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: alaei001@umn.edu