NIHR i4i TRAPS Project (2015-2017)
Transmission - Radiotherapy Active Pixel System (TRAPS):
Towards a Clinical Prototype for Real-Time 2D Verification of
Intensity Modulated Radiotherapy.
Background
Many cancer patients are treated using X-ray irradiation. For
some cancers this is very difficult if the tumour is located close
to organs sensitive to radiation. Advances in the way radiotherapy
is delivered to patients means that tumours can be much more
accurately targeted, greatly reducing the damage to surrounding
tissue and sensitive organs. Finely engineered components in
the treatment machine shape the radiation field directed at the
tumour; if the beam components are misaligned or are delivered in
the wrong sequence, it may not be easily recognised or immediately
spotted. Errors can result in the wrong treatment being delivered,
or as in some high-profile cases, delivery of a fatal overdose.
Checks are made before, and ideally during, treatments to avoid
such errors. The patient radiation dose needs reporting across the
whole radiation field and the radiation beam monitored without
perturbing it.
Our project team has developed a novel method for detecting
errors during treatment using a thin silicon panel that does not
interfere with the upstream radiation beam. The system, related to
digital camera technology, is fast and cost-effective, has been
proven to work for a range of standard radiotherapy treatments and
will now be extended to work for new radiation delivery systems
which move during treatment. The aim is to speed up data collection
and validate the system for real-time intervention in cases of
error. This will enable reporting of serious deviations from the
planned treatment and provision of detailed dose distribution
reports. Any errors can then be dealt with prior to treatment
completion.
Team
This project was a collaboration between clinical scientists,
medical physicists, radiographers and academics in the Medical
Physics & Bioengineering Department (MPB) in UH Bristol &
Weston NHS Foundation Trust, the HH Wills Physics Laboratory at the
University of Bristol, the College of Medicine in Swansea
University, the Rutherford Appleton Laboratory (STFC) and
industrial partners, IBA and vivaMOS. The project was led by
Dr Diane Crawford who is now retired but was a former Director of
MPB. The focus of the project was on further development of
the detector, covering a larger radiation field, extending from a
static to a dynamic system, commercial collaboration and clinical
application.
Results
The outcome of the project was the development of a novel
radiation detector with low beam attenuation (ie minimal reduction
in treatment beam intensity) and improved resolution, compared with
competing devices capable of monitoring errors during the treatment
of cancer with radiation (radiotherapy). This project focused
on redesigning our earlier device to demonstrate our ability to
monitor treatment of new dynamic radiation delivery systems that
move during beam delivery e.g. Volume Modulated Arc Therapy (VMAT),
and cover larger treatment areas, more typically required
clinically. We also developed methods to speed up data
collection and determined that the system is capable of real-time
intervention in cases of error. This will enable reporting of
serious deviations from the planned treatment and provision of
detailed dose distribution reports. Any errors can then be dealt
with prior to treatment completion.
During the project we sought input from patient and clinical
users and there was keen interest in this project at two focus
group workshops which we hosted. Understanding how this
device is viewed by patients has enabled us to establish key design
features for the final detector design. Patient and user
representatives also contributed to project steering group meetings
and their desire to ensure this development becomes a clinical
reality has also been a key motivator for the project team.
Team expertise in fabrication of radiation detectors and
modelling of clinical radiation equipment enabled us to achieve the
major project objectives. For 2 years the project work
focused on using Achilles sensors (6 x 6 cm) available for purchase
when the project work started. Subsequently a larger sensor
(LASSENA) became available for purchase which could cover a greater
treatment field area. NIHR agreed to our extending the project time
to enable us to demonstrate the potential for using this sensor
within the TRAPS system. Our results have been encouraging and
detailed discussions continue post-project with key commercial
companies who are actively considering bringing the device to
market.
