11. – 13. 9. 2014, athens 8th european conference on medical physics dosimetry audits in...
TRANSCRIPT
11. – 13. 9. 2014, Athens
8th European Conference on Medical Physics
DOSIMETRY AUDITS IN RADIOTHERAPY
IN THE CZECH REPUBLIC
Irena KoniarováDaniela EkendahlIvana HorákováVladimír Dufek
Michaela Kapuciánová
National Radiation Protection InstitutePrague, Czech Republic
Situation in the Czech Republic
Population ≈ 10 million
Radiotherapy patients ≈ 22 thousand per year
Radiotherapy departments
Total number 36
- using high energy beams 28
- using IMRT or IMAT 18
Irradiation units infrastructure
Independent audits
Physical segment of radiotherapy
TLD postal audit
On-site audit
performed regularly for purposes of the State Office for Nuclear Safety or on request of radiotherapy centres
Whole system of radiotherapy
Clinical audit
in progress
National Radiation Protection Institute
License holder
TLD auditBiennial
LA, Co-60, Cs-137 (1435 beams)
Beam calibration check
Dose checks for various non-reference conditions
Assymetric fields
Rectangular fields
Wedge fields
Oblique incidence
inhomogeneities
Basic TLD audit TLD audit using phantoms
Dose checks in radiation fields formed by MLC
TLD audit of LA with MLC
Methodologies were developed in the frame of IAEA’s CRP
On-site audits of radiotherapy equipment after acceptance test
LA and gamma units (535 beams), X-ray units (103), BRT (32)
Checks of selected dosimetric and geometric parameters
Check of non-dosimetric parameters and imaging functions of TPS using QUASAR phantoms
Basic audit TPS audit
LA with MLC and IMRT
Check of selected parameters
Advanced audit
On-site audits of IMRT prostate treatment21 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
< -10 -10 -6 -3 0 3 6 100
10
20
30
40
50
60
70
80
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
[%]DD
Nu
mb
er
of
be
am
s
N = 1332 m = -0.2% s = 3.0%
D = (DTLD/Ds - 1) · 100%D 3% - acceptance level
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 results21 plans evaluated
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)
Dosimetry part Planning part
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
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
On-site audits: prevention of accidental exposure
All serious errors were caused by human mistakes and were related to the performance of acceptance test.
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
The role of TLD audit
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!