1016 / 1096
S1000
ESTRO 36
_______________________________________________________________________________________________
Conclusion
Both the 6-field IMRT and the VMAT technique can be used
to spare the humeral head and surrounding tissues as
aimed for in the ESTRO guidelines while still achieving
proper target coverage. The IMRT technique discussed in
our study resulted in a lower dose in the OARs and
consequently this technique has been implemented in our
institute.
EP-1825 Evaluation for the usability of the Varian
Standard Couch modeling using Treatment Planning
System
Y.M. Yang
1
, Y.M. Song
1
, J.M. Kim
1
, J.M. Choi
1
, B.K. Choi
1
1
Samsung Medical Center, Radiation Oncology, seoul,
Korea Republic of
Purpose or Objective
When a radiation treatment, there is an attenuation by
Carbon Fiber
Couch.
In this study, we tried to evaluate the usability of the
Varian Standard Couch(VSC) by modeling with Treatment
Planning System (TPS)
Material and Methods
VSC was scanned by CBCT (Cone Beam Computed
Tomography) of the Linac(Clinac IX, VARIAN, USA),
following the three conditions of VSC, Side Rail Out
Grid(SROG), Side Rail In Grid(SRIG), Side Rail In Out Spine
Down Bar(SRIOS). After scan, the data was transferred to
TPS and modeled by contouring Side Rail, Side Bar Upper,
Side Bar Lower, Spine Down Bar automatically.
We scanned the Cheese Phantom(Middelton, USA) using
Computed Tomography(Light Speed RT 16, GE, USA) and
transfer the data to TPS, and apply VSC modeled
previously
with
TPS
to
it.
Dose was measured at the isocenter of Ion Chamber(A1SL,
Standard imaging, USA) in Cheese Phantom using 4 and 10
MV radiation for every 5° gantry angle in a different filed
size(3X3cm², 10X10cm²) without any change of MU(=100),
and then we compared the calculated dose and measured
dose. Also we included dose at the 127° in SRIG to
compare the attenuation by Side Bar Upper.
Results
The density of VSC by CBCT in TPS was 0.9g/cm³, and in
the case of Spine Down Bar, it was 0.7g/cm³. The radiation
was attenuated by 17.49%, 16.49%, 8.54%, and 7.59% at
the Side Rail, Side Bar Upper, Side Bar Lower, and Spine
Down Bar. For the accuracy of modeling, calculated dose
and measured dose were compared. The average error was
1.13% and the maximum error was 1.98% at the 170°beam
crossing the Spine Down Bar.
Conclusion
To evaluate the usability for the VSC modeled by TPS, the
maximum error was 1.98% as a result of compassion
between calculated dose and measured dose. We found
out that VSC modeling helped expect the dose, so we think
that it will be helpful for the more accurate treatment.
EP-1826 Analysis of dose distribution with change of
the air gap when proton therapy using line scanning
S. Seo
1
1
samsung medical center, radiation oncology, Seoul,
Korea Republic of
Purpose or Objective
When proton therapy of cranio-spinal irradiation (with
prone position) using line scanning technique, there is a
motion of spinal code caused by breathing. According to
our clinical experience, we could find out the length of
breathing motion is up to 20mm. Because of this motion,
the air gap(defined as the distance from nozzle to surface)
could be changed. In this study, we are going to find out
the target dose distribution in various air gap.
Material and Methods
Sumitomo proton therapy machine(SHI, JAPAN) and
robotic couch(Forte, USA) have been used for this study.
CT scans were performed using GE Discovery CT-590 RT.
In order to measure the target dose, glass dosimeter(AGC
Techno, JAPAN) and atom phantom(Norflok, CIRS, USA)
were used. For treatment planning, Ray Station(Ray
search ver. 5.0, USA) has been used. Mean and D95 were
analyzed shifted points from isocenter in PTV of lower
spine which has significant effect from patient’s
respiratory motion. The shifted pitch was ±10mm, ±20mm.
Results
As a result of analysis, D95 dose at each depth are as
follows:
iso-center:
2347.4(100%),
iso-10mm:
2302.3(98.1%), iso+10mm: 2341.9(99.7%), iso-20mm:
2281.4(97.2%), iso+20mm: 2361.7(100.6%). And mean dose
at each depth are as follows: iso-center: 2389.2(100%),
iso-10mm: 2355.1(98.6%), iso+10mm: 2394.7(100.2%), iso-
20mm: 2335.3(97.7%), iso+20mm: 2415.6(101.1%).
Conclusion
The main purpose of this study is to confirm that the air
gap changes may affect the target dose or not when
proton therapy using line scanning. The difference of
prescribed dose due to a change of air gap is only D95: -
2.8% ~ 0.6%, mean: -2.3% to 1.1%. So even though the air
gap changes, it dose not affect to target dose. Therefore,
line scanning proton therapy can be seen clinically useful.
EP-1827 Dosimetric comparison of 3D-CRT, IMRT and
VMAT for bilateral breast irradiation
H.M. Hung
1
1
Princess Margaret Hospital, Department of Oncology-
Radiotherapy Centre, Kowloon, Hong Kong SAR China
Purpose or Objective
Breast cancer is the most common cancer worldwide
amongst females and ranked the 5th cause of cancer death
in 2012. There were 1.67 million new breast cancer cases
diagnosed, and contributed to more than 25% of the total
number of new cases of cancer diagnosed. The incidence
rate of female breast cancer in Hong Kong has been tripled
in the past twenty years. Some of the patients may
suffered from synchronous bilateral breast cancer which
involved a more complex radiotherapy planning as both
lungs, the heart and a large irradiated volume are
involved. The aim of this study was to evaluate the
dosimetric difference between three breast irradiation
techniques: 3-Dimensional Conformal Radiotherapy (3D-
CRT), Intensity-modulated Radiotherapy (IMRT) and
Volumetric-modulated Arc Therapy (VMAT) on bilateral
breast radiotherapy.
Material and Methods
20 breast cancer patients were previously treated with
adjuvant radiotherapy, with the prescription of 50Gy over
25 daily fractions to 100% isodose level. 3-dimensional CT-
based treatment planning of the three bilateral breast
irradiation techniques was performed and all plans were
calculated by Acuros External Beam (AXB) algorithm. The
cardiac dose, lung dose, conformity, homogeneity, low
dose spillage, the overall planning, simulation and
treatment time were analyzed and compared.