ESTRO 36 Abstract Book

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S504 ESTRO 36
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maximum frame per second (fps) under different settings
of pixel binning. The maximum fps of our current system
is limited to 0.98, 1.61 and 3.11 under 1×1, 2×2 and 4×4
pixel binning setting which corresponds to a spatial
resolution of 0.259, 0.518 and 1.036 mm/pixel
respectively. By tracking the movement of the edge of
leaves, the speed could be calculated. Further the
machine trajectory log files were also analyzed for
comparison and t-test was performed to evaluate the
statistical significance between our measured speeds and
those calculated from log file.
Results
The calculated speed of leaf #30 for both carriage A and B
is listed in Table 1. By analyzing the machine log file, the
speed of the same leaf was calculated to be 25.00±0.10,
15.05±0.12 and 4.99±0.12mm/s for carriage B;
25.00±0.12, 15.05±0.11 and 4.99±0.13mm/s for carriage A
under nominal speed 25, 15 and 5mm/s respectively. Our
measured MLC speed for 1×1 pixel binning setting and that
extracted from log data are also plotted in figure 1. T-test
results show that the p values are all larger than 0.3,
which suggest the measured results are not statistically
distinguishable from log data and our measurement is
accurate compared with log data. Similar results were also
obtained for other leaves.
Conclusion
The fluorescent screen-CCD based dosimetry system can
serve as an independent and reliable tool for QA of MLC
speed, whose temporal resolution as a motion monitor can
be further improved by using the camera with higher fps.
PO-0910 Is Linac-Based Total Body Irradiation (TBI) on
the coach by VMAT Feasable?
B. Tas 1, I.F. Durmus1, A. Okumus1, O.E. Uzel1
1 Yeni Yuzyil University Gaziosmanpasa Hospital,
Radiation Oncology, Istanbul, Turkey
Purpose or Objective
In our study, we investigate the use of Linac-Based TBI by
VMAT tecnique at nominal SAD on the coach. Eight TBI
patient’s treatment planning were performed using
Monaco5.1® treatment planning system with dual arc
VMAT tecniques for each patient.
Material and Methods
For treating patients, Versa HD ® (Crawley, Elekta) linear
accelerator with 6 MV, equipped with Agility ® collimator
system, XVI 5.0 cone beam CT was used as a Image Guided
Radiation Therapy (IGRT) method for VMAT delivery.
Agility ® collimator system included 160 MLC, minimum
leaf width was 5 mm. MLC effective speed was 6.5 cm/sec
and leaf travel was 15cm over the central axis. VMAT plans
were generated on Monaco 5.1 ® (Crawley, Elekta)
treatment planning system with Monte Carlo algorithm. All
calculation parameters were grid spacing 0.3
cm, minimum segment width 1.0 cm, Max. 180 of control
Points Per Arc, Fluence smoothing medium, Statistical
Uncertainty 1% per plan, increment of gantry 30° and dose
to medium.
The VMAT-TBI tecnique consisted of three isocentres and
three dual overlapping arcs from top of head to the
bottom of pelvis region. The prescribed dose was 90% of
target volume receiving dose of 12Gy. Mean dose to lung
and kidney were restricted less than 10Gy and maximum
dose to lens were restricted less than 6Gy. The plans were
verified using 2D array IBA Matrixx ® and CC13 ion chamber.
The comparison between calculation and measurement
were made by γ-index (3%-3mm) analysis and absolute
dose measurement at the isocentre.
Results
An average total delivery time was determined 923±34
seconds and an average monitor unit (MU)s was
determined 2614±231MUs for dual arc VMAT technique.
When we evaluated organ at risk(OAR)s, mean dose to
lungs was 9.7±0.2Gy, mean dose to kidneys was
8.8±0.3Gy, maximum dose to lens was 5.5±0.3Gy and
maximum point dose was 14.6±0.3Gy, HI of PTV was
1.13±0.2, mean dose to PTV was 12.6±0.15Gy and mean γ-
index (%3-3mm) pass rate was %97.1±1.9. Absolute doses
were measured by CC13 ion chamber and we determined
%2.0±0.6 dose difference between measurement and
treatment planning system's (TPS) calculation at the
isocentre.
Conclusion
The results show that dose coverage of target and OAR’s
doses are feasible for TBI using VMAT tecnique on the
coach. A benefit could be demonstrated with regard to
dose distribution and homogeneity and dose-reduction to
organs at risk. Additionally,we determined highly precise
dose delivery by patient QA and point dose measurement
at the isocentre. Based on the dose distributions we have
decided to plan TBI in our clinic with dual arc VMAT
technique on the treatment coach.
PO-0911 Can the therapeutic benefits of microbeam
radiation therapy be achieved using a clinical linac?
N. Suchowerska1, V. Peng1, L. Rogers1, E. Claridge-
Mackonis 1, D.R. McKenzie2
1Chris O'Brien Lifehouse, Radiation Oncology,
Camperdown- Sydney, Australia
2University of Sydney, School of Physics, Sydney,
Australia
Purpose or Objective
The increasing availability of high definition multileaf
collimators (HDMLCs) with 2.5mm leaves provides an
opportunity for ‘grid’ therapy to more closely approach
the clinical outcomes of Microbeam Radiation Therapy
(MRT). However, periodic spatial modulation of the dose
in the target volume runs counter to current clinical
practice. To optimize the modulation, a better
understanding of cell dose responses to such treatments is
needed. The aim of this study is to determine if some of
the therapeutic benefits of MRT can be achieved using a
clinical linac with HDMLCs and if so, to develop a
predictive model to optimize the benefits of such
treatments.
Material and Methods
Varian Novalis Tx TM HD120-MLCs were used to generate
grid patterns of 2.5mm and 5.0mm spacing, which were
dosimetrically characterized using GafchromicTM EBT3 film
[Figure 1]. Clonogenic survival of normal (HUVEC) and
cancer (lung NCI-H460, breast HCC-1954, melanoma
MM576) cell lines were compared in vitro for the same