**

PTW Roos 0.895 0.901 0.895 0.896 --

Exradin A12 0.918 0.906 0.910 -- 0.904

R50 {cm}

K’ R

50

* E. Mainegra-Hing, I. Kawrakow, D. W. O. Rogers, MedPhys 30, 179 (2003) ** L. Buckley and D. W. O. Rogers, MedPhys 33, 455 (2006)

K. Zink and J. Wulff, PMB 53, 1595 (2008)

192Ir brachytherapy

• SK=21000-38000 U• dsrc-det=25-70 mm

192Ir brachytherapy

A. Sarfehnia and J. Seuntjens, MedPhys 37, 1914 (2010)

192Ir brachytherapy

MethodRelative Diff from Water Calorimetry

Chamber -0.83%

Radiochormic film 0.83%

TG-43 0.55%

Proton therapy

• Scanned beam consisted of superposition of 15 Bragg peaks.

• Minimized the dose variation in a 1 cm range around thermistors < 0.4% and 0.2% in scattered and scanned beams.

Proton therapy

A. Sarfehnia et al, MedPhys 37, 3541 (2010)

Proton therapy

% diff Calorimetry &T1 Chamber (IAEA TRS-

398)

Scattering 0.34%

Scanning 0.42%

Conclusions

• Water calorimetry is feasible in high energy electron beams, scattered and scanned proton beams, as well as in Ir- 192 HDR brachytherapy.

• This work paves the way toward establishment of Dw primary standard for these beams at Standard lab level.

CONCLUSIONSEnergy kht

1-sigmauncertainty (%)

6 MV 1.01 0.46

6 MeV 1.022 1.03

9MeV 1.011 0.52

12 MeV 1.010 0.49

16 MeV 1.010 0.51

20 MeV 1.012 0.52

Scattered (250 MEV) 0.996 0.38

Scanned (128-150 MeV) 0.953 0.64

Ir-192 0.963 1.90

Electron

Photon

Proton

Brachytherapy

Conclusions

• Water calorimetry is feasible in high energy electron beams, scattered and scanned proton beams, as well as in Ir- 192 HDR brachytherapy.

• This work paves the way toward establishment of Dw primary standard for these beams at Standard lab level.

AcknowledgmentsHARVARD

UNIVERSITY

MASSACHUSETTSGENERAL HOSPITAL

National Research Council of Canada

Sources of Funding:

Natural Sciences and Engineering Research Council of Canada MUHC Doctoral Research Award