Electromagnetic redesign of the HYPERcollar applicator: 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 * Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands Grant DDHK 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 : o mean SAR in target o max 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)

-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)

+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

+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 and **Trefna et al  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 * Paulides et al Int. J. Hyperthermia 23(1): 59–67 **Trefna et al 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 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 : > % (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

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