RPCs IMRT Phantoms October 2007 SWAAPM RPCs Phantom Team Paola - - PDF document

RPC’s IMRT Phantoms

SWAAPM

October 2007

RPC’s Phantom Team

Paola Alvarez Carrie Amador Teresa Collier David S. Followill Sarai Garcia Franklin Hall Nadia Hernandez Geoffrey S. Ibbott Sophia Jaramillo Mary Lou Lesseraux Jessica Lowenstein Andrea Molineu Robert Pinney

Brief background

• Originated through agreement between

AAPM and CRTS

• Founded in 1968 to monitor institution

participation in clinical trials

• Funded continuously by NCI as structure of

cooperative group programs have changed

• Now 39 years of experience of monitoring

institutions and reporting findings to study groups and community

Why do we do this?

We have an NCI grant to:

• 1. Assure NCI and cooperative groups

that institutions participating in clinical trials deliver prescribed doses that are comparable and consistent.

• 2. Help institutions to make any

corrections that might be needed.

• 3. Report findings to the community.

RPC Phantoms

Pelvis (4)

Thorax (9) Liver (2) H&N IMRT (25) SRS Head (4)

Number of phantom mailings

50 100 150 200 250 300 2001 2002 2003 2004 2005 2006 2007

Year Phantom s Mailed

SRS Head Liver Prostate Thorax H&N

The thermoluminescent dosimetry (TLD) program

• Largest of its kind in operation (> 30 years)
• Verifies dose output and energy on

megavoltage units (>9100 beams in 2006).

• Measure consistency of institutions based
• n TLD history
• Provides independent audit of the output as

required by many states

Radiochromic film

• Originally used MD-55
• Currently use EBT
• Good for doses 2-10 Gy
• Read on densitometer by Photoelectric
• Currently working with CERR group at

Washington University on 2D analysis software package

Densitometer

Densitometer

Dose Response Curve. Lot 36306-002I

y = 40.511x3 - 22.121x2 + 6.9223x R2 = 0.9988

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900

Net OD Dose (Gy)

Dose Response Curve

• Poly. (Dose Response Curve)

IMRT H&N phantom

• Primary PTV

4 cm diameter 4 TLD

• Secondary PTV

2 cm diameter 2 TLD

• Organ at risk

1 cm diameter 2 TLD

• Axial and sagittal

radiochromic films

• 1º PTV treated to 6.6 Gy
• 2º PTV treated to 5.4 Gy
• OAR limited to < 4.5 Gy

Secondary PTV Primary PTV Organ at Risk

Designed in collaboration with RTOG; Molineu et al, IJROBP, October 2005

Criteria for credentialing

• RPC/Inst dose in PTVs: 0.93-1.07
• distance to agreement in high gradient

region near OAR: ≤ 4 mm

Distance to agreement region Dose regions

IMRT H&N phantom results

• 419 irradiations were analyzed
• 322 irradiations passed the criteria
• 68 institutions irradiated multiple times
• 97 irradiations did not pass the criteria
• 322 institutions are represented

Only 76% of institutions passed the criteria on the first irradiation.

• 65 failed by absolute dose only
• 13 failed by DTA only
• 19 failed by both absolute dose

and DTA

IMRT H&N phantom results cont

• 15 -17

0.57-1.23 0.49-1.15 range 419 721 1447 count 2.9 0.046 0.050 std dev 0.1 0.98 0.99 mean Displ.(mm) 2PTV 1PTV

Good HN profile

Right Left Profile

2 4 6 8

• 4
• 3
• 2
• 1

1 2 3 4 5 6 7 8 Distance (cm) Dose (Gy)

RPC Film Institution Values

Primary PTV

Secondary PTV

Right Left

Anterior Posterior Profile

2 4 6 8

• 4
• 3
• 2
• 1

1 2 3 4 Distance (cm) Dose (Gy)

RPC Film Institution Values RPC Regression Institution Regression

Primary PTV

Organ at Risk

Anterior Posterior

Average displacment 0 mm 0 mm 1 mm 0 mm

Not so good HN profile

Right Left Profile

2 4 6 8

• 4
• 3
• 2
• 1

1 2 3 4 5 6 7 8 Distance (cm) Dose (Gy)

RPC Film Institution Values

Primary PTV

Secondary PTV

Right Left

Anterior Posterior Profile

2 4 6 8

• 4
• 3
• 2
• 1

1 2 3 4 Distance (cm) Dose (Gy)

RPC Film Institution Values RPC Regression Institution Regression

Primary PTV

Organ at Risk

Anterior Posterior

TLD 5-8% low 10 mm shift

Not so good HN profile

Anterior Posterior Profile

2 4 6 8

• 4
• 3
• 2
• 1

1 2 3 4

Distance (cm) Dose (Gy)

Primary PTV

Organ at Risk

Anterior Posterior

Average displacment 4 mm

Plan vs. Treatment

Examples of failures

Comparison: planned vs. delivered distribution

Hot spots (~10%) and odd differences in dose distribution

Couch indexing error

Institution’s Plan Delivered Dose

Hot spots (~20%) due to indexing error

HN results grouped by accelerator manufacturer

19 13 65 419 total 14 8 39 301 80 Varian 1 5 22 73 TomoTherapy 4 2 10 56 71 Siemens 1 2 11 35 60 Elekta 5 100 BrainLab Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Linear Accelerator Manufacturer

HN results grouped by TPS

19 13 65 419 total 2 3 24 79 Other 5 4 7 59 73 XiO 1 5 22 73 TomoTherapy 8 4 33 168 73 Pinnacle 3 4 10 114 85 Eclipse 1 7 32 75 Corvus Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Treatment planning system

HN results grouped by machine/TPS

19 13 65 418

total

1 5 26 77

Other

2 1 13 77

Varian/Other

3 2 4 37 76

Varian/XiO

5 3 22 121 75

Varian/Pinnacle

3 3 9 110 86

Varian/Eclipse

1 5 22 73

Varian/Corvus

1 1 6 67

Siemens/Other

1 1 1 13 77

Siemens/XiO

3 5 27 70

Siemens/Pinnacle

1 8 88

Siemens/Corvus

2 4 50

Elekta/Other

1 1 2 9 56

Elekta/XiO

1 6 21 67

Elekta/Pinnacle

1 1

Elekta/Corvus Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Manufacturer/TPS Combination

HN results grouped by technique

19 13 65 419 total 1 1 Experimental 1 3 17 76 TomoTherapy 15 10 47 279 74 Segmental 1 5 12 50 IMAT 3 2 9 110 87 Dynamic MLC Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) IMRT technique

Physicist per machine

10 20 30 40 50 60 70 80 90 ≤0.5 0.51-0.75 0.76-1.0 1.01-1.25 1.26-1.5 ≥1.51

Physicist per Machine Pass Rate

Number of machines

10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 6 ≥7

Number of Machines Pass Rate

HN QA Dose criterion

148 institutions reported point dose measurements and criterion

> 5% 52 4% - 5% 96 2% - 3% Number of Institutions Dose Criterion

HN QA DTA criterion

111 institutions reported distance to agreement measurements and criterion

4 2 mm 12 5 mm 11 4 mm 84 3 mm Number of Institutions DTA Criterion

HN dose adjustments based on QA

• 11 institutions adjusted MU delivered based
• n their QA
• 4 of these institutions failed anyway
• 63 of the failing institutions reported making

no changes based on QA measurements

• 13 of these measured dose in the same

direction as the failure

Prostate Phantom

Prostate phantom inserts

Imaging insert Dosimetry insert

Bladder Bladder Femoral Head Femoral Head Prostate Rectum Rectum Prostate

Prostate phantom

Prostate phantom

• 6 Gy to prostate
• 50% of bladder limited to 5.7 Gy
• 25% of bladder limited to 6.3 Gy
• 50% of rectum limited to 5.0 Gy
• 25% of rectum limited to 6.0 Gy

Prostate phantom Rx

Criteria for credentialing

• RPC/Inst dose in PTV: 0.93-1.07
• distance to agreement in high gradient

regions near OARs: ≤ 4 mm

Distance to agreement region Dose region

IMRT prostate phantom results

• 93 irradiations were analyzed
• 76 irradiations passed the criteria
• 7 institutions irradiated multiple times
• 17 irradiations did not pass the criteria
• 85 institutions are represented

Only 79% of institutions passed the criteria on the first irradiation.

• 0 failed by absolute dose only
• 16 failed by DTA only
• 1 failed by both absolute dose

and DTA

Prostate phantom results cont

• 5 - 7
• 8 - 18

0.92 - 1.06 range 91 92 184 count 2.483 3.926 0.029 std dev 0.89

• 0.52

1.00 mean DTA rectum (mm) DTA bladder (mm) PTV

Good prostate profile

Anterior Posterior Profile- Sagittal Plane

1 2 3 4 5 6 7 8

• 7
• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6 7

Distance (cm) Dose (Gy)

Rectum Anterior Posterior

Average displacement 1 mm

Prostate

Not so good prostate profile

Superior Inferior Profile - Coronal Plane

1 2 3 4 5 6 7 8

• 7
• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6 7

Distance (cm) Dose (Gy)

Superior Inferior Prostate Bladder

Average displacement

• 8 mm

8 mm DTA

Prostate results grouped by accelerator manufacturer

1 16 93 total 1 11 69 83 Varian 2 100 TomoTherapy 3 17 82 Siemens 2 5 60 Elekta Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Linear Accelerator Manufacturer

Prostate results grouped by TPS

1 16 93 total 1 2 10 70 Other 3 17 82 XiO 9 45 80 Pinnacle 2 21 90 Eclipse Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Treatment planning system

Prostate results grouped by machine/TPS combo

1 16 93 total 3 100 Other 1 10 90 Varian/XiO 7 32 78 Varian/Pinnacle 2 21 90 Varian/Eclipse 1 1 5 60 Varian/Corvus 2 7 71 Siemens/XiO 8 100 Siemens/Pinnacle 1 2 50 Siemens/Corvus 2 5 60 Elekta/Pinnacle Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) Manufacturer/TPS Combination

Prostate results grouped by technique

1 16 93 total 2 100 TomoTherapy 12 69 83 Segmental 2 3 33 IMAT 1 2 19 84 Dynamic MLC Dose and DTA DTA Dose Criteria Failed Attempts Pass Rate (%) IMRT technique

Explanations for failures

not adjusting plan to account for dose differences measured with ion chamber inadequacies in beam modeling at leaf ends (Cadman, et al; PMB 2002) incorrect PDD in TPS incorrect output factors in TPS

Explanations for failures cont

Treatment planning bug errors in couch indexing with Peacock system target malfunction MLC sag setup errors 2 mm tolerence on MLC leaf position

Changes made by institutions that resulted in acceptable phantom irradiation

replaced target more accurate setup upgraded MLC leaves updated software version adjusted leaf end modeling remeasured PDD and modeled beam based on new values input new output factors

Conclusions

• The RPC’s IMRT phantoms

provide a comprehensive evaluation of IMRT for clinical trials

• QA of IMRT is important!

The investigation was supported by PHS grants CA10953 and CA81647 awarded by the NCI, DHHS.

http://rpc.mdanderson.org/rpc/