Comparison of two different 70 MHz applicators for large extremity lesions: simulation and application.
BACKGROUND
Motivation for this research was a patient with large and bulky melanoma lesions on a leg, treated with hyperthermia in a special set-up with an open water bolus and two opposing applicators. Treatment planning was used to find the most suitable heating method, comparing 70 MHz capacitive contact flexible microstrip applicators (CFMAs) and 70 MHz waveguides.


METHODS
The first three sessions were performed with CFMA applicators; the last session with waveguides. Power and water temperature were adjusted to achieve clinically relevant temperatures. Finite difference time domain (FDTD) simulations were performed for a CFMA and waveguide on a fat-muscle geometry to compare effective field size (EFS) and effective heating depth (EHD). A CT scan of the patient's leg was automatically segmented into muscle, fat and bone; tumour lesions were outlined manually. Patient simulations were performed to evaluate the 3D heating pattern and to compare CFMAs and waveguides for equal power and water temperature.


RESULTS
Hyperthermia treatment was well tolerated. Temperature measurements indicated mainly superficial heating with CFMAs. Simulated EHD was 2.1 and 2.4 cm for CFMA and waveguide, respectively and EFS was 19.6 x 16.2 cm(2) and 19.4 x 16.3 cm(2). Simulation results confirmed the better performance of the waveguides. For normal amounts of fat tissue, approximately twice as much power is absorbed in fat with CFMAs compared to waveguides. [corrected] Simulations showed that a relatively high water temperature ( approximately 42 degrees C) improves the overall temperature distribution.


CONCLUSIONS
CFMAs and waveguides have a similar EFS and EHD, but for large extremity lesions, the performance of 70 MHz waveguides is favourable compared to 70 MHz CFMA applicators.
Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. H.P.Kok@amc.uva.nl
H Petra
HP
Kok
Martijn
M
de Greef
Niek
N
van Wieringen
Davi
D
Correia
Maarten C C M
MC
Hulshof
Paul J
PJ
Zum Vörde Sive Vörding
Jan
J
Sijbrands
Arjan
A
Bel
Johannes
J
Crezee
D000465:Algorithms; D001831:Body Temperature / Q000528:radiation effects; D003198:Computer Simulation; D004566:Electrodes; D017809:Fatal Outcome; D006801:Humans; D006979:Hyperthermia, Induced / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D007866:Leg / Q000473:pathology*; D008297:Male; D008545:Melanoma / Q000473:pathology / Q000532:radiotherapy / Q000628:therapy*; D008875:Middle Aged; D019047:Phantoms, Imaging; D000078702:Radiofrequency Therapy; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D017211:Treatment Failure