Radiological Physics Center

David Followill, Ph.D.

and RPC Staff

Radiological Physics Center• Formed in 1968 and located at

MD Anderson Cancer Center (1 of 12 longest running grants).

• Our Mission is to assure NCI and cooperative groups that institutions participating in clinical trials deliver prescribed radiation doses that are comparable and consistent, (minimize dose uncertainty), make corrections and report findings to the community.

• Funded continuously for 44 years as cooperative clinical trial groups have changed and expanded internationally

• Use of remote and onsite dosimetry audits

RPC Scope of Monitoring•Monitoring 1888 inst. participating in clinical trials - includes 210 non-North American sites 41 countries (since 2006 45%) - ~23,000 beams - ~3500 machines

Components of RPC QA Program

1. Remote audits of machine output 1,888 institutions, ~14,000 beams measured with

TLD and OSLD in North America and Internationally

2. Patient Treatment record reviews 474 charts reviewed for GOG, NSABP, NCCTG,

RTOG (brachytherapy)

3. On-site dosimetry reviews 41 institutions visited in 2011

(~150 accelerators/450 beams measured)

4. Credentialing - Phantoms ~500 irradiations in 2011

Reference calibration(NIST traceable)

Correction Factors:Field size & shape

Depth of targetTransmission factors

Treatment time

Evaluated byRPC Dosimeters

Evaluated byRPC visits and chart review

RPC Verification of Institutions’ Delivery of Tumor Dose

Tumor DoseEvaluated by

RPC phantoms

So, how are we doing?

OSLD/TLD Beam Output Checks

3-4% of the beams require a repeat

BEAM CALIBRATIONRPC Onsite Visits

75%

80%

85%

90%

95%

100%

1975 1980 1985 1990 1995 2000 2005 2010

YEAR

Per

cen

t w

ith

in 3

% C

rite

rio

n

Photon

Electron

TG-21 Implementation

TG-51Implementation

Comprehensive On-Site Audits

Reference Beam Calibration

Percent of Inst. with ≥ 1 beam out of Criteria

(since 2002)

Photons Electrons

OSLD/TLD (±5%) 7-11% 6-12%

Visits (±3%) ~13% ~15%

Discrepancies Regarding:Number of InstitutionsReceiving rec. (n = 156)

Review QA Program 115 (74%)

Photon Field Size Dependence (small FSD) 62 (40%)

Wedge Factor (WF) 50 (32%)

Off-axis Factors (OAF)/Beam symmetry 46 (29%)

Electron Calibration 27 (17%)

Photon Depth Dose 25 (16%)

Electron Depth Dose 18 (12%)

Photon Calibration 13 (8%)Review Temp/Press Correction 11 (7%)

Change to TG-51 9 (6%)

Electron Cone Ratios 8 (5%)

Using Multiple Sets of Data 8 (5%)

Discrepancies Discovered (Jan. ’05 – Mar. ’11)

On-Site Dosimetry Review Audit

Monitor Units =Prescription Dose

(calibration) • (FSD) • (WF) • (depth dose) • (OAF)Monitor Units =

Prescription Dose

(calibration) • (FSD) • (WF) • (depth dose) • (OAF)

Treatment record reviews•RPC performs independent retrospective review and

recalculation of doses for RTOG, NCCTG and GOG brachy. patients

•Errors in dose calculation and doses reported to study groups are discovered and corrected

•The RPC review has resulted in changing the reported dose on 546 (27%) of the1993 protocol patients reviewed since 2005.

- 13% are EBRT dose errors - 87% are brachytherapy dose errors

We revise the dose data in 1 of every 3 charts

RPC Phantoms

Pelvis (10)

Thorax (10)

Liver (6)H&N (30)

SRS Head (10)

Spine (8)

• Independent “end to end” audit

• Imaging

• Planning/dose calculation

• Setup

• delivery

• Uniform phantoms and dosimeters

• Standardized analysis

• Uniform pass/fail criteria

• Allows inst. to inst. comparison

• Established infrastructure

Phantom Patient

Benefits of RPC Phantoms

PhantomPatient

Phantom Results

Phantom H&N Prostate Spine Lung

Irradiations 1139 313 120 458

Pass686

(79%)162

(82%)22

(63%)178

(75%)Fail 187 35 13 59

Criteria 7%/4mm 7%/4mm5%/

3mm5%/

5mmRTOG Inst. Acceptable

557 (54%)

206 (20%)

83 (8%)

289 (28%)

Pass928

(81%)265

(85%)78

(65%)361

(79%)

Fail 211 48 42 97

Comparison between institution’s plan and delivered dose.

0

100

200

300

400

500

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

Year

Ph

an

tom

s M

ailed

Spine

SRS Head

Liver

Prostate

Lung

H&N

Phantom ResultsComparison between institution’s plan and

delivered dose.H&N Prostate Spine Lung

Irradiations (all years) 1139 313 120 458

Pass (all years) 928 (81%) 265 (85%) 78 (65%) 361 (79%)

Fail (all years) 211 48 42 97

         

Irradiations (2011) 109 56 40 80

Pass (2011) 101 (93%) 45 (80%) 31 (78%) 68 (85%)

Fail (2011) 8 11 9 12

Criteria 7%/4mm 7%/4mm 5%/3mm 5%/5mm

Failure rate doubles going to ±5%/3mm criteria

Why do we continue to find errors?1. Too busy

2. Advanced technology/ Don’t understand process

3. Communication/Fear of punishment

4. Training/Failure to ask for help

5. Can’t accept the fact that an error could be mad

WHO report on “Radiotherapy Risk Profile” states that 60% of all radiotherapy incidents are

attributable to human error.

Human Errors!

Let’s get past these

hurdles!

Questions?