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statistically significantly reduced for all other treatment
technique combinations when compared with IMRT in FB,
and when proton therapy in DIBH was compared to proton
therapy in FB. Heart dose and the ERRs of myocardial
infarction and heart failure were significantly reduced
when proton therapy in DIBH was compared to IMRT in
DIBH. However, when proton therapy in FB was compared
to IMRT in DIBH no statistically significant differences
were seen for any doses or ERRs. To further analyze the
differences between proton therapy in FB and IMRT in
DIBH, the paired differences in heart dose from the
techniques were calculated (proton therapy in FB minus
IMRT in DIBH). The resulting median difference was 0.0 Gy
(range -4.3 to 3.5), revealing that the relative benefit of
these two techniques with respect to heart dose is
patient-specific. Furthermore, mean DVHs for the heart
show that, on average, the volume of the heart receiving
a dose above about 7 Gy is greater for proton therapy in
FB than it is for IMRT in DIBH (Figure 1).
Conclusion
DIBH and proton therapy both reduced the dose to cardiac
structures and the risk of cardiac toxicity, compared to
IMRT in FB, but no significant difference was found
between IMRT in DIBH and proton therapy in FB.
Therefore, with respect to cardiac toxicity, these data
suggest that given a choice in techniques, IMRT in DIBH
and/or proton therapy should be selected. However, the
difference between IMRT in DIBH and proton therapy in FB
is variable and should be evaluated on a patient-specific
basis.
PO-0814 The Influence of scans parameters on
effective dose of CBCT scans used for IGRT proce dures
Abuhaimed
1
, C. J. Martin
2
, M. Sankaralingam
3
1
King Abdulaziz City for Science and Technology,
Department of Applied Physics, Riyadh, Saudi Arabia
2
University of Glasgow, Department of Clinical Physics,
Glasgow, United Kingdom
3
Beatson West of Scotland Cancer Centre, Department of
Radiotherapy Physics, Glasgow, United Kingdom
Purpose or Objective
A new software with a version of (V2.5) of On-Board
imager (OBI) system, which is utilized in the clinic for
image guided radiation therapy (IGRT) procedures, was
released recently by Varian with new scan protocols. This
study aimed to investigate the influence of parameters of
the new protocols on the effective dose (E) compared to
the previous version (V1.6).
Material and Methods
Effective dose of three scan protocols (head, t horax, and
pelvis) were estimated using Monte Carlo s imulations.
BEAMnrc and DOSXYZnrc user codes were used to simulate
the OBI system integrated into a TrueBeam linac, and to
calculate organ doses resulting from the protocols
employed. Organ doses were evaluated for the ICRP adult
male and female reference computational phantoms. The
main differences between the software versions (V1.6)
and (V2.5) are: (1) the beam width was extended to 214
mm instead of 198 mm, (2) the mAs values were increased
to (150, 270, 1080) compared to (147, 267, 1056) for head,
thorax, and pelvis, respectively, and (3) the projections
number was increased to 500 for head scan compared to
367, and to 900 for thorax and pelvic scans instead of 660.
Results
The use of the scan protocols implemented in V2.5
resulted in increasing E of head scan by 13% and 12%,
where E of V1.6 was 0.27 mSv and 0.44 mSv for male and
female phantoms compared to 0.31 mSv and 0.49 mSv for
V2.5, respectively. Parameters of the new protocols, also,
led to rise E of thorax and pelvic scans by 16% and 17% for
male, respectively, and by 16% for female. E of thorax and
pelvic scans increased from 3.32 mSv and 5.95 mSv to 3.86
mSv and 6.88 mSv for male, respectively, and from 3.97
mSv and 11.38 mSv to 4.65 mSv and 13.16 mSv for female,
respectively.
Conclusion
CBCT scans play a major role in radiotherapy treatment.
The scan protocols with the new parameters were
implemented into the new software to improve the image
quality acquired with the scans, and to extend the field of
view. This helps to improve the patient positioning on the
treatment couch and deliver the specified dose to the
patient with a high accuracy, and hence optimising the
treatment output. The new head, thorax, and pelvic scans
only increased E values by 12 – 13%, 16 – 17%, and 16%,
respectively, for male and female. These increases are
acceptable when compared to improvement of the
treatment output.
PO-0815 External neutron spectra measurements for a
single room compact proton system
R. Howell
1
, E. Klein
2
, S. Price Hedrick
3
, M. Reilly
4
, L.
Rankine
5
, E. Burgett
6
1
UT MD Anderson Cancer Center Radiation Physics,
Radiation Physics, Houston- TX, USA
2
Northwell Health System, Medical Physics, Lake Success,
USA
3
Provision Center for Proton Therapy, Radiation
Oncology, Knoxville, USA
4
Washington University, Radiation Oncology, St. Louis,
USA
5
The University of North Carolina, Radiation Oncology,
Chapel Hill, USA
6
Idaho State University, Nuclear Engineering, Pocatello,
USA
Purpose or Objective
Secondary external neutrons are produced within the
physical components of the proton beam line e.g., the
double scatterer, modulation wheel, compensator, and
field aperture. In passive scattered proton therapy,
external neutrons account for a majority of neutron dose
equivalent for small fields and up to 50 % for large fields.
Spectra measurements are needed to fully and accurately
understand neutron dose equivalent from external
neutrons. Such data should be reported for proton
beamlines from each manufacturer. Here, we focused on
the single room compact proton system manufactured by