Transcript Prezentace aplikace PowerPoint

8th European Conference on Medical Physics
11. – 13. 9. 2014, Athens
DOSIMETRY AUDITS IN RADIOTHERAPY
IN THE CZECH REPUBLIC
Irena Koniarová
Daniela Ekendahl
Ivana Horáková
Vladimír Dufek
Michaela Kapuciánová
National Radiation Protection Institute
Prague, Czech Republic
Situation in the Czech Republic

Population ≈ 10 million

Radiotherapy patients ≈ 22 thousand per year
Radiotherapy departments
Total number
- using high energy beams
- using IMRT or IMAT
36
28
18
Irradiation units infrastructure
Independent audits
National Radiation
Protection Institute
Physical segment of
radiotherapy
License holder
Whole system of
radiotherapy

TLD postal audit
Clinical audit

On-site audit
in progress
performed regularly for
purposes of the State Office
for Nuclear Safety or on
request of radiotherapy
centres
TLD audit
Biennial
Basic TLD audit
LA, Co-60, Cs-137 (1435 beams)
Beam calibration check
TLD audit using phantoms
Dose checks for various nonreference conditions

Assymetric fields

Rectangular fields

Wedge fields

Oblique incidence

inhomogeneities
TLD audit of LA with MLC
Dose checks in radiation fields
formed by MLC
Methodologies were developed in the frame of IAEA’s CRP
On-site audits of radiotherapy equipment
after acceptance test
Basic audit
LA and gamma units (535 beams),
X-ray units (103), BRT (32)
Checks of selected dosimetric and
geometric parameters
Advanced audit
LA with MLC and IMRT
Check of selected parameters
TPS audit
Check of non-dosimetric
parameters and imaging functions
of TPS
using QUASAR phantoms
On-site audits of IMRT prostate treatment
21 plans verified in 2013
Check of dose to PTV and rectum, evaluation of DVH

use of a special pelvic phantom representing standard patient

measurements with ionizing chambers and gafchromic films

use of QUASAR phantoms (CT numbers to RED)

DVH analysis – gEUD (PTV, rectum, bladder), HI, NTCP (rectum)
TLD audit – Results of beam calibration checks in 1997 - 2012
80
70
N = 1332
m = -0.2%
s = 3.0%
Number of beams
60
50
40
30
20
10
0
< -10
1997
1998
-10
1999
2000
-6
2001
-3
2002
2003
0
3
DD [%]
2004
2005
2006
2007
6
2008
D = (DTLD/Ds - 1) · 100%
D  3% - acceptance level
2009
10
2010
2011
2012
On-site audit – Results in 1996 - 2000
On-site audit – Results in 2001 - 2004
On-site audit – Results in 2005 - 2008
On-site audit – Results in 2009 - 2013
End-to-end audit results
21 plans evaluated
Dosimetry part

Planning part
Mean total deviation from
planned dose in PTV 0,991
±0,004 (deviation expressed as
measured to planned doses)

Mean deviation for beam
calibration in water 1,008 ± 0,002

Mean deviation due to the
transition from water to phantom
material 0,981± 0,002

Mean deviation due to the
transition from a square field in
the phantom to IMRT field in the
phantom 1,003 ± 0,003
4 plans out of tolerance limit (3%) for
total dose in PTV

Gamma criteria 4%/3 mm,
tolerance: 95% pixels in the dose
matrix to satisfy
5 plans out of tolerance (in 4
cases because of the
uncertainties in phantom
positioning on the couch)

Comparison to QUANTEC

Prescription according to ICRU except 2 cases

Homogeneity in PTV was outstanding

Different doses to rectum (based on gEUD
intercomparison, regarding the uncertainty in
the parameter a)
On-site and TLD audits - experience
All serious errors were caused by human mistakes and
were related to the performance of acceptance test.
On-site audits: prevention of accidental exposure



to pay more attention to acceptance tests of RT equipment
to reserve enough time for commissioning of new equipment and
new methods
relevant education, experience and training of the staff
The role of TLD audit


TLD audit contributes to improvement of clinical dosimetry, and
it is appreciated by most of radiotherapy departments
The more advanced versions of TLD audit are very useful for dose
verification in non-reference conditions, they can help to reveal
some potential problems
Future plans




Continue with on-site audits after acceptance test and
regular TLD postal audits
Implement end-to-end test with prostate phantom into
the system of audits (i.e. after implementation of new
technology in department)
Repeat end-to-end test for more complex techniques –
IMRT of head and neck (dosimetry and planning)
Participate in the IAEA activities – audit with CIRS
Thorax Phantom
Thank you!