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Brachytherapy Dose Calculation Formalism, Dataset Evaluation, and Treatment PlanningDataset Evaluation, and Treatment Planning
System Implementation
Mark J. Rivard, Ph.D. and Christopher Melhus, Ph.D.Tufts University School of MedicineTufts University School of Medicine
Jeffrey F. Williamson, Ph.D.Vi i i C lth U i itVirginia Commonwealth University
AAPM Summer School: Clinical Dosimetry Measurements in Radiotherapy23 June 2009 at Colorado College, CO
Full Disclosure
As related to the contents of this presentation,
Rivard has received research support from:
Varian Medical Systems and IsoRay Medical
Williamson has received research support from:
Varian Medical Systems and Philips Medical Systems
Learning Objectives / Purpose
l i t b h th d l l ti f li• explain current brachytherapy dose calculation formalism
• dosimetry parameter evaluation methodsdosimetry parameter evaluation methods
• consensus data formulation
• clinical implementation
• background on AAPM advances
Low-Energy Brachytherapy Sources
0.8 mm
4.1 mm
4.5 mm
Laser Welded Ends(0.1 mm wall)
Inorganic Substrate w/Cs-131 AttachedGold X-Ray Marker (0.25 mm diameter)
Titanium Case (0.05 mm wall)
4.0 mm
4.5 mm
IsoRay model CS-1 Rev2
High-Energy Brachytherapy Sources
Brachytherapy Dose Calculation Geometry
2004 AAPM TG-43U1Brachytherapy Dosimetry Formalism (2-D)
LG r,
LK L
L 0 0
,D r, S g r F r,
G r ,
dose rate to water in water at point P(r,S air kerma strength D r,
SK air kerma strength dose rate constant( ) di l d f tigL(r) radial dose function
GL(r,) geometry function (line source approximation)F(r,) 2-D anisotropy function
2004 AAPM TG-43U1Brachytherapy Dosimetry Formalism (1-D)
0( , )LG r 0
0 0
( , ) (r) ( )
( , )L
K L anL
G rD(r) = S g r
G r
dose rate to water at point P(rS air kerma strength
D(r)
SK air kerma strength dose rate constant( ) di l d f tigL(r) radial dose function
GL(r,) geometry function (line source approximation)( ) 1-D anisotropy function( )an r
Comparison of 1-D Formalisms( )G r BAD 0
P0 0
( , )g (r) ( )
( , )L
K anL
G rD(r) = S r
G r
BAD 2
0K L
rD r S g r ( r ) BAD
2
K L anD r S g r ( r )r
GOOD 2
0K P an
rD r S g r ( r )
r
BEST 0( , ) (r) ( )LG rD(r)= S g r
r
BEST 0
0 0
(r) ( )( , )K L an
L
D(r) = S g rG r
Intent of 2004 AAPM TG-43U1
• provide a revised definition of air-kerma strength;
• eliminate apparent activity for specification of source strength;• eliminate apparent activity for specification of source strength;
• eliminate the anisotropy constant in favor of the distance dependent 1-D anisotropy function;
• provide guidance on extrapolating tabulated TG 43 parameters• provide guidance on extrapolating tabulated TG-43 parameters to longer and shorter distances; and
• eliminate minor inconsistencies and omissions in the original protocol and its implementation.
• literature review of experimental and Monte Carlo Consensus Dataset Formulation Methodology
dosimetry results for brachytherapy sources• comparisons of all candidate datasets• average MC and average EXP from literature
CON = (MC + EXP)CON (MC EXP )2
• g(r) and F(r ) candidate datasets transformed using• g(r) and F(r,) candidate datasets transformed using common L, possibly with Leff = S × N
• g(r) and F(r ) typically taken from Monte Carlo• g(r) and F(r,) typically taken from Monte Carlo• (r) calculated from consensus F(r,dataset
fi l lt t b l t d ith h• final results tabulated with common mesh
Example Dosimetry Parameter Dataset
prefer AAPM-recommended datasetsotherwise use AAPM/RPC Registry data and original pubswebsites (ESTRO, Univ. Carleton, etc) also post datasets
Dosimetry Parameter Data Trail Part 1
Dosimetry Parameter Data Trail Part 2
Dosimetry Parameter Data Trail Part 3
2( )S K d d
Revised Air Kerma Strength Definition
( )KS K d dKS air kerma strength
air kerma rate in vacuo at specification
l h t t ff i l d d
( )K d air kerma rate in vacuo at specificationpoint d with energy cutoff , typically 5 keV
low-energy photon cutoff includedmeasurement conditions specified
NIST WAFACNIST WAFAC
Seed Calibrations at NIST + ADCLs
NIST WAFAC Bx source HDR-1000+
Correction of Errors and Inconsistencies
• g(r) presented for dimensionless units, consistency with investigator g(r), and 5th order polynomial
• explicit contraindication for erroneous 1-D equation
( )G r 0L
0 0
( , ) g (r) ( )
( , )P
K anP
G rD(r) = S r
G r
• elimination of Aapp and anisotropy constant
• methodology to extrapolate dose calculations for large and small distances
Need for Uncertainty Analyses
Recent Monte Carlo uncertainty analysis for Cs-131Rivard, Med. Phys. 34, 754-762 (2007)
Removal of Antiquated Terms
apparent activity: Aapp anisotropy constant: anchoice of ()x may lead to dosimetric errors cannot accurately reproduce dose r < 1 cmAAPM specifies SK for source strength errors result under specific circumstances
Recommendations to Dosimetry Investigators
• experimental measurement descriptors– description of internal and external source geometry– source irradiation geometry, orientation, irradiation timeline– detector calib. technique & energy response function, E(r)
di ti d t t d d t t– radiation detector and readout system– measurement phantom composition– phantom dimensions and use of backscatterphantom dimensions and use of backscatter– estimation volume averaging effect at all detector positions– # of repeated readings with standard deviation, # of sourcesp g ,– NIST SK value and uncertainty for measured source– uncertainty analysis section (statistical and systematic)
Recommendations to Dosimetry Investigators
• Monte Carlo calculation descriptors– radiation transport code, version, and major options– cross-section library name, version, and customizations– radiation spectrum of source
i hi h d t t d i k t th– manner in which dose-to-water and air-kerma strength are calculated (i.e., tally used)
– source geometry, phantom geometry, and sampling spaceg y, p g y, p g p– composition and mass density of materials in the source– composition and mass density of materials in the phantom– physical distribution of radioisotope within the source– uncertainty analysis section (statistical and systematic)
Recommendations to Dosimetry Investigators
• Monte Carlo recommended good practices– primary calculations in 30 cm diameter liquid water phantom,
ith t l t 5 f b k tt t i lwith at least 5 cm of backscatter material– use sufficient histories to limit statistical uncertainty
1 2 % for r < 5 cm in water; 1 1 % for s calculations1 2 % for r < 5 cm in water; 1 1 % for sK calculations– modern cross-section libraries should be used – verify manufacturer’s source dimensionsy– Volume averaging effects should be limited to < 1 %– model k(d) as a function of polar angle for sK simulation– point source modeling is unacceptable– mechanical mobility of internal source structures
2004 AAPM TG-43U1 Includes Reference Data
NIST-specified source spectra, half-lives, and atomic composition for air and water
MBq–1MBq–1
2008 AAPM Calibration Recommendations
Medical PhysicsThird-party brachytherapy source calibrations and physicistresponsibilities: Report of the AAPM Low Energy BrachytherapySource Calibration Working Group
Compiling and clarifying recommendations established by previous AAPMTask Groups 40, 56, and 64 were among the working group’s charges,which also included the role of third-party handlers to perform loading andassay of sources. This document presents working group findings on theresponsibilities of the institutional medical physicist and a clarification ofthe existing AAPM recommendations in the assay of brachytherapy
Th AAPM l it t th di ti f th i tit ti l di lsources. The AAPM leaves it to the discretion of the institutional medicalphysicist whether the manufacturer’s or institutional physicist’s measuredvalue should be used in performing dosimetry calculations.
© 2008 American Association of Physicists in Medicine
Butler et al., Med. Phys. 35, 3860-5 (2008)
2008 AAPM Calibration Recommendations
2008 AAPM Calibration Recommendations
Systematic Approach to RTP QA
Example datasets (from TG-43UXX or published literature)
Methods for data entry (HDR & LDR)
Check RTP for list of key functions
Tests of all RTP field entries (SK linearity, test of decay, dose superposition, shield attn factor for HDR, etc)
Impact of coarse data grid (interpolation technique & errors)
QA comparison of hand calc with RTP point dosesQA comparison of hand calc with RTP point doses
Compare printed/plotted isodose images
Documentation (use e-records)
AAPM Therapy QA Guidance Documents
TG-40: General Radiotherapy QA
TG-43: Bx Dosimetry Parameters & Dose Calc. Algorithm
TG-53: RTP QA
TG-56: Bx Code of PracticeTG-59: HDR Tx DeliveryTG-64: LDR Prostate Tx DeliveryThese reports focus on treatment-related QAThese reports focus on treatment-related QA
AAPM TG-40 Guidance
Source strength decay of inventory
Global scaling of dose rate with SK and
Test source localization tools over full range of clinical use
Accuracy and implementation of shield attenuation factor
I t f id iImpact of grid size
AAPM TG-43 Guidance
Dosimetry parameters: SK and gL(r), F(r,), and (r)taken from consensus datasetstaken from consensus datasets
Parameter units: r [cm] and [degrees] except for [radians][ ] [ g ] p [ ]ensure consistency with RTP
Dosimetry algorithm:
LK L
G r,D r S g r F r
K L
L 0 0D r, S g r F r,
G r ,
AAPM TG-53 Guidance
RTP specs and ATP
Hardcopy printout accuracy
Temporal dose rate correlation with radionuclide decay
Accuracy and consistency of parameter units
C t t t d itComputer systems storage and security
AAPM Committee Structure
Chairs and LiaisonsBrachytherapy Subcommittee (BTSC) Mark RivardBrachytherapy Subcommittee (BTSC), Mark Rivard
Special Brachytherapy Modalities Working Group (SBM), Bruce ThomadsenHigh-Energy Brachytherapy Source Dosimetry Working Group (HEBD), Jose Perez-CalatayudRobotic Brachytherapy Working Group (RoboBx), Bruce Thomadsen and Yan YuLow-Energy Brachytherapy Source Dosimetry Working Group (LEBD), Michael Mitchgy y y y g ( )Brachytherapy Source Registry Working Group (BSR), Geoff Ibbott
TG-129 Eye Plaque Dosimetry, Sou-Tung Chiu-TsaoTG-143 Dosimetry for Elongated Brachytherapy Sources, Ali MeigooniTG-144 Dosimetry & QA Procedures for 90Y Microsphere Brachytherapy for Liver Cancer, Andy DezarnTG 137 P t t C D P i ti R d ti R i d N thTG-137 Prostate Cancer Dose Prescription Recommendations, Ravinder NathTG-138 Brachytherapy Dose Evaluation Uncertainties, Larry DeWerdTG-167 Investigational Brachytherapy Source Recommendations, Ravinder NathTG-182 Electronic Brachytherapy Quality Management, Bruce ThomadsenTG-186 Model-Based Dose Calculation Techniques for Advanced Dosimetry, Luc Beaulieuq y,
American Brachytherapy Society (ABS), Zoubir OuhibEuropean Society for Therapeutic Radiology & Oncology (ESTRO), Jack Venselaar
AAPM Plan to Address Dosimetry Advances
TG-186 charged to review– next-generation dose calculation algorithms– studies evaluating advanced algorithms for
• phantom size effect• inter-seed attenuation• material heterogeneities within the body• interface and shielded applicators• interface and shielded applicators• directional brachytherapy (azimuthal asymmetry)
– commissioning issuescommissioning issues– patient-related input data– potential clinical issue risks and limitationspotential clinical issue, risks, and limitations
Recently Published Vision 20/20 Paper
M di l Ph iMedical PhysicsThe evolution of brachytherapy treatment planning
Mark Rivard,1 Jack L. M. Venselaar,2 and Luc Beaulieu3
1Department of Radiation Oncology, Tufts University School of Medicine, Boston, Massachusetts, USA2Department of Medical Physics, Instituut Verbeeten, P.O. Box 90120, 5000 LA Tilburg, The Netherlands3Département de Radio-Oncologie et Centre de Recherche en Cancérologie de l’Université Laval, Quebecp g g , Q
Brachytherapy is a mature treatment modality that has benefited from technological advances.Treatment planning has advanced from simple lookup tables to complex, computer-based dosecalculation algorithms. The current approach is based on the AAPM TG-43 formalism with recentg ppadvances in acquiring single-source dose distributions. However, this formalism has clinicallyrelevant limitations for calculating patient dose. Dose-calculation algorithms are being developedbased on Monte Carlo methods, collapsed cone, and the linear Boltzmann transport equation. Inaddition to improved dose-calculation tools, planning systems and brachytherapy treatmentp , p g y y pyplanning will account for material heterogeneities, scatter conditions, radiobiology, and imageguidance. The AAPM, ESTRO, and other professional societies are coordinating clinicalintegration of these advancements. This Vision 20/20 article provides insight on these endeavors.Med. Phys. 36, 2136-2153 (2009)Med. Phys. 36, 2136 2153 (2009)
Sensitivity of Anatomic Sites to Dosimetric Limitations of Current Planning Systems
anatomic site photon energy
absorbed dose attenuation shielding scattering beta/kerma
dose
prostatehigh
prostatelow XXX XXX XXX
breasthigh XXXlow XXX XXX XXX
GYNhigh XXXlow XXX XXX
skinhigh XXX XXX
skinlow XXX XXX XXX
lunghigh XXX XXXlow XXX XXX XXX
penishigh XXXlow XXX XXXhigh XXX XXX XXX
eyelow XXX XXX XXX XXXRivard, Venselaar, Beaulieu, Med Phys 36, 2136-2153 (2009)
Photon Attenuation and Absorption
Rivard, Venselaar, Beaulieu, Med Phys 36, 2136-2153 (2009)
High-Z Photon Attenuation
Rivard, Venselaar, Beaulieu, Med Phys 36, 2136-2153 (2009)
Phantom Size and 192Ir Photon Scattering
Melhus and Rivard, Med Phys 33, 1729-1737 (2006)
Conventional TPS Fails to Accurately Calculate Brachytherapy Dose
air water?
tissue water?
contrast impact?contrast impact?
source superposition?
source shielding?source shielding?
radiation scatter?
Is the Future Monte Carlo-based TPS?
Medical PhysicsAn approach to using conventional brachytherapy software for clinical treatment l i f l M t C l b d b h th d di t ib tiplanning of complex, Monte Carlo-based brachytherapy dose distributions
Mark Rivard,1 Chris Melhus,1 Domingo Granero,2 Jose Perez-Calatayud,2 Facundo Ballester3
1Department of Radiation Oncology, Tufts Medical Center, Boston, Massachusetts 021112Radiation Oncology Department, “La Fe” University Hospital, Valencia, Spain3Department of Atomic, Molecular, and Nuclear Physics, University of Valencia, Spain
Med. Phys. 36, 1968-1975 (2009)
Summary
• current dose calculation formalism presented
d i t t l ti d• dosimetry parameter evaluation and consensus methods for uniform datasets derivation
li i l i l t ti b d AAPM t• clinical implementation based on AAPM reports
• AAPM current status and areas for future advancement