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Figure 2: Gamma passing rate for the plans (6 MV) with
errors, normalized to the detectability threshold,
measured by SRS, 729 (merged) and 1500 (merged)
dosimeters.
Conclusion
Improving the resolution of the planar detector used for
QA increases the points with gamma<1.
The SRS matrix can detect delivery errors in almost all
cases at 2%L/1mm.
Reference
[1]
G. A. Ezzell et al., 'IMRT commissioning: Multiple
institution planning and dosimetry comparisons, a report
from AAPM Task Group 119,” Med. Phys
36
, 5359 (2009)
.
OC-0532 QA of stereotactic radiotherapy combined
with electromagnetic MLC tracking by a silicon
detector
M. Petasecca
1
, M.K. Newall
1
, M. Duncan
1
, V. Caillet
2
, B.
James
1
, J.T. Booth
2
, M.L.F. Lerch
1
, V. Perevertaylo
3
, P.
Keall
4
, A.B. Rosenfeld
1
1
University of Wollongong, Centre for Medical Radiation
Physics, Wollongong NSW, Australia
2
Royal North Shore Hospital, Northern Sydney Cancer
Centre, Sydney - NSW, Australia
3
SPA-BIT, Microelectronics, Kiev, Ukraine
4
University of Sydney, Radiation Physics Laboratory-
School of Medicine, Sydney - NSW, Australia
Purpose or Objective
Optimisation of treatment delivery based on patient-
specific intra-fractional changes in anatomy is compulsory
in organs affected by breathing or cardiac cycle. MLC
tracking by using electromagnetic transponders implanted
in the tumor is one strategy to adapt the beam shape and
position in real-time. MLC tracking combined with highly
conformal delivery modalities such as SRT has been shown
to be feasible for lung and liver cancer treatment on a
standard linac. QA for such treatments requires
specialised tools with high spatial resolution for accurate
measurement of sharp dose fall-off and high timing
resolution for verification of the interplay of effects
between organ motion and modulation of the irradiation
fields. A dosimetry system for fast verification of the
performance of MLC tracking in SRT is proposed.
Material and Methods
A monolithic 2D silicon detector, known as DUO, has been
developed and comprises 512 pixels each with size
40x800mm
2
and pitch 0.2mm arranged in two linear
orthogonal arrays. The DUO is read out by a multichannel
electrometer synchronised with the linac. For evaluation
of the accuracy and effectiveness of MLC tracking in both
soft tissue and lung, we placed DUO in a solid water
phantom, homogeneous timber phantom and timber
phantom with a solid water spherical hidden target of 1
cm diameter. We installed the phantoms on a moving
platform supplied with a set of patient-specific motion
patterns. The commercial Calypso system provides real-
time position of the target to the MLC software which has
been tested using a predictive and non-predictive tracking
algorithm. We planned the target dose using 3DCRT (a 2
cm diameter field) and IMRT (with 5mm margins)
treatments. Measurements performed by DUO are
compared to EBT3 film for cases with and without motion,
as well as motion with the MLC tracking algorithms
enabled.
Results
Fig.1 shows the comparison of the SUP-INF 3DCRT static
beam profile measured by DUO in the solid water phantom
and the same beam delivered using a patient specific
breathing motion pattern with and without MLC tracking.
The predictive tracking has a lower discrepancy with
respect to the static beam showing a reduction of the
beam misplacement from ±70% to ±12% and ±58% to 20% in
the solid water and timber phantom respectively.
Discrepancies between DUO and EBT3 are within 2.4%
overall. Temporal analysis shows the interplay effects
between beam position and target motion with clear
difference between predictive and non–predictive
algorithms.
Conclusion
It is observed that motion distorts the planned dose profile
in both solid water and lung phantom. MLC tracking
reduces dose smearing significantly as demonstrated by
the no-motion and motion-tracking results. The DUO
detector has proven to be an effective tool for pre-
treatment verification of real-time adaptive stereotactic
deliveries with both high spatial resolution for dose
profiling and high temporal resolution for pulse by pulse
dose reconstruction.
OC-0533 ADAM: a breathing phantom for testing
radiotherapy treatment on moving lesions
S. Pallotta
1
, L. Foggi
1
, S. Calusi
1
, L. Marrazzo
1
, C.
Talamonti
1
, L. Livi
2
, G. Simontacchi
2
, R. Lisci
3
1
University of Florence, Department of Medical Physics,
Firenze, Italy
2
University of Florence, Department of Radiotherapy,
Firenze, Italy
3
University of Florence, Department of Agricultural-
Food and Forestry System, Firenze, Italy
Purpose or Objective
Dose delivery to moving targets can be approached
following different strategies. For stereotactic
radiotherapy treatments motion-encompassing methods,
respiratory-gating
techniques
and
respiration-
synchronized techniques permit the treatment during
lesions motion using different dose planning/delivering
solutions. In all cases the complexity of the proposed
methods needs the development of solutions for accurate
Quality Assurance tests as stated also by AAPM TG76. For
this purpose we developed a new phantom: ADAM
(Anthropomorphic Dynamic breAthing Model), capable of
simulating realistic patient movements. The phantom and
some preliminary tests showing ADAM performances are
here presented.
Material and Methods
ADAM is a 3D printed anthropomorphic phantom created
using a real patient CT data. The central portion of the