PhamThiQue

VIETNAM NATIONAL UNIVERSITY, HA NOI
VNU UNIVERSITY OF SCIENCE
FACULTY OF PHYSICS

----------------

Pham Thi Que

COMPREHENSIVE QUALITY ASSURANCE FOR
RADIATION ONCOLOGY

Submission of a partial fulfillment of the requirement for the degree of
Bachelor of Science in Physics
(Advanced Program)

Hanoi, 2017


VIETNAM NATIONAL UNIVERSITY, HA NOI
VNU UNIVERSITY OF SCIENCE
FACULTY OF PHYSICS

----------------

Pham Thi Que

COMPREHENSIVE QUALITY ASSURANCE FOR
RADIATION ONCOLOGY

Submission of a partial fulfillment of the requirement for the degree of
Bachelor of Science in Physics

(Advanced Program)

Supervisor: Nguyen Xuan Ku, MSc

Hanoi, 2017


ACKNOWLEDGEMENT

First of all, I would like to express my deep gratitude to my research
supervisor, Master Nguyen Xuan Ku for his kind guidance, endless support
and the great adviser to me. I would like to thank him for encouraging me and
giving me opportunity to do the research on this topic, which also helped me
to know about many new things. His advices are priceless on my both
research as well as my future career.
Secondly, I always appreciate all teachers, lectures, researchers and
other seniors in Faculty of Physics, particularly Department of Nuclear
Technology, VNU University of Science, Vietnam National University for
creating good conditions for students like us to work and experience.
And finally, I want to give my special thanks to my family and friends
who have supported me in not only my research but also my whole studying.
They have become my strong motivation to pass through the hard time.

Student,
Pham Thi Que


Comprehensive QA for Radiation Oncology

LIST OF ABBREVIATION

AAPM

American Association of Physicists in Medicine

ADCL

Accredited Dosimetry Calibration Laboratory

BEV

Beam’s-eye-view

CT

Computerized Tomography

DVH

Dose Volume Histogram

HDR

High Dose Rate

ICRU

International Commission on Radiation Units and Measurement

ISCRO

Institutional Stem Cell Research Oversight Committee

JCAHO

Joint Commission on the Accreditation of Health Care Organization

LDR

Low Dose Rate

MLC

Multileaf Collimator

MRI

Magnetic Resonance Imaging

MU

Monitor Unit/Minute

NIST

National Institute of Standard and Technology

PDD

Percent Depth Dose

QA

Quality Assurance

QAC

Quality Assurance Committee

R&V

Record and Verify

SAD

Source Axis Distance

SSD

Source Surface Distance

TLD

Thermoluminescent Dosimeter

TMR

Tissue Maximum Ratio

TPR

Tissue Phantom Ratio

3D

Three-dimension


Comprehensive QA for Radiation Oncology

Table of contents
PART A: INFORMATION FOR RADIATION ONCOLOGY
ADMINISTRATORS ................................................................................... 2
1.

Radiation Oncologist. ......................................................................... 3

2.

Radiation Oncology Physicist. ............................................................ 3

3.

Radiation Therapist............................................................................. 4

4.

Medical Radiation Dosimetrist. .......................................................... 4

PART B: CODE OF PRACTICE................................................................ 5
CHAPTER 1: COMPREHENSIVE QA PROGRAM ............................ 5

1.1.

Introduction ................................................................................. 5

1.2.

QA Committee ............................................................................. 5

1.3.

Comprehensive QA Team ............................................................ 5

1.4.

Policies and Procedures Manual ................................................... 6

1.5.

Quality Audit ............................................................................... 6

1.6.

Resources and Continuous Quality Improvement. ........................ 6

CHAPTER 2: QA OF EXTERNAL BEAM RADIATION THERAPY
EQUIPMENT ........................................................................................... 8
2.1.

QA of Medical Electron Accelerators .......................................... 8

2.2.

QA of Simulators ....................................................................... 10

2.3.

QA of CT Scanners .................................................................... 10

2.4.

QA of Measurement Equipment ................................................. 11

CHAPTER 3: TREATMENT PLANNING COMPUTER SYSTEM . 12
3.1.

Program Documentation ............................................................ 12

3.2.

Test Procedures .......................................................................... 12

CHAPTER 4: EXTERNAL BEAM TREATMENT PLANNING ....... 14
4.1.

Treatment Planning Process ....................................................... 14

4.1.1 Prescription ............................................................................ 14
4.1.2. Positioning and Immobilization .............................................. 15
4.1.3. Data Acquisition ..................................................................... 15

Comprehensive QA for Radiation Oncology

4.1.4. Contouring .............................................................................. 15
4.1.5. Data Transfer ......................................................................... 16
4.1.6. Target volume and Normal Organ Definition ......................... 16
4.1.7. Aperture Design ...................................................................... 16
4.1.8. Computation of Dose Distributions ......................................... 17
4.1.9. Plan Evaluation ...................................................................... 17
4.1.10. Computation of Monitor units ............................................. 17
4.1.11. Beam modifiers ................................................................... 18
4.1.12. Plan Implementation ........................................................... 18
4.2.

Treatment Planning QA for Individual Patient ........................... 19

4.2.1. Treatment Plan Review ........................................................... 19
4.2.2. Monitor Unit Calculation Review ........................................... 19
4.2.3. Plan Implementation ............................................................... 19
4.2.4. In Vivo Dosimetry ................................................................... 20
CHAPTER 5: BRACHYTHERAPY ..................................................... 22
5.1.

Sealed Sources ........................................................................... 22

5.1.1. Description of Sources ............................................................ 22
5.1.2. Calibration of Sources ............................................................ 23
5.1.3. Brachytherapy Source Calibrators.......................................... 25
5.1.4. Brachytherapy Applicators ..................................................... 27
5.1.5. Source Inventories .................................................................. 28

5.2.

Treatment Planning and Dosimetry ............................................ 29

5.2.1. Planning ................................................................................. 30
5.2.2. Localization ............................................................................ 30
5.2.3. Dose Calculation Algorithms .................................................. 30
5.2.4. Patient Dose Calculation ........................................................ 31
5.2.5. Delivery of Treatment ............................................................. 31
5.2.6. Documentation........................................................................ 31
5.3.

Remote loading .......................................................................... 32


Comprehensive QA for Radiation Oncology

5.3.1. Calibration ............................................................................. 32
5.3.2. Verification of Source Position ............................................... 32
5.3.3. End effects .............................................................................. 33
5.3.4. Safety ...................................................................................... 33
CHAPTER 6: QA OF CLINICAL ASPECTS ...................................... 34
6.1.

New Patient Planning Conference .............................................. 34

6.2.

Chart Review ............................................................................. 34

6.3.

Chart Check Protocol ................................................................. 35

6.3.1. Review of New or Modified Treatment Field ........................... 35
6.3.2. Weekly Chart Review .............................................................. 35
6.4.

Film Review .............................................................................. 36

6.4.1. Portal Images ......................................................................... 36
6.4.2. Ongoing and Verification Images ........................................... 36
CONCLUSION ........................................................................................... 37
REFERENCES ........................................................................................... 38


Comprehensive QA for Radiation Oncology

List of Table

Table 1: The performance tests, tolerances, frequencies of medical electron
accelerators .................................................................................................... 8
Table 2: The performance tests, tolerances, frequencies of simulators .......... 10
Table 3: The performance tests, tolerances, frequencies of measurement
equipment..................................................................................................... 11
Table 4: QA for treatment planning systems and monitor unit calculations .. 13
Table 5: Factors effecting monitor unit (minute) calculations ....................... 17
Table 6: Summary of QA recommendations for individual patients ............. 20
Table 7: Source QA tests and their frequency and tolerances for
brachytherapy source calibrator .................................................................... 25

Table 8: The QA tests for brachytherapy source calibrator ........................... 25
Table 9: QA tests for brachytherapy applicators ........................................... 27
Table 10: Procedure specific parameter verification ..................................... 31
Table 11: QA of remote afterloading brachytherapy units ............................ 32


Comprehensive QA for Radiation Oncology

PREFACE
Nowadays, the frequency of cancers in the Asia-Pacific region has
increased essentially over the past several years. If the projection is right, the
quantity of cancer cases in Asia is set to increase from 3.5 million in 2002 to
8.1 million by 2020 if the current management strategies are not changed.
And Vietnam is not an exception. According to statistics of K Hospital and
Oncology Hospital-HCM City, there are 75.000 people died because of cancer
and 120.000 to 150.000 people who are diagnosed getting cancer every year.
Therefore, radiotherapy plays an important role in the treatment of cancer.
Beside of the treatment process, the quality assurance in radiation
oncology is important too. However, the QA program in radiation oncology
has not been set in all treatment facility in over our country. This happened
because of lacking fully aware about the issue importance, funding,
investment or because radiation oncology members have not trained in a basic
way. Now, it is time for us to treat quality as the primary goal and QA
program is concerned.
In order to have a comprehensive look about QA program, I figure out
the topic named “Comprehensive QA for Radiation Oncology”. This thesis
includes 2 parts: part A is for administrators, and part B is a code of practice
in six chapters. The first chapter of part B describes a comprehensive QA
program in which the importance of a written procedural plan administered by
a multidisciplinary committee is stressed. The second chapter of part B

concerns QA of external beam therapy equipment. The third chapter describes
QA for treatment planning computers. The fourth describes the treatment
planning process and QA procedures for individual patients. The fifth
considers the new details of source strength and emphasizes the use of
redundant systems for source strength calibration and checking. The sixth part
is the most clinical and discusses new patient conferences, film review, chart
review, and a detailed protocol for chart checking.

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Comprehensive QA for Radiation Oncology

PART A: INFORMATION FOR RADIATION ONCOLOGY
ADMINISTRATORS

Delivery of treatment in an accurate and predictable way is not easy to
achieve, because the radiation therapy process is a complex interweaving of
number of related tasks for designing and delivering radiation treatments. It
includes a determination of the extent of the disease and a determination of
patient’s particular parameters (e.g. surface anatomy, internal organs, and
tissues including the tumor) in order to determine the size, extent and location
of the tumor (target volume). Then, the intended radiation dose distribution is
calculated by software algorithms of a treatment planning system. To treat the
patients as planned requires accurately calibrated treatment unit, the
accessibility of treatment aids and immobilization gadgets for positioning and
maintaining the patient in the planned position.
The International Commission on Radiation Units and Measurements
has recommended that the dose be delivered to within 5% of the prescribed
dose [12]. If there are many steps required in delivering dose to a target

volume, each step must be performed with an accuracy much better than 5%
to achieve the ICRU recommendation. But in reality, it is difficult to evaluate
an accuracy and consistency estimate required in each step.
To meet such standards required the availability of important facilities
and equipment including treatment and imaging units, radiation measuring
devices, computer treatment planning systems and the appropriate staffing
levels of qualified radiation oncologists, radiation oncology physicists,
dosimetrists, and radiation therapists. Furthermore, the increasing of the
complexity of treatment modalities can lead to the increase of expectations on
the quality of treatment, which makes QA procedures more complex.
To cope with this situation, it is important that QA processes and
procedures emanate from a QA committee. This committee always draws its
immediate authority from the administrator of the departure of radiation
oncology. The members of the QA committee should include a representative
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Comprehensive QA for Radiation Oncology

from each of the subdisciplines. The roles and responsibilities of the members
of four of the subfields, namely radiation oncologists, radiation oncology
physicists, dosimetrists, and radiation therapists are therefore discussed
below. However, the QA committee is a significantly larger entity and should
include nurses, the department administrator, a representative of the hospital’s
QA committee, and others as justified.
1.

Radiation Oncologist.
Only the radiation oncologists with hospital privileges can be in charge

of consultation, dose prescription, on-treatment supervision and treatment
summary reports. Furthermore, they should be in charge of the chart review of
any patient who dies during the treatment course or any patient with an
unusually serve or sudden respond to treatment. That is reason why the
radiation oncologists in QA team should be certified by one of recognized
boards.
2.

Radiation Oncology Physicist.
Radiation Oncology Physicists are fundamentally and professionally

engaged in the evaluation, delivery and optimization of radiation therapy.
Their major responsibility is to provide a high standard of clinical physic
service and supervision.
They have to calibrate the Radiation Oncology Equipment to make sure
that all treatment machines and radiation sources are correctly calibrated
according to accepted protocols. They need to define the Specifications of
Therapy Equipment including external beam, brachytherapy units, therapy
simulator, CT, ultrasound units, therapy imaging system. Beside, they also
need to establish Dose calculation Procedure, Treatment Planning, Treatment
Procedures or QA Procedures.
Moreover, the radiation oncology physicist is responsible for
Acceptance Testing, Commissioning and QA of treatment planning systems
or Beam Data Measurement and Analysis or Supervision of Therapy
Equipment Maintenance.

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Comprehensive QA for Radiation Oncology

Finally, they have a responsibility to provide education and training in
medical physic for physicians, radiation therapists, dosimetrists, nurses,
medical technical assistants, as well as student physicists and technical staff.
3.

Radiation Therapist.

The Radiation Therapists are highly skilled professionals to provide
radiation therapy under supervision of a radiation oncologist or radiation
oncology physicist. The radiation therapist is expected to recognize any
change in the patient’s condition, know the safe limits of equipment
operation, understand treatment method and protocols, detect any equipment
deviations or malfunctions to withhold or terminate treatment until the
problem has been resolved.
4.

Medical Radiation Dosimetrist.
The medical radiation dosimetrist is in charge of the efficient

translation of clinical and physical requirements, calibration and procedures
into a coherent individually planned radiation course for the cancer patient.
The dosimetrist generates two-dimension or three-dimension isodose plans
following the specifications of radiation oncologist by utilizing the data
acquired during the planning process. They are responsible for manual or
computer-generated dose calculation as well as radiation measurement by
utilizing ion chambers, TLD, or film. Moreover, the dosimetrist may also
assist with machine calibrations and ongoing QA under the radiation
oncology physicist supervision.

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Comprehensive QA for Radiation Oncology

PART B: CODE OF PRACTICE

CHAPTER 1: COMPREHENSIVE QA PROGRAM

1.1.

Introduction
A comprehensive QA program is a quality system built on a quality

plan. “Every patient with cancer deserves to receive the best possible
management to achieve cure, long-term tumor control or palliation” this is the
major goal of cancer management [15]. The “quality” of radiation oncology is
defined as the totality of features or characteristics of the radiation oncology
service that bear on its ability to satisfy the stated or implied goal of effective
patient care. “Quality assurance” is all those planned or systematic actions
necessary to provide adequate confidence that the radiation oncology service
will satisfy the given requirements for quality care [3]. And The Joint
Commission on the Accreditation of Health Care Organizations (JCAHO) has
the role of evaluating the quality of patient management.
1.2.

QA Committee
A QA committee should represent the many disciplines within radiation

oncology in order to assure that the many aspects of quality in the radiation

oncology service. At least, the QAC should consist of a member from each
area of medicine, physic and treatment.
QAC is recommended to oversee the QA program and have responsible
of assisting the entire radiation oncology staff to adjust the recommendations
and other reports to their radiation oncology practice, monitoring and audit
the QA program.
Along with its arrangement and task of obligations, the QAC should be
given the authority by the department chairmen and support by the top
hospital administration to perform its tasks.
1.3.

Comprehensive QA Team

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Comprehensive QA for Radiation Oncology

The comprehensive QA team includes radiation oncologists, radiation
oncology physicists, radiation therapists, dosimetrists, nurses, and data entry
managers. Each member of the QA team should know his/her responsibilities,
be trained to perform them, and know what actions are to be taken should a
test or activity give a result outside the limits of set up acceptable criteria.
1.4.

Policies and Procedures Manual

A policies and procedure manual should contain a clinical procedures
for evaluating the patient, plan of treatment, follow up, mortality and
morbidity review, technical procedures for treatment, treatment planning,

machine QA, and radiation safety. It is required by JCAHO (1987, 1992) and
should be updated as procedures change, and should be reviewed once per
year by the QAC and signed and dated by the appropriate section heads [16].
1.5.

Quality Audit

Quality audit is a systematic and independent examination and
evaluation to determine whether quality activities and results comply with
planned arrangements and whether the arrangements are implemented
effectively and are suitable to achieve objectives [3]. Sometimes the audits
may be made by persons within the association according to written
procedures, but they should also be periodically performed by an outside
group. Quality audit can be conducted for external or internal purposes. And
external monitoring is an example of it. For example, a mailed
thermoluminescent dosimeter (TLD) service can be utilized to verify that the
treatment unit calibration is consistent with national and international
standards.
1.6.

Resources and Continuous Quality Improvement.
The chairman of the radiation oncology department should assure that

resources are available in order to have an effective QA program. Resources
include personnel; QA test tools and equipment; assigned time for
performance of QA program (e.g., machine availability for dosimetry QA,
auditing of charts); assigned time for in-service educational programs
including presentations of the QA program; external review (e.g., external
6

Comprehensive QA for Radiation Oncology

audit of program by outside experts, TLD service for redundant monitoring of
the treatment machines).
The quality of patient management within the radiation oncology
service should improve as needs be. The QA Team and the QAC should keep
pace and use new information to improve the quality of patient care, and the
documented QA program should reflect these improvements.

7


Comprehensive QA for Radiation Oncology

CHAPTER 2: QA OF EXTERNAL BEAM RADIATION
THERAPY EQUIPMENT

A QA program should be based on an exhaustive investigation for
baseline standards at the time of the acceptance and commissioning of the
equipment for clinical use [6]. This section describes a QA program for
commonly used radiation therapy equipment such as medical electron
accelerators or simulators.
A list of tests for typical QA program is summarized in Tables 1-3.
These tables include performance tests, tolerances, and frequencies. The tests
are distributed among daily, monthly, annually tests.
2.1.

QA of Medical Electron Accelerators
Medical electron accelerators presently occupy the majority of

radiation therapy treatment units. The machine parameters and tolerance
values in Table 1 include the parameters described in AAPM Report 13
(AAPM, 1984) and some additional parameters appropriate to the newer
generation equipment.
The tolerance values are more stringent for monthly output checks
because these are performed by a physicist with an ionometric dosimetry
system that is adequate for calibration by an Accredited Dosimetry
Calibration Laboratory. While the tolerance values for daily output checks
have lower accuracy because of limited time or less precise devices.
Table 1: The performance tests, tolerances, frequencies of medical electron
accelerators [3]

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Comprehensive QA for Radiation Oncology

9


Comprehensive QA for Radiation Oncology

2.2.

QA of Simulators
Simulators are designed to duplicate the geometric conditions of the

radiation therapy equipment. They should be checked for image quality
according to establishes guidelines for analytic radiography units. QA test for

them are described in Table 2.
Table 2: The performance tests, tolerances, frequencies of simulators [3]

2.3.

QA of CT Scanners

CT Scanners used commonly in radiation therapy treatment planning
should be necessary part of the QA program. An imitated laser system used
on the simulation and treatment units should be mounted in the CT suite and
the alignment of laser should be checking daily. Moreover, the position of the
intersection of the lasers on CT scans with patient’s skin is usually determined
by placing radio-opaque catheters on the laser-skin intersection prior to the
initiation of scanning. Furthermore, the image quality and other parameters of
CT scanner should be checked in QA protocol provided by the manufacturer.

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Comprehensive QA for Radiation Oncology

2.4.

QA of Measurement Equipment
QA of measurement equipment is an important part of QA program as

well as other radiation treatment equipment. The QA tests, their frequency
and the tolerance limits are given in Table 3.
Table 3: The performance tests, tolerances, frequencies of measurement
equipment [3]

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Comprehensive QA for Radiation Oncology

CHAPTER 3: TREATMENT PLANNING COMPUTER SYSTEM

The treatment planning computer system is an important component of
the entire treatment process. It can calculate dose distribution and design
significant method of patient treatments. These systems need to undergo strict
acceptance tests and commissioning, and a QA program can be established
and implemented. Moreover, it is important that these systems should come
with complete and clear documentation.
3.1.

Program Documentation

Program documentation is one of the most basic portions in a treatment
planning system. The user of any new system always expects that the
manufacturer will provide full documentation about the hardware and
software of a treatment planning system. This documentation includes beam
data library, dose calculation models, and operating instruction and data I/O.
The manufacturer should give clear documentation on procedures for
acquiring and transferring beam and other necessary data to treatment
planning system’s data library. And they also should provide a complete
description about physical models used for calculating dosimetry.
3.2.

Test Procedures

Initial Manufacturer’s Tests. The manufacturer should make their own

documentation of software testing’s program of the treatment planning system
and supply information on error rate or type of errors discovered in system’s
field operation. Additionally, they also should provide a schedule for software
upgrades too.
Initial User Test Procedures. The user should commission computer
software for each treatment machine, energy, modality and for each isotope at
the time of software’s purchase and every time a software upgrade is
installed. Moreover, they should compare the calculated dose distributions for
select set of treatment conditions in standard phantom with measured dose
distribution for the same phantom. In addition, it is needed to use

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Comprehensive QA for Radiation Oncology

manufacturer’s dose calculation algorithms or an alternate algorithm. It is
necessary to establish a reference set of treatment planning test cases included
dose distributions for each energy, mode for external beam therapy or each
source for brachytherapy and type of treatment plan arrangement. And this set
can be used for annual recommissioning of the treatment planning system.
Tests After Program Modification. QA tests are always performed on
the treatment planning system after program modification. The tests should
utilize a reference set of QA treatment plans and the results should be
compared with the initial accepted test results.
Ongoing tests. The QA tests should be regularly performed in treatment
planning system as given in Table 4. A monthly checksum of data and object
files should be compared against the previous checksums. If checksum is not

available, a monthly spot-checks on a subset of the initial planning reference
set can replace them. A daily QA procedure to test the input-output should be
established.
Table 4: QA for treatment planning systems and monitor unit calculations [3]

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Comprehensive QA for Radiation Oncology

CHAPTER 4: EXTERNAL BEAM TREATMENT PLANNING

In this part, QA for the treatment planning process is discussed. QA in
treatment planning refer to any of three distinct processes [3].
The first process is nongraphical planning. It is used for single and
parallel opposed fields. The monitor units (minutes) for the prescribed dose to
a point on the central axis is usually calculated by using central axis depth
dose, tissue phantom ratios (TPRs) or tissue maximum ratios (TMRs), and
beam output calibration tables. Moreover, the field apertures, which define
the treatment volume, are usually designed on radiographs obtained during
simulation.
The second process is traditional graphical planning used for many
patients. In this way, a target volume is defined from orthogonal simulation
films, and the patient’s contour is either obtained using a mechanical device
(e.g., lead solder wire) or from CT. The field arrangements are designed and
dose distributions calculated on a limited number of axial cross sections using
a computerized treatment planning system. Then the radiation oncologist
prescribes the dose to a point or an isodose curve, and the field apertures are
usually defined from simulation films.
And the third method is 3D treatment planning. This method differs

from two methods above in that target volumes, normal tissue volumes, and
surface contours are obtained directly from CT. Moreover, the field apertures
are designed using beam’s-eye-view (BEV) rather than from simulation
radiographs.
4.1.

Treatment Planning Process
Treatment planning is a process that starts with patient data acquisition

and through graphical planning, plan implementation and treatment
verification. And it is described in the following sections.
4.1.1 Prescription
The prescription should be written, signed and dated by the radiation
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Comprehensive QA for Radiation Oncology

oncologist prior to treating patient. It should contain the dose per fraction,
total dose, number of fraction, number of fraction per day and the prescription
point or isodose curve (or surface). In addition, if the tolerance dose for
critical structure differs from departmental policy, it should be written into the
prescription. The prescription should also include a definition of the target
volume, which is common in graphical planning or when designing field
apertures for single or opposed fields. Moreover, the target volume and field
apertures should be signed and dated by the radiation oncologist.
4.1.2. Positioning and Immobilization
Positioning patients comfortably and reproducibly on the simulator,
CT, MRI, and treatment units, and maintaining them in a fixed position
during the course of imaging and treatment are really important. A number of

techniques such as tape, casts and bite block systems can be used for
immobilization.
4.1.3. Data Acquisition
Diagnostic units including simulations, CT, MRI, and ultrasound are
utilized for acquiring patient contours and target and normal organ volume.
Immobilization devices should be attached to the diagnostic and treatment
couches and imaged with CT, MRI and ultrasound without artifacts. It is
important to keep patient stay still during the treatment planning process or
treatment course. Since patient motion can distort MRI and CT images and
then change linear attenuation coefficients derived from CT.
The registration of patient data between CT, MRI, other diagnostic
devices, simulators and treatment units should be verified. This can be
performed by imaging phantoms on the different imaging and treatment
units. In addition, it is necessary to obtain or confirm the relationship between
CT number and electron density [3].
4.1.4. Contouring
The most common technique of obtaining body outlines is to contour a
strip of solder wire or plaster of paris to the body of the patient, transfer the
contouring device to a sheet of paper, and trace the patient’s contour. It is
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Comprehensive QA for Radiation Oncology

important to measure the distance between at least three points which have
been marked on the contour. Since offset errors are not uncommon, the
calipers which used to measure the distance should be checked regularly.
Specialized mechanical devices such as pantographs may be used to
obtain patient contours because they may have better accuracy and
reproducibility. In addition, Moire photography, other optical techniques and

ultrasound are also utilized. The contouring accuracy is recommended within
0.5 cm [4].
4.1.5. Data Transfer
One method of inserting patient data into the treatment planning
computer is to digitize plane film or hard copy CT. Data transfer errors can
occur because of digitizer nonlinearities and malfunctions, so digitizers
should be checked daily. On the other hand, data can be transferred more
directly through tape, floppy discs, or computer network. Data transfer
routines should be intended to check the integrity of the transfer.
4.1.6. Target volume and Normal Organ Definition
The target volume uncertainties are related to uncertainties in the tumor
mass size and the extent of microscopic spread of disease. Therefore, high
quality imaging on treatment simulators and other imaging devices are
important. For example with CT, the contrast setting can affect the size of the
target volume.
In designing target volumes, an extra margin should be included to
compensate for organ movement, setup errors, and other technical
uncertainties. Contrast agents are used, when appropriate, to identify critical
organs.
4.1.7. Aperture Design
In treatment planning, field apertures are often determined from
simulation films. Therefore, precise specification of the magnification
components is important. In three-dimensional treatment planning systems,
apertures can be defined interactively using beam’s-eye-view (BEV)

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Comprehensive QA for Radiation Oncology

computer displays in which volumes are projected onto a plane along ray lines
that emanate from the source. BEV accuracy, which is a function of gantry
angle, collimator angle, field size and isocentre distance, should be confirmed
before using, after software modifications and checked as a part of ongoing
QA.
4.1.8. Computation of Dose Distributions
The accuracy of dose distribution calculations relies on machine input
data, approximations made in dose calculation algorithms, patient data
including inhomogeneities. The accuracy of treatment machine parameters
such as flatness and symmetry should be maintained. The dose computation
algorithms should be checked as major aspect of the commissioning and
ongoing QA of the treatment planning system.
4.1.9. Plan Evaluation
The evaluation of treatment plans usually contains review of isodose
distributions as displayed on a video monitor or hard copy. Dose volume
histograms (DVHs) are often added to the 3D treatment planning systems
review process. The dose distribution calculations can be sensitive to the grid
size, and dose volume histograms can additionally be sensitive to the dose bin
size [10].
4.1.10. Computation of Monitor units
The number of monitor units (or minutes) required to fulfill the
prescription is obtained either directly from the treatment planning system,
by an independent computerized monitor unit calculation routine, or by
“hand calculations” using percent depth dose (PDD), TPRs, TMRs, and
machine calibration tables [8]. The accuracy of these calculations is affected
by a number of factors, which are listed in Table 5.
Table 5: Factors effecting monitor unit (minute) calculations [3]

17