Thyroid Cancer Clinical Trial
Official title:
Evaluation of Lancet Blood Sampling for Radioiodine Dosimetry in Thyroid Cancer
Recently published European guidance recommends the evaluation of the radiation dose to the
bone marrow in patients undergoing radioiodine therapy for thyroid cancer. The methods
described in these guidelines require serial blood samples to be taken from the patient,
followed by a sophisticated analysis to determine the radiation dose. However, radiation risk
assessments carried out locally have indicated that a relatively high radiation exposure will
be received by the operator taking the blood samples, which may prohibit this procedure being
carried out routinely.
The radiation dose to the operator will be lowered if the duration of the blood sampling
procedure were reduced. The investigators hypothesize that the use of a lancet and pipette to
collect blood from the finger tip will greatly reduce the time spent in proximity to the
patient, significantly reducing the operator exposure and allowing this procedure to be
performed routinely. The proposed method is also less invasive for the patient compared to
the intravenous sampling recommended in the guidelines. A proof-of-principal pilot project
using radioiodine diluted to the expected concentration in blood has indicated that using
very small volumes of blood (such as from a lancet) does not compromise the accuracy of the
dosimetry measurement when compared to large-volume standard blood samples.
The primary aim of this study is to investigate whether sampling a small volume of blood
using a lancet and pipette can replace standard intravenous blood samples for bone marrow
dosimetry in patients undergoing radioiodine treatment for thyroid cancer. Statistical tests
will determine whether there is a significant difference between the doses calculated using
each blood sampling method. In addition, the investigators will measure the radiation
exposure received by the operator during each procedure using Electronic Portable Dosimeters.
The results of these measurements will be used to quantify the reduction in operator
radiation exposure afforded by the new technique.
Recruitment:
Patients will be recruited to the trial from the pool of routine referrals for this therapy.
Potential participants will receive an information leaflet via the post several weeks in
advance of attendance at clinic. Patients will have the opportunity to telephone the study
team during this time to answer any questions. Patients who are interested in participating
will have the procedure further explained verbally by a physicist on the study team upon
attending for therapy. The patient will then have time to consider whether or not to
participate in the study. Written consent will be sought before commencing the therapy.
Procedures:
In light of the recent guidelines, the proposed new clinical protocol will include blood
samples taken from the patient during the in-patient stay. On the day of treatment, blood
samples will be taken at 2h and 6h after radioiodine administration, at the same time as the
clearance measurements. Thereafter, a blood sample will be taken from the patient once per
day, at the same time as one of the clearance measurements. In addition, a further blood
sample will be taken when the patient attends for whole-body and SPECT/CT scans. These blood
samples will then be analysed in the laboratory using standard radiation measurement
procedures to determine the blood dose according to the European guidelines.
This study will involve the patient having blood samples taken by two different methods at
each of the time points described above. In the first method, a butterfly needle will be used
to gain intravenous access at the antecubital fossa, and a heparinised vacutainer will be
used to collect a 4ml blood sample. The needle will then be removed and the venepuncture site
dressed with a plaster. In the second method, a single-use safety lancet will be used to
puncture the skin on the finger, and a small pipette used to collect a small quantity of
blood. The entire pipette will be transferred to a sample tube for later processing. The
puncture site on the finger will then be dressed with a small plaster. The exact start and
end times for each sample will be recorded using a radio-controlled standard clock.
While carrying out blood sampling, the operator will wear an electronic portable dosimeter
(EPD) to measure radiation exposure. This device will be positioned on the operator's chest
to reflect the whole body dose received, and will be configured to record the radiation dose
as a function of time during the procedure. After the procedure, the data from the EPD will
be downloaded and split into two segments representing each blood sampling procedure, using
the recorded timing information. Each segment will then be integrated to give the total
radiation exposure received by the operator for each procedure. At the end of the treatment,
patients will be asked which of the two blood sampling methods were the most tolerable.
Each sample will be labelled with the patient identification number, the date, time and
radioisotope (I-131). To minimise the risk of spills, the samples will be transferred to a
tray and moved to the Nuclear Medicine Department using a trolley. Sample manipulations will
be carried out in the low level counting laboratory in the Nuclear Medicine Department. Three
1ml aliquots of whole blood will be removed from each vacutainer and transferred to
appropriately labelled sample containers using an Eppendorf pipette. The volume of the
samples collected by pipette will be determined by measuring the weight of the sample and
subtracting the previously determined combined weight of the empty pipette and sample tube.
Once all the blood samples have been collected and processed, measurements will be taken in
an automated gamma counter to determine the concentration of radioiodine. The counting time
for the pipette samples will be increased compared to the intravenous samples, in order to
ensure the final dosimetry calculations are not influenced by the statistical uncertainty in
the measured counts from the smaller volume samples. The resulting data will then be used in
the detailed dosimetry calculations, in accordance with the published European guidelines.
Sample Size:
There is no published data available on the intra-patient variation of bone marrow dose using
either of the two proposed blood sampling methods. Without knowledge of the expected
variances of the measurements in question, accurate sample size calculations are not possible
prior to commencing the study. A sample size of 35 patients will be used in this pilot study
- this sample size was chosen based on the number of patients seen in the department for this
therapy. Recruiting a sample size of 35 patients is achievable within a 2 year time frame.
However, the study will be stopped early if the total annual radiation exposure to the
operators, combined with the total radiation exposure due to normal clinical workload, is
likely to exceed the annual UK dose constraint of 2mSv for whole body radiation exposure (The
Ionising Radiations Regulations 1999, SI 1999/3232).
Data Analysis:
Using the measured concentrations of radioiodine in the blood samples, the radiation dose to
the bone marrow of each participant will be calculated following the methods described in
European guidance (Luster et al, Eur J Nucl Med Mol Imaging 35(10) 1941 2008). This
calculation will be performed for each of the two blood sampling methods, creating paired
measurements of the same variable for each participant. The statistical significance of the
percentage difference in bone marrow dose calculated from each blood sampling method will
then be assessed using a Wilcoxon matched pairs test with the null hypothesis that there is
no difference in the calculated bone marrow doses. This study has 80% power to demonstrate at
the 5% level of statistical significance a difference of no less than 5% between the mean
values for the two bone marrow doses. Therefore statistical analysis of the differences has
80% power to show that the null hypothesis that the difference is no greater than 5% is
tenable, if indeed this null hypothesis holds true in the population.
The radiation exposure received by the operator during each blood sampling procedure will be
measured using an Electronic Portable Dosimeter (EPD) worn on the chest of the operator. The
data will be split into two using the known start and end times of each blood sampling
procedure. The data will then be integrated over each time period to calculate the total
radiation dose for each interval. This will create paired measurements of the same variable
for each blood sampling event for each participant. The statistical significance of the
percentage difference in the radiation exposures received by the operator during each blood
sampling method will then be assessed using a Wilcoxon matched paired test with the null
hypothesis that there is no difference between the measured radiation doses. The aim in this
case is to show statistically that the null hypothesis of no difference in the mean radiation
doses for the 2 techniques is untenable.
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