advances in brachytherapy planning · 2019-03-22 · advances in brachytherapy planning: impact on...

Advances in Brachytherapy Planning: Impact on Imaging and Modelling of Applicators on the efficiency in treatment planning

Peter Bownes

Leeds Cancer Centre,Leeds, UK

About Leeds

• Large Brachytherapy service • 150 prostate I-125 seed implants per

annum• HDR MicroSelectron Unit• 175 IGBT HDR Patients• Conformal HDR Plans 216• HDR Fractions 529

Leeds

London

Brachytherapy Workload

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50100

150

200250

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450

2008 2009 2010 2011 2012

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ad

HDR Patients HDR Fractions Conformal Plan

HDR Fractions - Standard Plan I-125 Seed Patients/Plans

IGBT HDR Brachytherapy has arrivedHDR Plans

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2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

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Cervix

Norman Simon (Heymans)

Miami

H&N

Prostate

Rectal

Other

Oesophagus

Outline

Focus on advances important to brachytherapy planning:

• Imaging• Applicator reconstruction

• Applicator modelling• Uncertainties & Efficiency

• Algorithms

Treatment Accuracy

3D Imaging

Target Localisation

Target Definition

Insertion

- Applicator fixation

Applicator Reconstruction

Dose Calculation

Biological Model

HDR Accuracy

- time/position

“A chain is no stronger than its weakest link”

Uncertainties in IGABT CervixTanderup et al Radiother Oncol 107 (2013) 1-5

Quality Assurance Overview

HDR Unit

QA

TPS

QA

Imaging

QA

System QA Patient QA

•Independent Physics Check of Plans

•Independent Check of Dose Calculation

Audit – Clinical, Process, Dosimetric

Imaging

Applicator reconstruction

Algorithms

Classical Brachytherapy of Cervix- Manchester System- Orthoginal Radiographs

Verification• Applicator Geometry• Applicator Position

• Post Plan Dosimetry• Target volume• Pt A and B• ICRU 38 - bladder and rectal doses

Applicators for Cervix Brachy

Images Courtesy of Elekta

Background IGBT

https://www.embracestudy.dk

Why IGBT?

Why?• Aware standard brachytherapy was inadequate for some patients

for• Tumour coverage• OAR dose

Benefits• Accurate verification of applicator position• Accurate definition of OAR dosimetry• Improved conformal dose distributions to tumour volume and OAR• Improved dosimetric reporting using DVHs• Opportunity to dose escalate

Clinical impact of MRI assisted dose volume adaptation and dose escalation in brachytherapy of locally advanced cervix

cancer. Potter R et al,Radiother Oncol 83 (2007) 148–155

• 145 Patients• 1998 – 2000 73 Patients

– Standard Brachy– Median FU 75 months

• 2001 – 2003 72 Patients– MRI based brachy – Dose adaption / dose escalation– Median FU 44 months

• Tumour Size 2-5cm 67 patients• Tumour Size > 5cm 78 patients• Progression Free Survival for true

pelvis local control; tumour size >5cm– 1998-2000 64%– 2001 – 2003 82%

• GI and GU Late morbidity (G3/G4)– 1998-2000 10%– 2001 – 2003 2%

Dose–effect relationship for local control of cervical cancer by magnetic resonance image-guided brachytherapyDimopoulos J et al, Radiother Oncol 93 (2009) 311–315

• 141 Patients• Dose response dependence on local recurrence evaluated

Conclusions: A significant dependence of local control on D100 and D90 for HR CTV was found. Tumour control rates of >90% can be expected at EQD2 doses >67 Gy and 86 Gy, respectively.

IGBT Pathway

Applicator Insertion Imaging Contouring

Applicator Reconstruction

Treatment Planning -

Optimisation

Plan Evaluation

Treatment Repeated for Each Fraction

Imaging – Applicator Insertion

• Aid selection of appropriate applicators

• US Guidance• Aid placement• Verify placement• Check for perforation

MR without ApplicatorMR without ApplicatorMR without ApplicatorMR without Applicator MR with ApplicatorMR with ApplicatorMR with ApplicatorMR with Applicator CT with ApplicatorCT with ApplicatorCT with ApplicatorCT with Applicator

TimingTimingTimingTiming 4 days prior to insertion Day of insertion(fraction 1 only)

Day of insertion(all fractions)

Scan Scan Scan Scan ParametersParametersParametersParameters

T2 weighted TSESagittal (4mm slice Thickness)Paratransversal (2.5mm ST)

T2 weighted TSEParaSagittal (4mm slice Thickness)Paratransversal (2.5mm ST)

Spiral CT 2mm slice sep.

UseUseUseUse Aid GTV & HRCTV definition; Applicator choice

GTV & HRCTV DefinitionOAR (if MR for fraction)

OAR definition (if no MR)Catheter Reconstruction

Imaging

Contouring

GTV and Topography change significantly during EBRT+/- Chemo

Haie-Meder et al Radiother Oncol 74 (2005) 235-245

High Risk CTV

HRCTVBrachy =GTVB = macroscopic tumour

extension at time of BT as detected by clinical examination and as visualised on MRI

+Whole Cervix+Extra-cervical tumour extension

at the time of BT (palpation + MRI findings)

+”Grey Zones” (residual

intermediate MR signal in location of macroscopic tumour at diagnosis)

OAR

Bladder• outer bladder wall of the

entire bladder is contoured Rectum

• outer rectal wall from above the anal sphincter to the level of the transition into the sigmoid

Sigmoid• outer sigmoid wall is to be

contoured from the recto-sigmoid flexure to 2cm above the parametria and the uterus

Small Bowel• outer small bowel wall is to be

contoured to 2cm above the parametria and the uterus

CT v MRI Based ContouringViswanathan et al, Int J Radiat Oncol Biol Phys 2007; 68(2):491-8.

Conclusions: Computed tomography-based or MRI-based scans at brachytherapy are adequate for OAR DVH analysis. CT tumor contours can significantly overestimate the tumor width, resulting in significant differences in the D(90), D(100), and volume treated to the prescription dose or greater for the HR-CTV compared with that using MRI. MRI remains the standard for CTV definition.

Critical Structure Movement in Cervix BrachyAnderson C et al Radiother Oncol 107 (2013) 39-45

Imaging


Algorithms

Geometric AccuracyCT – Baltas Phantom

MRI – Known Target Phantom

Row A

Row B

Row C

Row D

Row E

Applicator Reconstruction - Need for Applicator Modelling

• Applicator Reconstruction (On pre v4.0 OCB)• Direct reconstruction in ECS• Issues with reproducibility, accuracy• Longer• Need CT or orthogonal radiographs• Image registration of CT – MRI based on applicator

• No plan library for standards

• Will this effect planning efficiency? • Will this effect planning accuracy?

Applicator Reconstruction- Difficulties with curved applicators

Movie courtesy of Elekta

• Source Path– Does not follow channel centre– Does not follow CT marker wire– Non circular Path– Is applicator dependent

Consequences of random and systematic reconstruction uncertainties in 3D image based brachy in cervical cancer Tanderup et al Radiother

Oncol 89(2) (2008) 156-163

• Modelled reconstruction uncertainties by translation (±5mm) and rotation (±15°)• Assessed by effect on DVH parameters for 20 patients

(10 IC only, 10 IC + needles)

Results• Rectum & Bladder5-6% per mm Ant-Post• Other direction & structuresBelow 4% per mm

Conclusions:•Comprehensive QC in afterloader, applicators and imaging required to prevent systematic errors in app recon

• If avoid systematic errors, uncertainties in DVH parameters can be kept below 10% in 90% patient population

•Random errors minimised by small slice thickness

1 Fraction

4 Fractions

Delivered Dose relative to TPS for 90% of the Patients(Recon errors in longitudinal direction)

Applicator Reconstruction - Oncentra Brachy v4.0 +

• Leeds involved in Beta Testing• Applicator Library

• Help ensure more accurate and reproducible applicator reconstruction

• Plan Library• Improved workflow

• Plan efficiency

Key Features• Actual source path embedded into applicator model – acquired

using digital camera of source & simulator images• Only DPs in library can be used• Can request custom source paths• Anchor points

Commissioning Applicators and Applicator Library

• Must validate actual source position against applicator library• Perform all applicators used clinically• Regular QA of applicators• Overlay autoradiograph with source position defined on Oncentra Brachy

SDP Max difference Account for daily QA

(mm)(pixels) (mm)

1 11.05 0.87 0.37

6 12.08 0.95 0.45

12 3.16 0.25 -0.25

16 15.13 1.19 0.69

23 22.47 1.77 1.27

30 16.55 1.31 0.81

Ring Applicator: 45°30mm (4) Autoradiographs: Batch 3, Daily QA: -0.5mmSDP1 angle from vertical:Autoradiograph: 38.3°OMP: 36.0°

•Most of our applicators have been <1.5mm from measured•Two applicators required custom source paths – clinic measure then send to elekta•4 of the same applicator – 3 out of 4 matched

Regular Applicator QA

Plan Library

•Why use it?•Speed up process•Reduces errors•Standard plans good starting point for manual optimisation

•Includes•Dwell Positions•Dwell Weights•Point A (L & R)•Normalised to Point A•Prescription•Channel Mapping / Length Setting

Using Applicator and Plan Library

• Case 1 – separate insertion for each fraction• 26mm diameter ring, 45 degree• Case 1a First Fraction• Case 1b Second Fraction

• Each planned by multiple planners twice • Direct reconstruction (manual)• Applicator library (library)

• Assessed vector difference between planned DP to measured DP• Looked at 4 of the standard dwell positions used routinely

• Repeated for case 2 interstitial ring• Looked at all standard dwell position used routinely

• For all plans, single operator placed the same conformal plan on each reconstruction to assess DVH impact

Planning Accuracy – Planned DP V Measured DP

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

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-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Z (

cm)

X (cm)

Dwell Position Reconstruction Case 1b - 26mm Ring Diameter, 45 Degree

7 Planners

Manual

Library

Measured

1mm FromMeasured DP

Planning Accuracy

Applicator library gives the following benefits:

• Improved accuracy compared to the manual direct reconstruction method.• Improved reproducibility between fractions• Improved reproducibility between operators

Case 1bApplicator Library

Mean 0.07Std Dev 0.04max 0.15min 0.02

Difference to Measured Dwell Position (cm)

0.110.050.200.02

Manual Recon

Case 1aApplicator Library


Difference to Measured Dwell Position (cm)Manual Recon

0.190.090.330.05

-1.6

-1.4

-1.2

-1

-0.8

-0.6

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0.2

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-2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Z (

cm)

X (cm)

Dwell Position Reconstruction Case 2 - 34mm Interstitial Ring Diameter, 60 Degree

5 Planners Manual

Library

Measured

1mm From Measured DP

Case 2Applicator Library


Difference to Measured Dwell Position (cm)Manual Recon

0.130.070.290.02

Planning Efficiency – Applicator &Plan Library (LIB) v Direct Reconstruction (DR)

2 Planners3 Plans

Mean Time (sec)

DR LIB LIB/DR

Planner 1 App Recon + Std Plan 404.67 158.33 0.39

Planner 2 App Recon + Std Plan 429.67 293.00 0.68

MR Alone Reconstruction

•Applicator modelling / surface rendering make it feasible•Advantages

• Removes the need for registration of CT-MR• Removes fusion uncertainties

• No CT – IR(ME)R advantage• Reduces planning time • Streamlines pathway for patient

• Less movement• Less time out of department

•Additional Requirements•Para-transversal with small slice thickness•Para-sagittal improves accuracy of sup-inf reconstruction (auto-registration)•Marker wire useful – water•Interstitial – use aqua-gel in holes•Assess magnitude of geometrical distortion

•<2mm

MR Alone – Planning Efficiency MR Applicator & Plan Library (MR-LIB) v CT/MR Applicator & Plan Library v Direct Reconstruction (DR)

1 Planner3 Plans

Mean Time (Sec)

DR LIB - CT/MR MR -LIB MR-LIB/DR MR-LIB/(LIB-CT/MR)

Registration 530 530 0

App Recon + Std Plan 404.67 158.33 281.33

Total934.67

(15.6 min)688.33

(11.5min)281.33

(4.7min)0.30 0.41

MR-LIB cf DR

MR-LIB cf LIB CT/MR

Difference 10.9 min 6.8min

Imaging


Algorithms

AAPM TG43-U1 –Current Standard, Simple formalism, Dwater, full scatter water medium

Limitations

Phantom Medium – Absorbed Dose

Phantom Medium – Attenuation

ISA

Applicator Interactions

Scattering

- Patient size

- Site location

Differences in absorbed dose and attenuation between phantom medium –Rivard et al Med Phys 36(6) 2009 2136-2153

Inter source/applicator radiation interactions

•Applicator shielding (Ir-192) – need geometry and composition

•Attenuation of water replaced by high-Z material

•Interseed Attenuation (I-125)

• ~ D90, D98 reduction < 5%

For 6711 seed ISA effects only

Differences in radiation scattering

•Not all sites have full scatter conditions

•Breast, head and neck, moulds

•Missing backscatter close to the tissue boundary.

•For Ir-192 dose differences greater than 5% are possible if the phantom boundary is within 10cm of source.

(Melhus et al Med Phys 33 1729 (2006))

Sensitivity to dosimetric limimitations –Rivard et al Med Phys 36(6) 2009 2136-2153

Algorithm Summary

•TG43-U1 is generally appropriate for Gynae and prostate•Advanced algorithms for HDR sites

– Lack of scatter, eg. H&N, moulds, breast– Shielded applicators – require applicator library– Large tissue inhomogenities

Conclusions

• Imaging advances• Improved target definition• Allowed introduction of advanced TPS functionality

• Advanced planning tools improve workflow efficiency• Applicator libraries improve treatment plan quality (accuracy,

reproducibility, and efficiency)• Applicator reconstruction – anchor points; 3D surface rendering• Actual Source Path

• MR Alone reconstruction feasible (para sagittal, aqua gel, measurements)

• Plan libraries – fast implementation of standard plan and starting point for conformal plan.

• Applicator commissioning essential to verify source paths in TPS• Avoid systematic errors, see GEC-ESTRO guidance• Verify applicator reconstruction for each patient• Advance algorithms require geometry and composition of

applicators and tissue information

THANK YOUThank You

Acknowledgements•Liz Brearley, Carolyn Richardson•Aaron Huckle, Gavin Wright•Leeds Brachy Physics Team

advances in brachytherapy planning · 2019-03-22 · advances in brachytherapy planning: impact on...

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