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ESTRO 36
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IMRT for a Varian Clinac 2100 C/D with Millennium 80 and
two analogous plans for a Varian Clinac 2300iX with a
Millennium 120. For this last machine, a RapidArc plan was
also calculated. A HT treatment for Tomotherapy Hi-Art
was also planned for every patient.
Results
ID and NTID are 27% and 33%, respectively, larger for HT
compared to 6MV-IMRT Eclipse treatments. Statistically no
difference has been found for ID and NTID values between
RapidArc and IMRT treatments.
For IMRT treatments, no influence has been observed on
the size of MLC, the delivery technique (step-and-shoot or
sliding-window) and the number of fields. However, an ID
and NTID increments of 8% and 10%, respectively, are
reported when moving a plan from Eclipse to XiO. (Table
1).
The mean DVHs in Fig 1 show some differences depending
on the isodose evaluated. Higher values calculated below
20 Gy are compensated by the region from 20 Gy to 30 Gy,
where this technique minimizes the volume encompassed
by these isodose curves. For HT, there is no compensation,
as the volumes below 20 Gy are much higher than for the
other techniques. From 20 Gy to 30 Gy, the values are
comparable to IMRT, showing no advantage in terms of ID.
NORMAL TISSUE INTEGRAL DOSE (NTID) (·10
7
cGy·g)
Patie
nt
PTV
Volu
me
(cm3
)
IMR
T
XIO
SW
80
IMRT
ECLI
PSE
SW80
IMRT
ECLI
PSE
SW12
0
IMRT
ECLI
PSE
SS80
IMRT
ECLI
PSE
SS12
0
RAPIDA
RC
HT
1
181.2
0
1.2
9 1.26 1.23 1.25 1.23 1.23
1.6
4
2
140.9
4
0.9
8 0.92 0.90 0.91 0.90 0.91
1.2
7
3
228.9
6
1.4
4 1.39 1.36 1.39 1.35 1.35
1.7
3
4
180.4
2
1.3
1 1.28 1.26 1.28 1.25 1.24
1.6
3
5
234.2
2
1.3
6 1.33 1.29 1.33 1.28 1.29
1.7
2
6
204.1
4
1.6
3
1.43 1.39 1.43 1.39 1.40
1.8
5
7
175.3
8
1.5
2
1.31 1.27 1.31 1.27 1.27
1.7
2
8
276.0
4
1.8
3
1.63 1.60 1.62 1.59 1.65
2.1
1
9
209.7
8
1.4
0
1.23 1.22 1.23 1.21 1.21
1.5
4
10
256.6
0
1.9
4 1.76 1.73 1.75 1.72 1.75
2.2
7
Aver
age
208.
77
1.4
7
1.35
1.33
1.35
1.32
1.33
1.
75
SD
41.06
0.2
8
0.23
0.23
0.23
0.22
0.24
0.2
8
Typi
cal
error
(k=2)
0.1
8
0.14
0.14
0.14
0.14
0.15
0.
18
Table 1. NTID calculated from the dose volume
histograms, for every treatment plan, IMRT, RAPIDARC or
HT. For IMRT treatments, both delivering technique (SW
for sliding-window and SS for step-and-shoot) and MLC
characteristics (80 or 120 leaves) are indicated.
Fig 1. Dose volume histogram for the whole body averaged
over the 10 patients of this study, comparing every
treatment technique.
Conclusion
The source for higher values of ID and NTID for HT is the
larger volume receiving dose below 20 Gy. No differences
were found in the election of IMRT delivery. For RapidArc
plans, ID and NTID values are similar to IMRT.
EP-1472 Dosimetric E2E verification using 3D printing
and 3D dosimeter for brain stereotactic radiotherapy
M.S. Kim
1
, K.H. Chang
1
, J. Kwak
1
, G.M. Back
1
, T.Y. Kang
1
,
S.W. Kim
1
, Y. Ji
1
1
Asan Medical Center- Univ of Ulsan, Radiation Oncology,
Seoul, Korea Republic of
Purpose or Objective
To evaluate the dosimetric accuracy of brain stereotactic
radiotherapy (SRT) with a 3D dosimetry system and MRI,
we investigated dosimetric end-to-end verification using
3D printing technology and 3D dosimeter.
Material and Methods
We implemented an anthropomorphic head and neck
phantom with a 3D printed insert made using a 3D printer
designed by the Autodesk software and two gel-filled
spherical glass flasks as a patient having multiple target
brain cancer. For the feasibility study of the gel
dosimeter, the dose linearity, dose rate dependence, and
reproducibility for the gel dosimeter were verified. Gel-
filled vials were irradiated with 6 MV beams to acquire a
calibration curve of dose relation to R2 (1/T2) values in
9.4T MR images. Graded doses from 0 to 8 Gy with an
interval of 2 Gy were delivered. Two PTVs (PTV1,2) were
contoured on the MR images of phantom have dosimetric
gel tumor. To evaluate geometric and dosimetric
accuracy, a treatment plan was created such that D95s for
PTV1 and intentional PTV2 were more than the prescribed
dose. The intentional PTV2 was produced by intentionally
shifting by 5mm from the true target position. 2 arc VMAT
plan was created to deliver 35 Gy in 5 fractions. After
irradiation, calibration vials and phantom were scanned
by 9.4T MRI and then acquired images were analyzed using
an ImageJ and DCMTK software libraries. Scanned MRI
images of phantom were imported to a treatment planning
system and registered to CT images to compare dose
distributions. We also compared the agreement result
between the planned and the measured data in 1D (ion
chamber), 2D (gafchromic film), and 3D (Gel dosimeter).
Results
The best dose linearity was 0.99 (R
2
) at 180 TE (ms).
Reproducibility and dose rate dependency were less than
2.2% and 3.5%, respectively for 180 TE. Point dose
differences in plan vs. ion chamber were 1.08%, 0.47%,
and -2.82%, respectively, for PTV 1, 2, and intentional
PTV. And its differences between plan and gel were 0.98%,
1.66% and 3.76%, respectively, for PTV 1, 2, and shifted
PTV. Gamma passing rates with 3%/3mm criteria were
greater than 99% for all plans. Isodose distributions and