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Calculating Organ Dose from Calculating Organ Dose from FluoroscopyFluoroscopy
Parham Alaei, Ph.D.Parham Alaei, Ph.D.Department of Therapeutic RadiologyDepartment of Therapeutic Radiology--Radiation OncologyRadiation Oncology
University of MinnesotaUniversity of MinnesotaMinneapolis, MinnesotaMinneapolis, Minnesota
Imaging Symposium: Patient Dose in Fluoroscopy: Estimating Patient-Specific Radiation Dose from Fluoroscopy
2011 Joint AAPM/COMP Meeting
Is there a need to calculate patientIs there a need to calculate patient--specific organ dose?specific organ dose? Effective dose for long, complex interventional
procedures could exceed 50 mSv Possibility of modeling organ dose prior to
procedure to avoid radiosensitive organs Estimate biological response Compare with and add the dose to that from
other techniques/technologies (CT, etc.)
Outline:Outline: Brief review of methods of organ dose Brief review of methods of organ dose
computation from fluoroscopycomputation from fluoroscopy Use of a treatment planning system for organ Use of a treatment planning system for organ
dose calculation in fluoroscopydose calculation in fluoroscopy Magnitude of organ doses encountered in a Magnitude of organ doses encountered in a
sample proceduresample procedure
Common organ dose calculation methods:Common organ dose calculation methods: DAPDAP--derivedderived
Dose-Area Product(DAP) Measurements
Organ Doses CalculatedBy MC Modeling
Dose Conversion Coefficients (DCCs) [organ doses per unit
DAP]
Calculate Organ Dose
Calculate Effective Dose
Common organ dose calculation methods:Common organ dose calculation methods: DAPDAP--derivedderived
Phys. Med. Biol. 54 (2009) 3613–3629
… if patient size is neglected when choosing a DCC, the organ andeffective dose will be underestimated to an underweight patient and will be overestimated to an overweight patient, with errors as large as 113% for certain projections.
Common organ dose calculation methods:Common organ dose calculation methods:
Extrapolation/interpolation from entrance/exit Extrapolation/interpolation from entrance/exit dosedose Entrance surface dose (ESD) to organ dose Entrance surface dose (ESD) to organ dose
conversion using MCconversion using MC--generated tables (generated tables (NRPB R262 NRPB R262 and NRPB SR262)and NRPB SR262)
Computational/MCComputational/MC CDRH organ dose handbooksCDRH organ dose handbooks A combination of aboveA combination of above
*NRPB: National Radiological Protection Board (UK)
Using a Treatment Planning System: Using a Treatment Planning System: Commonly used in radiation therapyCommonly used in radiation therapy
Pros:Pros: Ability to get a Ability to get a ““customizedcustomized”” dose distribution for a dose distribution for a
patient, accounting for beam quality, patient anatomy, patient, accounting for beam quality, patient anatomy, size, heterogeneities, size, heterogeneities, ……
Ability to segment organs and obtain dose statistics Ability to segment organs and obtain dose statistics within each organwithin each organ
Cons:Cons: Extensive initial setup/commissioning Extensive initial setup/commissioning Need a CT scan of the patientNeed a CT scan of the patient
Convergence of diagnostic and therapeutic Convergence of diagnostic and therapeutic radiologyradiology
Depth dose curves of various diagnostic beams (HVL: ~2-4 mm AL)From: Fetterly et. al Med. Phys. 28 (2), 2001
Depth dose curve of Elekta XVI cone beam CT beam (HVL: ~7 mm Al)From: Spezi et. al Med. Phys. 36 (1), 2009
Convergence of diagnostic and therapeutic Convergence of diagnostic and therapeutic radiologyradiology
kV cone beam CT dose distribution
Previous work in modeling Previous work in modeling diagnostic beams using diagnostic beams using
radiation therapy treatment radiation therapy treatment planning systemplanning system
Med. Phys. 26 (8), August 1999
Med. Phys. 27 (12), December 2000
Med. Phys. 28 (2), February 2001
Beam Modeling in the treatment planning Beam Modeling in the treatment planning system (Philips Pinnacle)system (Philips Pinnacle)
Collecting and importing depth dose/cross profilesCollecting and importing depth dose/cross profiles Selecting modeling parameters (beam spectra, etc.)Selecting modeling parameters (beam spectra, etc.) Simulating heel effectSimulating heel effect Obtaining the best match between measured and Obtaining the best match between measured and
modeled datamodeled data
Med. Phys. 28 (2), February 2001
Measured: Modeled:
Depth dose and cross profile data of a 120 kVp beamDepth dose and cross profile data of a 120 kVp beam
Modeled beams CT scan
Dose distribution within body
Kilovoltage beam dose distribution in phantomKilovoltage beam dose distribution in phantomOne 120 kVp beam
Three 100 kVp beams
Kilovoltage beam dose distribution in phantomKilovoltage beam dose distribution in phantom Dose Volume HistogramsDose Volume Histograms::
One 120 kVp beam
Three 100 kVp beams
Left lung
Right lungHeart
Heart
Lungs
Modeling a cardiac Modeling a cardiac angiography procedure using angiography procedure using a treatment planning systema treatment planning system
Sample calculationSample calculation--Cardiac angiography procedureCardiac angiography procedure Data obtained from a Data obtained from a Siemens Artis Zee Siemens Artis Zee unit*unit*
Acquisition ProtocolDose Area
Product (Gym2)Dose (RP)
(Gy)FOV area
(cm^2)dose rate (cGy/min)
Positioner Primary Angle (deg)
Positioner Secondary Angle (deg) Beam on time (s) KVP (kV)
FL Low LD 0.000059 0.00522 113.0 4.9 0.0 0 6.4 81.0
FL Low LD 0.000036 0.00447 80.5 2.9 40.6 -0.6 9.2 81.0
FL Low LD 0.0001985 0.03502 56.7 17.7 52.0 -30.8 11.9 112.0
Coro HDR Low 0.0006967 0.12294 56.7 145.6 52.0 -30.8 5.1 124.0
FL Low LD 0.000017 0.0027 63.0 4.9 41.2 21.7 3.3 82.0
Coro HDR Low 0.0002776 0.04377 63.4 46.9 41.2 21.7 5.6 101.0
FL Low LD 0.000011 0.00199 55.3 3.6 -25.7 30.6 3.3 81.0
Coro HDR Low 0.0002164 0.03796 57.0 43.8 -25.7 30.6 5.2 97.0
FL Low LD 0.000037 0.0065 56.9 6.6 -23.8 -28.9 5.9 88.0
Coro HDR Low 0.0002409 0.04247 56.7 51.0 -23.8 -28.9 5.0 104.0
FL Low LD 0.000056 0.00755 74.2 1.7 11.6 -4 26.7 81.0
FL Low LD 0.0001024 0.01389 73.7 3.3 27.1 -4 25.3 81.0
FL Low LD 0.000007 0.00098 71.4 4.9 37.9 15.3 1.2 81.0
Coro HDR Low 0.0002946 0.04139 71.2 46.6 37.9 15.3 5.3 99.0
FL Low LD 0.00001 0.00178 56.2 5.3 -2.6 38.1 2.0 85.0
Coro HDR Low 0.0002478 0.04316 57.4 45.7 -2.6 38.1 5.7 98.0
*Courtesy Ken Fetterly, Mayo Clinic
Sample calculationSample calculation--Cardiac angiography procedureCardiac angiography procedure Data as entered into the treatment planning systemData as entered into the treatment planning system
Cine 1000.09-381777.616
Fluoro 810.03-381777.515
Cine 1000.09-152188.414
Fluoro 810.02-152188.513
Fluoro 810.4242078.612
Fluoro 810.4441928.611
Cine 1000.08291567.510
Fluoro 810.10291567.59
Cine 1000.09-311547.68
Fluoro 810.06-311547.47
Cine 1000.09-222218.06
Fluoro 810.06-222217.95
Cine 1200.08312327.54
Fluoro 1120.20312327.53
Fluoro 810.1512219.02
Fluoro 810.11018010.61
Beam TypeTime (Min.)CouchGantryField SizeBeam #
Sample calculationSample calculation--Cardiac procedureCardiac procedure
Sample calculationSample calculation--Cardiac procedureCardiac procedure
Sample calculationSample calculation--Cardiac procedureCardiac procedure
Sample calculationSample calculation--Cardiac procedureCardiac procedure
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on Rando phantom
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on Rando phantom
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on Rando phantom
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on Rando phantom
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on a male chest CT dataset
Sample calculationSample calculation--Cardiac procedureCardiac procedure
16 Beams incident on a female chest CT dataset
Limitations of the method:Limitations of the method:
Skin dose calculations not accurate:Skin dose calculations not accurate: Difficulty in measuring and modeling dose on surface Difficulty in measuring and modeling dose on surface
and shallow depthsand shallow depths Uncertainty in algorithmsUncertainty in algorithms’’ calculation accuracy on calculation accuracy on
surfacesurface
Bone dose underestimatedBone dose underestimated Algorithm developed for megavoltage beamsAlgorithm developed for megavoltage beams
Results could be improved by post processingResults could be improved by post processing
Future directions:Future directions:
New algorithms for dose calculation in kilovoltage New algorithms for dose calculation in kilovoltage beams (kV CBCT, fluoroscopy, CT, etc.)beams (kV CBCT, fluoroscopy, CT, etc.)
This will lead to accurate calculation of dose to This will lead to accurate calculation of dose to bone and bone marrowbone and bone marrow
Acknowledgement:Acknowledgement:
Ken Fetterly, Ph.D.Ken Fetterly, Ph.D.Mayo ClinicMayo Clinic
Questions?E-mail: [email protected]