TG-40 and TG-142

Samir Laoui

Date: July 29th, 2015

AAPM Task Group 40 Report “Comprehensive QA for Radiation

Oncology” 1994

Introduction

“Every patient with cancer deserves to receive the best possible management to achieve cure, long-term tumor control or palliation”

Inter-Society Council for Radiation Oncology (ISCRO, 1986)

Delivery of treatment in an accurate and consistent manner is by no means easy to achieve, since the radiation therapy process is a complex interweaving of a number of related tasks for designing and delivering radiation treatments

Background

Quality Assurance: “the maintenance of a desired level of quality in a service or product, especially by means of attention to every stage of the process of delivery or production”. online dictionary

In radiation therapy : A set of procedures that ensure a safe dose delivery to the tumor site while sparing normal tissue, and minimal exposure to the personnel

To achieve this goal, institutions are required to establish a set of baseline standards

Processes of Machine QA

Acceptance Testing

Commissioning

Quality Assurance

Clinical Needs and Purchase

Baseline

Type of radiation equipment QA

Quality Assurance of Linear Accelerator

Quality Assurance of Simulator

Quality Assurance of Brachytherapy

Quality Assurance of Diagnostics CT

Quality Assurance of treatment Planning System (TPS)

Quality Assurance of QA tools

AAPM Task Group 40 Report “Comprehensive QA for Radiation Oncology” 1994

Scope: Guidelines for administrators

QA for External Beam Radiation Therapy Equipment Co-60 Units (Table I)

Linear Accelerators

Simulators

CT scanners

QA of measurement equipment

Treatment planning computer system

External beam Treatment planning

Brachytherapy

Treatment plans QA for individual patients

Tolerances: TG-40

Adopted from AAPM Report 13 (AAP, 1984)

Report 13 used the method of quadratic summation to set the tolerance values

The overall dosimetric uncertainty of ± 5% (ICRU, 1976). This can be only be achieved if every individual task is performed with an accuracy better than ±5%

55522

Linac QA TG-40 (1994)/ Daily

Could seriously affect patient positioning/ registration of radiation fields with target volume

Directly affect dose delivery

Directly affect patient safety

RX may continue for 3-5 % output

Action Level set at 5%, RX has to be halted

Linac QA TG-40 (1994)/ Monthly

Smaller impact on patient

Not likely to change on daily basis

Linac QA TG-40 (1994)/ Annual

Baseline verification

TG-40: Other machines QA

QA of Simulators (Table III)

Should be subject to routine mechanical checks as Linacs

Image quality

QA of CT scanners (No table)

Laser alignment should be checked daily

Image quality has to be checked periodically

Electronic density check is annual

QA of measurement equipment (Table IV)

Redundancy in dose calibration equipment is recommended using Sr-90 source

Other equipment should be calibrated

TG-40: QA of treatment planning

Treatment planning computer system QA (Table V)

(Van Dyke et al, 1993, ICRU 42)

Beam data library

Dose calculation models

Operating instructions

Treatment planning system process (Table VI) Prescription Positioning and Immobilization Data Acquisition Contouring

Data Transfer Dose computation Plan Evaluation Computation of Monitor Units

Beam modifiers Plan implementation

Treatment planning QA for individual patient Treatment planning review

Monitor Unit review

Plan implementation

TG-40: Brachytherapy

Higher tolerances compared to external beam’s, 15%

Sealed sources description and calibration Independent source activity strength verification Traceability

Treatment planning and dosimetry Planning (TPS) Localization (CT) Dose calculation algorithms Patient dose calculation (Checked to within +/-15%) Delivery of treatment Documentation

Remote afterloading Calibration Verification of source position

AAPM Task Group 142 Report “Quality Assurance of Medical

Accelerators” 2009

AAPM Task Group 142 Report “Quality Assurance of Medical Accelerators” 2009

Specific to Linacs

Does Include QA of MLC (TG-50) Include QA of Portal imaging (TG-58) Respiratory Motion (TG-76) Kilovoltage localization (TG-104)

Does not Include instructions for performing QA tests Accelerator commissioning (TG-106) QA for Tomotherapy (TG-148) QA for Robotic Radiosurgery (Tg-135) Positioning (TG-147) VMAT/Arc therapy are not covered (TG-119)

AAPM Task Group 142 Report “Quality Assurance of Medical Accelerators” 2009

Scope: Quality assurance for medical accelerators

Test frequencies

Guidelines for tolerance values

Ancillary treatment devices not in TG-40

Asymmetric jaws

Dynamic/Virtual/Universal wedge

MLC

Radiographic Imaging

Respiratory gating

Special procedures/SRS/SBRT/TBI/TSET/IMRT

TG-142: General

Baseline dosimetric values entered into treatment planning systems to characterize and model the treatment machine directly after calculated plans

Values can deviate from baseline values as a result of Linac malfunction

Accidents

Mechanical breakdown

Linac part replacement

Wear and tear

QA procedures are made in place to detect these changes

The report recommends that institution be proactive in detecting changes based on workload (IMRT, MLC)

TG-142: General

A beam output constancy is an important quantity for an accurate and reproducible dose coverage

The report includes monthly tolerance values that are specific to a constant beam shape. Central axis output (BP) as well as off-axis output are defined during commissioning

TG-40 TG-142

TG-142: Guidelines for Tolerance Values

Acceptance testing Commissioning and acceptance test set the baseline for future dosimetric and

mechanical measurements. This will ensure that the machine is operating within tolerance values

Tolerance and Action Levels* Level 1: Inspection is required

Level 2: Maintenance must be scheduled in the near future

Level 3: Immediate action and/or treatment is halted

* TG-142 does not explicitly define the action level values

Linac QA TG-142 (2009)/ Daily

The tables are differentiated

into non-IMRT/Stereotactic

machines and

IMRT/Stereotactic machines

Linac QA TG-142 (2009)/ Monthly

MONTHLY

TG-142 Vs. TG-40

Linac QA TG-142 (2009)/ Annual

Linac QA TG-142 (2009)/ Annual

•

Ancillary RX devices: Dynamic/Virtual Wedge

•

•

Multileaf Collimation QA

Imaging QA

•

Example: Acuity Daily QA

Reference TG-76

Dynamic phantom which simulate human organ motion are recommended to test target localization and respiratory gated treatment accuracy

Tests include: Beam Energy constancy

Beam output constancy

Temporal accuracy of phase/Amplitude gating windows (example: 250 and 1500 ms with 100 ms tolerance)

Respiratory Gating QA

Summary

TG-142 is considered to be flexible compared with TG-40

TG-142 recommend establishing institution-specific baseline values

Tolerances vary depending on the machine functionality (Non-IMRT, IMRT, SRS/SBRT)

There are overlaps of daily, monthly and annual tests that helps cross check the machine performance with independent techniques

Summary

Recommends that the QA equipment be calibrated per TG-106

Recommends an end-to-end check if a new/revised procedure is introduced

During annual QA, absolute machine output should be calibrated as per the TG-51 calibration protocol (Baselines)