13 Ken Javedan-IMRT with decimal solid modulators - small.pdf


13 Ken Javedan-IMRT with decimal solid modulators - small.pdf

IMRT with .decimal solid modulators forradiotherapy of malignant pleuralmesothelioma (MPM) post extrapleuralpneumonectomy (EPP)Department of Radiation OncologyH. Lee Moffitt Cancer CenterKhosrow Javedan M.S,Craig Stevens MD, Ph.D.,Ken Forster Ph.D.1

THANKS• X. Ron Zhu, Ph.D.• Chris Warner, M.S• Kenneth Cashon, M.S• Richard Sweat, CEO• .decimal• CMS2

PURPOSE:The purpose of this study was to investigateCompensator-Based Intensity Modulated RadiationTherapy (CB-IMRT) as an alternative to MLC-basedIMRT for large field IMRT. We investigated thepotential of this modality to treat malignant pleuralmesothelioma (MPM) post Extra PleuralPneumonectomy (EPP).3

Introduction:Treating MPM requires large IMRT fieldsMPM is a fatal aggressive cancer of the pleura2000 new cases per year in the united states(1)Increased incidence is strongly associated exposure to asbestosLiterature shows exposure to asbestos for as little as 1-2months could cause mesothelioma 20-50 years laterMales are affected more than females(2)National Cancer Institute's (NCI)Surveillance, Epidemiology, and End Results Program(SEER) in 2003, projected the total number of Americanmale mesothelioma cases to be approximately 71,000 by theyear 2054(3)4

Pleura (layer) on Lungon Chest wallNormal LungDiaphragmMesothelioma5

No cure for this diseaseLocal controlPalliationNational Cancer Institute (NCI) sponsors clinical trialsdesigned to seek new treatment modalities and improve oncurrent treatment techniques6

Traditionally radiation dose was administered usingConventional radiation therapy treatment techniques:External beam photon and electron beams (4, 5)Intraoperative-brachytherapy with post operative 45Gy mixed photon irradiation (6)In traditional radiotherapy, normal tissue sparing wasachieved using conventional photon or electron blocks7

PRESCRIPTION DOSE:• 30 Gy, 3 Gy DailyA prospective assessment of 22 patients with chest pain dueto malignant mesothelioma, receiving 30Gy in 10 dailyfractions, showed palliation effect was short lived at this doselevel and was diminished after 5 months (7)• 36 Gy, 2.4 Gy Daily• Low response rate for malignant mesothelioma has beenobserved when a median dose of 36 Gy given in 2.4 Gy dailydose resulted in local palliation of at least 39% -50% ofpatients that were treated (8)8

PRESCRIPTION DOSE CONT.:45-54 Gy, 1.8 Gy DailyA median dose of 54 Gy, range: 45-54 Gy administered to hemi-thorax with a combination of photon and electron technique hasbeen reported with improved local control and survival withacceptable toxicity (9)This seems to demonstrate thatsufficient dose was needed for palliation and local control of thedisease9

The use of IMRT allowed for further dose escalation to largeTarget volumes while maintaining tolerance doses toabutting radiation sensitive structures (10)The use of IMRT required the contouring of the clinicaltarget volumes (CTVs) which includedThe tumor bed (post EPP)Regions at risk for seeding of this disease10

To account for uncertainties in contouring the CTV:1 cm margin added to:The most superior/inferior surgical clipThe anterior, posterior and lateral margins were defined byadding 0.75 cm to violated spaces clipped at the skin11

CTV extends from apex of thorax down to inferiorpole of the kidneys.12

Large 6745 cc, irregular convex and concave shaped PTVTarget overlaps parts of liver and kidney.IMRT can be advantageous for large irregular targets, inclose proximity to critical structures. Dosimetric study byMeeks et al.(17)13

Current techniques often utilize IMRTWith specific treatment planning system coupledwith specific beam delivery and verify systemsForster et. al found Corvus, Pinnacle and Eclipse treatmentplanning systems were capable of generating acceptable IMRTplans for MPM after EPP (12)Zhu et al did a formal comparison of treatment planning systemsand foundCorvus 2786 MU, 1050 segmentsEclipse 1813 MU, 173 segments14

Current technique cont.IMRT Shows promising early local controlPost operative Intensity Modulated Radiation Therapy(IMRT) administered to the chest has shown promising earlylocal control (13,11)15

Why CB-IMRT?• Delivery of large IMRT fields with MLC is limited by• MLC design (14)• For example the Siemens Oncor machine with the 82 leafOptifocus MLC system allows:• Maximum IMRT field size of 22x40 cm 2X carriage travel limit is 10 cm passed the CAXMaximum conformal field size = 40x40 cm 2– ( desirable for large field CB-IMRT with MLC blocking)16

Treatments with multiple isocenters to overcome the MLC fieldsize limitations have been proposed by other investigators (15)17

It is essential that the modulator (MLC or brass compensator)reproduce the intended fluence mapA number of IMRT fields for three out of 4 right sided cases,required a minimum IMRT field width of 26 cmIMRT field modulation with solid modulators may be analternative solution to the problem of large field IMRT deliverywith the Siemens Oncor machine18

Why Solid modulator IMRT?IMRT with solid modulators safely used for more than adecade(16,17)CB-IMRT technique offers continuous intensity odulationDesirable for large IMRT fields treated on the SiemensOncor machineDesirable technique for moving targetsDelivers the intended modulated dose to all points within afield relatively instantaneously• Delivery time depends on machine dose rate19

IMRT with .decimalWe use CB-IMRT for:Lung,Esophagus,pelvic and rectal cancersThe average weight for the compensators usedrange from 4 to 20 lbs.Excellent absolute and relative dose agreement20

Methods and materialsIMRT with compensators and segmented multi-leafcollimator (SMLC) were planned using CMS XIO TPS forfour right sided and one left sided malignant mesotheliomapost EPP casesThe 6MV beams were delivered on a Siemens Oncormachine with 82 leaf Opti-focus MLCAbsolute dose points and relative dose distributions weremeasured21

Plan evaluation:• 2D isodose distribution for visual inspection of targetcoverage• DVH analysis• Conformity number (CN) as proposed by Van’t t Riet etal (19)• and homogeneity index (HI) were calculated to measureconformal plan qualityQuality Assurance:• Map check• Ion chamber• EDR2 Film and RIT 113 4 dosimetry system4Radiological Imaging Technology, Inc. 637A Elkton Drive, Colorado Springs, CO 8090722

A treatment strategy for a patient with MPM is surgery,chemotherapy and radiation therapy• Surgery– Extra pleural Pneumonectomy (EPP),– Involves the removal of the ipsilateral lung (removemotion),– hemidiaphragm resection, and reconstruction withGore-Tex– Mediastinal lymph node resection– Chest wall resection and reconstruction23

To assist the radiation oncologist with the contouring,– Surgeons place surgical clips to identify the entireoutline of the resected hemi-diaphragm and resectedmargins– These margins are otherwise difficult to identifypostoperatively24

Radiation Therapy• Simulation CT,MR,PET fusion• CT data transfer to TPS• Contour• Treatment planning• Quality assurance25

Radiation Therapy• Simulation:• 6-8 weeks post surgerySurgical scars were wired and covered with bolus0.50 cm bolus, 7 cm wide and extended 4 cm proximally anddistally taped over the surgical scarsPatient immobilized supine on the CT couchwith arms up using the T bar and the Med Tec wing boardwith the blue cradle both indexed to the couchat least 100 CT slices5 mm slice thicknesslarge bore Phillips Brilliance 16 slice computerized tomographyscanner (Phillips Medical System Inc. Cleveland OH)26

Bolus placement,immobilization, CT Simulation27

ContoursRadiation oncologist draws CTVMargin added to account for uncertainties in contouring:1 cm margin added above the most superior surgical clip1 cm margin added below the most inferior surgical clipAnterior, posterior and lateral margins were definedby adding 0.75 cm margin to violated spaces clipped atthe skin• Treatment planning• QA28

Contours cont.,Resident, physicist, dosimetrist draw OAR’s:Liver,kidneys,heart,esophagus,cord,lung,Small intestine,extend CTV 0.5 cm to PTV, andavoidance structures and the skin29

Dose volume constraintsTargets & OARsCTVPTVLIVERLUNGHEARTKIDNEYESOPHAGUSSPINAL CORDGoal doses45 Gy 25 fractions45 Gy to 95%< 30% > 30 Gy< 20% > 4 Gy,MLD 45 Gy< 20% > 15 Gy< 30% > 55 Gy< 10% > 45 GyNo portion > 50 Gy30

IMRT PLAN STRATEGY•CMS XIO•6MV beams aimed at center of PTV were designed•5-7 Gantry angles•Minimize entrance and limit exit dose to contra-lateral lungusing a BEV tool•No AP, No beam directly over the patient•The first gantry angle was 180 degrees and the rest were atabout 30 degrees interval•If ports contained significant portions of Liver, Lung use 3inch compensator, split fields to manage the weight, otherwiseuse 2 inch compensator31

• Intensity Modulation Range:• Inherent 6mm base plate• (~7.5-100%) for 3inch thick• (~20-100%) for 2 inch thick32

CMS/XIOSuperposition was used for final dosecomputationSuperposition is more accurate inheterogeneous media, Miften et al. compareddata and BEAM MC and showed 3%, 3mmagreement with MC(4)From XIO ref. library33

EAC• Effective attenuation coefficient forcompensator material is shown to depend onphoton beam energy and spectrum, materialtype and field size.• F. C. du Plessis et al., indicated that EAC forbrass can vary as much as 13% over a depthrange of 4 cm to 39 cm(12).34

Compensator transmission file• The treatment planning system computesthe compensator transmission array• The file is electronically sent to .decimalSanford, FL35

Ray line Compensator Transmissionand thickness arrays• The compensator transmission array is calculated for each fan line• ( i, j ) as,• T ( i, j ) un-comp, un-norm = D (i, j ) goal / D ( i, j ) un-com• T( i, j ) norm = T( i, j ) un-norm / T( i, j ) high point•• The brass alloy thickness t (i, j) is an array of values each representing the filter thickness for eachray and is calculated as• t ( i, j ) = - ln [ Trans ( i, j) ] / u eff• Info from xio reference library.36

Left sided case:5 Gantry angle Non Coplanar Fields3 inch thick brass compensatorsAcceptable dose distributionsShort delivery timeHeavy modulatorsUp to 33 lbsLargest field size28x39 cm 237

FIG 1. Two of the 5 field brass compensatoralloys for left side mesothelioma. From leftCompensator weights are 30, and 25 LbsCompared to one of 7 field prostatecompensator at 4 Lbs.39

7 gantry 11 fieldsMixed 2 and 3 inch thick solid modulators40

Liver in field,use 3 inch thick comp.8.8/11.3 x 0.20/20.0Field A~20x2041

2 inch thick comp.9.9/11.2 x 18.7/2.4Field A1~21x2142

Planning• Set up fields• Conform MLC to PTV• Set up IMRT Prescription page• Distance between Calc. points 4x4x4• Set up Optimization parameters• Select the compensator for modulator• 15 min43

• Start optimization– Beam let calculation 15 min– 33 iterations 60 minGenerate CompensatorsFinal dose Calculation 7 min44

Review compensatorsVisual aid for proper tray mount orientationSplit fieldNon split3 inch. 2 inch.45

Highly Modulated fielduse 3 inch compOrder CompensatorsSupSup3 inch liver block46

Less modulationuse 2 inch comp.47

Weight: (11.5(11.5-22.0lbs)Median weight = 16.5 lbsSiemens Upper Wedge Tray 18 verifiable codes inIMPAC S2N01-S2N1819.5 lbs20 lbs22 lbs16.5 lbs18.5 lbs22 lbs18 lbs16.5 lbs17.5 lbs16.5 lbs11.5 lbs48


Dose DistributionR sidea) Compensator b) MLC52

Dose DistributionL sidec) Compensator d) MLC10 Gy isodose line off lung53

PTV45 95% Both PlansCTV45 99% Both PlansPTVD552.2Gy55.4GyCord better spared with compensators.54

PTV45 97% 98%CTV45 100% Both PlansPTVD551.6Gy51.6Gy55.3GyCord better spared with comp.55

Liver R side casesPLAN IDLIVER VolumeccMean doseGyV30%1RC1904.625.0271RM1904.621222RC1550.127333RC1690.730354RC2251.23140Avg. RC18492834Range(1550.1-2251.2(25-31)(28-40)5. Liver DVH parameters for 4 right sided cases are shown. Note that MLC plans resulted in slightly lower average mean and V30 values compared with compensator plan56

Targets & OARsGoal doseComp.R sideMLCL sideComp. MLCCTV45Gy >98% volume99%99%100100PTV45Gy > 95% volume95.4%95.3%9798LIVER30Gy

Conformity Number (CN),an index proposed by Van’t Riet et al (18)takes into account the quality of coverage of the target and the volume ofhealthy tissue receiving at least the prescribed doseCN=(TV RI/TV)*(TVRI/V/VRI)Use DVHs to Calculate:Target volume in cc covered by reference isodosevolume (45Gy)Volume of tissue and non tissues in cc covered byreference isodose volume (45Gy)58

Conformity Number and Homogeneity indexPLAN ID(TV RI/TV)(TV RI/V RI)CNHI1RC0.950.960.921.291RM0.950.960.911.432RC0.950.820.781.483RC0.950.900.861.194RC0.950.930.881.245LC0.970.850.831.25LM0.980.810.801.5Avg. RC0.950.900.861.30Avg. LC0.970.850.831.20Avg. RLC0.960.890.851.2559

QAThe first QA looked at each individual filedwith gantry incident at zero degrees for all beamsUsing this QA plan, single field coronal profiles at 10 cm depth weremeasured and analyzed using the Map CHECK diode array deviceThe second QA plan looked at the composite dose overlayComposite QA plan was generated for a large Lucite phantom constructedfor this work.The third QA plan was generated for a 30 cm cube IMRT phantomThis phantom enables one to measure dose on EDR2 film at fourtransverse planes as well as the absolute dose with a cross calibrated ionchamber with true gantry angles incident on the phantom.60

Absolute doseIon chamber measurement results:61

MapCheckCalculated Coronal profiles for each field were placed in a QAdirectory on the department network.Phantom Irradiation:setup device surface at 98.65 SSD,8 cm added solid water.For each field,Profiles were measured, and compared with the calculated.62

3 inch thick compensator98% pass 3%, 3mm DTA63



Table.5 The average beam on time per field for compensator plans 1RC-4RC and 5LC,was calculated based on 300 cGy/MU. Total treatment time in minutes for thecompensator delivery included entering the treatment room, and replacing thecompensator for each field. 1RC and 1RM denote plan 1 for the right sided case withcompensator and with SMLC respectively.PLANID1RC1RM2RC3RC4RCAverageMU/Field89181879497Total MU976199396210401039Average Beam ontime / FieldSec18198181919Total treatment timeMin3336333535Avg. RC92100418.5345LC8088216305LM13114421013366

RESULTS:COMPENSATOR PLANS:All 5 compensator plans achieved the prescription target coverageSingle beam 89 MU (80-94 MU)Median weight = 16.5 lbs (11.5-22 lbs)Single beam on time 18 sec (16-19sec)TOTAL MU 982 MU (882-1061 MU)Treatment time including replacing compensators 33 minutesSMLC PLANS:Only Two SMLC-IMRT cases could be plannedThree meso cases required minimum IMRT field width of 26 cmSingle beam 188 MUSingle beam on time 198 secTOTAL MU 2071 MUTotal segments 204Treatment time 36 minutes67

CONCLUSIONS• Mesothelioma can be treated post-op with CB-IMRTIMRT with solid modulators adds the capability to the existing Linacs intreating large IMRT fields for MPM post surgery• It is possible and reasonable to deliver IMRT with compensators forfields this size (30x40) with most conventional linear accelerators whichmakes CB-IMRT an attractive alternative• 7 gantry 11 coplanar beams produce acceptable plans68

CONCLUSIONSCompensator weight was found manageable by therapistSingle beam treatment on time was significantly shorter for compensatorplans compared with MLCTotal MU was 50% less for compensator plansCompensator plans showed acceptably conformal dose distributionsconfirmed by multiple measurement techniquesTherapists prefer CB-IMRT over SMLC-IMRT for large field deliveryon the Siemens machine69

Thank you70

When brass alloy (copper and Zinc) is placed in thepath of a megavoltage photon beam,The primary photon spectrum incident on thepatient is hardened and attenuated.Filter may block scattered electrons generated inthe accelerator head.Filter replaces contaminant photons andelectrons.71

Conclusions• Mesothelioma can be treated post-op with IMRT.• Compensator plans showed acceptable conformal dosedistributions.• IMRT with solid compensators is a feasible technique formeso IMRT.• 7 gantry 11 coplanar beams produce acceptable plans.• The average weight for each compensator is 18 lbs– Compensator delivery time per field is significantly shorter– 18 sec versus 198 sec for SMLC• Beam-on time favors compensatorsCompensator 982 MUSMLC 2063 MU, 199 segments (Xio)72

FIELDSSD (cm)FIELD SIZEcm 25 field non coplanar,LA092.828.1X38.2Heavy filtersLPO88.721.5X39.4RAO88.020.1X38.1ASO90.038.0X22.3AIO90.030.7X22.7DEPTH (cm)7.311.612.210.010.0MU9215410110697Treatment time(sec)18.430.820.221.219.4• TABLE 1. 5 fields 6MV beam parameters. Note the totaltreatment time is 110 seconds with dose rate at 300 cGy/ min, however the resulting compensators are too heavyfor clinical use. The average weight was found to be 30lbs.78

Treatment planning• In General:• Large 6000-9000 cc, irregular convex and concave shaped PTV nearareas of electronic disequilibrium pose treatment planning anddosimetry challenges for MPM.• Planning Right sided mesothelioma is more challenging than the leftdue to liver dose constraintsNo more than 30% to get 30.0 Gy.• Maintain CTV 50 Gy.• Split beams typically 25x20 cm 2 .• 3 inch brass compensators.• Long calculation times for large volumes.• 3mm to 4mm calculation grid size.• 5-7 gantry angles.79

R-side mesotheliomaLarge PTVNotice Liver, and other dose limiting critical structureswith respect to target.81

R-Side Mesothelioma82

Treatment planning• We generated Fluence profiles using CMS/XIOmodulated with MLC and solid brass compensators.• Right Mesothelioma Plan:• 14 split coplanar beams• 7 gantry angles• Left mesothelioma plan:• 13 split beams• 5 gantry angles83

Review compensator utility in XIO to:Help Check compensator mount orientationElectronically order dot decimal compensator84

• R TO L: CTV, PTV (Red), LIVER (green),SPINAL CORD (dark blue), LUNG-L (orange),• KIDNEY-L (blue)•85

R-Sided MesotheliomaHealthy Lung DVH for 7 gantry split beams.Less than 1% L-Lung receives 20.0 GyMean L-Lung dose is 5.62 Gy86

ADose DistributionB50Gy45Gy30Gy10Gy88

EAC values decrease with increasing depth, field size, andcompensator thickness. Measured data is for 6MV beam.0.3800.3700.360Brass EAC 6MV1 cm thick at dmax1 cm thick at d103 cm thick at d55.08 cm thick at dmax5.08 cm thick at d10Poly. (1 cm thick at dmax)Poly. (1 cm thick at d10)Poly. (3 cm thick at d5)Poly. (5.08 cm thick at dmax)Poly. (5.08 cm thick at d10)EAC 1/cm0.3500.3400.3300.320-7%-9%0.3100.000 5.000 10.000 15.000 20.000 25.000 30.000 35.000field size94

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