Dosimetric Impact of Silastic Insert Thickness in COMS Eye ...chapter.aapm.org/nccaapm/z_meetings/2019-04-26/04...– Digital Caliper used to measure the lip height, and determine

Dosimetric Impact of Silastic Insert Thickness in COMS Eye Plaque for I-125 Brachytherapy

Courtney OareNCC-AAPM Spring Meeting

La Crosse, WIApril 26th, 2019

Background- Ocular Melanoma

• 1400 cases of ocular melanoma are diagnosed annually

• Treatment options:– Radiation Therapy (>75%)

• Eye plaque • Proton therapy• Gamma Knife

– Enucleation (

Background- COMS

• 1985 Collaborative Ocular Melanoma Study (COMS) was formed to evaluate two methods of tumor control and survival:1) 20 Gy external beam therapy prior to enucleation vs. no

radiation prior to enucleation• Radiation did not improve survival

2) Enucleation compared to I-125 eye plaque therapy• No difference in survival!

• COMS findings standardized plaque brachytherapy

Chiu-Tsao et al., Med Phys 2012

Background- COMS PlaqueA. Iodine-125 seeds

– Mean photon energy: 28 keV– T1/2: 59.4 days

B. Silastic seed carrier insert (Dow Corning Corp., Midland, MI)– MDX-4210, a medical grade

elastomer – Places seed 1mm from Sclera

C. Gold-alloy backing (Trachsel Dental Studio, Rochester, MN)– 10 – 22mm


Problem: Inconsistent Silastic Thickness

• The COMS Silastic insert is described as 2mm thick, placing source 1mm from Sclera

• Inserts appear to be manufactured with varying thickness – Especially for large, 22mm plaques– Added thickness increases distance between source and prescription point– How does this effect dose to the tumor? Normal eye structures?


Methods1) Measure thickness of 13 inserts

– All 22mm COMS plaque– Digital Caliper used to measure the lip height, and

determine thickness2) Dose Calculations using BrachyVision (TG-43)

– Vary distance from source to prescription point based on ranging Silastic thickness (2, 2.5 or 3mm)

– Account for different tumor apex heights (5, 7, 10mm)• Adjust activity to deliver 85 Gy to tumor apex (as recommended by

American Brachytherapy Society)

– Calculate doses to critical structures • tumor apex, sclera, lens, macula, opposite retina, and optic disk

Rivard et al., AAPM TG-43 update 2004ABS-OOTF Committee, Brachytherapy 2014

1.5

2.0

2.5

3.0

3.5

0 1 2 3 4 5 6

Sila

stic

Inse

rt M

easu

red

Thic

knes

s (m

m)

nStandard Medium Thick

Results: Measured Silastic Thickness

Based on measurements inserts were grouped into standard, medium, and thick

Mean thicknesses were rounded to nearest half millimeter (2, 2.5, 3mm)

Grouping n Mean (mm)Standard 5 1.93Medium 2 2.36Thick 6 3.22

2 2.5 3

Results: Dose Calculations• Percent prescription dose (%PD), relative to 85 Gy at

the tumor apex, is determined for critical eye structures based on:

1) Silastic Thickness 2) Tumor Size

SilasticTumor Apex Size: 5mm 7mm 10mm 5mm 7mm 10mm 5mm 7mm 10mmTumor Apex 100.3 100.0 99.8 92.6 92.7 92.9 85.8 86.0 86.6Sclera 268.7 364.6 568.1 232.3 315.1 491.1 204.9 277.9 433.1Lens Center 27.6 37.5 58.4 25.9 35.1 54.8 24.3 33.0 51.4Macula 41.6 56.4 87.9 38.7 52.5 81.8 36.1 48.9 76.3Opposite Retina 10.7 14.5 22.6 10.1 13.8 21.4 9.6 13.1 20.3Optic Disk 52.1 70.6 110.1 48.0 65.1 101.5 44.4 60.2 93.9

Standard, 2mm Medium, 2.5mm Thick, 3mm

Reference Point Doses

22 mm plaque, 4 day treatmentNot used in abstract -->

Silastic*Normal, 2mmMedium, 2.5 mmThick, 3 mm3.5 mm4.0 mm*Amount of silastic beyond 1 mm seed insert

Tumor Apex **5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm**Activity altered to achieve 85 Gy at prescription point

Reference PointDose (cGy)A5mm3.42

Apex 8502.48497.98483.27872.37880.178987291.37308.27358.76758.96782.36862.96263.56299.16406.2A7mm4.64

%PD100.399.9899.892.6292.7192.9285.7885.9886.5779.5279.7980.7473.6974.1175.37A10mm7.23

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.16758.99169.914288.56263.58497.913241.4

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.3479.52107.88168.173.6999.98155.78

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.315605.221172329901414119185.529894.6

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07183.59249.08388.12166.36225.71351.7

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.71940.52632.74102.31824.92475.93857.9

%PD27.6337.4858.425.935.1354.7524.332.9751.3722.8330.9748.2621.4729.1345.39

Macula3534.54795.374723288.24461.26951.43065.94159.56481.32864.33886.16055.22680.736375667.1

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.2533.745.7271.2431.5442.7966.67

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5776.51053.51641.6737.810011559.8

%PD10.6814.4922.5810.1313.7521.429.6213.0520.339.1412.3919.318.6811.7818.35

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.53501.64750.77402.63257.44419.46886.3

%PD52.0670.63110.0547.9965.11101.4544.460.2493.8641.255.8987.0938.3251.9981.02

Activity (U)3.424.647.233.424.647.233.424.647.233.424.647.233.424.647.23

Time (days)4.004.004.004.004.004.004.004.004.004.004.004.004.004.004.00

Tumor apex (mm) 5.007.0010.005.507.5010.506.008.0011.006.508.5011.507.009.0012.00

Sheet2

Silastic:Standard, 2mmMedium, 2.5mmThick, 3mm

Reference Point:Tumor Apex:5mm7mm10mm5mm7mm10mm5mm7mm10mm

Apex Dose (cGy)8502.48497.98483.27872.37880.17898.07291.37308.27358.7

%PD100.3100.099.892.692.792.985.886.086.6

Inner ScleraDose22841.830990.048288.419743.726786.741738.817412.823624.436811.3

%PD268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens CenterDose 2348.33186.04964.32201.12986.34653.22065.62802.44366.7

%PD27.637.558.425.935.154.824.333.051.4

MaculaDose3534.54795.37472.03288.24461.26951.43065.94159.56481.3

%PD41.656.487.938.752.581.836.148.976.3

Opposite RetinaDose 907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.714.522.610.113.821.49.613.120.3

Optic DiskDose 4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.170.6110.148.065.1101.544.460.293.9

Activity (U)3.424.647.23



Apex Dose (cGy)8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Inner ScleraDose (cGy)22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens CenterDose (cGy)2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

MaculaDose (cGy)3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite RetinaDose (cGy)907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic DiskDose (cGy)4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86


Reference Point:Apex Size:5mm7mm10mm5mm7mm10mm5mm7mm10mm

Tumor ApexDose (cGy)8502.48497.98483.27872.37880.17898.07291.37308.27358.7

%PD100.3100.099.892.692.792.985.886.086.6


%PD268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens CenterDose2348.33186.04964.32201.12986.34653.22065.62802.44366.7

%PD27.637.558.425.935.154.824.333.051.4

MaculaDose3534.54795.37472.03288.24461.26951.43065.94159.56481.3

%PD41.656.487.938.752.581.836.148.976.3

Opposite RetinaDose907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.714.522.610.113.821.49.613.120.3

Optic DiskDose 4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.170.6110.148.065.1101.544.460.293.9

Sheet6

SilasticStandard, 2mmMedium, 2.5mmThick, 3mm

Tumor Apex Size:5mm7mm10mm5mm7mm10mm5mm7mm10mm

Tumor Apex100.3100.099.892.692.792.985.886.086.6

Sclera268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens Center27.637.558.425.935.154.824.333.051.4

Macula41.656.487.938.752.581.836.148.976.3

Opposite Retina10.714.522.610.113.821.49.613.120.3

Optic Disk52.170.6110.148.065.1101.544.460.293.9

Sheet3

Sheet1

22 mm plaque, 4 day treatment

Silastic*Normal, 2mmMedium, 2.5 mmThick, 3 mm

Tumor Apex **5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm

Reference PointDose (cGy)

Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.1

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.34

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86

22mm COMS Plaque, 5mm Tumor Apex

SilasticStandardMediumThick7 mm7 mm7 mm10 mm10 mm10 mm


Apex 8502.47872.37291.38497.97880.17308.28483.278987358.7

%PD100.392.6285.7899.9892.7185.9899.892.9286.57

Calibration 5mm8502.47872.37291.311535.510680.69892.317974.516642.415414.1

%PD100.0392.9685.78135.71125.65116.38211.46195.79181.34

Inner Sclera22841.819743.717412.83099026786.723624.448288.441738.836811.3

%PD268.73232.28204.86364.59315.14277.93568.1491.05433.07

Lens Center2348.32201.12065.631862986.32802.44964.34653.24366.7

%PD27.6325.924.337.4835.1332.9758.454.7551.37

Macula3534.53288.23065.94795.34461.24159.574726951.46481.3

%PD41.5838.6836.0756.4252.4848.9487.9181.7876.25

Opposite Retina907.9861.3817.61231.81168.61109.31919.31820.91728.5

%PD10.6810.139.6214.4913.7513.0522.5821.4220.33

Optic Disk4424.94079.23774.16003.45534.45120.49352.48623.77978.5

%PD52.0647.9944.470.6365.1160.24110.05101.4593.86


SilasticStandardMediumThickCritical Structure Coordinates

Dose to Apex8502.47872.37291.3Structurexyz

Reference Point%Prescription Dose5mm Tumor Apex0.500.000.00

Apex 100.392.6285.78Inner Sclera0.000.000.00

Inner Sclera268.73232.28204.86Lens Center1.28-0.730.00

Lens Center27.6325.924.3Macula1.831.070.00

Macula41.5838.6836.07Opposite Retina2.200.000.00

Opposite Retina10.6810.139.62Optic Disk0.711.030.00

Optic Disk52.0647.9944.4

Sheet5

SilasticNormal, 2mmMedium, 2.5 mmThick, 3 mm

Tumor Apex 5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm

Apex100.0%100.0%100.0%92.6%92.7%93.1%85.8%86.0%86.7%

Sclera268.7%364.7%569.2%232.2%315.2%492.0%204.8%278.0%433.9%

Lens27.6%37.5%58.5%25.9%35.1%54.9%24.3%33.0%51.5%

Macula41.6%56.4%88.1%38.7%52.5%81.9%36.1%48.9%76.4%

Opposite Retina10.7%14.5%22.6%10.1%13.8%21.5%9.6%13.1%20.4%

Optic Disk52.0%70.6%110.2%48.0%65.1%101.7%44.4%60.3%94.1%

1

0.0117966692

1

0.0117649134

2.6865120437

0.03160637





Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.1

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.34

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86





Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

1110.9258915130.92729968580.93101659750.8575578660.86000070610.8674438891

2.68651204373.64678332295.69223877782.32213257433.15215523844.92017163332.04798645092.78002800694.3393177103

0.27619260440.37491615580.58519190870.25887984570.35141623220.54851942660.2429431690.32977559160.5147467937

0.41570615360.56429235460.88079969820.38673786230.5249767590.81943134670.36059230330.489473870.7640159374

0.10678161460.14495345910.22624717090.10130080920.13751632760.21464777440.09616108390.1305381330.2037556582

0.52042952580.70645688931.10246133530.47977041780.65126678361.01656214640.44388643210.6025488650.9405059412

Apex5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm1110.925891512984569180.927299685804728320.931016597510373360.857557866014301950.860000706056790460.86744388909845327Lens5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.2761926044410990.374916155756128020.585191908713692870.258879845690628550.351416232245613640.548519426631459810.242943168987579980.329775591616752410.51474679366276865Macula5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.415706153556642870.564292354581720220.880799698227084040.386737862250658650.524976758963979330.819431346661636970.360592303349642480.489473870014944910.76401593738211993Optic Disk5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.520429525780955910.706456889349133311.10246133534515270.479770417764395940.651266783558290821.01656214635986420.443886432066240120.60254886501370930.94050594115428132

%Prescription Dose

Sheet4

Silastic Measuremnts

22mm Inserts

SizeNo.Thickness (mm)Lip (mm)StandardMediumThick

Thin11.891.98~1 mm from source11.892.363.15TypeThickness (mm)

~2 mm21.941.9421.942.553.18Standard1.89

32.002.0532.003.30Standard1.94

41.881.9841.883.24Standard2.00

51.941.9451.943.14Standard1.88

Medium12.362.3063.31Standard1.94

~2.5 mm22.552.551.932.463.22Medium2.36

Thick13.153.10~1.5 mm from source0.04795831520.13435028840.0745654075Medium2.55

~3 mm23.183.01Thick3.15

33.303.32Thick3.18

43.243.22~2mm from sourceThick3.30

53.143.09Thick3.24

63.313.29Thick3.14

Thick3.31

1.891.9421.881.942.362.54999999999999983.153.183.33.243.143.31

Standard1234561.891.9421.881.94Medium1234562.362.5499999999999998Thick1234563.153.183.33.243.143.31

Silastic Insert

Measaured Thickness (mm)

Reference Pt Coordinates

Reference Point Coordinates (cm)

Tumor Apex

5mm Depth Inner ScleraLens CenterMaculaOpp RetinaOptic Disk0.5 cm0.7 cm1.0 cm

x0.500.001.280.832.200.710.500.701.00

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.05 cm Silastic


x0.550.051.330.882.250.760.550.751.05

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

.1 cm Silastic


x0.600.101.380.932.300.810.600.801.10

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.15 cm Silastic


x0.650.151.430.982.350.860.650.851.15

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.2 cm Silastic


x0.700.201.481.032.400.910.700.901.20

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

Structurexyz

Tumor Apex0.500.000.00

5mm Depth Reference Point0.500.000.00

Inner Sclera0.000.000.00

Lens Center1.28-0.730.00

Macula0.831.070.00

Opposite Retina2.200.000.00

Optic Disk0.711.030.00

Critical Structure Coordinates

Results: Dose Calculations (cont.)

• As Silastic thickness increases, %PD decreased • As tumor apex increases, %PD to normal eye

structures increased, as expected

SilasticTumor Apex Size: 5mm 7mm 10mm 5mm 7mm 10mm 5mm 7mm 10mmTumor Apex 100.3 100.0 99.8 92.6 92.7 92.9 85.8 86.0 86.6Sclera 268.7 364.6 568.1 232.3 315.1 491.1 204.9 277.9 433.1Lens Center 27.6 37.5 58.4 25.9 35.1 54.8 24.3 33.0 51.4Macula 41.6 56.4 87.9 38.7 52.5 81.8 36.1 48.9 76.3Opposite Retina 10.7 14.5 22.6 10.1 13.8 21.4 9.6 13.1 20.3Optic Disk 52.1 70.6 110.1 48.0 65.1 101.5 44.4 60.2 93.9

Standard, 2mm Medium, 2.5mm Thick, 3mm

Reference Point Doses

22 mm plaque, 4 day treatmentNot used in abstract -->

Silastic*Normal, 2mmMedium, 2.5 mmThick, 3 mm3.5 mm4.0 mm*Amount of silastic beyond 1 mm seed insert

Tumor Apex **5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm**Activity altered to achieve 85 Gy at prescription point

Reference PointDose (cGy)A5mm3.42

Apex 8502.48497.98483.27872.37880.178987291.37308.27358.76758.96782.36862.96263.56299.16406.2A7mm4.64

%PD100.399.9899.892.6292.7192.9285.7885.9886.5779.5279.7980.7473.6974.1175.37A10mm7.23

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.16758.99169.914288.56263.58497.913241.4

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.3479.52107.88168.173.6999.98155.78

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.315605.221172329901414119185.529894.6

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07183.59249.08388.12166.36225.71351.7

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.71940.52632.74102.31824.92475.93857.9

%PD27.6337.4858.425.935.1354.7524.332.9751.3722.8330.9748.2621.4729.1345.39

Macula3534.54795.374723288.24461.26951.43065.94159.56481.32864.33886.16055.22680.736375667.1

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.2533.745.7271.2431.5442.7966.67

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5776.51053.51641.6737.810011559.8

%PD10.6814.4922.5810.1313.7521.429.6213.0520.339.1412.3919.318.6811.7818.35

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.53501.64750.77402.63257.44419.46886.3

%PD52.0670.63110.0547.9965.11101.4544.460.2493.8641.255.8987.0938.3251.9981.02

Activity (U)3.424.647.233.424.647.233.424.647.233.424.647.233.424.647.23

Time (days)4.004.004.004.004.004.004.004.004.004.004.004.004.004.004.00

Tumor apex (mm) 5.007.0010.005.507.5010.506.008.0011.006.508.5011.507.009.0012.00

Sheet2



Apex Dose (cGy)8502.48497.98483.27872.37880.17898.07291.37308.27358.7

%PD100.3100.099.892.692.792.985.886.086.6


%PD268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens CenterDose 2348.33186.04964.32201.12986.34653.22065.62802.44366.7

%PD27.637.558.425.935.154.824.333.051.4

MaculaDose3534.54795.37472.03288.24461.26951.43065.94159.56481.3

%PD41.656.487.938.752.581.836.148.976.3

Opposite RetinaDose 907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.714.522.610.113.821.49.613.120.3

Optic DiskDose 4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.170.6110.148.065.1101.544.460.293.9

Activity (U)3.424.647.23



Apex Dose (cGy)8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Inner ScleraDose (cGy)22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens CenterDose (cGy)2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

MaculaDose (cGy)3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite RetinaDose (cGy)907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic DiskDose (cGy)4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86


Reference Point:Apex Size:5mm7mm10mm5mm7mm10mm5mm7mm10mm

Tumor ApexDose (cGy)8502.48497.98483.27872.37880.17898.07291.37308.27358.7

%PD100.3100.099.892.692.792.985.886.086.6


%PD268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens CenterDose2348.33186.04964.32201.12986.34653.22065.62802.44366.7

%PD27.637.558.425.935.154.824.333.051.4

MaculaDose3534.54795.37472.03288.24461.26951.43065.94159.56481.3

%PD41.656.487.938.752.581.836.148.976.3

Opposite RetinaDose907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.714.522.610.113.821.49.613.120.3

Optic DiskDose 4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.170.6110.148.065.1101.544.460.293.9

Sheet6

SilasticStandard, 2mmMedium, 2.5mmThick, 3mm

Tumor Apex Size:5mm7mm10mm5mm7mm10mm5mm7mm10mm

Tumor Apex100.3100.099.892.692.792.985.886.086.6

Sclera268.7364.6568.1232.3315.1491.1204.9277.9433.1

Lens Center27.637.558.425.935.154.824.333.051.4

Macula41.656.487.938.752.581.836.148.976.3

Opposite Retina10.714.522.610.113.821.49.613.120.3

Optic Disk52.170.6110.148.065.1101.544.460.293.9

Sheet3

Sheet1





Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.1

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.34

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86


SilasticStandardMediumThick7 mm7 mm7 mm10 mm10 mm10 mm


Apex 8502.47872.37291.38497.97880.17308.28483.278987358.7

%PD100.392.6285.7899.9892.7185.9899.892.9286.57

Calibration 5mm8502.47872.37291.311535.510680.69892.317974.516642.415414.1

%PD100.0392.9685.78135.71125.65116.38211.46195.79181.34

Inner Sclera22841.819743.717412.83099026786.723624.448288.441738.836811.3

%PD268.73232.28204.86364.59315.14277.93568.1491.05433.07

Lens Center2348.32201.12065.631862986.32802.44964.34653.24366.7

%PD27.6325.924.337.4835.1332.9758.454.7551.37

Macula3534.53288.23065.94795.34461.24159.574726951.46481.3

%PD41.5838.6836.0756.4252.4848.9487.9181.7876.25

Opposite Retina907.9861.3817.61231.81168.61109.31919.31820.91728.5

%PD10.6810.139.6214.4913.7513.0522.5821.4220.33

Optic Disk4424.94079.23774.16003.45534.45120.49352.48623.77978.5

%PD52.0647.9944.470.6365.1160.24110.05101.4593.86


SilasticStandardMediumThickCritical Structure Coordinates

Dose to Apex8502.47872.37291.3Structurexyz

Reference Point%Prescription Dose5mm Tumor Apex0.500.000.00

Apex 100.392.6285.78Inner Sclera0.000.000.00

Inner Sclera268.73232.28204.86Lens Center1.28-0.730.00

Lens Center27.6325.924.3Macula1.831.070.00

Macula41.5838.6836.07Opposite Retina2.200.000.00

Opposite Retina10.6810.139.62Optic Disk0.711.030.00

Optic Disk52.0647.9944.4

Sheet5

SilasticNormal, 2mmMedium, 2.5 mmThick, 3 mm

Tumor Apex 5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mm

Apex100.0%100.0%100.0%92.6%92.7%93.1%85.8%86.0%86.7%

Sclera268.7%364.7%569.2%232.2%315.2%492.0%204.8%278.0%433.9%

Lens27.6%37.5%58.5%25.9%35.1%54.9%24.3%33.0%51.5%

Macula41.6%56.4%88.1%38.7%52.5%81.9%36.1%48.9%76.4%

Opposite Retina10.7%14.5%22.6%10.1%13.8%21.5%9.6%13.1%20.4%

Optic Disk52.0%70.6%110.2%48.0%65.1%101.7%44.4%60.3%94.1%

1

0.0117966692

1

0.0117649134

2.6865120437

0.03160637





Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

%PD100.399.9899.892.6292.7192.9285.7885.9886.57

Calibration 5mm8502.411535.517974.57872.310680.616642.47291.39892.315414.1

%PD100.03135.71211.4692.96125.65195.7985.78116.38181.34

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

%PD268.73364.59568.1232.28315.14491.05204.86277.93433.07

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

%PD27.6337.4858.425.935.1354.7524.332.9751.37

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

%PD41.5856.4287.9138.6852.4881.7836.0748.9476.25

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

%PD10.6814.4922.5810.1313.7521.429.6213.0520.33

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

%PD52.0670.63110.0547.9965.11101.4544.460.2493.86





Apex 8502.48497.98483.27872.37880.178987291.37308.27358.7

Inner Sclera22841.83099048288.419743.726786.741738.817412.823624.436811.3

Lens Center2348.331864964.32201.12986.34653.22065.62802.44366.7

Macula3534.54795.374723288.24461.26951.43065.94159.56481.3

Opposite Retina907.91231.81919.3861.31168.61820.9817.61109.31728.5

Optic Disk4424.96003.49352.44079.25534.48623.73774.15120.47978.5

1110.9258915130.92729968580.93101659750.8575578660.86000070610.8674438891

2.68651204373.64678332295.69223877782.32213257433.15215523844.92017163332.04798645092.78002800694.3393177103

0.27619260440.37491615580.58519190870.25887984570.35141623220.54851942660.2429431690.32977559160.5147467937

0.41570615360.56429235460.88079969820.38673786230.5249767590.81943134670.36059230330.489473870.7640159374

0.10678161460.14495345910.22624717090.10130080920.13751632760.21464777440.09616108390.1305381330.2037556582

0.52042952580.70645688931.10246133530.47977041780.65126678361.01656214640.44388643210.6025488650.9405059412

Apex5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm1110.925891512984569180.927299685804728320.931016597510373360.857557866014301950.860000706056790460.86744388909845327Lens5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.2761926044410990.374916155756128020.585191908713692870.258879845690628550.351416232245613640.548519426631459810.242943168987579980.329775591616752410.51474679366276865Macula5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.415706153556642870.564292354581720220.880799698227084040.386737862250658650.524976758963979330.819431346661636970.360592303349642480.489473870014944910.76401593738211993Optic Disk5 mm7 mm10 mm5 mm7 mm10 mm5 mm7 mm10 mmNormal, 2mmMedium, 2.5 mmThick, 3 mm0.520429525780955910.706456889349133311.10246133534515270.479770417764395940.651266783558290821.01656214635986420.443886432066240120.60254886501370930.94050594115428132

%Prescription Dose

Sheet4

Silastic Measuremnts

22mm Inserts

SizeNo.Thickness (mm)Lip (mm)StandardMediumThick

Thin11.891.98~1 mm from source11.892.363.15TypeThickness (mm)

~2 mm21.941.9421.942.553.18Standard1.89

32.002.0532.003.30Standard1.94

41.881.9841.883.24Standard2.00

51.941.9451.943.14Standard1.88

Medium12.362.3063.31Standard1.94

~2.5 mm22.552.551.932.463.22Medium2.36

Thick13.153.10~1.5 mm from source0.04795831520.13435028840.0745654075Medium2.55

~3 mm23.183.01Thick3.15

33.303.32Thick3.18

43.243.22~2mm from sourceThick3.30

53.143.09Thick3.24

63.313.29Thick3.14

Thick3.31

1.891.9421.881.942.362.54999999999999983.153.183.33.243.143.31

Standard1234561.891.9421.881.94Medium1234562.362.5499999999999998Thick1234563.153.183.33.243.143.31

Silastic Insert

Measaured Thickness (mm)

Reference Pt Coordinates

Reference Point Coordinates (cm)

Tumor Apex


x0.500.001.280.832.200.710.500.701.00

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.05 cm Silastic


x0.550.051.330.882.250.760.550.751.05

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

.1 cm Silastic


x0.600.101.380.932.300.810.600.801.10

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.15 cm Silastic


x0.650.151.430.982.350.860.650.851.15

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

0.2 cm Silastic


x0.700.201.481.032.400.910.700.901.20

y0.000.00-0.731.070.001.030.000.000.00

z0.000.000.000.000.000.000.000.000.00

Structurexyz

Tumor Apex0.500.000.00

5mm Depth Reference Point0.500.000.00

Inner Sclera0.000.000.00

Lens Center1.28-0.730.00

Macula0.831.070.00

Opposite Retina2.200.000.00

Optic Disk0.711.030.00

Critical Structure Coordinates


0.0%

100.0%

200.0%

300.0%

400.0%

500.0%

600.0%

5 mm 7 mm 10 mm 5 mm 7 mm 10 mm 5 mm 7 mm 10 mm

Normal, 2mm Medium, 2.5 mm Thick, 3 mm

% P

resc

riptio

n D

ose

Apex Sclera Lens Macula Opposite Retina Optic Disk


0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

5 mm 7 mm 10 mm 5 mm 7 mm 10 mm 5 mm 7 mm 10 mm

Normal, 2mm Medium, 2.5 mm Thick, 3 mm

% P

resc

riptio

n D

ose

Apex Lens Macula Optic Disk

*Sclera and Opposite Retina not included

• As Silastic thickness increases, %PD decreased

Discussion

• Unaccounted for, thick silastic inserts will add distance from source to tumor apex– ~7% loss of prescription dose for each additional 0.5mm of

Silastic thickness• Even larger effects would be expected after

heterogeneity corrections– TPS measurements consider only water (Zeff=7.4), not

Silastic (Zeff=11)– Higher electron density Silastic is more attenuating

• Normal eye structures saw reduction in dose– Distance is advantageous in this case

Conclusions

• As Silastic insert thickness increases, the tumor receives a lower dose than prescribed

• Recommendations: – Quality Assurance procedures should be

developed to verify Silastic insert thickness– Communicate with vendor if Silastic molds are not

in agreement with standards

Acknowledgments

• Clara Ferreira• David Sterling• Dara Koozekanani• Kathryn Dusenberry

References

• Margo CE. The Collaborative Ocular Melanoma Study: An Overview. Cancer Control 2004; 11(5): 304-309.

• Jovanovic P, Mihajlovic M, Djordjevic-Jocic J, Vlajkovic S, Cekic S, Stefanovic V. Ocular Melanoma: an overview of the current status. Int J Clin Exp Pathol 2013; 6(7):1230-1244.

• Aronow, ME, AK Topham, AD Singh. Uveal Melanoma: 5-year Update on Incidence, Treatment and Survival (SEER 1973-2013). Ocular Oncology and Pathology 2018; 4:145-151

• Chiu-Tsao, ST, MA Astrahan, PT Finger, DS Followill, AS Meigooni, CS Melhus, F Mourtada, ME Napolitano, R Nath, MJ Rivard, DWO Rogers, TM Thomson. Dosimetry of I-125 and Pd-103 COMS eye plaques for intraocular tumors: Report of Task Group 129 by the AAPM and ABS. Med Phys 2012; 39(10): 6161

• Rivard MJ, Coursey RM, DeWerd LA, Hanson WF, Huq MS, Ibbott GS, Mitch MG, Nath R, and Williamson JR. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004; 31:633-674

• ABS-OOTF Committee. The American Brachytherapy Society consensus for plaque brachytherapy of uveal melanoma and reintoblastoma. Brachytherapy 2014; 13(1):1-14

Dosimetric Impact of Silastic Insert Thickness in COMS Eye Plaque for I-125 BrachytherapyBackground- Ocular MelanomaBackground- COMSBackground- COMS PlaqueProblem: Inconsistent Silastic ThicknessMethodsResults: Measured Silastic ThicknessResults: Dose CalculationsResults: Dose Calculations (cont.)Results: Dose Calculations (cont.)Results: Dose Calculations (cont.)DiscussionConclusionsAcknowledgments References

Documents

Dosimetric Impact of Silastic Insert Thickness in COMS Eye ...chapter.aapm.org/nccaapm/z_meetings/2019-04-26/04...– Digital Caliper used to measure the lip height, and determine