799 / 1096
S783
ESTRO 36
_______________________________________________________________________________________________
Conclusion
The manufacturer's defined criteria for beam matching are
not strict enough and should be evaluated before to
interchange patients between two matched linacs. We
described a method of evaluation and a procedure of beam
matching for VMAT
.
EP-1466 Implementation of a linac head-mounted
matrix detector to clinical use for dynamic technique
L. Szczurek
1
1
International Oncology Centre Affidea Poznan, Medical
Physics, Poznan, Poland
Purpose or Objective
Quality assurance of VMAT plans based on the results in 2D
phantom plane is not sufficient. Clinical interpretation of
2D measurements is difficult. The main purpose of this
study is transition from 2D QA to 3D dose reconstruction in
a patient CT scan which could be achieved using dose
reconstruction method from 2D detector array in the
Compass system. The first step in the clinical introduction
of this system, instead of currently used 2D QA in OmniPro
system, is to test reliability of dose reconstructions. In this
work we investigated the validation of the method with
OmniPro results as a reference. We check whether the
Compass QA measurements of VMAT plans fulfill the QA
requirements.
Material and Methods
50 different treatments according to VMAT plans were
selected from our database; 20 prostate, 20 gynecology
and 10 brain. The QA results were divided based on the
mean gamma index and the 3%/3mm and 1%/1mm criteria.
Results from OmiPro were compared with Compass and
TPS. Additionally, recalculation plan from TPS (Monte
Carlo) in Compass system based on the different algorithm
(Collapse Cone Convolution) were performed. MLC tests
(3ABUT, 7SegA, FOURL plan) were implemented before
each set of measurements for evaluation of interleaf
leakage, tongue and groove effect.
Results
Mann-Whitney test showed good agreement between
Compass 3D-reconstructed dose and OmniPro results
(mean gamma 0.23 ±0.03 for 3%/3mm and 0.53±0.06 for
1%/1mm criteria). Scatter plot of results from TPS vs.
Compass against TPS vs. OmniPro showed small
differences in the region of gamma between 0.2 and 0.4.
Comparison TPS vs. Compass mean dose in PTV and OAR
did not reveal significant differences for prostate 50.04
Gy±0.4, 50.35Gy±0.33, bladder 32.04 Gy±0.41, 32.45
Gy±0.23; gynecology 45.07 Gy±0.34, 45.02 Gy±0.25,
bladder 35.04 Gy±0.74, 35.75 Gy±0.49; brain 60.07
Gy±0.53, 60.02 Gy±0.71, brain stem d
max
40.04 Gy±0.83,
39.08 Gy±0.33 respectively.
Conclusion
Agreement between results obtained from Compass and
OmniPro was reached. 3D dose reconstructions in CT
patient allowed to evaluate the dosimetric errors and
their clinical relevance. Compass reconstruction offers
good opportunities to examine dynamic plans and check
characteristics of MLC.
EP-1467 IPEM Code of Practice for proton and ion
beam dosimetry: update on work in progress
S. Green
1
, R. Amos
2
, F. Van den Heuvel
3
, A. Kacperek
4
,
R.I. MacKay
5
, H. Palmans
6
, D. D'Souza
2
, R. Thomas
6
1
Hall-Edwards Radiotherapy Research Group- Queen
Elizabeth Hospital, Medical Physics, Birmingham, United
Kingdom
2
University College London Hospitals, Radiotherapy
Physics, London, United Kingdom
3
Churchill Hospital, Radiotherapy Physics, Oxford,
United Kingdom
4
Clatterbridge Cancer centre, Physics Department,
Wirral, United Kingdom
5
The Christie NHS Foundation Trust, Medical Physics,
Manchester, United Kingdom
6
National Physical Laboratory, Radiation Dosimetry
Group, London, United Kingdom
Purpose or Objective
Current standard methods for reference dosimetry of
proton and ion beams typically involve the use of an
ionization chamber calibrated in a cobalt-60 beam, with a
beam quality correction factor applied to account for the
difference between the chamber response in the proton
and the calibration beams. This approach gives rise to
uncertainties (at 68% confidence level) on the reference
dosimetry of 2.4% for proton beams and 3.4% for carbon
ion beams when using a plane-parallel ionization chamber.
This poster provides an update on the development of a
new Code of Practice for reference dosimetry of proton
and ion beams, applicable to both scanned and scattered
beam configurations. It is aimed to deliver an uncertainty
on reference dosimetry for protons of approximately 2%
and will utilise a primary standard graphite calorimeter
that is robust and portable enough to be used in the end-
user facility.
Material and Methods
This project involves a core team (authors on this
submission) plus a group of experts in the field to provide