1

A Comprehensive Study on the Heterogeneity Dose Calculation Accuracy in IMRT using an Anthropomorphic Thorax Phantom

S Davidson1, R Popple2, G Ibbott1, D Followill1

1The University of Texas M. D. Anderson Cancer Center,

Houston, TX2University of Alabama Birmingham, Birmingham, AL

2

Purpose

• Survey the accuracy of several commercial dose calculations

• Check the consistency of superposition-convolution implementations

• Baseline: RPC anthropomorphic thorax phantom

3

Methods & Materials

• IMRT Treatment Planning Systems (TPS)• Superposition-Convolution

• Pinnacle• Eclipse AAA• TomoTherapy

• Pencil-beam w/ effective pathlength correction• Corvus• Eclipse

4

Methods & Materials

TPS Beams MLC

Pinnacle • 5 beams• 4 coplanar beams

(35°, 90°, 150°, 190°)• 1 non-coplanar beam

(90° couch kick, 30° gantry angle)

Static

Corvus Static

Eclipse, AAA Dynamic

Eclipse, pencil-beam

Dynamic

TomoTherapy Helical; pitch 0.3, field-width 2.5cm

5

Methods & Materials

Corvus TPS

Corvus delivery:MLC & MU

Corvus calculation

Pinnacle re-calculation

Eclipse TPS

Eclipse delivery:MLC & MU

Eclipse PB

Eclipse AAA

6

Methods & Materials• Radiological Physics Center (RPC)

Anthropomorphic Thoracic Phantom• CIRS Lung insert (cylinder) with embedded tumor

• Fitted for TLD (tumor, heart, cord) and Radiochromic Film (tumor/lung)

S

LL

A

Dimensions (cm): 40W x 30H x 30DDisassembled Lung Insert

FilmSlits

Tumor (TLD)

Lung

Tumor(TLD)

Heart

Cord

Lung

LR

7

Methods & Materials

• TLD • Corrected for daily output

• Radiochromic Film • TLD normalization

• All plans repeated 3 times

8

Dose Calculation

Delivery MLC & MU

IMRT QA IC correction

factor (calc-to-meas)

Pinnacle Pinnacle 1.027

Corvus 1.055

Pinnacle 1.043

Eclipse, PB 1.007

Eclipse, AAA 0.993

TomoTherapy TomoTherapy 1.016

Eclipse

Corvus

• IMRT QA: IC in water phantom

• Corvus beyond 5% in IMRT QA

Results & Discussion

9

• Tumor Point Dose Comparison (corrected)

• All calculations corrected in response to IMRT QA

Dose Calculation

Delivery MLC & MU

corrected ratio of

calc/meas

Pinnacle Pinnacle 0.992

Corvus 1.050

Pinnacle 1.009

Eclipse, PB 1.049

Eclipse, AAA 1.036

TomoTherapy TomoTherapy 1.025

Corvus

Eclipse

Results & Discussion

10

Results & Discussion• Dose Profiles, Pinnacle

Pinnacle Calculation and Delivery Medial-Left Lateral Profile

0

500

1000

1500

2000

2500

-40 -20 0 20 40 60 80

Distance (mm)

Abs

olut

e D

ose

(cG

y)

Film Avg

Pinnacle

-5% or 3mm

+5% or 3mm

GTV

PTV

11

Corvus Calculation and Delivery Medial to Left Lateral Profile

0

500

1000

1500

2000

2500

-40 -20 0 20 40 60 80Distance (mm)

Ab

solu

te D

ose

(cG

y)

Film Avg

Corvus

-5% or 3mm

+5% or 3mm

GTV

PTV

Results & Discussion• Dose Profiles, Corvus

12

Pinnacle Calculation with Corvus MLC files Medial to Left Lateral Profile

0

500

1000

1500

2000

2500

-40 -20 0 20 40 60 80

Distance (mm)

Abs

olut

e D

ose

(cG

y)

Film Avg

Pinnacle-Corvus(MLC)

-5% or 3mm

+5% or 3mm

GTV

PTV

Results & Discussion• Dose Profiles, Pinn. Re-calc/Corvus Beams

13

Eclipse-AAA Calculation and Delivery Medial-Left Lateral Profile

0

100

200

300

400

500

600

700

800

-40 -20 0 20 40 60 80

Distance (mm)

Ab

solu

te D

ose

(cG

y)

Film Avg

Helios-AAA

-5% or 3mm

+5% or 3mm

GTV

PTV

Results & Discussion• Dose Profiles, Eclipse AAA

14

Eclipse PB Calculation and Delivery Medial-Left Lateral Profile

0

100

200

300

400

500

600

700

800

-40 -20 0 20 40 60 80

Distance (mm)

Dos

e (c

Gy)

Film Avg

Eclipse PB

+5% or 3mm

-5% or 3mm

GTV

PTV

Results & Discussion• Dose Profiles, Eclipse pencil-beam

15

TOMO Calculation and Delivery Medial-Left Lateral Profile

0

100

200

300

400

500

600

700

-40 -20 0 20 40 60 80

Distance (mm)

Abs

olut

e D

ose

(cG

y)

Film Avg

TOMO

-5% or 3mm

+5% or 3mm

GTV

PTV

Results & Discussion• Dose Profiles, TomoTherapy

16

Results & Discussion• Binary Agreement Maps:

GTV

GTV GTVGTVGTV

Pinnacle Corvus Pinnacle calc/Corvus

Color Code

not testedFails all criteria

±7%/7mm±5%/3mmTest Criteria

Color Code

not testedFails all criteria

±7%/7mm±5%/3mmTest Criteria

17

Results & Discussion• Binary Agreement Maps:

GTV

GTV GTVGTVGTV

Color Code

not tested

Fails all criteria

±7%/7mm±5%/3mmTest Criteria

Eclipse AAA Eclipse PB TomoTherapy

GTV

18

Percentage of pixels passing criteria

79

99

66

96100100

85

50

9097

61

96

0

20

40

60

80

100

Pin

nacl

e, S

C

Cor

vus,

PB

Pin

nacl

e(C

orvu

sde

liver

y)

Ecl

ipse

AA

A,

SC

Ecl

ipse

, PB

Tom

oThe

rapy

,S

C

±7%/7mm

±5%/3mm

Results & Discussion• Binary Agreement Maps: Summary

19

Conclusions

• The accuracy of dose calculations from several common IMRT TPSs was evaluated. • Superposition convolution based- algorithms met

the ±5%/3 mm criteria• Pencil-beam with an effective pathlength

correction did not meet the criteria

• Pinnacle, Eclipse AAA, and TomoTherapy apply superposition convolution accurately.

20

References1 S. Davidson, K. Prado, G. Ibbott, and D. Followill, "SU-FF-T-255:

Hetergeneity Dose Calculation Accuracy in IMRT Using An Anthropomorphic Thorax Phantom," Medical Physics 33 (6), 2106 (2006).

2 N. Papanikolaou, J. J. Battista, A. L. Boyer, C. Kappas, E. E. Klein, T. R. Mackie, M. Sharpe, and J. Van Dyk, "Tissue Inhomogeneity Corrections for Megavoltage Photon Beams," AAPM Task Group #65 Radiation Therapy Commitee (2004).