Electromagnetic redesign of the HYPERcollarapplicator: towards improved deep local

head-and-neck hyperthermia

*P. Togni, Z. Rijnen, W.C.M. Numan, R.F. Verhaart, J.F.

Bakker, G.C. van Rhoon and M.M. Paulides

Journal Club 08-04-2013Journal Club 08-04-2013

* p.togni@erasmusmc.nl

• Department of Radiation Oncology, Erasmus MC-Daniel den Hoed

Cancer Center, Rotterdam, The Netherlands

Grant DDHK2009-4270

Submitted to : Physics in Medicine and Biology

Content

Introduction

Methods

Results

Discussion

Conclusion

Introduction

Research question:

Can we improve treatment quality with a new antenna arrangement?

Goal:

Evaluate quality improvements using a new antenna arrangement

implemented in a mechanically redesigned HYPERcollar:

• hot-spot

• target coverage

• heating capability

Methods: applicator models

clinical experience

Methods: applicator models

clinical experience

• 12 antennas• 2 rings• circular array

arrangement • bulging WB

Methods: applicator models

clinical experience

• 12 antennas• 2 rings• circular array

arrangement • bulging WB

• 20 antennas • 3 rings• ‘horse-shoe’’ array

arrangement• bulging WB

Methods: applicator models

clinical experience

• 12 antennas• 2 rings• circular array

arrangement • bulging WB

• 20 antennas • 3 rings• ‘horse-shoe’’ array

arrangement• bulging WB

• 20 antennas • 3 rings• ‘horse-shoe’’ array

arrangement• reduced diameter• flat-end WB

Methods: applicator models

current study

clinical experience

• 12 antennas• 2 rings• circular array

arrangement • bulging WB

• 20 antennas • 3 rings• ‘horse-shoe’’ array

arrangement• bulging WB

• 20 antennas • 3 rings• ‘horse-shoe’’ array

arrangement• reduced diameter• flat-end WB

Methods: applicator models

Methods: patient inclusion

first 26 patient treated with HYPERcollar applicator

Methods: optimization and evaluation parameters:

• Hotspot importance :

• Tumor coverage :

• Target heating capability :

omean SAR in target

omax theoretical system power (antenna use uniformity)

Results: ‘horse-shoe’ array arrangement justification

HYPERcollar model (I)

Results: ‘horse-shoe’ array arrangement justification

• Limited contribution of dorsal antenna (< 0.16)• Indirect contribution via the head-rest high sensitivity to slight off-sets dorsal antenna excluded from HYPERcollar (I) optimizations

HYPERcollar model (I)

Results: hot-spot reduction (HTQ) tumor coverage (TC25)

Results: hot-spot reduction (HTQ) tumor coverage (TC25)

-27 % -32 %

• ‘Horse-shoe’’ layout introduce a importance reduction

Results: hot-spot reduction (HTQ) tumor coverage (TC25)

-27 % -32 %

+3 % +2 %

• Limited improvement of coverage when used as optimization function

Results: hot-spot reduction (HTQ) tumor coverage (TC25)

-27 % -32 %59 %

81%73%

• Coverage improvement for worst cases “hard to heat” patients

Results: mean SAR target (Pin = 1W)

Results: mean SAR target (Pin = 1W)

+53%

+170 %

Results: mean SAR target (Pin = 1W)

+53%

+170 %

+34%+112 %

Results: mean SAR target (Pin = 1W)

+53%

+170 %

+34%+112 %

• New desing over-perform modified HYPERcollar reduced back plane diameter (400 mm 320 mm)

Results: maximum system power

Results: maximum system power

+59%+62%

Results: maximum system power

+59%+62% +28%+37%

Results: maximum system power

+59%+62% +28%+37%

• Applicators with “horse-shoe’’ perform better more uniform contribute of antennas

Discussion

new array arrangement alone substantially reduce hotspot importance

(HTQ -27% model II, HTQ -32% model III)

increased number of antennas produce a better power focusing

in agreement with *Paulides et al. 2007 and **Trefna et al. 2010

possibility to choose 12 antennas out of 20 allow a more uniform antenna use

reduced probability of power to be treatment limiting

reduced ground plane diameter allowed better focus capability

in agreement with *Paulides et al. 2007

* Paulides et al. 2007 Int. J. Hyperthermia 23(1): 59–67**Trefna et al. 2010 Int. J. Hyperthermia 26(2): 185–197.

Discussion

new design did not outperformed mod. HYPERcollar in TC25

bulging WB allow a better power deposition in targets extending

outside applicator ground plane (6/8 ‘neck’ patients)

bulging WB has low reproducibility increased treatment quality

variation in clinic.

solution applicator tilted 30° for ‘neck’ patients

WB extensions in caudal direction to be investigated

Discussion

two SAR-based optimization function were used (HTQ + TC25) because a quality

parameter predictive for H&N HT outcome was not established yet:

• HTQ: best correlate with T50 in DHT (*Canters et al. 2009)

• TC25: target totally cover by 25% iso-SAR best factor for prediction clinical

outcome in recurrent breast carcinoma (**Myerson et al. 1990, ***Lee et al.

1998)

both are used to prove robustness of new design for H&N HT

* Canters et al. 2009 , Phys Med Biol 54: 3923–3936.** Myerson et al. 1990, Int J Radiat Oncol Biol Phys 18(5): 1123–1129*** Lee et al. 1998, Int J Radiat Oncol Biol Phys 40(2): 365–375

Discussion

uncertainties evaluation in HT simulation studies:

• SAR patterns robustness to patient positioning variations in DHT

(*Canters et al. 2009)

• role dielectric and perfusion uncertainties on HTP (**de Greef et al. 2010)

In our case large number of patients (26) with targets in different locations

represents an ‘anatomy-based’ uncertainties evaluation

more relevant to verify heating capability improvement and design

robustness

* Canters et al. 2009 , Phys Med Biol 54: 3923–3936.** de Greef et al. 2010 Med Phys 37(9): 4540–4550.

Conclusions

HYPERcollar array arrangement sub-optimaI

limited contribution of dorsal antennas

“Horse-shoe” array arrangement integrated in mechanical redesign

hot-spot : – 32 % (HTQ)

target coverage : + 2 % (TC25)

focus capability : > + 112 % (mean SAR target

[1W ])

max system power : 981 W (+49 %)

Substantial improvement theoretical H&N treatment quality

Combination with mechanical redesign improved reproducibility

expected strong improvement in clinical treatment quality

Thank you for you attention

questions?

Grant DDHK2009-4270