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.

In 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 this
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. In order to make clear 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, four 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.

Four groups of 10 patients are distinguished in this study:
1. Standard headrest without rotary table
2. Standard headrest with rotary table
3. Individual headrest without rotary table (after approval METC)
4. Individual headrest with rotary table (after approval METC)

In 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 the Klarity R550-T has been selected. The costs of these headrests
are funded by the firm and the HMC.

In 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. In the radiotherapy, the
positioning inaccuracies are analyzed according to the method of "van Herk et
al.".

In the described analysis, day-to-day variations (interfraction) are analyzed
after patient position correction for the four different situations. In
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. In
Excel, this data is processed and displayed. Eventually, the results of the
four different groups described above, are compared.

In 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.

In the software program, the 'match' will be performed with a predetermined
clip box, which will be executed according to the current protocol. In
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.