Improvement of reproducibility during radiation treatment in Head and Neck cancer patients

At the radiation therapy department of the Haaglanden Medical Center (HMC)
Antoniushove, approximately 1,700
patients are irradiated annually, with an average of 60 patients being treated
in the Head and Neck area (H&N).
A benchmark survey had been performed between the radiation therapy departments
in the Netherlands in 2016,
demonstrating that the radiation therapy technique for the H&N patient group of
the HMC Antoniushove needs to be
improved.
The department started to optimize the H&N radiation technology in May 2017.
The plan is to start with a Volumetric
Arc Therapy (VMAT) irradiation technique from October 2017. This means that
with the same dose in the target area,
the critical organs will be avoided as much as possible with a faster treatment
time. The aim is to reduce the toxicity of
the treatment.
ln addition, since April 2017, HMC has used another method of position
verification in the H&N area, the so-called
ConeBeamCT (CBCT). As a result of this improved imaging procedure ('matching'
procedure}, the radiation therapists
can perform the 'match' more accurately. Also, the target area by the attending
radiation oncologist can be checked
daily for changes by comparing it with the planning CT. Finally, the HMC will
use a table to correct for rotations in the
patient position and in doing so optimize the radiation treatment. With these
new methods, multiple CBCT's are made
to monitor the patient accurately during the radiation treatment.
By changing the radiation technique, the reproducibility of the location of the
H&N patients is even more important
because the 95% isodoseline at VMAT is encompassing the target area more
closely. Adding an individual headrest
could improve the reproducibility of the patient's position. Another gain is
that, due to better reproducibility, the margin
of the target area can be reduced from 5 to 3mm. And thus the risk of toxicity
might further decrease.

Currently, a 5-point mask and a standard headrest is used in the H&N patients.
By replacing the standard headrest for
an individual headrest that includes both the head, neck and part of the
shoulders, it is expected that the translations
and rotations will be reduced because the patient is more firmly fixed compared
to the standard headrest. With the
benefit that the radiation oncologist can maintain smaller margins around the
target area, thus saving more healthy
tissue. The individual headrest CBCT's are evaluated both with and without the
rotation of the rotation table. ln order to
clarify what profit the individual headrest adds to the standard headrest and
the use of the rotation table

To find out what the benefits of the different applications are, three
different groups of patients are compared. The use of
the individual headrest as well as the addition of the rotary table are
distinguished.
The acquired data with the new patient positioning technique is used to compare
the data obtained with the addition of
the individual headrest.
Three groups of 10 patients are distinguished in this study:
1. Standard headrest without rotary table
2. Standard headrest with rotary table
3. Individual headrest with rotary table (after approval METC)
ln this way, a distinction can be made between the added value of the
individual headrest and the added value of the
rotary table.

The type of individual headrest was determined by the research team after
testing various types of headrests in healthy
volunteers (working in the HMC radiotherapy department) advised by a team of
two RTTs and two technicians. The
headrest of Klarity: R550-T has been selected. The costs of these headrests are
funded by the firm and the HMC.
ln the HMC, we work with an on-line correction method in which we correct for
positioning inaccuracies on a daily
bases for each individual patient. The positioning differences are determined
by using CBCTs. ln the radiotherapy, the
positioning inaccuracies are analyzed according to the method of "van Herk et
al.".
ln the described analysis, day-to-day variations (interfraction) are analyzed
after patient position correction for the three
different situations. ln addition, the intrafractional variations are
calculated (difference in position before and
immediately after irradiation).
The translations and rotations we find in each patient are collected and count
for the entire group. Based on the
collected data, the vector, the mean translation and rotation can be determined
between the different fractions.
Eventually, the results of the three different groups described above, are
compared.

ln order to be able to measure the patient's inter- and intrafractional
variation, CBCTs are made before irradiation and
after irradiation, according to the current protocols. This method is used by
default when introducing new techniques.
Which profit in accuracy can be achieved with the addition of the rotary table
will be measured as well.
The CBCT is made with a pre-set that meets the requirements to detect changes
in tumor volume according to the
current protocol. The pre-sets of the CBCT in the HMC are adjusted to minimize
the dose in the patient.
ln the software program, the 'match' will be performed with a predetermined
clip box, which will be executed according
to the current protocol. ln addition, the displacement in the shoulder area
will also be registered. This will be done using
a 'mask', which will be placed at a representative point. This 'mask' image
processing takes place after the treatment.

Making of an individual headrest of the head and the shoulders.

An individual headrest will be made on the day of the CT scan, this will take
ten minutes extra on the day of the CT
scan.