Biomedical Engineering Reference
In-Depth Information
be irradiated by high energy photons. This allows a better protection of organs at
risk and escalation of dose inside the tumour.
Major research areas in IMRT are:
IMRT with mixed photon and electron beams Electron and photon beams are
combined to create dose distributions that feature a steep dose fall-off at large
depths similar to pure electron beams and flat beam profiles and sharp and depth-
independent beam penumbras as in photon beams.
IMRT simultaneous integrated boost (SIB) Sophisticated technique where high
precision treatment is required. The SIB allows a dose-escalation. That means to
deliver higher total doses of radiation to smaller treatment volumes. A biologic
effect of accelerated fractionation can occur within the tumour.
Light ion radiation therapy Intensity-modulated light ion beams are the ultimate
tool in clinical practice. Intensity modulated proton therapy may be able to cure
even the most advanced hypoxic and radiation-resistant tumours. Low ionization-
density hydrogen ions and high ionization-density carbon ions are used. The high
LET component is located only in the high-dose tumour volume. The low LET
component is located in the surrounding normal tissues.
Tumour immobilization devices Tumour motion between and even during radiation
treatments represents a major uncertainty. Efforts are required to ensure accurate
conformal radiation therapy. The gate breathing system allows delivery of the
radiation beam only in particular moments of the respiratory cycle and prevents
it when the tumour is out of the beam.
Tomotherapy IMRT
is an intensity modulated radiation therapy with daily serial
or helical CT localization. It allows optimum target coverage and doing a frameless
stereotaxis.
Stereotactic radiation therapy
is a technique that delivers a large single fraction
or multiple fractions of radiation to a number of small, stationary portals at different
angles. Thus, usually small volumes are treated. Beams intersect at a common
point within the body after entering through different points distributed over the
skin surface. Extra precision regarding target localization and treatment geometry
is required since high-dose gradients at field edges minimize dose deposition
outside the target volume. In cranial stereotactic radiation therapy the patient's
immobilization is done by fixing a semicircular stereotactic frame to his skull
or using a mask. The collimator moves circumferentially along the frame. New
stereotactic radiation therapy delivery machines allow the treatment of localizations
different from intracranial tumours.
Intraoperative radiation therapy
is a treatment technique that uses electron
external beam irradiation for deep-seated cancers. The irradiation is concentrated
to the tumour volume while the adjacent, surgically mobilized normal tissues, can
be avoided.
High Dose-Rate (HDR) Brachytherapy
is illustrated in Fig.
24.5
. Brachytherapy
consists of placing sealed radioactive sources very close to or in contact with
the target tissue. With HDR, high doses can be safely delivered to a localized
