CriTcal organ doses, per KAP (μGy/(Gy.cm2)), of the cardiologist as a. funcTon of
energy ... Increasing the tube voltage – increases the organ doses per KAP for.
Study of the spatial variation of the dose-‐rate distribution in an interventional cardiology room using Monte Carlo calculations M. Bap'sta, C. Figueira, P. Teles , G. Cardoso, P. Araújo, P. Vaz
Outline • Introduc'on • Aim of the work • Valida'on methodology • Dose and Dose rate distribu'on • Voxel phantom study • Conclusions
Introduction • Interven'onal cardiology (IC) procedures: • long exposure 'mes;
• the operator has to work near the pa'ent, next to the X-‐ray source – high radia'on doses;
• the scaRered radia'on (pa'ent and medical equipment), makes medical staff exposed to a non-‐uniform radia'on field;
• a significant exposure of sensi've organs and 'ssues of the body, such as the eye lens, thyroid and extremi'es.
Aim of the work • Assess the dose and dose rate distribu'on around the fluoroscopic equipment; • Calculate the dose in cri'cal organs such as: eye lens, thyroid, tes'cles and legs.
Validation methodology • Equipment: Siemens Ar's zee biplane
Siemens Medical
Validation methodology • Interven'onal Cardiaology room
Control Room
(HGO floor plan)
Procedure Room
Validation methodology • Thermo-‐Luminescent Dosimeter (TLD) measurements • 4 TLDs LiF:Mg,Ti; • The holder has two detec'on zones, with specific filters to obtain the values of Hp(10) and Hp(0,07)
TLD crystal Aluminium card Filter for Hp (10) Filter for Hp (0,07)
Validation methodology • TLD placement • Floor stand, with X-‐ray tube under and image detector over the pa'ent table; • Posterior-‐Anterior (PA) projec'on; • 4 set of measurements.
Detector 120 cm
TLD placement 60 cm
Acquisi'on parameters Voltage (kVp)
80
Current (mA)
20
Irradia'on Time (s)
10
Mode
Fluoroscopy
Field of view (cm2)
15x15
Validation methodology • State of the art Monte Carlo code MCNPX 2.7.0 was used: • • • • •
Tally F6 (energy deposi'on over a cell) –Hp (10) and Hp (0,07); X-‐ray spectrum of 80 kVp generated by IPEM 78; X-‐ray simplified to point source – emission of a cone of photons; Only primary radia'on was taken into account; 108 primary par'cles simulated – sta's'cal uncertainty less than 1%.
Validation methodology • Results: TLD Measurements vs Simula'on
• Uncertain'es: •
Small changes on the TLDs posi'on, in rela'on to the primary x-‐ray beam.
•
TLD measurements uncertain'es are of about 10-‐20%;
•
Material considered for the pa'ent table (composi'on is not well-‐known);
•
Spa'al and energy distribu'on and the intensity of the photon fluence could be of
the order of 15%-‐20%.
Dose and dose rate distribution • X-‐ray spectrum of 80 kVp generated by IPEM 78; • PA projec'on acquisi'on; • 8 spheres of air were distributed, at 100cm from the floor, over 4 radial distances (50, 100, 150 and 200 cm) ; • Tally F4 (photon fluence in a cell) was used.
Dose and dose rate distribution • The Tally F4 results were normalized with Kerma-‐area product (KAP) – air sphere over 30cm of X-‐ray source; • 109 par'cles simulated – sta's'cal uncertainty between 1% and 5%.
Image obtain with SURFER 11 sojware
Dose and dose rate distribution
• Isodose curves for the dose rate distribu'on were obtained with Mesh Tally card (Type 1)
• Dose rate of about 200-‐400 mGy/hour – primary X-‐ray beam; • Dose rate of about –20mGy/hour – medical staff may be posi'oned; • Pa'ent not simulated – shielding or scaRer effects not taken into account.
Voxel phantom study • Voxel phantom: Golem • Adult male, 38 years old, 1.76 m height and a weight of 68.9 kg • Resolu'on: 2.08 x 2.08 x 8 mm3;
Thyroid Collar (0,35 mm Pb) Lead apron (0,5 mm Pb)
Voxel phantom study • Geometry simulated
Voxel phantom study • X-‐ray spectrum generated by IPEM 78 sojware of: 60, 80, 100 and 120 kVp; • Between 5x108 and 1x109 primary par'cles were simulated; • Tally F6 was used; • Pa'ent was simulated as a box of water; • The cri'cal organ doses were normalized with KAP: cm2
• 15x15 of area and 1cm thick air cell was placed between opera'on table and pa'ent
Organ
Nº of voxels
Eye lens
26
Thyroid
709
Tes'cles
581
Right Leg (adipose)
72680
Lej Leg (adipose)
70165
Voxel phantom study • Cri'cal organ doses, per KAP (μGy/(Gy.cm2)), of the cardiologist as a func'on of energy for the PA projec'on were: Organ Doses (μGy/(Gy.cm2))
1.2
60 kVp
1.0
80 kVp 100 kVp
0.8
120 kVp
0.6 0.4 0.2 0.0 LeO leg
Right leg Eye Testes Thyroid Eyelenses lens Testicles
• Increasing the tube voltage – increases the organ doses per KAP for all organs (linearity) • Eye lens – High radiosensi'vity, but not shielded
Conclusions • We were able to simulate a C-‐Arm fluoroscopic system, considering the good agreement achieved between the MCNPX simula'on values and TLD measurements. • The exposure to the primary X-‐ray beam may occur when the cardiologist manipulates catheters and guidewires within the imaging field of view, resul'ng in high doses (200-‐400 mGy/hour). • Organs doses, per KAP, depend on tube voltage, proximity with x-‐ray source, radiosensi'vity and the use of personal protec've equipment. • In the future, we hope to validate more complex scenarios (other projec'ons irradia'ons) in order to perform a more detailed dose assessment, both for pa'ent and medical staff.
References Ay, M. R. (2005). Assessment of different computa'onal models for genera'on of X-‐rayspectra in diagnos'c radiology and mammography. Medical Physics, 32. Koukorava, C. C. et al.(2011). Study of the parameters affec'ng operator doses in interven'onal radiology using Monte Carlo simula'ons. Radia3on Measurements, 46, 1216-‐1222. Siiskonen, T. T. et al. (2007). Monte Carlo simula'ons of occupa'onal radia'on doses in interven'onal radiology. The Bri3sh Journal of Radiology, 80, 460-‐468. Siemens Medical. (2008). Ar's zee/ Ar's zeego -‐ Operator manual volume 2: System opera'on. Siemens AG, Medical Solu3ons, 103.
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