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Corresponding author: KR Muralidhar; Department of Radiation Physics, American Oncology Institute Nallagandla, Lingampally, Hyderabad, India.
Cite this article as: Muralidhar KR, Rout BK, Mallikarjuna A, Poornima A, Murthy PN. Commissioning and quality assurances of the Intrabeam In-
tra-Operative radiotherapy unit. Int J Cancer Ther Oncol 2014; 2(4):020415. DOI: 10.14319/ijcto.0204.15

A part of this research was presented at Standards, Applications and Quality Assurance in Medical Dosimetry, which was held in Nov 2010 at IAEA, Vienna

Commissioning and quality assurances of the Intrabeam
Intra-Operative radiotherapy unit

KR Muralidhar1, Birendra Kumar Rout2, Adavala Mallikarjuna2, A Poornima2, P Narayana Murthy3

1Department of Radiation Physics, American Oncology Institute Nallagandla, Lingampally, Hyderabad, India
2Department of Radiation Physics, Indo-American Cancer Institute, Hyderabad, India

3Department of Radiation Physics, Nagarjuna University, Guntur, India

Received August 20, 2014; Revised October 15, 2014; Accepted October 19, 2014; Published Online October 20, 2014

Abstract
Purpose: The authors report comprehensive commissioning and quality assurance (QA) procedures for Intrabeam, In-
tra-Operative radiotherapy (IORT) unit. The Intrabeam system miniature X-ray source is a 50 kV and 40 µA unit. Methods: The
authors’ tests include measurements of output, beam deflection, isotropy, kVp and mAs measurements, quality index, isodose,
reproducibility, linearity, depth dose verification, and 3D dose distribution. IC ionization chamber and the UNIDOSE dosimeter
were used for the output commissioning. Probe adjuster/ionization chamber holder (PAICH) was used to check the mechanical
straightness of the probe. For radiation tests, NACP parallel plate chamber, Standard Imaging electrometer, 30 × 30 × 30 cm3
IAEA water phantom, solid water slabs, EDR-2 Films with RIT software, and ionization based survey meters were used. Unfors
Xi platinum edition kVp meter was used to measure the kVp and mAs. Results: In mechanical QA test, X-Beam position (-0.09
mm), Y-Beam position (0.01 mm), and radial position (0.11 mm) errors were within the tolerance level. Isotropy test with PDA,
survey meter, ion chamber, and film measurements also produced results within the specifications. Output measurements with
PAICH and external chamber measurements were matched. Beam quality, linearity, and reproducibility values were ascer-
tained at 50KV and 40 µA and found to be within limits. Isodose, 3D dose distribution, transverse, and horizontal profiles
showed the good isotropy of the source. Conclusion: The authors’ methodology provides comprehensive commissioning and
calibration procedures for the Intrabeam system.

Keywords: IORT; Intrabeam; X-Ray Source; Isotropy; Photo Diode Array

Introduction
Intrabeam system (Carl Zeiss Surgical GmbH, Oberkochen,
Germany) is a mobile unit used for Intraoperative Radio-
therapy (IORT), especially for localized tumor irradiation and
for sharp fall of dose from the source. The heart of this system
is a miniature with high dose rate and low energy X-ray
source (XRS) equipped with a 10 cm long (ø 3.2 mm) probe.
The tip of the XRS probe is placed into a lesion or a tumor
bed. It is a truly flexible system for IORT. The Intrabeam
delivers treatment by a number of methods, including in-
traoperative, interstitial, intra-cavity, and surface treatments.
In IORT facility, the quality assurance needs to be more
stringent due to miniature x-ray source and its high dose
rate.1-2 Since Intrabeam system installed at our center was the
first of its kind in India, various quality assurance procedures
and radiation safety issues were to be addressed at the time of
commissioning both from regulatory as well as operational
standpoints.

While a number of reports exist describing the quality as-
surance for IORT, very few papers deal with the QA aspects
in detail. These tests (mechanical, dynamic offset, isotropy
test with photodiode array (PDA), and probe adjust-
er/ionization chamber holder (PAICH) output check (dose
rate)) are well evaluated as part of the commissioning process;
however, there is no discussion about the complementary
procedures to ensure its clinical use. In this study, after
commissioning the system by measuring the parameters
proposed by the manufacturer, a number of procedures have
been proposed before the system can be applied in clinical
use. These tests (beam quality test, linearity test, and repro-
ducibility test, isotropy test with survey meter and EDR-2
film, external kVp and mAs measurements, isodose and depth
dose measurements with film) were complementary proce-
dures to check the correct installation and calibration. The
use of proposed parameters might be helpful to check if doses
are correctly delivered from the system measurement using a
tank of water. Another interesting test is to obtain the

Original Article

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transverse and horizontal profile information and 3D dose
distribution using RIT software with EDR-2 films. All these
tests make sure that the system is within the manufacturer
specified values and further improve this technology towards
dedicated computerized planning system. The main purpose
of this study was to create enough confidence on the Intra-
beam system by performing additional quality assurances as
specified by the authors.

Methods and Materials
Intrabeam operation
This Photon Radio surgery system (PRS) comprises an XRS
[Figure 1], PRS 500 control console, quality assurance tools,
and mobile gantry.

FIG. 1: Intrabeam system.

The miniature X-ray source [Figure 2] is a 50 kVp and 40 µA
unit capable of delivering 1.32 mGy/min at 1 meter from the
source.

FIG. 2: X-ray source with internal radiation monitor (IRM): (1)
XRS-4 cable connector, (2) Beam deflector, (3) Probe tip, (4) X-ray

probe, and (5) IRM (courtesy Carl Zeiss)

High voltage is generated by the XRS from the low direct
current voltage supplied by the PRS 500 control console, and
is used to direct an electron beam into the X-ray probe.
The electron beam strikes a hemispherical gold target, ap-
proximately 1 µm thickness at the end of the X-ray probe,

generating X-radiation.3 The X-ray system produces
low-energy photons (30-50 kVp) with a steep dose falloff in
soft-tissue; hence, no special shielding is required in the
room. The production of an x-ray pattern is spherical in shape
about the tip of the drift tube. Adjustment of beam steering
and the angle of precession allow the isotropic distribution to
be optimized.4 The probe tip is made of beryllium (Be), a
material transparent to X-radiation. The exterior surface of
the XRS probe is provided with a protective coating.

In order to use the XRS, it must be connected to the PRS 500
control console with the XRS interface cable. X-radiation
produced at the tip of the X-ray probe features a spherical
radiation characteristic. As a result, part of the radiation
re-enters the XRS through the probe. The IRM detects this
X-radiation in the XRS. The radiation output measured by the
IRM is then used during treatment as an indirect measure of
radiation delivered at the probe tip. There are few important
tests that should be covered prior to clinical use of this unit.
These tests typically include the mechanical and radiation
measurements. The PRS is supplied with a set of components,
which facilitate accurate alignment of the XRS probe as well
as quality assurance checks.5

Mechanical Tests
Mechanical straightness check of the probe is very important.
For this test, probe adjuster/ionization chamber holder
(PAICH) can be used. Performing this verification step is
must if the isotropy verification is unsuccessful or the XRS
probe is suspected to be bent. Specifically, in order to check
the mechanical straightness, the probe should be inserted into
the PDA (Photo Diode Array), and the PAICH and the XRS
need to be connected to the control console using the ap-
propriate cables. After successful cable connection, rotate the
PAICH completely to 360° or less to measure the highest
value of deviation. The plunger is then depressed and released
to straighten the XRS probe. This procedure is repeated until
the Run out value is less than 0.10 mm.

Radiation Tests
In our study, inbuilt radiation tests (alignment (probe ad-
juster), steering (quick check, dynamic offsets), Isotropy and
IRM (PDA), Output (PAICH)) were done to check the dy-
namic offset, isotropy, and dose rate. New quality assurances
(beam quality test, linearity test, and reproducibility test,
isotropy test with survey meter and EDR-2 film, external kVp
and mAs measurements, isodose and depth dose measure-
ments with film) were done by using film, ionization cham-
ber, survey meter, kVp, and mAs meter.

Dynamic Offset
This technique is used to align the direction of the electron
beam with the mechanical center of the XRS probe by beam
deflection adjustment. The XRS and PDA photodiode array
were aligned with the help of +X and +Y markings on them



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and were connected to control console using the appropriate
cables. In the system calibration procedure, adjustment was
performed automatically for the selected XRS source at a
specific high voltage.

Isotropy test with PDA
The PDA was used to measure and, if needed, to adjust the
isotropy of the radiation emission from the XRS probe tip.
The PDA incorporates five photodiodes, placed in a centered
position on the four side faces and the top face of a cube, such
that all are equidistant from the center of radiation of the XRS
probe tip. The signals from the PDA were displayed in the
screen mask and were used to measure the distribution
(isotropy) of X-radiation emitted from the tip of the probe.
The isotropy of the radiation field was automatically adjusted
on the basis of these measured values. The Isotropy Adjust
procedure was performed using the maximum beam current
and the same beam voltage that was selected for the relevant
XRS.

PAICH Output Check (dose rate)
This procedure is used to determine the dose rate of the XRS
by means of the inbuilt ionization chamber and the
UNIDOSE dosimeter. The dose rate was checked against a
specific expected value from the calibration data given by the
manufacturer. To perform this test, the PAICH was attached
to the XRS. Ionization chamber was then inserted into the
holder of PAICH and connected to the dosimeter. The output
dose rate value indicated in Gy/min is the value computed
internally.

Beam Quality test
Dose rates were measured at 5 cm and 3 cm distances from
the cone in the water phantom [Figure 3] for three days with
0.6 CC ionization chamber (IBA Dosimetry GmbH, Germa-
ny). The measured dose rate values were used to verify the
energy stability. Dose gradients are typically steep within 2
cm distance from the source. In order to avoid the uncer-
tainties, it is always advisable to take the readings at greater
than 3 cm.

FIG. 3: Measurements in water phantom.

Depth dose measurement
Depth-dose curves were obtained by measuring the ioniza-
tion chamber output at distances between 1 to 10 cm away
from the probe tip in a water phantom of dimensions 30 × 30
× 30 cm3. The ionization chamber was placed at the center of
the phantom in the Perspex enclosure. The position of the
x-ray source is shown in the Figure 3. Care was taken to
maintain the straightness of the probe. The minimum dis-
tance away from the probe tip at which the ionization
chamber could be positioned was 10 mm from the center of
the chamber. We acquired depth dose data in water to reduce
the uncertainties involved in converting from an air meas-
urement to the measurement in water. Additionally, a com-
parison was made between the measured depth doses and
corresponding values obtained from the manufacturer.1

Linearity Test
The linearity of the intrabeam system was ascertained at 50
kVp and 40 µA for the range of 1 to 5 minutes. Measurements
were taken at 4 cm distance from the source with parallel
plate ionization chamber.

Reproducibility Test
Reproducibility of the x-ray output was investigated for in-
trabeam under 10 exposures. Each exposure was controlled
using a preset timer. A beam voltage of 50 kVp and beam
current of 40 µA were used. Ten measurements were made
for exposures equivalent to 1 minute each at a distance of 4
cm from the surface in water phantom.

Isotropy test with the survey meter
In this study, x-ray radiation was measured in a series of
square projections from x-ray source by means of an ion
chamber based survey meter. Isotropy was estimated with the
help of the obtained data. This is one of the simple procedures
to check the isotropy of the system.

Isotropy test with EDR-2 film and RIT software
Five EDR-2 films were used to test the isotropy of the source.
All films were kept at 5 cm from the source in five directions
(00, 900, 1800, 2700, and perpendicular to the source). Five
exposures, each of one minute duration were made. The
exposed films were scanned in Vidar film scanner and ana-
lyzed using Radiological Imaging Technology (RIT®) Soft-
ware. This software provides precise QA analysis for images
from many different sources (CT, X-ray, etc.). The difference
between the horizontal and vertical profiles gives the dose
difference at any given point in that particular plane. A good
isotropy shows the negligible difference between these two
profiles. If the difference is significant (>1%), mechanical test
and dynamic offset test should be done to get the good isot-
ropy.



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Isodose and depth dose measurements with film
Isodose measurements were done by exposing the film ver-
tically down from the source. Film analysis was done by RIT
software and percentage depth doses were obtained by nor-
malizing the values at 2 cm depth from the surface where the
output was compared with an ionization chamber.

External kVp and mAs measurements
Unifors Xi platinum edition kVp meter was used to study the
kVp measurement. To measure the kVp, the setup was such
that the IORT Cone positioned vertically on the surface of the
kVp meter. This kVp meter was connected to the personal
computer with loaded software which shows the readings
continuously in digital and wave form. Measurements were
taken with few exposures.

Results
Mechanical Test
Distance from the tip of the drift tube was measured and
compared with the stated length. Geometric accuracy de-
pends upon the variation between these two values. The
maximum variation of the drift tube from its longitudinal
axis was found to be less than 0.08 mm. This verification test
is passed by succeeding in centering the XRS Probe to a run
out of the maximum deviation of value less than 0.10 mm.

Radiation Tests
Dynamic Offset
The X, Y, and radial beam position errors were < ± 0.1 mm
according to manufacturer recommended value (< 0.1 mm)

Isotropy test with PDA
The measurements for the five bars were ranged from 5.7 to
5.75, and these values were within the tolerance level.

PAICH Output Check (dose rate)
Readings on the UNIDOS® E dosimeter displayed the dose
rate values. The maximum % of variation with the calibrated
value was less than 2% observed.

Beam Quality
The measured quality indexes for three consecutive days
were 0.312, 0.313, and 0.310, respectively, which proved
that the system has good energy stability [Table 1]. The
d5/d3 is the ratio of the meter readings at depth 5 cm and 3
cm, respectively.

TABLE 1: Quality index Intrabeam System.

Day d5/d3 Quality index
1st Day 0.714 / 2.286 0.312
2nd Day 0.715 / 2.284 0.313
3rd Day 0.710 / 2.289 0.310

Depth dose Measurement
Sharp dose fall off (approximately 1/r3) in water was ob-
served [Figure 4] with respect to the depth. These measure-
ments satisfied the values obtained by Carl zeiss3 calibrated
values.

FIG. 4: Output measurement.

Linearity test
For all five readings, plot of dose measured versus exposure
time was found to be linear [Figure 5]. In all the exposures,
the ionization chamber distance was 4 cm from the source in
the water phantom.

FIG. 5: Linearity test.

Reproducibility
The measurements of reproducibility were carried out for
ten measurements as shown in [Figure 6]. We observed that
the reproducibility was, in terms of mean deviation, better
than 0.44%.

FIG. 6: Reproducibility.

FIG. 7: Exposure rate measurements.



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FIG. 8: Isotropy check with EDR-2 Films and RIT software.

FIG. 9: Difference between horizontal and vertical profile.

FIG. 10: 3D View of the IORT dose distribution.

Isotropy check with survey meter
Exposure rates in different directions have shown almost
similar results. The reading of the survey meter at 5 cm, 50
cm, 100 cm, and 200 cm from the source were taken in four
directions and analyzed with graph. Figure 7 shows the good
isotropy along with the radiation safety in Operation Theatre
itself.

Isotropy check with EDR-2 Film
The analysis of EDR-2 films with RIT shows an excellent
isotropy. The isodose measured in all directions are at the
same distance from the source center. Inline and cross line
measurements are also shown in the Figure 8.

With the help of inline and cross line profiles, we can find
the dose difference between either sides of the source at the

same distance. The difference in dose at 2 cm and 12 cm
distance from the center of the exposure were 1.7% and 0.7
%, respectively. In one typical case, the difference between
horizontal and vertical profiles were analyzed through RIT
software as shown in Figure 9. The 3D dose distribution also
gives us the clear view of the isotropy through RIT software
as shown in Figure 10.

FIG. 11: Analysis of EDR2 films after exposing with IORT source.



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The Figure-11 clearly shows the values which proved that
the system displays good isotropy. The maximum % of dif-
ference in dose between films in all directions was 4% and
the difference between maximum dose deposited on each
film was 0.5%.

Isodose and depth dose measurements with film
Depth doses and isodoses were derived through film meas-
urements [Figure 12]. The dose rate was normalized to 100%
at 2 cm depth in the film to simulate the water phantom
depth doses, which were used for the output measurements.
It was found through film measurements that the beam at-
tenuation varies by 1/r3 as provided by the manufacturer.
This concept can be implemented on CT planning in the
treatment planning system.

FIG. 12: Isodose curves from film measurements.

External kVp and mAs measurements
Reading for one minute exposure was taken for four times
and the deviations were observed. These values closely re-
sembles with the value (50 kVp) that was kept inside the
console (PRS500). The maximum and minimum of variation
in percentage were 2% and 0.8%, respectively.

Discussion
In the past ten years, there has been an increasing interest in
the IORT technique because of the development of mobile
accelerators 6-8 producing only electron beams. Clinical use
of IORT, given as a single fraction, was tested using electrons
(Intraoperative Radiotherapy with Electrons [ELIOT])9,
brachytherapy10, or low-energy X-rays (Targeted Intra- op-
erative Radiation Therapy [TARGIT]).11 It is, however, im-
portant to appreciate the different characteristics of the ap-
plicators and take advantage of its special features.12 In-
traoperative radiotherapy is useful for giving high radiation
to the tumor, and at the same time, it spares the normal
structures with the ability to stop radiation with less pene-
tration because 50 keV energy is increasingly popular, espe-
cially among intact breast cases. Installation, commissioning,
and operation of this equipment are limited across the globe
as they have been in use for last few years. We have recently
installed this machine. As it is a very delicate apparatus, care

should be taken to handle the source and other equipments
associated with this device.

In built quality assurance procedures should be done to start
the exposure.13 This is a very good feature for the accurate
treatment. From the radiation safety point of view, there
were no issues as it is 50 keV and 40 µA machine, and it is
also very easy to handle because the dose decreases steeply
with the radial distance, r (approximately proportional to r3).
For every month, over one year period, we observed a devia-
tion of baseline values for output, isotropy, and mechanical
straightness of the probe to be less than ±1%. This compares
favorably with the output constancy of ± 2% recommended
by the European Commission in 1997.14

Conclusion
We have summarized the simple QA procedures to test the
various parameters of the IORT unit (50 keV, 40 µA). The
output measurement with ion chamber, kVp Meter, isotropy
measured with EDR films and survey meter were matched
perfectly with the inbuilt quality assurance measurements.
Percent depth dose measurements were found to be in very
good agreement with the manufacturer given data after
normalization.

Furthermore, the IORT generally comes with manufacturer
recommended tests to check the quality of the device. It is
very important to verify the isotropy, kVp and mAs meas-
urements, quality index, isodose, reproducibility, linearity,
depth dose measurements, and 3D dose distribution along
with manufacturer recommended tests. In conclusion, uni-
form irradiation was proved and checked frequently in the
sphere of equivalence which defines a novel target volume
with low energy x-rays. The measurement techniques pre-
sented in this study are helpful to verify the manufacturer
recommended values and to implement QA procedures with
high accuracy at the institution.

Conflict of interest
The authors declare that they have no conflicts of interest.
The authors alone are responsible for the content and writ-
ing of the paper.

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