Results from Voluntary Independent External Peer Review

of Beam Output Presented by: Rebecca M. Howell PhD, DABR, FAAPM

What do we hope to achieve with independent peer review?

• Independent peer review is an important tool for improving quality of the clinical physics program. – Enhance patient safety

– Ensure the best possible treatment for our patients

– Meet regulatory requirements

Independent Peer Review Around the World

United States • MD Anderson

– RDS – IROC-H – ADCL – MDADL

• University of Wisconsin

– ADCL – RCL

The World • IAEA/WHO – International Atomic

Energy Agency and World Health Organization

• ACDS - Australian Clinical Dosimetry Service Radiotherapy Trials Quality

• RTTQA - Radiotherapy Quality Assurance (UK)

• JCOG – Japan Clinical Oncology Group

• EORTC - European Organization for Research and Treatment of Cancer (audits by IROC-H)

MD Anderson Cancer Center Section of Outreach Physics

Outreach Physics

IROC-H RDS ADCL MDADL

Radiation Dosimetry Services RDS

Independent Peer Review Services

• Beam output for external beam RT: – megavoltage photon (2 - 25 MV) – electron (4 - 20 MeV) – orthovoltage (1.9 mm Al - 3 mm Cu HVL) – Cobalt-60

• Dose verification for special procedures: – total body dosimetry – total skin dosimetry

• Absorbed Dose in Blood Irradiators

• Dose Verification Cell Irradiations (in development)

Imaging and Radiation Oncology Core Houston IROC-H

Independent Peer Review Services (for clinical trial participants)

• Beam output for external beam RT: – megavoltage photon (2 - 25 MV) – electron (4 - 20 MeV) – Cobalt-60 – Single beam small field checks

• Advanced technology end-to-end testing: imaging, planning, delivery – Head and neck – Prostate – Lung (motion phantom) – SRS – Spine SBRT – Liver (motion and multi-target)

• Site Visits – on site review of dosimetry – TPS versus IROC physicist measurements of basic dosimetry parameters (PDD, OF, WF, OAF) – Mechanical evaluations (linac, IGRT, MLC) – Programmatic reviews (QA program, staffing, )

• Virtual Site Visits (analogous to site visit without measurements)

Also available for fee through MDADL

Accredited Dosimetry Calibration Laboratory ADCL

AAPM Accredited Calibrations Offered

• Electrometers – Charge and Current Scales

• External Beam Ionization Chambers: – Co-60 Absorbed Dose to Water – Co-60 Exposure/Air Kerma – X-Ray (Orthovoltage)

• Well-Ionization Chambers: – High Dose Rate (Ir-192) – Low Dose Rate (Pd-103, I-125, Cs-131, Cs-137 and Ir-192)

• Brachytherapy Sources – Low Dose Rate (Pd-103, I-125, Cs-131, Cs-137 and Ir-192) – See Joint AAPM/IROC Registry for current available source models

EBRT Monitoring RDS versus IROC Who, What, How Often

RDS • Users

– Any institution that requests service

• Beams Monitored – MV photon and electron,

orthovoltage, blood irradiations, ”specials”

• Frequency of Service – Annual, biannual, quarterly,

monthly, on request

IROC • Users

– Clinical trial participants

• Beams monitored – All photon and 3 electron

energies (alternating years), small field

• Frequency of Service – Annual

Note: Some institutions use RDS to supplement electron monitoring or to increase frequency of monitoring.

History of RDS • In 1968, the Texas Regional Medical Physicists

(TRMP) was formed by Dr. Shalek, to provide independent peer review.

• In 1974, the NCI funded the six Centers for Radiological Physics (CRP); TRMP became the Southern CRP to provide QA audit services.

• In 1985, when the NCI terminated the CRP contracts, Drs. Shalek and Stovall created a new for-fee service, the RDS.

• Dr. Stovall served as the Director of the RDS for 30 years, 1986 – 2015 (65 years at MDA since 1951)

• I was appointed Associate Director of RDS in 2015 and promoted to Director in 2016.

RDS Users Since 2001 • Since 2001, RDS has monitored ∼ 21,000 unique EBRT beams at

> 2,000 institutions in the United States and 150 institutions

Current Users Frequency of Service

Frequency of Service

Number of Institutions

Annual 1005 Quarterly 92 Monthly 12 Bi-annual 19 Semi-annual 345 By-request 799 Other 43 Total 2315

• Most institutions monitor beam output on annual basis.

• Of the 799 institutions set-up for by-request services, 150 placed at least one order in the past year.

Note: Total number of distinct institutions is 2014, ∼ 10% of institutions use different monitoring frequency for different machines/beam types.

Dosimeters

• TLD-100 (LiF:Mg,Ti) powder from Quantaflux LLC (San Jose, CA)

• Fully characterize each new batch – Batch is named for year in which it is purchased

(Currently using B14) – Do not reuse

• Controls are irradiated weekly on 60Co unit at the MD Anderson ADCL

• Full review of control irradiations every quarter.

Phantoms

• Acrylic mini-phantoms (3 TLD photon and 6TLD electron)

• Dimensions based on the type of beam and the energy. – Electrons: sufficient for full phantom

scatter. – Photons: the dimensions are sufficient

for electronic scatter equilibrium, but not photon scatter equilibrium.

Why mini-phantoms? shipping $$ • But….

requires BSF to determine output in full phantom.

What about the Uncertainty in the TLD Dose?

• TLD system is calibrated based on the signal-to-dose conversion established with reference TLD irradiated in 60Co (ADCL), with reference dose of 300 cGy.

• Uncertainty in the dose determination is 1.3% for TLD.

• This accuracy allows for a tolerance of ±5% to be used.

Alvarez, Kry, Stingo, and Followill. TLD and OSLD dosimetry systems for remote

audits of radiotherapy external beam calibration. Rad Meas. In press

Quality Assurance TLD Reading Process

• Measure the mass of every single TLD on high accuracy digital scales.

• There are 3 TLD for each measurement. – SD of reading/mass is reviewed during QC – Tolerance is 3%, but is typically < 1.5% • Read standards during every session, which

includes 24 sets of 3. – Read 9 standards per session: 3 at beginning, 3 at

middle, 3 at the end.

Quality Assurance TLD Dose Calculation

• Detailed review of results for each session. • Any inconsistencies are investigated…

– e.g., Institution X, has historically calibrated in muscle, but “in water” was reported for the current set of TLD

– Check the documentation from physicist

– Email physicist to confirm – Modify calculation as appropriate

Quality Assurance TLD Dose Calculation

• Detailed review of results for each beam.

Quality Assurance Review Historical Results

• Comparison with historical results.

Results

• Confidentiality is a key component of participation.

• All results are reported in aggregate.

• Individual examples are anonymized.

Summary Statistics 2001- 2016 All EBRT Beams

• RDS monitored 155,237 EBRT beams

0.1%

0.2% 0.6% 2.

0%4.

7%11

.8%

20.3

%26

.0%

17.8

%9.

6%4.

1% 1.6%

0.6%

0.2%

0.1%

0.1%

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

1.09

1.10

Num

ber o

f Rep

orts

Dose Ratio (Measured/Expected)

64.1% were within ± 1% 85.5% were within ± 2% 94.3% were within ± 3%

< 6% of beams monitored by RDS are outside of ± 3%.

Average 0.999±0.018

Summary Statistics 2001- 2016 All MV Photon Beams

• RDS monitored 52,257 MV photon beams

0.1%

0.2% 1.

1%3.

1%10

.0%

20.7

%29

.2%

20.0

%9.

9%3.

7% 1.2%

0.4%

0.1%

0.1%

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,0000.

900.

910.

920.

930.

940.

950.

960.

970.

980.

991.

001.

011.

021.

031.

041.

051.

061.

071.

081.

091.

10

Num

ber o

f Rep

orts

Dose Ratio (Measured/Expected)

• Distributed ∼ equally between positive and negative ratios

Average 1.000 ± 0.016

Summary Statistics 2001- 2016 All Electron Beams

• RDS monitored 101,399 electron beams

0.1%

0.2% 0.7% 2.

4% 5.5%

12.8

%20

.2%

24.5

%16

.7%

9.4%

4.3% 1.8%

0.7%

0.3%

0.1%

0.1%

0

5,000

10,000

15,000

20,000

25,0000.

900.

910.

920.

930.

940.

950.

960.

970.

980.

991.

001.

011.

021.

031.

041.

051.

061.

071.

081.

091.

10

Num

ber o

f Rep

orts

Dose Ratio (Measured/Expected)

• Distributed somewhat more toward ratios <1.00

Average 0.999±0.019

Comparison with IROC Results

Similar • Averages ∼ 1.0 with most ± 3%

0

500

1000

1500

2000

2500

3000

0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.1

# re

sults

OSLD/Institution

●Electron beamsAverage: 1.000 ± 0.01810791 results(↑ 22% compare 2014)

●Photon beamsAverage: 1.002 ± 0.0179578 results(↑ 29% compare 2014)

480 beams need repeat OSLD

Summary Statistics 2001- 2016 All Orthovoltage Beams

• RDS monitored 1319 orthovoltage beams

0.1% 0.

9%1.

5% 1.9%

3.1%

4.7%

6.4%

5.7%

12.1

%11

.9%

14.1

%10

.8%

9.9%

6.8%

4.1%

2.4%

1.7% 0.

8%

0.6%

0.5%

0.0%

0

20

40

60

80

100

120

140

160

180

2000.

900.

910.

920.

930.

940.

950.

960.

970.

980.

991.

001.

011.

021.

031.

041.

051.

061.

071.

081.

091.

10

Num

ber o

f Rep

orts

Dose Ratio (Measured/Expected)

Average 0.995±0.033

Outside of Criteria “Setup/documentation” Issues

• SAD vs SSD deliver (and vv) • Water vs Muscle (and vv) • Wrong field size (20 x 20 vs 10 x 10)

– Often happens when do electrons 1st

• Wrong energy – For electrons trouble shoot with PDD

• 100 MU or 200 MU vs 300 MU • And one not to worry about, I left the others

in room (out of beam)

Outside of Criteria “Real” Issues

Beam Type Institution's Frequency of

Service Initial Description Repeated

Cobalt-60 Monthly 1.03 Physicist found a problem with timer correction factor from most recent calibration. 1.00

6 MV photon Monthly 1.04 - 1.06 Physicist had ion chamber recalibrated; ADCL determined chamber required repair. 0.98 - 1.01

15 MV photon Quarterly 1.22 Physicist found an 18% error in calibration of a newly commissioned linac. 1.00

10 MV photon 6 - 15 MeV electrons

Annual 1.05 - 10.8 Physicist reported incorrect solid water correction factor had been applied, resulting in a 3% calibration error. Error was corrected.

1.02 - 1.03

6 and 18 MV photons

6 - 20 MeV electrons

Monthly 1.04 - 1.07 Physicist determined that mercury barometer was malfunctioning, resulting in a 4% error in calibration of a newly commissioned linac.

1.00 - 1.03

6 MeV electron Quarterly 1.09 Physicist found two problems; depth of dmax was incorrect due to a change in energy, and measured depth dose data did not include a correction for chamber radius.

1.02

Outside of Criteria Recent Scenario…..

• New linac • Wanted beam

output verification prior to 1st patient.

• Rush order – Notified by email of

results.

Energy Ratio (MDA/reported)

6 MV 0.93 10 MV 0.94 15 MV 0.95 6 MeV 0.95 9 MeV 0.93

12 MeV 0.92 15 MeV 0.95 18 MeV 0.93

They did all the right things….

• Repeated measurements with different – Ion chamber – Electrometer – Physicist

• Got same result that beams were all properly calibrated and delivering 1cGy/MU.

• Then…..

They did all the right things….

• When taking down equipment, the BNC cable fell apart.

• Repeated measurements with new cable – Results paralleled

those reported by RDS.

– Tuned each of the beams as needed.

Repeat TLD Results

Energy Ratio (MDA/reported)

6 MV 1.01 10 MV 1.01 15 MV 1.00 6 MeV 1.02 9 MeV 1.02

12 MeV 1.00 15 MeV 1.02 18 MeV 1.00

Conclusions

• Independent peer review of beam output is IMPORTANT because effects every patient!

• Only a small fraction of beam are outside of 3%. – Often attributed to set-up errors, but some

are actual calibration errors. • Don’t dismiss it, verify it.

– Even the best physicists can make mistakes & measurement equipment can malfunction.

Thank you

Rebecca Howell, PhD, Director, RDS; David Followill, PhD, Director, IROC Houston QA Center; Rita Weathers (Retired 8/2016, Part-time); Debbie Tanner, Office Manager; Loretta Davis, Program Coordinator; Deborah Durdin, Research Technician II; Tera Jones, QA Dosimetrist; Ferrell Munson, Radiological Physics Technician II; Michael Sifuentes, Radiological Physics Technician I; Irene Harris, Research Dosimetrist; Jacob Palmer, Computational Scientist; David Campos, Radiological Physics Technician I; Natosha Ellis, Sr. Data Entry Operator; Ying Qiao, Computational Scientist; Susan Smith, Supervisor QA Dosimetry Services; Sharon McCallister (Retired 12/2016); Samantha Murray, Sr. Coordinator, Research Data; Kimberly Joseph, Sr. Secretary; and TaShun Thomas, Sr. Administrative Assistant. Francisco Aguirre, Medical Physicist.

rds.mdanderson.org/

Anthropomorphic Phantom Service (for Fee Service) • End to end testing: planning and delivery • Available services are:

– IMRT Head and Neck – IMRT Prostate – IMRT Spine – Lung (± Motion Table) – SRS Head – SRS Single Beam

MD Anderson Dosimetry Laboratory MDADL