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Conclusion
The investigated beam model showed excellent
agreement with measured data over a wide range of field
sizes and measurement depths with improved agreement
for small field sizes. These commissioning results are a
solid basis for ongoing investigations focusing on more
complex treatment types such as IMRT and VMAT and
heterogeneous phantoms.
PO-0806 Dosimetric end-to-end test procedures using
alanine dosimetry in scanned proton beam therapy
A. Carlino
1,2
, H. Palmans
1,3
, G. Kragl
1
, E. Traneus
4
, C.
Gouldstone
3
, S. Vatnitsky
1
, M. Stock
1
1
EBG MedAustron GmbH, Medical Physics, Wiener
Neustadt, Austria
2
University of Palermo, Department of Physics and
Chemistry, Palermo, Italy
3
National Physical Laboratory, Radiation dosimetry,
Teddington, United Kingdom
4
Raysearch
laboratories AB, Particle therapy, Stockholm, Sweden
Purpose or Objective
At MedAustron (MA) a quasi-discrete scanning beam
delivery with protons has been established. The clinical
implementation
of
this
technology
requires
comprehensive end-to-end testing to ensure an accurate
patient treatment process. The purpose of such end-to-
end testing is to confirm that the entire logistic chain of
the radiation treatment, starting from CT imaging,
treatment planning, patient positioning, monitor
calibration and beam delivery is operable and leads to the
dose delivery within a pre-defined tolerance. We present
dosimetric end-to-end procedures for protons based on
customized anthropomorphic phantoms and different
dosimetric techniques.
Material and Methods
A homogeneous polystyrene phantom and two
anthropomorphic phantoms (pelvis and head phantom)
have been customized to allocate different detectors such
as radiochromic films, ionization chambers and alanine
pellets. During testing, the phantoms were moving
through the workflow as real patients to simulate the
entire clinical procedure. The CT scans were acquired with
pre-defined scan protocols used at MA for cranial and
pelvic treatments. All treatment planning steps were
performed with RayStation v5.0.2 treatment planning
system (TPS). A physical dose of 10 Gy was planned to
clinically shaped target volumes in order to achieve
uniformity better than 0.5% on the dose delivered to the
alanine pellets. In the treatment room the plans were
delivered to the phantoms loaded either with alanine
pellets and radiochromic EBT3 films (figure 1) or two
Farmer chambers. The alanine pellets (5.0 mm diameter
and 2.3 mm thickness) and their read-out were provided
by the National Physical Laboratory (NPL). One of the
challenges of alanine for dosimetry in particle beams is
the known response dependency (quenching) on the
charge, the fluence and the energy of the particles
constituting the mixed radiation field. Corrections for this
were derived by a Monte Carlo dose calculation platform
implemented in a non-clinical version of RayStation.
Results
The measured absolute dose to water obtained with the
Farmer chamber in all delivered plans was within 2% of the
TPS calculated dose. A lateral 2D homogeneity of 3% inside
the treatment field was measured with EBT films. Doses
determined with the alanine pellets after correction for
the quenching effect showed a mean deviation within 3%
and a maximum deviation below 7% in the homogeneous
and anthropomorphic phantoms.
Conclusion
The end-to-end test procedures developed at MedAustron
showed that the entire chain of radiation treatment works
efficiently and with accurate dosimetric results. Our
experience shows that alanine pellets are suitable
detectors for dosimetry audits and developed procedures
can be used to support implementation of scanning beam
delivery technology in clinical practice
.