Assessment of spatial uncertainties in the radiotherapy process with the Novalis system.
ABSTRACT The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX) system with statistical analysis retrospectively in order to determine the tolerance of systematic components of spatial uncertainties with the Novalis system.
Three factors of geometrical accuracy related to the ETX system were evaluated by phantom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, accuracy of the automated calculation by the image fusion algorithm in the patient registration software was evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the Novalis system was evaluated.
As to the location dependency of the detection ability of the infrared system, the detection errors between the actual position and the detected position were 1% in translation shift and 0.1 degrees in rotational angle, respectively. As to the accuracy of patient verification software, the repeatability and the coincidence of the calculation value by image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the ETX isocenter and the mechanical isocenter was 0.313 +/- 0.024 mm, in a suitable procedure.
The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient setup, and daily quality assurance for the Novalis system are achieved in the routine workload.
- [show abstract] [hide abstract]
ABSTRACT: To evaluate the geometric accuracy of the isocenter of an image-guidance system, as implemented in the exactrac system from brainlab, relative to the linear accelerator radiation isocenter. Subsequently to correct the x-ray isocenter of the exactrac system for any geometric discrepancies between the two isocenters. Five Varian linear accelerators all equipped with electronic imaging devices and exactrac with robotics from brainlab were evaluated. A commercially available Winston-Lutz phantom and an in-house made adjustable base were used in the setup. The electronic portal imaging device of the linear accelerators was used to acquire MV-images at various gantry angles. Stereoscopic pairs of x-ray images were acquired using the exactrac system. The deviation between the position of the external laser isocenter and the exactrac isocenter was evaluated using the commercial software of the exactrac system. In-house produced software was used to analyze the MV-images and evaluate the deviation between the external laser isocenter and the radiation isocenter of the linear accelerator. Subsequently, the deviation between the radiation isocenter and the isocenter of the exactrac system was calculated. A new method of calibrating the isocenter of the exactrac system was applied to reduce the deviations between the radiation isocenter and the exactrac isocenter. To evaluate the geometric accuracy a 3D deviation vector was calculated for each relative isocenter position. The 3D deviation between the external laser isocenter and the isocenter of the exactrac system varied from 0.21 to 0.42 mm. The 3D deviation between the external laser isocenter and the linac radiation isocenter ranged from 0.37 to 0.83 mm. The 3D deviation between the radiation isocenter and the isocenter of the exactrac system ranged from 0.31 to 1.07 mm. Using the new method of calibrating the exactrac isocenter the 3D deviation of one linac was reduced from 0.90 to 0.23 mm. The results were complicated due to routine maintenance of the linac, including laser calibration. It was necessary to repeat the measurements in order to perform the calibration of the exactrac isocenter. The deviations between the linac radiation isocenter and the exactrac isocenter were of an order that may have clinical relevance. An alternative method of calibrating the isocenter of the exactrac system was applied and reduced the deviations between the two isocenters.Medical Physics 03/2012; 39(3):1418-23. · 2.91 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Dust and hybrid-mixture explosions continue to occur in industrial processes that handle fine powders and flammable gases. Considerable research is therefore conducted throughout the world with the objective of both preventing the occurrence and mitigating the consequences of such events. In the current work, research has been undertaken to help move the field of dust explosion prevention and mitigation from its current emphasis on hazards (with an accompanying reliance on primarily engineered safety features) to a focus on risk (with an accompanying reliance on hierarchical, risk-based, decision-making tools). Employing the principles of quantitative risk assessment (QRA) of dust and hybrid-mixture explosions, a methodological framework for the management of these risks has been developed.The QRA framework is based on hazard identification via credible accident scenarios for dust explosions, followed by probabilistic fault-tree analysis (using Relex – Reliability Excellence – software) and consequence severity analysis (using DESC – Dust Explosion Simulation Code – software). Identification of risk reduction measures in the framework is accomplished in a hierarchical manner by considering inherent safety measures, passive and active engineered devices, and procedural measures (in that order). An industrial case study is presented to show how inherent safety measures such as dust minimization and dust/process moderation can be helpful in reducing dust and hybrid-mixture explosion consequences in a 400-m3 polyethylene storage silo.Journal of Loss Prevention in The Process Industries - J LOSS PREVENT PROC IND. 03/2013;
- [show abstract] [hide abstract]
ABSTRACT: New technologies continue to be developed to improve the practice of radiation therapy. As several of these technologies have been implemented clinically, the Therapy Committee and the Quality Assurance and Outcomes Improvement Subcommittee of the American Association of Physicists in Medicine commissioned Task Group 147 to review the current nonradiographic technologies used for localization and tracking in radiotherapy. The specific charge of this task group was to make recommendations about the use of nonradiographic methods of localization, specifically; radiofrequency, infrared, laser, and video based patient localization and monitoring systems. The charge of this task group was to review the current use of these technologies and to write quality assurance guidelines for the use of these technologies in the clinical setting. Recommendations include testing of equipment for initial installation as well as ongoing quality assurance. As the equipment included in this task group continues to evolve, both in the type and sophistication of technology and in level of integration with treatment devices, some of the details of how one would conduct such testing will also continue to evolve. This task group, therefore, is focused on providing recommendations on the use of this equipment rather than on the equipment itself, and should be adaptable to each user's situation in helping develop a comprehensive quality assurance program.Medical Physics 04/2012; 39(4):1728-47. · 2.91 Impact Factor
5TH JUCTS AND THE 5TH S. TAKAHASHI MEMORIAL INTERNATIONAL JOINT SYMPOSIUM
ASSESSMENT OF SPATIAL UNCERTAINTIES IN THE RADIOTHERAPY PROCESS
WITH THE NOVALIS SYSTEM
NAOKI HAYASHI, M.SC.,*yYASUNORI OBATA, M.D.,yYUKIO UCHIYAMA, M.SC.,z
YOSHIMASA MORI, M.D.,* CHISA HASHIZUME, M.D.,* AND TATSUYA KOBAYASHI, M.D.*
*Nagoya Radiosurgery Center, Nagoya Kyoritsu Hospital, Nagoya, Japan;yGraduate school of Medical Science, Nagoya University,
Nagoya, Japan; andzSchool of Health Sciences, Gifu University of Medical Science, Gifu, Japan
Purpose: The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX)
tial uncertainties with the Novalis system.
Methods andMaterials: Threefactors of geometrical accuracy related to theETX system wereevaluatedby phan-
tom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, ac-
curacy of the automated calculation by the image fusion algorithm in the patient registration software was
evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was
evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the
Novalis system was evaluated.
Results: As to the location dependency of the detection ability of the infrared system, the detection errors between
the actual position and the detected position were 1% in translation shift and 0.1?in rotational angle, respectively.
As to the accuracyof patient verification software, the repeatability and the coincidence of the calculationvalue by
image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the
ETX isocenter and the mechanical isocenter was 0.313 ± 0.024 mm, in a suitable procedure.
Conclusions: The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient
setup, and daily quality assurance for the Novalis system are achieved in the routine workload.
? 2009 Elsevier
Spatial uncertainty, Image-guided radiotherapy, Geometrical accuracy, Patient setup, Stereotactic radiotherapy.
quality assurance (QA) and quality control (QC) (10–12). The
delivery of radiation at a sufficient dose to a planning target
volume (PTV) is an ideal of external beam radiation therapy.
In the late 1990s, new image-guided patient positioning
devices were developed for a clinical linear accelerator
(LINAC). In addition, BrainLAB (Germany) recently manu-
factured a Novalis radiotherapy system which was dedicated
to highly precise radiotherapy. The Novalis system for ster-
eotaxy consists of a micro-multileaf collimator (m3) and an
ExacTrac X-ray (ETX) positioning system. The characteris-
tics of a micro-multileaf collimator were reported by many
scientists and physicists, and its usefulness for clinical appli-
cation has already been proven. The ETX system of the
Novalis system is a kilovoltage X-ray-based two-dimen-
localization device dedicated to stereotactic radiosurgery
and stereotactic radiotherapy. Two X-ray tubes and two
flat-panel detectors are at a fixed position in the treatment
room, suspended from the clinical LINAC. The ETX system
is one of the commercially available patient positioning
devices produced by BrainLAB. The ETX system combines
based system. Two IR cameras are fixed to the ceiling. Two
kilovoltage X-ray beams are projected from the two X-ray
tubes in oblique directions for the purpose of verifying
patient localization. The procedure for patient setup with
the ETX system consists of three steps: in step one, the initial
patient setup according to the IR body markers is performed.
Reprint requests to: Naoki Hayashi, M.Sc., School of Medical
Science, Fujita Health University, 1-98, Dengakugakubo, Kutsu-
kake, Toyoake, Aichi, Japan 470-1192. Tel: +81-562939424; Fax:
+81-562934595; E-mail: email@example.com
This study was presented in part at the 5th AnnualJapan-US Can-
cer Therapy Symposium in Sendai, Japan. September 7-9, 2007.
Conflict of interest: none.
Acknowledgment—The authors thank Mr. Kengo Kojima and
Mr. Thomas Jelinek for technical support.
Received Oct 28, 2008, and in revised form Feb 11, 2009.
Accepted for publication Feb 16, 2009.
Int. J. Radiation Oncology Biol. Phys., Vol. 75, No. 2, pp. 549–557, 2009
Copyright ? 2009 Elsevier Inc.
Printed in the USA. All rights reserved
0360-3016/09/$–see front matter
Normally, the IR body markers are placed asymmetrically on
the patient’s body surface. The placement of each IR marker
is detected by two IR cameras, and then the IR-based patient
localization is completed by the automatic couch movement.
In step two, two X-ray images are taken and compared with
a digitally reconstructed radiograph (DRR) by the registra-
tion software for the purpose of calculating the setup error.
In step three, X-ray image-based patient localization is com-
pleted by the automatic couch movement.
Clinical experiences with the Novalis system were
reported by several investigators (9, 13–16). Many proce-
dures of these studies were done with a previous type of
ETX system(Qualisys type). The present upgraded ETX sys-
tem is version 5, and the geometrical system has been
changed to a Polaris type, which is smaller and simpler
than the previous type (Fig. 1). The source-to-isocenter dis-
tance and the source-to-detector distance of the Polaris type
ETX are 2.2 m and 3.5 m, respectively. The purpose of this
study was to evaluate the mechanical accuracy of (17–18)
anew ETXsystem andits spatial uncertaintyintheradiother-
apy workload with the Novalis system.
METHODS AND MATERIALS
As a fundamental study of geometrical accuracy with the Novalis
system, three factors of the patient setup with ETX system were
Location dependency of the IR system
Six IR-reflective spherical markers, each with a diameter of 15
mm, were placed asymmetrically on the graph sheet, fixed on the
exact couch top (Fig. 2). A front pointer was put on the gantry
The gantry angle, the couch angle, and the collimator angle were
each set to 0?. A reference position was defined on the origin of
the graph sheet. After the intentional offsets of the couch shift/angle
were set to the exact couch angle, the actual locations were com-
pared to the ETX detective locations under each condition. The
actual location was measured on the enlarged image of the graph
sheet with a highly precise digital camera. The intentional move-
ments of couch shift were 0, 50, and 100 mm in longitudinal and lat-
eral directions. The intentional couch angles were tried at 0?, 45?,
Accuracy of the patient verification software
After five IR-reflective spherical markers were placed asymmet-
izontally on the CT table (Fig. 3). Simulation CT scanning was
performed under suitable conditions. The slice thickness, the tube
voltage, and the field of view of CT were 1.25 mm, 120 kV, and
500 mm, respectively. A CT-based treatment plan was designed
by Brainscan, and then the reference point was placed at the center
of the lumbar phantom. After the coordinate data were transferred to
the ETX system, the lumbar phantom was set up at the isocenter by
the ETX system and kept at its position. Correction and verification
procedures were repeated many times under different X-ray image
conditions. After automatic verification was repeated 50 times via
Fig. 1. Comparison of two types of ETX system.
550I. J. Radiation Oncology d Biology d Physics Volume 75, Number 2, 2009
one X-ray image, the statistical analysis of deviation was done. The
X-ray images with the same mA conditions were taken at tube volt-
ages of 60, 80, 100, and 120 kV. The reference couch angle was 0?.
The Winston-Lutz test has been used to estimate the geometrical
accuracy of the mechanical isocenter since the late 1980s (19).
However, it is not adequate to define geometrical accuracy when
patient localization is done by the ETX system. Sometimes, there is
deviation between the mechanical isocenter and the ETX isocenter
because the ETX system exists independently of a Novalis linear
accelerator. The range of deviation among the coordinates depends
on the calibration procedure used for the ETX system (Fig. 4).
Therefore, calibration accuracy based on two types of X-ray calibra-
tion phantoms were evaluated as a comparative study. The size and
implant markerplacement ofeach phantomwerebasicallythesame.
A hollow X-ray calibration phantom (Phantom A) has a hole at the
center, and a solid X-ray calibration phantom (Phantom B) does not
have a hole (Fig. 5).
Routine Winston-Lutz tests were performed with a Winston-Lutz
kit (BrainLAB) as daily QA in our hospital. Routine isocenter ver-
ification and X-ray calibration were performed every day and two
times per week, respectively. In addition, a WL-module test, a spe-
cial program used to check the offset distance between the mechan-
ical isocenter and the ETX isocenter, was applied, calculation of
by a pinhole camera model algorithm by the following formula:
u ¼p11x þ p12y þ p13z þ p14
p31x þ p32y þ p33z þ p34;
Where x, y, and z are three-dimensional coordinates of a point in
the imaging object, u and v are two-dimensional coordinates of its
projection on the kV X-ray images, and pijare unknown project
parameters determined by a dedicated phantom.
For this study, the WL-module test was done constantly during
every Winston-Lutz test (Fig. 6). Phantom A and Phantom B were
used for X-ray calibration for the initial 3 weeks and for the next
4 weeks, respectively. The Winston-Lutz test depended on the
mechanical isocenter, which was defined as the cross-line point of
the in-room laser alignment. The deviation between the mechanical
isocenter and the ETX isocenter based on vertical, longitudinal, and
lateral directions was evaluated by the WL-module test (Fig. 7).
Total deviation of coordinates between the mechanical isocenter
and the ETX isocenter was defined by the root sum of the square
of each direction. That is,
where, DTis the total deviation between the mechanical isocenter
and the ETX isocenter; Dxis the observed value in the lateral direc-
tion; Dyis the observed value in the longitudinal direction; and Dzis
the observed value in the vertical direction. The geometrical accu-
racy with each phantom was evaluated by the retrospective statisti-
cal analyses of these data.
v ¼p21x þ p22y þ p23z þ p24
p31x þ p32y þ p33z þ p34
Fig. 2. Schematic image of the first examination.
Fig. 3. Schematic image of the second examination. Basically, the size and the implant marker placement of the phantom
are the same. Phantom A has a hole at the center.
Spatial uncertainties in the radiotherapy process d N. HAYASHI et al.551
Location dependency in the IR system
Results of the examination for location dependency in
the IR system are shown in Table 1 and 2. As the results
of examination with the intentional translation shift are
shown in Table 1, the location dependency of the IR sys-
tem with translation shift was evaluated. All actual loca-
tions after the intentional movement were confirmed by
the enlarged image of the graph sheet with the digital cam-
era. On the other hand, the detected location of the ETX
system, which meant the IR coordinate of the ETX system,
was confirmed by the IR camera. The deviation of each co-
ordinate was calculated by subtraction from the IR coordi-
nate to the actual coordinate. The deviation between the IR
coordinate and the actual coordinate was observed in each
(lateral/longitudinal) direction. The deviation in the longitu-
dinal direction was larger than in the lateral direction; espe-
cially the deviation at the +100 mm shift point in the
longitudinal direction was 1.08 mm (1%) as the maximum
value. On the other hand, the misdetection of the table an-
gle in each intentional movement ranged within ?0.1?.
As to the results of examination with the intentional couch
system with the couch angle movement was evaluated. All
intentional angles, which defined actual angles, were con-
tor with the digital camera. On the other hand, the detected
locations of the ETX system, which meant the IR-based
Fig. 4. Calibration procedure of the ETX system.
Fig. 5. Two types of X-ray calibration phantoms.
552I. J. Radiation Oncology d Biology d PhysicsVolume 75, Number 2, 2009
angles, were confirmed by the IR camera. The deviation of
each angle was calculated by subtraction from the
IR-detected angle to the actual angle. The deviation of the
front pointer meant the error from rotation center.
An offset of the front pointer was less than 0.3 mm, and
errorsof the detected position of the ETX systemwere within
0.4 mm on the translation shift. The detection error of the
couch angle was less than 0.7?, and the maximum value
was detected at 45?of the couch angle.
Accuracy of the patient verification software
Results of an examination for the purpose of clarifying the
calculation accuracy of the patient verification software are
shown inFig.8.The purposeofthis examinationwas toeval-
in the patient registration as determined by the image fusion.
The image fusion was tried 50 times per each setup verifica-
tion. Each calculated value was analyzed statistically. The
graduation and the section of bar graph mean the average
and the standard deviation of 50 trials, respectively. From
the results, the values of 100 kV are smaller and more stable
than under other conditions. On the other hand, the values of
60 kV and 80 kV are larger and more variable than under the
couch angle settings.
the mechanical isocenter
Results of the WL-module test during the Winston-Lutz
test are shown in Table 3. By using the WL-module test, an
offset distance between the center of a microsphere and the
center of the ETX origin was evaluated. This value means
a deviation of the coordinate between the ETX origin and
the mechanical isocenter. The deviation values calibrated
by Phantom A and Phantom B were 0.455 ? 0.088 mm
and 0.313 ? 0.024 mm, respectively. These values mean
a sphere of 95% confidence level with each calibration phan-
tom. Sample numbers of Phantom A and Phantom B were 14
the ETX system with Phantom B was better than with Phan-
tom A, with an advantage of approximately 0.1 mm.
As to the location dependency in the IR system, results of
the first examination are divided into two categories: (1)
those in which the error of detection is increased in longitu-
dinal translation shift, and (2) those in which the error of de-
tection exists in couch rotation. The stereoscopic angle of the
Polaris type on the isocenter is sharper than the previous sys-
tem because the distance of each IR camera became shorter.
As a result, the detection accuracy of the Polaris type in lon-
gitudinal direction and/or couchrotation was worse thanwith
the previous ETX system.
As to the accuracy of the patient verification software,
results of the second examination are divided into two cate-
gories: (1) those in which calculation accuracy is precise
when the tube voltage is set to 100 kV,and (2) those inwhich
45?and 90?. The verification error is thought to be improved
bony structures or implant markers. In the couch rotation,
however, there were some uncertainties such as marker
placement and mechanical error, etc.
The preliminary study of the previous type of ETX system
was reported by Verellen et al. in 2003 (14). That study used
the previous ETX type and reported that results of preclinical
verification of the system and clinical validation were limited
to the DRR fusion approach based on bony structures. That
ing system, DRR fusion tests, and an overall deviation within
the ETX system. From their data, the authors found that the
average deviations between the IR tracking measurements
of theisocentricposition andtheactual position of thehidden
target with respect to the treatment isocenter were ?0.24 ?
0.33 mm, 0.45 ? 0.55 mm, and ?0.49 ? 0.59 mm in the ver-
tical, longitudinal, and lateral directions, respectively. Their
experiment featured an intrinsic uncertainty from the
Fig. 6. Schematic image of the third examination.
Fig. 7. WL module test program
Spatial uncertainties in the radiotherapy process d N. HAYASHI et al.553