METHODS
In the anthropomorphic phantom, the junction area and organ at risk doses were determined for eight
different craniospinal irradiation (CSI) techniques with the help of thermoluminescent dosimeter
(TLD) and treatment planning system (TPS). These techniques differ in terms of the parameters of the
table being angled/un-angled, using block/multi-leaf collimator, and being in supine/prone position.
RESULTS
There was no statistically significant difference between TPS and TLD doses of all techniques. The lowest
doses of cribriform plate are 1.82 Gy in PM, and 1.84 Gy in PAM. The lowest dose in lenses is 0.19 Gy
in PB. The lowest dose of thyroid is 1.27 Gy in PB and highest dose of PAM is 1.35 Gy. Average small
intestine dose of 1.92 Gy in non-table angle decreases to 1.08 Gy with table angle. The highest kidney
doses are 0.14 Gy in SM. Ovaries take an average dose of 0.09 Gy in non-table angled and average of 0.13
Gy in table-angled techniques.
CONCLUSION
It has been determined that CSI technique in supine without table angle and protected with special
blocks, is superior to other techniques due to its better dose homogeneity in treatment volume, providing
immobilization in daily use and ease of application.
Keywords: Awareness; educational level; electronic survey; knowledge; oral cancer; public health
Several methods have been improved to provide the
bonding between the brain and the spinal field, such
as adjacent area use, gap use, wedge filter entry, beam
straightening, and junction movement.[
One of the most commonly used techniques for CSI
is Asymmetric Collimation Techniques (ACT) and the
other is Divergence Matching Techniques (DMT). The
aim of the ACT, in which half of the beam is closed
asymmetrically with the help of collimators in mutually
parallel cranial areas and the upper spinal area, and
the other half is used, is to reduce the hot spots that
may occur at the field junctions by reducing the geometric
half shadow.[
In DMT; an appropriate angle is given in the right
and left cranium areas. In the spinal area, the table
is rotated 90° and the gantry angle is given so as to
eliminate the beam divergence. Thus, the beam edges
are made parallel to prevent the formation of hot
spots.[
In most radiotherapy department, CSI is performed
in the prone position, with the opposite fields enclosing
the entire brain and the upper cervical spine covering
the caudal extent of the singular sac. Since children
who are to be treated with CSI are required to undergo
anesthesia, they are treated with supine technique.[
In this study, using ACT and DMT, which are
widely used because of the simplest, most reliable and
useful techniques among CSI, the application of these
techniques in the prone and supine position was dosimetrically
investigated and block or Multi-Leaf Collimator
(MLC). The difference to be made by the protections
using MLC was measured. In addition, it was
investigated whether the table angle would be beneficial in reducing the hot spots caused by the overlap of
the areas due to the divergence of the rays in the neck
joint area.
The aim of this study is to show the effect of the
table angle on critical organ doses in the junction areas
of CSI, to determine the most appropriate technique
for clinical practice by increasing patient comfort and
to prevent set-up errors.
For this purpose, TLD slots in prepared containers
(density 0.99 g/cm3) are painted in green and red colors
and separated from each other (Fig.
TLD: Thermoluminescent dosimeter.
To precisely determine the location of the TLD
rods to be placed in the dose measurement points determined
in the junction areas and critical organs, 0.5
mm diameter and 6 mm long lead wires were placed
in the TLD slots in the prepared plugs and the CT of
the Rando Phantom was taken again under the same
conditions as the first installation. Dose measurement
points are contoured in CT sections that transferred to
the TPS (Fig.
While determining the treatment areas, to prevent set-up errors during irradiation, the origin was determined by placing markers in three points for each position, one on the front or back, and one on each side for the set-up of the supine and prone position at the level of the cervical 2nd vertebra. There are four treatment fields; two opposite cranial fields, the upper spinal, and the lower spinal fields, which are the standard treatment fields of the CSI technique.
In this study, treatment plans were made for all techniques with 6 MV photon energy suitable for CSI depth using Elekta linear accelerator.
With using TPS the treatment fields for different
parameters, including supine (SB: Supine, non-angled
table and blocked, SAB: Supine, angled table and
blocked, SM: Supine, non-angled table and with MLC,
and SAM: Supine, angled table and with MLC) and
prone (PB: Prone, non-angled table and blocked, PAB:
Prone, angled table and blocked, PM: Prone, non-angled
table and with MLC, and PAM: Prone, angled table
and with MLC) positions were determined using
ACT and DMT together (Fig.
Using ACT, the isocenters are placed at the same
depth and the axis passing through the isocenter circles
is centered on the spinal plane to ensure that the dose
distribution is homogeneous (Fig.
SB: Supine, non-angled table and blocked, PB: Prone, non-angled table and blocked, SAB: Supine, angled table and blocked, PAB: Prone,
angled table and blocked.
When planning the treatment, first the upper spine field was adjusted in the supine position 180° and in the prone position with a 0° gantry angle allow the beam enter to the body from the back. The upper limit is the cervical 2-3, vertebral level was set to pass under the jaw to protect the oral cavity and the largest treatment field was opened. The upper spinal field isocenters is 20 cm below the cranial field. The lateral borders were expanded to leave the vertebrae in 1 cm. Cranial fields; the cervical field opening asymmetrically to the 2-3. Vertebra level and the lower border rotated to overlap with the upper limit of the collimator upper spinal field, with the gantry angles of 90 and 270, with the area boundaries at the front, back and upper, 2 cm in the skull. For this study; the collimator angle was calculated to be 11° according to the field dimensions.
To ensure the homogeneous dose distribution an appropriate normalization point was determined in the center of the two opposite fields, not too close to the blocks, and a dose of 180 cGy/fraction was given.
The upper part of the lower spinal field was opened so that the jaws would open asymmetrically to intersect the upper spinal field at the level of the vertebrae and the lower border to enclose the sacral 2. vertebra where the subarachnoid space, the last seen of the cerebrospinal fluid, ended. While the lower spinal field, intervertebral and sacral foramens remain within the treatment field, blocks are drawn as if the other healthy tissues were in the lower spinal area protection. The dose is normalized to the appropriate depth on the central axis to cover the whole spine.
In the supine and prone position, DMT was also used
in addition to the standard fields prepared with ACT in
table angled and blocked/MLC plans (Fig.
In the supine position, the angle which should be given to the table in cranial fields and the angle given to gantry in the lower spinal field are calculated to eliminate divergence in the neck and spinal junction region.
The right cranial field was gantry 270° while the table
angle was -3°, and gantry 90° while +2° was given to
table for eliminate the divergence (Fig.
In the lower spinal area, the table is rotated 270°
and adjusted to the divergence of the lower limit of
the upper spinal field by giving a 169° gantry angle. In
the supine position, the divergence was eliminated by
giving a table angle of +2° when the right cranial field
was 90° and a table angle of -3° when the left cranial
field was 270°. The lower spinal area has a table angle of
2700 and a gantry angle of 110 (Fig.
Considering the necessity of taking the treatment dose of the cribriform plate completely, the most appropriate dose measured by TLD; 1.82 Gy with 101.11% in the PM technique, and the PAM technique also yielded a gain of 102.22%-1.84 Gy.
When critical organs are taken into consideration, it has been determined that the most appropriate dose of the cribriform plate, which is one of the most frequently encountered areas of recurrences, is obtained by PAM technique. Cribriform plate doses obtained with MLC protection showed an average reduction of 4% compared to those with specific block measures.
For all the techniques we applied, although the TLD doses we obtained in the lenses were very close to each other, the lowest dose was found to be 10.56% in the PB technique and 0.19 Gy/fraction. For the eight techniques we examined, the doses received by the lenses were extremely low and found to be within acceptable limits.
Cochleas within the entire volume treatment field need to be protected as much as possible from high doses. The lowest dose in this study was 94.44% at SB technique and 1.7 Gy/fraction; the highest dose was found to be 1.91 Gy/fraction with 106.11% in the PAM technique; and the values obtained with all techniques were within the limits.
The lowest doses for the thyroid were 70.66% in the PB and SAB techniques and 1.26 Gy/fraction of 25.6 Gy; the highest doses were seen in PAM from table-angled techniques with doses of 75% and 1.35 Gy/fraction.
For small bowel; the table is angled to the lower spinal field and the overlapping area resulting from the divergence in the junction region is removed, the nonangled table techniques dose was found an average of 106.66% with 1.92 Gy/fraction, dose to be reduced by an average of 60.14% and 1.08 Gy in planning techniques using a table angle.
The highest kidney dose was 7.78% with the SM technique and 0.14 Gy in the fraction was 2.8 Gy in total and was considered to be quite low and all techniques were feasible.
The table-angled techniques used to reduce excess doses in the SB receive an average of 0.09 Gy of 1.8 Gy/fraction, while the ovarian doses of the treatment area approaching the ovaries receive a total of 2.6 Gy of doses of 0.13 Gy/day.
The doses taken at the measuring point B1 on the spinal cord in the neck junction area are similar for all techniques examined. For all techniques, a 95% dose (1.71 Gy) of whole spine coverage was provided, and the maximum dose in the junction region was prevented from exceeding 107%.
In the spinal junction region, the measurement point S1 on the spinal cord is provided between 98% and 105% doses for the eight techniques. In addition, since the divergence has been removed from the junction area in the table angled techniques, it has been determined that the structures in the abdominal region prevent the excessive desire of the non-angled table techniques.
Planning and TLD measurement dose values of eight irradiated techniques were compared using the SPSS 13.0 statistical program.
As a result of Spearman and Pearson correlation
tests performed for planning and irradiation dose
profiles of different CSI techniques, no statistically
significant difference was found, and a strong correlation
was found between TPS and TLD measurements
(Table
The doses given to the cranium and spinal field vary
in CSI used in the treatment of diseases such as medulloblastoma,
ependymoma, germinoma, pinealoblastoma,
and acute lymphoblastic leukemia, which are
central nervous system tumors.[
CSI doses vary according to factors such as tumor
type, age of the patient, and protocol of treatment applied.
For medulloblastomas, we have a dose of 36 Gy
to the spinal field with 1.8 Gy fractions and 54 Gy with
an additional dose of 18 Gy in the cranial area and organ
doses in the study were evaluated on this dose prescription.[
The data obtained with TLD and TPS were found
to be compatible with each other in the techniques
applied in our study. If we need to evaluate the techniques,
we use to take the treatment dose of the cribriform
plate in full, the most appropriate dose is; PM
technique was obtained with 101.12% and 1.82 Gy,
respectively, while the PAM technique was found to
be 102.22% and 1.84 Gy. The highest obtained dose,
107.22% and 1.93 Gy, was found in the supine position,
table angled, and block-protected technique.
Cribriform plate doses obtained with MLC protection
showed an average reduction of 4% compared to those
with specific block measures. Hood et al.[
The minimum cataract formation doses for the lens
were given as 5 Gy for T5/5 and 12 Gy for T50/5. Despite
being very close for all the techniques, we are practicing,
the lowest dose is 10.9 Gy/fraction, and 5.7 Gy total/
fraction, in the case of the PB technique; the highest
dose was obtained in SM and SAM technique 12.22%
and 0.26 Gy/fraction in total 6.6 Gy. For eight techniques,
the doses taken by the lenses are extremely low
and within acceptable limits. Since there is no significant
difference between lens doses obtained with MLC and
special block protections, both are considered to be feasible.
Ozkan et al.[
The entire volume of the cochlea within the treatment
field should be protected from possible high
doses. The tolerance doses of Meniere"s syndrome for
cochleas are 60 Gy for T5/5 and 70 Gy for T50/5. In this
study, among the eight techniques examined, the lowest
dose was obtained in the SB technique yielding 94.44%
and 1.7 Gy/fraction, which is equivalent to a total dose
of 51 Gy with additional treatment regimen and is compatible
with the literature.[
For thyroid hypothyroidism tolerance doses of the
thyroid gland were 4.5 Gy for TD5/5 and 15 Gy for
TD50/5.[
The table angled in the lower spinal area has been
removed from the overlapping region resulting from
divergence in the junction area, preventing the intestinal
volume (about 160 cc) from being overdosed in this
region. While the non-angled table had an average of
106.66%/fraction, 1.92 Gy in the fraction, and 38.4 Gy
in total, the planning technique using the table angle
took an average of 60.14% and 1.08 Gy in the fraction
and 21.6 Gy in the fraction. Despite the advantages of
the table angled technique, it must be considered that it is a difficult technique to apply and causes the prolongation
of the treatment duration.
The minimum acute and chronic nephrosclerosis
doses for kidneys were 20 Gy for T5/5 and 25 Gy for
T50/5. For the eight techniques, we used in our study,
the highest supine position from the kidney dose was
considered to be 7.8% in the technique of table open
and MLC preservation, 0.14 Gy in the fraction and 2.8
Gy in the fraction, and all techniques were feasible. Lee
et al.[
Girls were given sterilization dose for ovaries 2-3
Gy for TD5/5 and 6.35-12 Gy for TD50/5.[
For the spinal cord, the tolerance of the 5 cm area is
TD5/5 50 Gy and TD50/5 is 65-70 Gy. After radiotherapy
2nd and 4th months, the spinal cord temporary radiation
demyelination (Lhermit Syndrome) may develop,
in which case the sensation of sudden electrification
that spreads from the hand to the arm and bicep when
the patient moves to cause the spinal cord to stretch.
This diagnosis heals spontaneously within 5 months.
When the tolerance doses of your spine are exceeded,
it is observed 6 months after the treatment of persistent
radiation myelopathy.[
In the current study, the doses received at the measurement
point B1 on the spinal cord in the neck junction
area were similar for all the techniques examined.
However, to prevent the dose, drop at the edge of the
field, the table angled technique has been shown to
increase the dose values at the junctional area, as the
normalization point non-angled table technique was chosen more deeply than the skin according to the
normalization point. For all techniques, a 95% dose
(1.71 Gy) of whole spine coverage was provided and
the maximum dose in the junction area was prevented
from increasing above 107%. It is preferable to use a
supine and non-angled table technique, which is easier
to apply and the dose distribution is more homogeneous.
In this study, it was ensured that the doses of measurement
point S1 on the spinal cord in spinal junction
area were between 98% and 105% of doses in all techniques.
However, it is seen that the supine technique is
better able to be implemented with fewer setup errors
because it is easier to make the spine parallels the treatment
table according to the supine technique. However,
since the prone technique can be controlled before
treatment, it is a safer technique, despite the difficulty
of application, compared to supine techniques. In addition,
the table angled techniques in the area of abdominal
constructions of the overdose, avoid overlapping.
When we consider all the techniques we examined in the study in general, it can be said that it is a safer technique compared to the supine techniques, since the junctional areas can be controlled before the treatment in the techniques planned in the prone position. However, since it is easier to keep the spine parallel to the treatment table in supine techniques compared to prone techniques, it is seen that they can be applied better with less set-up error.
The CSI technique, which is also used in our clinic, is planned in the supine position without using a table angle, and by protecting with special blocks; it has been determined that it is superior to other techniques due to its better dose homogeneity in the whole treatment volume, the compliance of critical organ doses to the literature, providing immobilization in daily use and ease of application.
Note: This study was presented as a poster presentation at the 9th National Radiation Oncology Congress in 2010 and was included in the abstract book.
Peer-review: Externally peer-reviewed.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: This was a phantom study. No patient data were used and no ethical committee approval was required.
Financial Support: None declared.
Authorship contributions: Concept - O.Ü., S.K., N.O., M.K., İ.O., Y.A., D.Y.; Design - O.Ü., S.K., N.O., M.K., İ.O., Y.A., D.Y.; Supervision - O.Ü., S.K., N.O., M.K., İ.O., Y.A., D.Y.; Funding - O.Ü., S.K., M.K.; Materials - O.Ü., S.K., M.K.; Data collection and/or processing - O.Ü., M.K.; Data analysis and/or interpretation - O.Ü., M.K.; Literature search - O.Ü., S.K., N.O., M.K.; Writing - O.Ü., S.K., M.K., N.O.; Critical review - O.Ü., S.K., N.O., M.K., İ.O., Y.A., D.Y.
