Dosimetry and Medical Radiation Physics
E2.40.15 Doctoral CRP on Quality Assurance of the Physical Aspects of Advanced Technology in Radiotherapy
Background:
Member States engaged in the field of cancer treatment by means of radiotherapy
are trying to increase the number of patients treated with curative intent.
For those cancers detected at an early stage, local control of the disease
can only be achieved if a tumourcidal dose can be delivered at an acceptable
level of radiation toxicity. In other words, too much dose delivered to
healthy critical structures located adjacent to the tumour results in high
complication rates and decreased quality of life. Too little dose to the
known tumour volume fails to cure the disease and may lead to patient death.
In the last two decades, there has been a revolution in imaging sciences.
X-ray computerized tomography (CT) and magnetic resonance imaging (MRI)
have increased knowledge about the location of tumours. In nuclear medicine,
single photon emission tomography (SPECT) and positron emission tomography
(PET) provide functional information that may alter the planned course of
radiotherapy. The coupling of imaging devices, both x-ray sources and imaging
detectors, to radiotherapy machines has enabled real-time imaging information
to be used to deliver image-guided radiotherapy to compensate for inter-fractional
and intra-fractional tumour motion.
The additional information from modern imaging systems has been matched
by improvements in treatment delivery technology. Multi-leaf collimators
(MLCs) are used to conform the dose distribution to the tumour volume. Improvements
in treatment planning systems (TPSs), including those based on Monte Carlo
codes, permit more rapid and accurate calculations of dose distributions.
New verification tools such as electronic portal imaging devices (EPIDs)
have become available. All these technologies require quality control (QC)
procedures to ensure the individual components are performing as expected
and quality assurance (QA) systems in place to ensure that the overall treatment
process is performed according to expectations.
Intensity Modulated Radiotherapy (IMRT) uses small beamlets to deliver the
dose to a tumour volume while reducing the risk of radiation toxicity by
minimizing the dose to near-by critical structures. It may also be possible
to increase the probability of local tumour control by escalating the dose
to specific targets of concern within the tumour volume. However, the process
of conforming the dose to the tumour volume is technically complicated.
Firstly, it is necessary to have excellent localisation of the volume to
be treated. Throughout the course of the therapy, QA is required to ensure
that the tumour remains within the irradiated field. Treatment planning
has to account for heterogeneities in the treatment field and Monte Carlo-based
dose calculations may be used to confirm that the intended dose distribution
is the one that is delivered. QC is also performed to ensure that the multi-leaf
collimator performs according to the treatment plan. IMRT has other open
issues that need to be addressed, such as how to derive effective and efficient
plans for the particular combination of treatment machine and planning system.
The final section of this document lists a selection of about 40 publications
in 2006 & 2007, indicating that IMRT continues to be a major topic of
current research in medical physics.
As the IMRT technique is refined and improved, its treatment scope will
enlarge and more centres will adopt it, including those in developing countries.
For example, at present, only about 70% of Canadian radiotherapy centres
are able to offer this treatment modality to their patients. To safely and
effectively implement IMRT, highly skilled physicists and dosimetry staff
members are needed to develop and implement the requisite dedicated QA programme.
These professionals are in short supply, especially so in developing countries
that frequently lack the educational and research facilities required for
proper training and education. Of these professionals, medical physicists
provide the technical and scientific backbone for the use of ionizing radiation
in medicine, and modern radiotherapy without their technical input simply
is not possible. Thus, an introduction of programmes for education and training
of medical physicists in developing countries is very important and the
IAEA is well suited to provide help in this endeavour through the CRP proposed
here. By pairing a host institution from a developing country with an agreement
institution from a developed country in a doctoral programme, the CRP would
have a positive impact on medical physics services, teaching and research
in the developing world. It would provide training at the doctoral level
for professionals who would introduce high technology radiotherapy when
required and, in the future, organize high level medical physics educational
programmes in their own countries, i.e., it would “train the trainers”.
The outcome of this CRP will be an optimised use of new treatment modalities
through QA leading to improved patient treatment, and an increased number
of medical physicists engaged in the implementation of this treatment technique.