Biomedical Engineering Reference
In-Depth Information
7
Numerical Modeling for
Simulation and Treatment
Planning of Thermal Therapy
Esra Neufeld
Foundation for Research on
Information Technologies in
Society (IT'IS) and Swiss Federal
Institute of Technology (ETHZ)
7.1 Need for Treatment Planning in Thermal Therapy ............................................................119
7.2 Hyperthermia Treatment Planning (HTP) .........................................................................121
7.3 Segmentation ............................................................................................................................121
7.4 Electromagnetic Simulations ................................................................................................ 122
7.5 Thermal Simulations .............................................................................................................. 123
7.6 Field Optimization ................................................................................................................. 125
7.7 Biological Effect Determination ........................................................................................... 126
7.8 Thermometry and Experimental Validation .......................................................................127
7.9 Tissue Parameters ....................................................................................................................127
7.10 Related Treatments ..................................................................................................................127
7.11 Challenges ................................................................................................................................ 128
7.12 Conclusions.............................................................................................................................. 129
References ............................................................................................................................................ 129
Maarten M. Paulides
Erasmus MC Daniel den
Hoed Cancer Center
Gerard C. van Rhoon
Erasmus MC Daniel den
Hoed Cancer Center
Niels Kuster
Foundation for Research on
Information Technologies in
Society (IT'IS) and Swiss Federal
Institute of Technology (ETHZ)
7.1 Need for treatment planning
in thermal therapy
associated with hyperthermia. It should also be noted that
even with prefect temperature mapping the problem of opti-
mal excitation would still not be solved, although approaches
exist for using multiple MR temperature maps from different
antennae settings as a basis for optimization [31].
• Treatment planning software can be used to train staff, to
develop new applicators [138], and to study the impact of
various physical [44, 171] and physiological parameters
(e.g., tissue characteristics, etc).
• Treatment planning provides visual information about
the treatment and might help further the understanding
and increase the acceptance of hyperthermia as a treat-
ment modality.
In the context of thermal therapy, numerical modeling and
treatment planning are needed for various reasons:
• Determination of the correct dose for a patient is not
straightforward.
• The commonly used antenna arrays are often hard to
steer and give rise to complex energy deposition patterns
that cannot easily be controlled [158]. Hot spots during
treatment are hard to predict and can limit the amount of
energy that can be deposited in a patient. They are pain-
ful and can ultimately damage healthy tissue. Treatment
planning helps to reduce hot spots [186] and thus helps to
reduce the risk of damage to thermally sensitive healthy
tissues such as the spinal cord [138].
• Monitoring temperature during treatment is difficult.
Invasive thermometry increases the risk of complications
[172]. Noninvasive magnetic resonance imaging (MRI) ther-
mometry is a promising alternative [176], but, even though
currently being refined for this application, suffers from the
following limitations: it is costly, not widely available, still not
applicable for all tissue types, not yet sufficiently accurate and
stable, and the MR adds to the claustrophobia issue already
Figure 7.1 shows how hyperthermia treatment planning
(HTP) can be embedded in the clinical flow. The following steps
have to be performed during hyperthermia treatment planning
(see Figure 7.2):
• Segmentation of medical images to generate a patient
model. In contrast to radiotherapy, all tissues have to be
segmented in accordance with their tissue type in order to
select the correct properties (electrical and physiological).
• Simulation of the electromagnetic (EM) fields generated
by the applicator antennas.
• Simulation of the induced temperature changes.
119
