11. – , Athens 8th European Conference on Medical Physics 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 number36 - using high energy beams28 - using IMRT or IMAT18
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 audit Biennial 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 auditTLD 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 auditTPS audit LA with MLC and IMRT Check of selected parameters Advanced audit
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 D = (D TLD /D s - 1) · 100% D 3% - acceptance level
On-site audit – Results in
On-site audit – Results in
On-site audit – Results in
On-site audit – Results in
End-to-end audit results 21 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!