Presentation on theme: "Motion in Radiotherapy"— Presentation transcript:
1Motion in Radiotherapy Martijn EngelsmanMay as well have been called “Radiotherapy in motion” because motion-management has been, and still is, a rapidly evolving important part of RadiotherapyMy feeling is that at least some of the previous presentations have gone pretty fast. Out of my own experience it is easy to assume basic understanding.Anecdote about treatment planning.I’ll try to be thorough and apologize to non-students and possibly even to students.
2Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motionMotion managementMotion in charged particle therapy
4Motion in radiotherapy Aim of radiotherapyDeliver maximum dose to tumor cells and minimum dose to surrounding normal tissues“Motion”Anything that may lead to a mismatch between the intended and actual location of delivered radiation dose
5Radiotherapy treatment process DiagnosisPatient immobilizationImaging (CT-scan)Target delineationTreatment plan designTreatment delivery (35 fractions)Patient follow-up
7PTV concept (1) (ICRU 50 and 62) High dose regionPTV (Planning Target Volume): = 8 cm, V = 268 cm3CTV (Clinical Target Volume): = 6 cm, V = 113 cm3GTV (Gross Tumor Volume): = 5 cm, V = 65 cm3Simplified (hej, patients are not square with round tumors, but as a physicist I’m allowed to shape reality into a comprehensive model), but the basis of radiotherapy treatment for the vast majority of patients
8PTV concept (2) Margin from GTV to CTV Margin from CTV to PTV Typically 5 mm or patient and tumor specificImproved by:Better imagingPhysician trainingMargin from CTV to PTVTypically 5 to 10 mmTumor location specificMotion managementSmart treatment planningGTVCTVPTVHigh Dose
9Example source of motion 35 Fractions=35 times patient setupFor the vast majority of radiations are isocentric meaning that for each fraction the patient is positioned with respect to the treatment machine isocenter and then the treatment is delivered as a whole.During a treatment fraction, the patient will be irriated from several, static, angles.Many patients set-up to lasers only.Many exceptions and more sophisticated approaches, but for explaining types of motion lasers will visualize nicely.35 fractions; never the same alignment twice.Patient skin is “loose” so markers can move. Patient can gain or loose weight resulting in “motion”The lasers have an inherent widthThe lasers may be half a mm displaced with respect to the iso-center of the linear accelerator. THAT’S WHY WE DO REGULAR QUALITY ASSURANCE
10Sources of motion Patient setup Patient breathing / coughing Patient heart-beatPatient discomfortTarget delineation inaccuraciesNon-representative CT-scanTarget deformation / growth / shrinkageEtc., etc. etc.I’ll discuss all of these in more detail within a few slides, this is just to give an idea.Patient setup: just imagine lining up to the lasers every fractionTarget delineation: The physician uses the CT-scan to draw where he thinks is target. Inherently flawed approachTarget deformation: Filled bladder / empty bladder. Gas in rectum, etc.
11Subdivision of motion Systematic versus Random Inter-fractional versus Intra-fractionalTreatment Preparation versus Treatment ExecutionLess commonly used
12Systematic versus Random Same error for all fractions (possibly even all patients).RandomUnpredictable. Day to day variations around a mean.Known but neitherBreathing, heartbeatRelatively known means neither type.Breathing can furthermore be both systematic and random
13Setup errors for three patients yBeam’s Eye ViewxImagine I’m looking at the patient in the direction of the treatment beam.Center of patient tumor is supposed to be aligned with the axis origin.
14Setup errors for a single patient Random (x)Random (y)Systematic (y)Systematic (x)Whenever there is random, there is also systematic.
15Inter-fractional versus Intra-fractional Variation between fractionsIntra-fractionalVariation within a fractionTreatment preparation errors affect the whole treatment -> hence: systematicTreatment execution errors
16Treatment preparation versus treatment execution Patient immobilizationCT-scanTarget delineationTreatment plan designTreatment delivery (35 fractions)Always systematicSystematic and/or randomTreatmentpreparationTreatmentexecution
20Treatment preparation Target deformation / motion 1/3BladderTargetNotice: variation in bladder shape due to bladder filling, may be different from day to dayBladder extends more downward in second scanVariation in rectum filling as well (both gasseous filling and non-gasseous filling)Note: overlap between bladder and target because of automatic expansion of the tumor volumeSystematicInter-fractionalTreatment preparationRandomIntra-fractionalTreatment execution
25Importance of motion Breathing motion / heart beat Systematic errors Raise your hand to voteBreathing motion / heart beatSystematic errorsRandom errorsLet’s “prove” itMostLeastAlmost leastOf course, it depends on the magnitude of motion you can typically expect. But, without telling you magnitudes what do you think?I’ll give you magnitudes later
26Simulation parameters (1) To enhance the visible effect of motion:High dose conformed to CTVGTVCTVPTVHigh DoseGTVCTVHigh Dose
27Dose (% of prescribed dose) distance from beam axis (mm) Simulation parameters (2)-60-50-40-30-20-1010203040506070809010095 %Dose (% of prescribed dose)distance from beam axis (mm)CTVParallel opposed beamsGTVCTVHigh DoseDirection of motion
31DVH reduction into: Tumor Control Probability (TCP) Assumption: homogeneous irradiation of the CTV to 84 Gy results in a TCP = 50 %
32Tumor motion and tumor control probability Amplitude of breathing motion(mm)Random setup errors (1SD)Systematic setup errorTCP(%)47.35-47.01046.31544.346.843.536.945.540.16.0Typical motion:
33Importance of motion Breathing motion / heart beat Systematic errors Therefore …Breathing motion / heart beatSystematic errorsRandom errorsMostLeastAlmost leastOf course, it depends on the magnitude of motion you can typically expect. But, without telling you magnitudes what do you think?I’ll give you magnitudes later
34Why are systematic errors worse ? Random errors / breathing blurs the cumulative dose distributiondoseSystematic errors shift the cumulative dose distributionCTVSlide byM. van Herk
35In other words… Systematic errors Same part of the tumor always underdosedRandom errors / Breathing motion / heart beatMultiple parts of the tumor underdosed part of the time, correctly dosed most of the timeBut don’t forget: Breathing motion and heart beat can have systematic effects on target delineation
37Radiotherapy treatment process Patient immobilizationCT-scanningTarget delineationTreatment plan designTreatment delivery
38Patient immobilization Leg pillowIntra-cranial maskGTC frameBreast board
39Benefits of immobilization Reproducible patient setupLimits intra-fraction motionPatient spends minutes on a not too comfortable treatment couch
40Radiotherapy treatment process Patient immobilizationCT-scanningTarget delineationTreatment plan designTreatment delivery
41CT-scanning Multiple CT-scans prior to treatment planning Reduces geometric miss compared to single CT-scan4D-CT scanningExtent of breathing motionDetermine representative tumor positionSee lecture “Advances in imaging for therapy”
42Radiotherapy treatment process Patient immobilizationCT-scanningTarget delineationTreatment plan designTreatment delivery
43Target delineation Multi-modality imaging CT-scan, MRI, PET, etc. Physician training and inter-collegial verificationImproved drawing tools and auto-delineation
44Radiotherapy treatment process Patient immobilizationCT-scanningTarget delineationTreatment plan designTreatment delivery
45Treatment plan design Choice of beam angles e.g. parallel to target motionSmart treatment planningRobust optimizationIMRTSee, e.g., lecture “Optimization with motion and uncertainties”
46Radiotherapy treatment process Patient immobilizationCT-scanningTarget delineationTreatment plan designTreatment deliveryLarge section on motion management in treatment delivery
47Magnitude of motion in treatment delivery Systematic setup errorLaser: S = 3 mmBony anatomy: S = 2 mmCone-beam CT: S = 1 mmRandom setup errorss = 3 mmBreathing motionUp to 30 mm peak-to-peakTypically 10 mm peak-to-peakTumor delineationSee next slideNumbers express order of magnitude and are a little bit fuzzy because they sometimes express setup error of bony anatomy, sometimes of actual tumor location.
48Tumor delineation 5? 22 Patients with lung cancer 11 Radiation oncologists from 5 institutionsComparison to median target surfaceRad. Onc. #Mean volume(cm3)Mean distance(mm)Overall SD136-6.415.1248-3.711.6353-4.313.9455-2.47.0558-3.312.7667-1.610.0769-1.26.2872-1.06.6976-0.27.410930.95.7111290.46.1All69 ( 25)-1.710.2Perhaps it is 5 mm for any given point on other targets. But then we are talking about the GTV.Delineation of the CTV may be more error-prone because it is by nature non-visible.Naturally, better imaging helps a lot, e.g. PET5?Steenbakkers et al.Radiother Oncol. 2005; 77:182-90
50Motion management for setup errors Portal imaging
51Obtained from Treatment Planning System Portal imagingObtained from Treatment Planning SystemObtained intreatment roomDigitally Reconstructed Radiograph
52Setup protocol NAL-protocol (No Action Level) Portal imaging for first Nm fractionsCalculate a single correction vector compared to markers for laser setupDaily imaging is the standard here at the proton center.Usually weekly imaging is performed with lasers used forde Boer HC, Heijmen BJ.Int J Radiat Oncol Biol Phys.2001;50(5):Lasers only
53Motion management for breathing In treatment plan designMargin increaseOvercompensating dose to marginRobust treatment planningSee, e.g., lecture “Optimization with motion and uncertainties”Control patient breathingBreath-holdGated radiotherapy
61Control / stop patient breathing Exhale position most reproducibleInhale position most beneficial for sparing lung tissue
62Breath hold techniques Voluntary breath holdRosenzweig KE et al. The deep inspiration breath-hold technique in the treatment of inoperable non-small-cell lung cancer. Int J Radiat Oncol Biol Phys. 2000;48:81-7Active Breathing Control (ABC)Wong JW et al. The use of active breathing control (ABC) to reduce margin for breathing motion. Int J Radiat Oncol Biol Phys. 1999;44:911-9Abdominal pressNegoro Y et al. The effectiveness of an immobilization device in conformal radiotherapy for lung tumor: reduction of respiratory tumor movement and evaluation of the daily setup accuracy. Int J Radiat Oncol Biol Phys. 2001;50:889-98Usually, lung cancer patients have an impaired lung function and can not really hold there breath that easily.
64Gated radiotherapy Gating window External or internal markers Usually 20% duty cycleSome residual motion
65Gating benefits and drawbacks +Less straining for patient than breath-holdIncreased treatment timeInternal markersDirect visualization of tumor (surroundings)Invasive procedure / side effects of surgeryExternal markersLimited burden for patientDoubtful correlation between marker and tumor positionIntra-fractionalInter-fractional-+-+-
73Passive scattering system ApertureRange Compensator+=LateralconformationDistalconformation
74Smearing the range compensator High-DensityStructureTargetVolumeBeamCriticalStructureRangeCompensatorBodySurface
75Smearing the range compensator High-DensityStructureTargetVolumeBeamCriticalStructureRangeCompensatorBodySurface
76C D Smear Setup Error A B 10 C D B10CDDisplayed isodose levels: 50%, 80%, 95% and 100%
77Motion management in particle therapy Passive scattered particle therapyFor setup errors and (possibly) breathing motionLateral expansion of aperturesSmearing of range compensatorsIMPTSee, e.g., lecture “Optimization with motion and uncertainties”