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Radiation therapy is always a balancing act. The high-energy
ionizing radiation must be applied in such a way that as
much tumour tissue as possible is destroyed while leaving
healthy tissue intact. This requires precise information about
the tumour and its metabolism, gathered through complex
mathematical calculations and various imaging techniques. In
most cases medical physi-
cists put together an indivi-
dualised radiation therapy
plan, working closely with
physicians. They have developedmethods for calculating the
distribution of each radiation dose in advance – using compu-
ted tomography to create a three-dimensional model of the
body. This method has become standard in radiation therapy.
Any kind of radiation that is capable of penetrating the body
and depositing part of its energy there through the ionization
of atoms is suitable for this kind of therapy. Ionization describes
a process in which an electron is expelled from an atom, lea-
ving the atom in the form of a positively charged ion. In this
way the atoms acquire new properties that can lead to the
breakdown of molecular bonds in the cell and cause serious
damage to their DNA – which can kill the cells. In order to
improve the recovery chances of healthy tissue, the total ra-
diation dose is divided into small portions, so-called fractions,
which are administered to the patient in a series of therapy
sessions. Ideally the tumour shrinks continuously, until it finally
dies completely. The problem that remains is how the healthy
tissue reacts and what side effects this entails. They set the
limits for the maximum dose of radiation to be administered.
This is where the linear accelerator comes in, a device wit-
hout which modern cancer therapy would be unthinkable. It
accelerates the electrons until they build up large amounts
of energy, then abruptly decelerates them. Part of the kinetic
energy created in the process is converted into high-energy
x-rays, which are then aimed at the patient's body. To keep
damage of healthy tissue to a minimum, a lamella collimator
attached to the linear accelerator adjusts the beam to the
contours of the tumour. The rotation of the beamline ensures
that via the lamella collimator, the tumor is targeted "from all
sides", so to speak.
For many tumours Intensity-Modulated Radiation Therapy
(IMRT) has increasingly become the technique of choice in
recent years. It uses lamella collimators not only to block off or-
gans at risk, but also tomodulate the intensity of the radiation.
During therapy the lamellae either move continuously above
the area under treatment or the beams target the area from
several different directions, in varying field configurations. In
the newest machines, the beamline and the lamellae rotate
dynamically so that almost any rotationally symmetric dose
distribution is possible in the body.
The newmethods have considerably reduced themassive side
effects of radiation therapy whichwere common only twenty
years ago. Yet they still teeter on the limits of what healthy
tissue can cope with. Even slight imprecisions in the dose can
provoke a wide range of side effects in the patient. However
in the past it was almost impossible tomeasure and check the
dose distribution – which is why for a long time many clinics
didn't use intensity-modulated radiation therapy.
The "Medical Radiation Physics" research group, which is jointly
run by the University of Oldenburg and the Pius Hospital, is
working on developing high-precision devices for measuring
dose distribution in intensity-modulated radiation therapy. To
do this theymeasure radiationdoses inbody-likematerials such
as water or synthetics that have been fitted with detectors.
Before the development of intensity-modulated radiation
therapy, the human body was treated mainly with simple
flat and homogenous intensity profiles. Measurements were
generally confined to the use of point-liked detectors. The
standard measuring device for this is the ionization chamber
– an air-filled chamber in which the voltage from two elec-
trodes creates an electric field. The electrons produced by the
radiation generate ions within the detector, which are in turn
collected by the electrodes, creating a signal proportional to
the magnitude of the deposited radiation dose.
Advances in radiation methods have made it necessary
to develop techniques for measuring more complex dose
distributions. Initially no one knew whether the methods
developed for relatively simple field forms could also be ap-
plied to the more complex and dynamic techniques of IMRT.
Comparing the calculated dose distribution with the dose
actually deposited in the body requires extremely precise,
multidimensional measurements.
X-ray films were commonly deployed here. But the research
also of the Oldenburg scientists has shown that these no
longer satisfy the higher requirements because they are not
accurate enough in their depiction of the radiation deposi-
The goal: to reduce the side
effects of radiation therapy
Die Autoren The Authors
Prof. Dr. Björn Poppe hat seit 2004 eine Stiftungsprofessur des Pius-
Hospitals Oldenburg für Strahlenphysik inne und leitet die Arbeits-
gruppe „Medizinische Strahlenphysik“ an der Universität.
Prof. Dr. Björn Poppe has held an endowed professorship in radiation
physics from the Pius-Hospital Oldenburg since 2004, and leads the
University's "Medical Radiation Physics" research group.
Dr.KayChristelWillbornistgeschäftskoordinierenderDirektordesKlinikzentrums
fürStrahlentherapie,HämatologieundOnkologieamPius-HospitalOldenburg.
Dr.KayChristelWillbornhasbeenmanagingdirectoroftheClinic Centerfor
RadiationTherapy andMedical Oncology at thePius-Hospital Oldenburg.
Dr. Hui Khee Looe ist seit 2007 Wissenschaftlicher Mitarbeiter der
Arbeitsgruppe „Medizinische Strahlenphysik“.
Dr. Hui Khee Looe has been a research fellow with the "Medical
Radiation Physics" research group since 2007.
Dr. Ndimofor Chofor, Wissenschaftlicher Mitarbeiter der Arbeitgrup-
pe „Medizinische Strahlenphysik“.
Dr. Ndimofor Chofor, research fellow with the "Medical Radiation
Physics" research group.