ImageImage--Based HDR Based HDR Brachytherapy Treatment Brachytherapy Treatment

PlanningPlanning

Jason J. Rownd, MSMedical College of Wisconsin

To understand important To understand important variables in applicator variables in applicator design and use.design and use.

emphasis on Tandem and emphasis on Tandem and Ring applicatorsRing applicatorsTandem and Ovoids, Tandem and Ovoids, Tandem and Cylinder, Tandem and Cylinder, similar treatment goalssimilar treatment goalscylinderscylinders

To understand the To understand the treatment planning treatment planning process for CT and MRIprocess for CT and MRI

Objectives:

Geometry: Cylinder GeometryGeometry: Cylinder Geometry

Simple geometry, Simple geometry, effectively a straight effectively a straight linelineCylinder diametersCylinder diameters

2.0cm, 2.0cm, 2.5cm, 2.5cm, 3.0cm, 3.5cm3.0cm, 3.5cm and and 4.0cm (4.0cm (CT/MR alsoCT/MR also))

Cylinder lengthsCylinder lengthsdomed segmentdomed segment2.5cm segments2.5cm segments

Orthogonal Films: CylinderOrthogonal Films: Cylinder

Fixed geometry Fixed geometry --applicator is fixed applicator is fixed togethertogetherChoose combination of Choose combination of diameter and physical diameter and physical length according to length according to anatomyanatomyDosimetry needed only Dosimetry needed only for 1st fractionfor 1st fractionAdapt fraction to fraction Adapt fraction to fraction if neededif needed

Vaginal Cylinders in CT PlanningVaginal Cylinders in CT Planning--traditional and traditional and compatiablecompatiable

2 cm and 4 cm diameter standard cylinders above

3.5 cm diameter CT/MR compatible cylinders to left

Surprisingly minimal artifacts on axial CT slices for the larger diameter cylinders

Cylinder: SummaryCylinder: Summary

Anything you can do with traditional films in treatment planning…

You can do with CT based planning.

Geometry: CT/MR Compatible Geometry: CT/MR Compatible Tandem & Ring Tandem & Ring

Same basic geometrySame basic geometryFIXED geometryFIXED geometry‘‘snapssnaps’’ in placein place

Slightly larger tandem Slightly larger tandem diameterdiameterSomewhat more fragileSomewhat more fragile

have broken one so farhave broken one so far

Minimal artifactsMinimal artifactseasier to see tissueeasier to see tissueharder to reconstructharder to reconstruct

Tandem & Ring ImplantTandem & Ring Implant

Fixed geometry Fixed geometry --tandem fixed in center tandem fixed in center of ringof ring

xx--ray marker strands ray marker strands help visualizehelp visualizereconstruction can show reconstruction can show errors in placement or errors in placement or connectionsconnectionsreconstructed geometry reconstructed geometry is often a double check is often a double check of the implant geometryof the implant geometry

Tandem & Ring PlanningTandem & Ring Planning--final final viewsviews

The applicator orthogonal axes (CT or MR)The applicator orthogonal axes (CT or MR)user defineduser defined--i.ei.e. ADJUST them . ADJUST them follows the natural planes of the follows the natural planes of the applicatorapplicatorxx--ray marker strands help identify ray marker strands help identify catheterscatheters

Easier for planning and display, but Easier for planning and display, but sometimes harder to contoursometimes harder to contour

native vs. reconstructed image qualitynative vs. reconstructed image qualitycontour on native CT axes viewscontour on native CT axes viewscompare/review in reconstructed viewscompare/review in reconstructed viewscompare both structures AND compare both structures AND applicatorsapplicators

Tandem & Ring PlanningTandem & Ring Planning

Dosimetry needed only for Dosimetry needed only for 1st fraction?1st fraction?

there can be extreme there can be extreme changes in normal changes in normal anatomy from fraction to anatomy from fraction to fractionfractionAdapt fraction to fraction as Adapt fraction to fraction as neededneededif you have to treat with a if you have to treat with a prior plan thenprior plan then……follow up with post follow up with post treatment dosimetrytreatment dosimetry

Various Points of InterestVarious Points of Interest

Applicator PointsApplicator Pointsrelative to relative to ‘‘Applicator Applicator AxesAxes’’keyboard entrykeyboard entryParaPara--Coronal viewCoronal viewReference from Smit Reference from Smit sleeve or cervical marker sleeve or cervical marker ball or applicator surface ball or applicator surface or or ……Point A is defined at a Point A is defined at a POINT, 2cm up from ring POINT, 2cm up from ring surface and 2cm lateral to surface and 2cm lateral to tandemtandemPoint B Point B -- 2cm superior 2cm superior from ring surface and 5cm from ring surface and 5cm lateral to midlinelateral to midlinePoint T Point T -- 1cm superior to 1cm superior to ring surface and 1cm ring surface and 1cm lateral to tandemlateral to tandem

Various Points of InterestVarious Points of Interest

Patient Points Patient Points (digitized from films or (digitized from films or CT images)CT images)

points of interest where we points of interest where we monitor dose identified by monitor dose identified by physician or physicistphysician or physicist

contoured normal tissuescontoured normal tissues

contrast based placementcontrast based placement•• choose expected hot spots choose expected hot spots

based on contrast based on contrast enhanced anatomyenhanced anatomy

points OR volumespoints OR volumes……

Planning SpecificsPlanning Specifics--TandemTandem

Dose optimization points are tapered Dose optimization points are tapered along the tandem axisalong the tandem axis

12mm, 14mm, 16mm, 18mm,20mm 12mm, 14mm, 16mm, 18mm,20mm down to level of Point Adown to level of Point A

Dwell locations down to ring, but not Dwell locations down to ring, but not caudal into the vaginacaudal into the vaginaCreates an approximate Creates an approximate ‘‘pearpear’’ shape shape Dose optimization points can also be Dose optimization points can also be used to modify the classic location of used to modify the classic location of dose specification (Point A)dose specification (Point A)1.8 cm, 1.5 cm, 1.2 cm lateral 1.8 cm, 1.5 cm, 1.2 cm lateral prescription distancesprescription distancesEven with film based planning, you can Even with film based planning, you can use CT scan information to get uterine use CT scan information to get uterine wall thickness and adjust dose wall thickness and adjust dose optimization AND prescription pointsoptimization AND prescription points

Planning SpecificsPlanning Specifics--RingRing

Activate dwell positions of 360Activate dwell positions of 360°° circle in accordance with disease circle in accordance with disease location and ring diameter (not entire ring) location and ring diameter (not entire ring)

symmetric sparing of anterior and posterior vaginal surface, closymmetric sparing of anterior and posterior vaginal surface, close to the se to the bladder and rectum, similar to Tandem and Ovoid treatmentsbladder and rectum, similar to Tandem and Ovoid treatmentsoptimize/prescribe to the surface of the ring 6 mm radial from doptimize/prescribe to the surface of the ring 6 mm radial from dwell well positions with a percentage of the prescription dosepositions with a percentage of the prescription dosepossible to have a slight posterior dose enhancementpossible to have a slight posterior dose enhancementwe never load the full ring for treatmentwe never load the full ring for treatment***Tandem and Cylinder treatments DO treat the entire radial sur***Tandem and Cylinder treatments DO treat the entire radial surface face within the active treatment length of the vagina, so be more cauwithin the active treatment length of the vagina, so be more cautioustious

Too Many Points?Too Many Points?Dose Optimization PointsDose Optimization Points

control the shape of the isodose distributioncontrol the shape of the isodose distribution

determine relative dwell weights by assigning relative determine relative dwell weights by assigning relative weights to the dose optimization pointsweights to the dose optimization points

e.g 100% to the tandem taper and 140% to vaginal e.g 100% to the tandem taper and 140% to vaginal surfacesurface

Prescription PointsPrescription Pointsdefine the absolute value of the isodose linesdefine the absolute value of the isodose lines

scale the entire dose distribution, turning relative dwell scale the entire dose distribution, turning relative dwell weights into absolute dwell times for treatment deliveryweights into absolute dwell times for treatment delivery

prescription can be defined in several waysprescription can be defined in several ways

true DVH planning/evaluationtrue DVH planning/evaluation……

•• multicatheter breasts, we prescribe a percent of multicatheter breasts, we prescribe a percent of the Rx to a percentage of the PTVthe Rx to a percentage of the PTV

•• NOT yet to the NOT yet to the ‘‘automatedautomated’’ planning stage of planning stage of using a goal or wish list set of treatment using a goal or wish list set of treatment parameters similar to IMRTparameters similar to IMRT

•• See ABS/GECSee ABS/GEC--ESTRO brachytherapy ESTRO brachytherapy recommendationsrecommendations

MRI PlanningMRI Planning

IF you use only the MR IF you use only the MR images for planningimages for planning

Improved tumor/target Improved tumor/target recognitionrecognitionNo commercial MRI No commercial MRI markers to visualize markers to visualize possible dwell positions?possible dwell positions?

Even harder to visualize Even harder to visualize applicatorsapplicators

Compared to CT scansCompared to CT scansHard to identify possible Hard to identify possible dwell positionsdwell positions

MRI FusionMRI Fusion

Fuse to orthogonal film informationFuse to orthogonal film informationiterative planningiterative planning

Fuse to CT scan informationFuse to CT scan informationour departmentour department’’s focuss focus

•• identify tip of tandemidentify tip of tandem

•• identify handles of applicatoridentify handles of applicator

contour on MRI for targetscontour on MRI for targets

fuse MRI to CTfuse MRI to CT

reconstruct applicators on CTreconstruct applicators on CT

add contours for normal tissues on add contours for normal tissues on CT (rectum, bladder and sigmoid)CT (rectum, bladder and sigmoid)

plan on CT imagesplan on CT images

minimal scan set up differences minimal scan set up differences neededneeded

MRI FusionMRI Fusion--continuedcontinued

Fuse to other MRI scansFuse to other MRI scansdifferent weightings to highlight different aspects of the imagedifferent weightings to highlight different aspects of the image

possibly enhance applicator and markerspossibly enhance applicator and markers

identity matched for easiest fusionidentity matched for easiest fusion

DifficultiesDifficultiesmultistep fusion is not possible(?), all fusion must be to one multistep fusion is not possible(?), all fusion must be to one base image set, usually the CT imagebase image set, usually the CT image

image quality of reconstructed views is not as good as native image quality of reconstructed views is not as good as native views (e.g. coronal and sagittal), depends on slice thicknessviews (e.g. coronal and sagittal), depends on slice thickness

still uncertain about dwell position locations in MRI scansstill uncertain about dwell position locations in MRI scans

DosimetryDosimetry--ConclusionsConclusions

Our prescription is implied for Our prescription is implied for the volume not just Point Athe volume not just Point A

We hope to move to We hope to move to consistent DVH consistent DVH prescription protocol based prescription protocol based on MRI targets but there on MRI targets but there are still uncertaintiesare still uncertainties

Must be clear and consistent in Must be clear and consistent in your planning process and your planning process and reportingreporting

redundant information is a redundant information is a necessity when adapting to necessity when adapting to different planning methodsdifferent planning methods

Team approach, be prepared Team approach, be prepared to communicate, inform and to communicate, inform and assist as necessaryassist as necessary