METHODS
Thirty lung cancer patients having palliative thoracic RT indication were randomized into three different
set-up positions using different immobilization devices (Group I: arm along the body, Group II:
lung board, and Group III: arm supported board). The treatment field center deviation was measured
on sternal (X and Y axis) and axillary (z and ? axis) cross. In addition, parameters such as age, pain,
pulmonary function test, set-up time, the temperature difference between the treatment room and the
outside environment, and patient education level that may cause set-up were evaluated.
RESULTS
Mean intra-fraction field center deviations of 5.66±4.15 mm were observed in the right (z) axis (p=0.049)
and 5.53±4.81 mm in the left (z) axis (p=0.015) in Group II which were statistically significantly larger
than the deviations in other groups. A statistically significant correlation was found between the indoor
and outdoor temperature difference and set-up time.
CONCLUSION
Both set-up positions of Groups I and III, gave better results than the position of Group II. According
to our results, if a lung board will be used, adding the arm supporting accessory will be necessary.
Random errors can be minimized and the set-up quality improved by using appropriate immobilization
devices, minimizing the total set-up time and balancing the in and outdoor temperature by air
conditioning system.
Keywords: Immobilization device; inter-fractional motion; intra-fraction motion; lung cancer; set-up error; thoracic radiotherapy
Thoracic RT is an important treatment modality that
is frequently used to palliate many symptoms such as
hemoptysis, cough, dyspnea, and pain, with a clinical response
rate of 50-80%.[
Minimizing set-up errors is the first step of the
treatment planning. Finding an ideal, simple position
with appropriate immobilization devices that is easily
reproducible daily as well as providing the best immobilization
without adversely affecting the dose distribution
is one of the factors that will increase the quality
of the treatment.
Today, many different expensive accessories are
used for immobilization in thoracic RT such as wing
boards, vacuum beds, lung boards. The choice of these
accessories depends on the needs of the patient, the RT
planning technique, the technical facilities of the clinic,
and of course, the cost of the equipment to be used. It is
known that in developing and less developed countries
obtaining expensive accessories are very difficult and
sometimes impossible. A consequence, some simple
and inexpensive accessories have to be used.
In this study, it was aimed to compare the treatment
field deviation values of patients diagnosed with lung
cancer who underwent palliative thoracic RT with AP/
PA fields, with different set-up positions and immobilization
devices if necessary such as arms along the body,
lung board, arm supported lung board, and to evaluate
the factors influencing these treatment field deviations.
Patients
The inclusion criteria were: Histopathologically obtained
lung cancer diagnosis, Karnofsky performance
scale score (KPS) ≥50, no severe dyspnea and pain, literate
≥18 years old. All patients were treated with two
AP/PA fields for palliative intent.
Simulation
The treatment position to be applied to the patients was
determined using the Random Numbers Table. The patients
were randomized to three arm positions through
this method by Sinmed® RT accessories.
• Group I: Arms along the body in supine, neutral
position (Fig.
• Group II: Arms fixed over the head on lung board
(Fig.
• Group III: Arms over the head on the lung board
and using bilateral arm supports board (Fig.
All patients were simulated in the supine position according to the randomization arm, and tomography was taken with a 5 mm slab thickness.
Technique and Dose of RT
Three-dimensional conformal RT was planned on
Oncentra Master Planning System® using Siemens®
Emotion Computed Tomography with anteroposterior
same isocenter fields with 18 MVX photon energy. The
patients were treated with median 10 (2-20) fractions.
Patient Set-ups
The information about the identity data, pathological
diagnosis, stage, pain scores (between 0 and 10), and
pulmonary function test (PFT) of the patients were
obtained before the treatment. On the treatment days,
before the patient entered the set-up, the outside air
temperature in the shadow and the treatment room
temperature were measured by the responsible physicist
using a digital thermometer to look for the influence
of temperature changes on field deviation.
After the set-up disposition, time was measured with a chronometer. Electronic portal imaging (EPI) was prepared, the treatment room was left, and the treatment was begun. The chronometer continued to work during the EPI control.
When the duration of the anterior field was completed, the researcher entered the treatment room, went by the patient and stated that s/he should still not move; the time of the anterior field was recorded from the chronometer and the field deviation measurements were measured on the six axes. After completion of the measurement process, as in daily practice, without any correction in the patient's position, the chronometer was reset for the posterior treatment field, and the same operations were repeated.
Measurement of Field Deviations
For measurement of the field deviations, three crosses
including two lateral (axillary line) and one anterior (on the sternum) were tattooed on the trunk (Figs.
These measurements were made in every fraction for total two-fraction treatments, in 1st, 3rd, and 5th fractions for total of 5-fraction treatments, in 1st, 3rd, 5th, and 10th fractions for total of 10-fraction treatments and in 1st, 5th, 10th, and 20th fractions in total of 20-fraction treatments.
Calculation of Intra-fractional Field Center Deviation
At the end of the treatment of the anterior and posterior
fields, the field deviations according to the center
of the laser crosses were recorded.
The study aimed to determine intra-fractional field deviation. The deviation of the center point of the laser cross on the patient with respect to the central axis of the treatment field was recorded. The absolute amount of movement of the patients, regardless of their direction, was calculated. This movement is mentioned in the text as the patient"s "field center deviation value" (FCDV).
These measurements have been explained with
three examples in Figs.
First example: In Fig.
Second example: In Fig.
Third example: In Fig.
Taking the "average" of these measured values for each fraction, the "mean total deviation" of each patient was calculated for each axis and these "mean deviation values" (MDV) were used for the statistical analysis.
Statistical Analysis
Non-parametric tests were used for statistical analyzes.
First, we evaluated the MDV of each axis for each
group, and then inter-fractional differences were evaluated
for each measurement.
In the comparison of the field deviation values, the deviation values among the groups in each axis were evaluated using the "Bonferroni corrected Kruskal- Wallis Test" and the in-group inter-fractional measured field deviations for each axis were evaluated using the "Non-parametric Friedman Test."
Parameters such as the pain score, PFT, age, educational status, indoor out-door temperature difference, and the set-up times that can affect the field deviation values were evaluated with the correlation test.
Statistical significance was accepted if p<0.05. The SPSS 15 version was used in the study.
Statistical Results of the Measurements
Assessment of Mean Intra-fractional Field Deviation
Values of the Axes
The field deviation values of the axes of all three groups
are displayed in Table
Assessment of Inter-fractional Field Deviation
Values Measured for Each Axis
The inter-fractional MDV and the maximum deviation
values in each axis within each group are demonstrated
in Table
Different types of in-group field center deviations were observed in different axes among fractions, although statistically significant difference was determined in none of the axes. Although not statistically significant, it was noticed that the inter-fractional field center deviations in the z axis were observed to be lowest in Group III patients. It was the highest in Group II patients. In Group II, the deviation values gradually decreased and the decrease was 2.5 times between fractions (from 8.1 mm in first measurement to 3.25 mm in last measurement).
In Group III the least field center deviation difference was observed for Z axis. In the other groups, the FCDV s were varying.
Correlation Test Data Regarding the Parameters Affecting
the FCDVs
A statistically significant correlation was found between
FCDV and the indoor and outdoor temperature
difference and between FCDV and the set-up time of
the patients (Table 4). No correlation was found between
FCDV and the pain scores and between FCDV
and education status. Most of the data about age and
PFT showed a statistically significant correlation with
FCDV but without any clinical importance due to inconsistent
results.
In the literature, different systems including the lung
board, T-bar, vacuum bed, chest mask, thermoplastic
mask covering the arms and the face, and vacuum pillow
are seen to be used for patient immobilization during
thoracic RT.[
Bentel et al.[
In a study attempting patient stabilization with the
thermoplastic chest mask, a reduction of 3-4 cm was
detected in chest wall movements.[
In the study of Halperin et al.,[
In another study, an air-injected blanket, which
covered the patient and could be fixed onto the table
and reduce the breathing amplitude was tried for immobilization
of the patients undergoing lung and abdomen
radiation. With this system that aimed to reduce
the respiration depth, the anteroposterior diaphragm
movements decreased to 0.7 cm from 2.6 cm and the
craniocaudal diaphragm movements decreased to 1.3
cm from 2.7 cm.[
In the study of Giraud et al.,[
Studies evaluating the comparison of two different
set-up positions have been identified in the literature. [
In our study, most of the major deviations were observed
in the patient treated with lung boards. In the literature,
it was seen that the measurements were made only
on the (x) and the (y) axis, and in the study of Giraud and
Halperin, additionally on the (z) axis.[8-10,13] However,
in our study, in addition to the (x), (y), right and left (z)
axis, the (θ) axis was measured in the craniocaudal direction
in the lateral crosses in a more detailed way.
We observed a significant deviation with different
accessories. In our study, it was found a deviation of
more than 5 mm in both right and left (z) axes in patients
who had been treated with the lung board (Group
II). The mean field center deviations were determined
as 5.66±4.15 mm in the right (z) axis (p=0.049), and
5.53±4.81 mm (p=0.015) in the left (z) axis. These values
detected on the (z) axis were found to be similar to
the proportions of the patients whose measurements
were made with Halperin's T-bar.
In our study, the mean field center deviation"s standard
deviation values measured in each axis in the
arm-supported lung board where the best stabilization
was provided (1.63-4.81 mm) were lower than the values
determined in the study of Halperin (3.7-5.4 mm).
The mean FCDV s (1.92-2.26 mm) in our study
were close to the values found in the study of Giraud
(2.2-3 mm). As a result of these data, the lung board
providing the worst immobilization was found to have
FCDV s similar to the literature.
In patients who had been treated with an arm along
the body, the most suitable for the anatomical position,
FCDV ranged between 0.41 and 3.06 mm. In this group,
the mean FCDV was found to be 2.12 mm on the right
and 2.13 mm on the left on the (θ) axis. These values were
found to be higher than the values of the other two groups,
although statistically non-significant. This difference was
suggested to be due to the positional arm movements.
In patients treated with arms along the body, although
the CT reference points were placed on the
body during the simulation, it was seen that the side
crosses coincided on the arm after the set-up. Although
the patients do not move their trunks, any movement in
the arms gives the impression that the fields are deviating.
For this reason, for patients who received treatment
with arms along the body, especially in posteriorly located tumors, it is suggested that planning the lateral
crosses to allow drawing on the body and evaluating the
set-ups by performing SSD control would be proper.
In our study, although the difference among the
treatment fractions measured in the three groups of
patients was not statistically significant, the deviation
values in the right (z) axis in Group II were determined
to gradually decrease in the following days of the treatment.
As a result of this finding, it can be thought that as
the treatment days progress, the patients get used to the
treatment and can be immobile during the treatment.
It should be noted that a 45 mm maximum field center
deviation was observed in this study. In addition, it
was observed that the maximum value of mean intrafraction
field center deviation could reach 15 mm. It
should be considered that these large deviations may
have important clinical consequences in hypofractionated
treatments such as SRS/SBRT which require high
conformality and a steep dose gradient.
In the inter-fractional measurements, for Group
I, the mean deviation value on the left (θ) axis was
observed to be about two-fold greater than the other
mean values, and the maximum value was 30 mm
maximum in one patient. When the data were analyzed,
the patient who had this value was found to be
under-educated, to have chronic obstructive lung disease,
advanced stage small cell lung carcinoma with
solid organ and lymph node metastases, KPS 60 and
a pain level of 6/10. This high FCDV was suggested to
develop from the above-mentioned negative factors.
In the review of Coen et al. investigating set-up errors,
in all studies including 8-35 patients and based
on EPI measurements, mean values were provided, as
in our study. The magnitude of systematic and random
errors was observed to range between 1.8 and 5.4 mm
in the review. Our range was similar to the literature.
The relationship between the FCDV and the general
condition, age, the patient"s pain, the indoor-outdoor
temperature difference, and the set-up time was investigated.
However, the statistical interpretation of some
parameters was incompatible with the clinical importance.
This situation is thought to be due to the small
number of patients.
The strength of our study was that the evaluation of
three different set-up positions using different devices
with four axes in thoracic irradiation and some possible
factors that may have affected the patient movements
was evaluated in the same study. The inadequacy
of our study was the margin of error due to manual
measurements and the insufficient quality of the EPI
films that were initially planned to be evaluated.
The authors thank Professor Dr. Ayse Nur Demiral for her contribution to the correction of the manuscript.
Peer-review: Externally peer-reviewed.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: The study was approved by the Dokuz Eylül University Ethics Committee (no: 2011/09- 19, date: 24/03/2011).
Financial Support: None declared.
Authorship contributions: Concept - Z.G., H.E., A.Y., L.Y., R.Ç.; Design - Z.G., H.E., A.Y., L.Y., R.Ç.; Supervision - Z.G., H.E., A.Y., L.Y., R.Ç.; Funding - Z.G., R.Ç. Materials - Z.G., R.Ç.; Data collection and/or processing - Z.G., A.Y., L.Y.; Data analysis and/or interpretation - Z.G., R.Ç., H.E.; Literature search - Z.G., R.Ç.; Writing - Z.G., R.Ç.; Critical review - R.Ç.
