dosimetry audit in radiotherapy, in greece costas j. hourdakis, a. boziari & v. kamenopoulou...

Dosimetry Audit in Radiotherapy, in Greece

Costas J. Hourdakis, A. Boziari & V. KamenopoulouGreek Atomic Energy Commission, EEAE

Athens, 12 September 2014

EFOMP Symposium,Athens -12 Sept 2014, ΕΕΑΕ, [email protected]

Regulatory Inspections

(Greek Atomic Energy Commission)

Management System Audits –

Accreditation Audits

Clinical Audits

Dosimetry Audits

(Greek Atomic Energy Commission)

Quality Control Quality Assurance

(QC-QA)

Internal Audits

Tools for Quality


Competent national regulatory authority in the fields of radiological protection and nuclear safety.

Greek Atomic Energy Commission (ΕΕΑΕ)

It is an independent public service, supervised by the General Secretariat for Research and Technology under the Ministry of Education & Religious Affairs.

Regulatory and legal duties Inspection duties Services (personnel dos., calibrations, environmental

controls, etc) Education and research duties Radiological emergency

Integrated Management System : ISO 9001 (TUV Hellas) Quality Management Systems : ISO 17020 and ISO 17025 (Hellenic Accreditation System - ESYD)


31 : Hospitals – Clinics (Aug 2014)

RT & BT in Greece

Total Public Private

≥ 3 systems (Linac or Co60) 4 2 2

2 systems (Linac or Co60) 13 9 4

1 Linac or Co60 9 8 1

Only BT (HDR or I125 seeds) 5 5


≈ 60 photon beams (6–23 MV) 7 60Co beams ≈ 130 electron beams (4-21 MeV)

IMRTat 5 RT centersfor ≈ 12 systems

4 linacs / 1 M population - 250,000 inhabitants / Linac

Tendency to growth : Replacement of old systems & new centers

RT & BT in Greece


EEAE inspections and dosimetry audits in RT and BT, in Greece

Scope :• Assessment of radiation protection of workers – patients – public• Assessment of safe performance of radiological equipment• Assessment of applied patient dosimetry• Assessment of applied clinical and dosimetry procedures and practices• Identification of errors and mal-practices / Investigation / Recommendations• Harmonization of dosimetry protocols at national level • Comparison of dosimetry results with other studies worldwide


Dosimetry Audits, ΕΕΑΕ

On site visits

• Ionization chambers - detectors• EEAE dosimetry & QC equipment

(independent from users’)• Calibration in IRCL/EEAE-EIM

SSDL • QC-QA and dosimetry protocols

(IAEA TRS 398) Applied to all RT & BT centers and systems

Rounds1st round : 2002 - 20062nd round : 2006 - 20113rd round : 2011 - ...


Dosimetry equipment

ABSOLUTE DOSIMETRY • Photons in water : Waterproof Farmer type 0.6 cc - IBA FC65 P IC-69 • Photons in Solid Water Phantom : Flexible IC 0.3 cc - PTW 31003• Electrons in water : Parallel plate - PTW MARCUS (since 2011)• Electrons in water : Parallel plate - PTW ADVANCE (after 2011)• Electrometer : PTW UNIDOS 10001

RELATIVE DOSIMETRY • IBA solid state / diodes for photons and electrons

Dosimetry Audits, EEAE


IBA RFA 200, 2D water phantomOmniPro-Accept software• Solid state diodes • Farmer IC• P-P electron IC

Solid Water Phantom• Insert for PTW flexible IC


Basic Phantoms



1. Assessment of Mechanical and Functional equipment performance2. Relative (PDD, profiles, etc) and Absolute dosimetry in water (Gy/MU)3. Assessment of TPS output4. Assessment of the overall radiotherapy procedure, for dosimetry

Dosimetry Audit performed in

4 levels[ performed in sequence : from basic to complex ]


Basic parameters : Field size Accuracy of gantry and collimator rotation Accuracy of table movement and rotation Stability of the isocentre (ISO) during rotations Laser accuracy

1. Assessment of Mechanical and Functional equipment performance


Deviations |δ| classified in three categories :

|δ| < 2 mm : Accepted2 < |δ| < 4 mm : Investigation|δ| > 4 mm : Non-accepted



0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

LIGHT-FIELDDIMENSIONS

LIGHT-COLLIMATOR

LIGHT-IRRADIATION

CROSS-HAIRGANTRY

CROSS-HAIRTABLE

CROSS-HAIRCOLLIMATOR

MECHANICALISOCENTRE

LASERISOCENTRE

LINAC < 2mm

Co-60 <2 mm

LINAC 2mm<D<4mm

Co-60 2mm<D< 4mm

LINAC <4mm

Co-60 <4 mm

x

> 4 mm

> 4 mm

235 tests for Linacs & 81 for Co-60



2. Relative and Absolute dosimetry


EEAE measures in water phantom

• TPR20,10, for photons • R50 for electrons• percent depth dose, PDD • beam profiles

Dose at reference point, Dw

ΕΕΑΕ measurements, DM, are compared with the center’s stated values, DS

r = DS/DM relative deviation, dr = [(DS/DM ) – 1] ×100%



Uncertainties of EEAE measurements

Measurement of Dose to Water Type A Type B

% %Calibration coefficient, ND,w, of IC + electrometer 0.90Long term stability of ND,w 0.10 Scale reading / resolution 0.00Stability of measurements 0.10 Temperature & Pressure 0.17 0.08Temperature difference (thermometer & maes. point) 0.00Uniformity of radiation beam 0.06Depth - IC positioning 0.29Field size, SSD, angle 0.50Leakage current 0.00Recombination loss 0.10Polarity effct 0.10Beam quality correction, kQ 1.00

QUADRATIC SUM 0.22 1.47Combined Standard Uncertainty, k=1 1.49 %EXPANDED UNCERTAINTY, k=2 2.98 %



Comparison - Acceptance

d ≤ 3 % : Accepted3% < d < 5% : Investigation

d ≥ 5% : Non-accepted

1st round 2nd round 3rd round

│dr│≤ 3% 79.2% 96.9% 93.5%

3% <│dr│< 5% 16.7% 3.1% 6.5%

│dr│≥ 5% 3.1% 0.0% 0.0%

2. Absolute dosimetry at reference point (Gy/MU) : Photons

Standard uncertaintyof DM : ~ 1.5 %


2. Absolute dosimetry at reference point (Gy/MU) : Electrons

1st round 2nd round 3rd round

│dr│≤ 3% 82.1% 71.1% 95.7%3% <│dr│< 5% 5.0% 28.9% 4.3%

│dr│≥ 5% 12.9% 0.0% 0.0%

Standard uncertainty~ 2.0 %


2. Absolute dosimetry : BT

Reference Air Kerma Rate (Gy h-1 @ 1m)



• Various clinical irradiation conditions are predefined in random, e.g. 18MV, field 12 x 7, depth 8.5 cm, SAD/SSD, Wedge 45o, etc. [Gantry=0o]

• TPS calculates the MU (or min), in order to deliver 1 Gy at the predefined depth and irradiation conditions

• The irradiation conditions are reproduced at Linac (or Cο60) in a water phantom & the irradiation performed for the calculated MU (or min)

• EEAE measures the Dw & deviations from 1 Gy are derived• Tests are performed for many & different irradiation conditions (> 15).

3. TPS output


data > 2011

3. TPS output

-10%-9%-8%-7%-6%-5%-4%-3%-2%-1%0%1%2%3%4%5%6%7%8%9%

10%Assesment of TPS output 6MV

18MV or 15MV

10MV

Dev

iati

on

, %





data > 2011

3. TPS output

-10%-9%-8%-7%-6%-5%-4%-3%-2%-1%0%1%2%3%4%5%6%7%8%9%

10%Assesment of TPS output 6MV

18MV or 15MV

10MV

Dev

iati

on

, %




“We do not complete th

e audit until w

e investigate &

resolve all deviations (d

> 3%)”


4. Assessment of overall RT procedure

Simulation of all RT steps, with a solid water phantom : CT scan

SimulationTreatment Planning

Positioning - VerificationIrradiation

Hospital’s procedures are followedAll steps are performed by the hospital’s staff



Flexible IC

IC’s reference point is at the geometrical center of the phantom (cross marking).


Initial preparation

Marking, with bee-bees, a hypothetical original

(anatomical) isocentre (ISO)


CT scan

Images are transfered to TPS


Treatment Isocenter determination

Anatomical ISO defined by the bee-bees

Treatment ISO is determined from the respective CT slice& it corresponds to the

geometrical centre of phantom


Therapy simulation – Offset determination

Deviation of treatment isocentre from phantom geometrical centre

d ≤ 2 mm

Followed TPS data : Offset from

Original – Anatomical Isocentre toTreatment Isocentre (should be at the phantom center)


Treatment planning

CUBE : BOX technique (4 diametrically fields)OBLIQUE : 1 vertical (0o) with wedge and 2 lateral (sideways, e.g. 105o and 255o)

MU calculation, in order to deliver

total dose to treatment isocentre

(from all fields)2 Gy


Phantom irradiation

• Phantom positioning : Cards from TPS are followed• EEAE measures the dose from each field, DM,i and the total dose,

DM,T

• Comparison of DM,I and DM,T with the dose values as stated by the RT staff, according to TPS output data.



d ≤ 5 % 5 % < d < 7 %

d ≥ 7 %-30%

-25%

-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

25%

30%Assesment of the overall RT procedure BOX-6MV

BOX-18MV

OBLIQUE-6MV

OBLIQUE-18MV

De

via

tio

n %


data > 2011



d ≤ 5 % 5 % < d < 7 %

d ≥ 7 %-30%

-25%

-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

25%

30%Assesment of the overall RT procedure BOX-6MV

BOX-18MV

OBLIQUE-6MV

OBLIQUE-18MV

De

via

tio

n %


data > 2011

“We do not complete th

e audit until w

e investigate &

resolve all deviations (d

> 3%)”


CONCLUSION

• Patient Dosimetry and Radiation Protection is at high level in Greece.

• EEAE applies system inspections and dosimetry audits in RT and BT (and elsewhere) over 14 years, continuously and systematically. The experience gained is important.

• Benefits: Improved dosimetry - harmonization - dissemination of information - strengthening the confidence of hospitals’ staff.

• Hospitals welcome and seek inspections and audits of EEAE.


Challenges and Future work

• Small field dosimetry

• Dosimetry in “New technologies” (Tomotherapy, Cyber-Knife Gamma-Knife)

• Reporting of accidents

• Clinical Audit

• Enhancement of “Safety culture” and “Security culture”

• “Quantity” vs “Quality” to be balanced in a few cases


I thank you for your attention

dosimetry audit in radiotherapy, in greece costas j. hourdakis, a. boziari & v. kamenopoulou...

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