Analysis of Interfractional Setup Errors and Intrafractional Organ Motions during IMRT for Head and

1
Analysis of Interfractional Set-up Errors and
Intrafractional Organ Motions during IMRT for
Head and Neck Cancers to Define an Appropriate
PTV-margins
Minoru Suzuki, a, b Yasumasa Nishimura, a
Kiyoshi Nakamatsu, a Masahiko Okumura, c
Hisayuki Hashiba, c Ryuta Koike, a Shuichi
Kanamori, a Toru Shibata, a a Department of
Radiation Oncology, Kinki University School of
Medicine, b Radiation Oncology Research
Laboratory, Research Reactor Institute, Kyoto
University c Depatment of Central Radiological
Service, Kinki University School of Medicine
Figs. 4 and 5. The distribution of the
interfractional set-up errors and intrafractional
organ motions of the mandible.

• The systematic intrafractional organ motion error
  for a specific patient, Sp-intra, is calculated
  as the mean value for intrafractional organ
  motion errors of that patient. The mean of
  Sp-intra over all patients in a given population
  is denoted by µ-intra, whereas its SD is given by
  S-intra. The random intrafractional organ motion
  errors for a specific patient, sp-intra, was
  calculated as the SD of the intrafractional organ
  motion errors from interval to interval. To
  characterize the random errors in a population,
  an appropriate average is calculated over the
  patient group, which is denoted by s-intra .
  Distribution of intrafractional organ motion
  errors in a given population is characterized by
  the set (µ-intra,S-intra, s-intra) as the
  interfractional set-up errors.

• Deviations of the coordinates of each bony
  landmark in the beam films from those in the
  simulation films were measured as the set-up
  error for each bony landmark.

? The purposes of the present study were to
analyze the interfractional set-up errors and
intrafractional organ motions and to define
appropriate planning target volume (PTV)-
margins.
L-R
Fig. 4 (a)
Fig.4(c)
A-P
Fig. 4 (b)
C-C
9
10
9
m -0.2 S-INTER
1.3 s-INTER 1.0
m -0.1 S-INTER
0.8 s-INTER 0.9

• To calculate displacement or standard deviations
  (SDs) for systematic and random errors, we
  referred to Rameijer et al. The systematic
  interfractional setup error for a specific
  patient, Sp-INTER, is calculated as the mean
  value for setup errors of that patient. The mean
  of Sp-INTER over all patients in a given
  population is denoted by µ-INTER, whereas its SD
  is given by S-INTER. The random setup error for a
  specific patient, sp-INTER, was calculated as the
  SD of the setup errors from fraction to fraction.
  To characterize the random errors in a
  population, an appropriate average is calculated
  over the patient group, which is denoted by
  s-INTER. Distribution of the interfractional
  setup errors in a given population is
  characterized by the set (µ-INTER, S-INTER,
  s-INTER).

m -0.2 S-INTER
1.0 s-INTER 0.7
9
8
8
8
7
7
7
6
6
Number
6
5
5
5
4
4
4
3
3
3
2
2
2
1
1
1
0
0
0
Materials and Methods
0.6 0.8
0.6 0.8
-0.2 0.0
0.0 0.2
0.2 0.4
0.4 0.6
0.8 1.0
1.0 1.2
1.2 1.4
1.4 1.6
1.6 1.8
1.8 2.0
2.0 2.2
2.2 2.4
2.4 2.6
2.6 2.8
2.8 3.0
3.0 3.2
3.2 3.4
3.4 3.6
3.6 3.8
3.8 4.0
4.0 4.2
4.2 4.4
-0.2 0.0
0.0 0.2
0.2 0.4
0.4 0.6
0.8 1.0
1.0 1.2
1.2 1.4
1.4 1.6
1.6 1.8
1.8 2.0
2.0 2.2
2.2 2.4
2.4 2.6
2.6 2.8
2.8 3.0
3.0 3.2
0.0 0.2
0.2 0.4
0.4 0.6
0.6 0.8
0.8 1.0
1.0 1.2
1.2 1.4
1.4 1.6
1.6 1.8
1.8 2.0
2.0 2.2
2.2 2.4
2.4 2.6
2.6 2.8
2.8 3.0
3.0 3.2
-2.6 -2.4
-2.4 -2.2
-2.2 -2.0
-2.0 -1.8
-1.8 -1.6
-1.6 -1.4
-1.4 -1.2
-1.2 -1.0
-1.0 -0.8
-0.8 -0.6
-0.6 -0.4
-0.4 -0.2
-3.2 -3.0
-3.0 -2.8
-2.8 -2.6
-2.6 -2.4
-2.4 -2.2
-2.2 -2.0
-2.0 -1.8
-1.8 -1.6
-1.6 -1.4
-1.4 -1.2
-1.2 -1.0
-1.0 -0.8
-0.8 -0.6
-0.6 -0.4
-0.4 -0.2
-0.2 0.0
-2.6 -2.4
-2.4 -2.2
-2.2 -2.0
-2.0 -1.8
-1.8 -1.6
-1.6 -1.4
-1.4 -1.2
-1.2 -1.0
-1.0 -0.8
-0.8 -0.6
-0.6 -0.4
-0.4 -0.2
Fig. 5 (a)
Fig. 5 (b)
Fig. 5 (c)
L-R
A-P
Interfractional set-up error analysis
12
12
10
10

• Consecutive ten patients with head and neck
  cancers treated with IMRT were evaluated for
  analysis of the interfractional set-up errors.
  Table 1 shows the summary of patients
  characteristics.

8
8
Number
6
6
Interfractional setup errors and intrafractional
organ motion errors
4
4
2

• The values for the set of parameters (µ-INTER,
  S-INTER, s-INTER) and (µ-intra, S-intra, s-intra)
  measured for four bony landmarks are shown in
  Tables 3and 4, respectively.

2

• All patients were immobilized with a
  thermoplastic mask covering the head, neck and
  shoulders (Uni-frame form MED-TEC, Orange City,
  IA, USA.) (Fig.1).

Intrafractional organ motion analysis
0
0
1.2 1.4
0.6 0.8
0.0 0.2
0.2 0.4
0.4 0.6
0.8 1.0
1.0 1.2
-0.2 0.0
0.6 0.8
0.0 0.2
0.2 0.4
0.4 0.6
0.8 1.0
1.0 1.2
1.2 1.4
1.4 1.6
1.6 1.8
1.8 2.0
-1.0 -0.8
-0.8 -0.6
-0.6 -0.4
-0.4 -0.2
-0.2 0.0
-3.8 -3.6
-3.6 -3.4
-3.4 -3.2
-3.2 -3.0
-3.0 -2.8
-2.8 -2.6
-2.6 -2.4
-2.4 -2.2
-2.2 -2.0
-2.0 -1.8
-1.8 -1.6
-1.6 -1.4
-1.4 -1.2
-1.2 -1.0
-1.0 -0.8
-0.8 -0.6
-0.6 -0.4
-0.4 -0.2

• In an analysis of intrafractional organ motion,
  nine with head and neck cancers and three with
  malignant glioma were evaluated. Table 2
  shows the summary of patient characteristics.
• The method for intrafractional organ motion
  analysis was as follows.
• First, on the X-ray simulator (Ximatoron EX,
  Varian Assoc., Palo Alto, CA) with same table
  coach as our treatment system (Clinac-600C
  accelerator, Varian Assoc., Palo Alto, CA, USA),
  the patient was positioned and fixed with
  immobilizing device used at irradiation.
• Second, for 15 minutes, the AP and lateral
  images were digitally stored at 3 minutes
  interval (6 times) (Fig. 3).
• Third, the coordinates of the same bony landmarks
  were determined using the software in Somavision.
  
• In the present study, intrafractional organ
  motion error was defined as deviation of the
  coordinate of each landmark at each interval from
  that at the initial image taken at the start of
  the analysis.

Displacement (mm)
Fig.1
PTV- and PRV-margin

• Stroom et al. proposed an equation for
  appropriate PTV margin recipe, PTV-margin 2S
  0.7s. McKenzie et al. proposed the recommended
  margin around the ORs, the planning organs at
  risk volume (PRV-margin). They proposed an
  equation of PRV-margin 1.3S 0.5s for serial
  ORs or small, parallel ORs.
• The calculated PTV-margins were summarized in
  Table 6.

• ? At our department, as one of the procedures for
  quality assurance (QA) of the IMRT, we took two
  orthogonal, anterior-posterior (AP) and lateral
  films, for verification of the isocenter. The
  orthogonal films taken with treatment beam (beam
  film) were referred to those taken on the table
  of the X-ray simulator (simulation film).
• Analysis of the interfractional set-up error was
  performed by comparing total 170 beam films (85
  AP and 85 lateral films) with 20 simulation films
  (10 AP and 10 lateral films) for the 10 patients.
  Since the magnitude of the movement of the head
  and neck tumors may be varied according to the
  location of the tumors, the each position of four
  visible bony landmarks relative to the isocenter
  was assessed. The four landmarks included
  maxilla, mandible, skull base, and cervical
  vertebrae (Fig.2).

Fig. 3

• The distribution of the interfractional setup
  errors of the mandible and the intrafractional
  organ motion errors is shown graphically in Figs
  4 (a) - (c) and Figs 5 (a)-(c).

• The validity of the 5-mm PTV-margin at our
  institution can be verified because of small
  variations in the interfractional set-up errors
  and intrafractional organ motion errors.