Evaluation of Ultrasound Probe for Use in Adaptive Bladder Radiotherapy
All experiments and data analysis will be performed in the Magnetic Resonance Imaging (MRI)
and Radiotherapy departments respectively, at the Queen Elizabeth Hospital.
Five volunteers will be recruited to this study. They will each be required to follow a
documented drinking protocol prior to each of three scan sessions. The drinking protocol is
specific to this study and will not be intended for use with patients. To address the
primary endpoint of the study (i.e. the precision of the ultrasound probe for measurement of
bladder volume), measurement of a wide range of bladder volumes is required. In order to
address this aim while making efficient use of the limited available MRI scanner time, the
drinking protocol has been designed such that the volunteer will begin each scan session
with an empty bladder and finish it with a full bladder. To this end, each volunteer will be
required to void their bladder upon arrival and then consume 500ml of water immediately
prior to the start of the scan session.
Each volunteer will then be positioned on the scanner couch according to the same protocol
used for patients and alternate MRI and ultrasound scans will then be acquired. Given the
time required for each scan it is anticipated that five MRI scans and fifteen ultrasound
scans (three scans at a time to reduce the noise on the results, i.e. ultimately giving five
ultrasound bladder volume measurements) will be acquired in each session. Each volunteer
will be asked to attend for three sessions over the course of a number of weeks so that the
repeatability of bladder filling patterns can be determined.
Data processing and analysis
The volume measurements from the ultrasound probe will be recorded and each of the MRI
images will be exported to the Radiotherapy department where the bladder volume will be
determined. The precise timings of all scan acquisitions will be recorded during the imaging
session. Bladder volumes measured by the ultrasound probe, which can be read instantly, will
be recorded during the session. To evaluate the primary endpoint, the precision and accuracy
of the ultrasound probe will be quantified by comparing the measured values to those
expected from the MRI volumes. Each volume measurement from the MRI scans will be checked by
a second observer to minimise any associated researcher error.
To evaluate the secondary endpoint, the imaging protocol described above will provide up to
15 MRI images for each volunteer that can be used to inform a comparison of the different
adaptive strategies. However, since patients are always asked to empty their bladder prior
to radiotherapy treatment (in order to minimise the volume that receives radiation), the
deliberately wide-ranging bladder volumes that will have been measured in this study will
not be representative of those that would be observed in clinical practice. To address this
problem, a suitable dataset that quantifies the distribution of bladder volumes encountered
in a typical patient cohort will be used (Christie dataset, permission obtained.Software
will be written to randomly assign a bladder volume to each day of each volunteer's
'treatment'. The MRI scan from that volunteer that most closely corresponds to the selected
volume will then be assigned for that day's treatment. This will be repeated for the full 20
days of treatment and the importance of each MRI scan can then be factored into the results
The treatment planning system within the Radiotherapy department will then be used with the
MRI scans to simulate a range of different 'treatments' according to each of the different
adaptive bladder radiotherapy strategies to be compared. The different strategies are
- Conventional strategy: This is the current standard treatment, in which the patient
plan is prepared based on an initial CT scan of the patient with an empty bladder and
no account is made of subsequent daily variations in bladder shape and volume.
- Plan-of-the-day strategy: Based on an initial CT scan of the patient with an empty
bladder, three different treatment plans are created based on an assumption of how the
bladder might expand. These are intended to simulate empty, partially full and full
bladders. The patient is scanned before treatment each day and the most appropriate
plan is selected for treatment.
- Dynamic strategy: Three different treatment plans are created based on a series of
initial CT scans of the patient with empty, partially full and full bladder. These
would be expected to directly represent the empty, partially full and full bladders for
the individual patient. The patient is scanned before treatment each day and the most
appropriate plan is selected for treatment.
- Composite strategy: The patient is CT scanned with an empty bladder and treated
according to the Conventional strategy for the first 7 days of treatment with daily
imaging. The first 5 daily scans of the patient are used to generate plans based on
small, partially full and full bladder. From the 8th day of treatment the daily image
is used to select which of these plans is appropriate for treatment.
Data processing of the MRI scans will be carried out retrospectively. The MRI scans will be
anonymised and exported to the Radiotherapy department. The data will then be used to (i)
acquire bladder volume information to compare with that acquired from the ultrasound probe
and (ii) prepare and evaluate radiotherapy treatment simulations to investigate the benefits
of different adaptive bladder radiotherapy strategies
Comparison of different adaptive techniques will focus on how much radiation is received by
the bowel and the extent to which the radiation misses the disease on any day of treatment.
Time Perspective: Prospective
Accuracy of ultrasound measurement of bladder volume in comparision with gold standard MRI measurement
The principal aim of this study is to quantify the accuracy of ultrasound measurement of bladder volume in comparision with gold standard MRI measurement. To do this, each of the five volunteers will have 5 repeat measurements of each imaging modality (ultrasound and MRI) within each 45 minute scan session as the bladder volume increases in response to the specified drinking protocol. Each volunteer will undergo three scan sessions over three weeks. Study participants will not receive follow-up. An accuracy of +/-10% would be considered sufficient to inform future studies.
Anjali Zarkar, FRCR
United Kingdom: National Health Service