Chapter 17Chapter 17Quality AssuranceQuality Assurance

Wang, Hui-Chuan

Quality assurance (QA)Quality assurance (QA)A program designed to control and maintain the standard of quality set for that program

For radiation oncology, to maintain the quality of patient care

Model QA program in radiation oncology have been proposed by ACR, AAPM, ACMP

1. ACR Physical aspects of quality assurance. Reston, VA: American College of Radiology, 1990.

2. AAPM. Physical aspects of quality assurance in radiation therapy. Report No. 13. Colchester, W: AIDC, 1984.

3. AAPM. Comprehensive QA for radiation oncology: report of the Radiation Therapy Task Group 40. Med Phys 1994;21:581-618for combined technical and professional charges

Total cost of QA program in radiation therapy amounts to approximately 3% of the annual billing

The goals of a QA programThe goals of a QA programThe purpose of a Quality Assurance Program is the objective, systematic monitoring of the quality and appropriateness of patient care. Such a program is essential for all activities in Radiation Oncology.

The Quality Assurance Program should be related to structure, process and outcome, all of which can be measured.

Structure includes the staff, equipment and facility.Process covers the pre- and post-treatment evaluations and the actual treatment application. Outcome is documented by the frequency of accomplishing stated objectives, usually tumor control, and by the frequency and seriousness of treatment-induced sequelae.

Quality assurance committee (QAC) be formed with appropriate personnel (e.g., radiation oncologist, physicist, dosimetrist, therapist, nurse, and administrator).

Minimum Personnel Requirements for Clinical Radiation TherapyMinimum Personnel Requirements for Clinical Radiation TherapyCategory Staffing

Radiation oncologist-in-chief One per programStaff radiation oncologist One additional for each 200-250 patients treated annually; no

more than 25-30 patients under treatment by a single physicianRadiation physicist One per center for up to 400 patients annually; additional in

ratio of one per 400 patients treated annuallyTreatment planning staff

dosimetrist or physics assistant One per 300 patients treated annually physics technologist (mold room) One per600 patients treated annuallyRadiation therapy technologist

supervisor One per center staff (treatment) Two per megavoltage unit up to 25 patients treated daily per u

nit; four per megavoltage unit up to 50 patients treated daily per unit

staff (simulation) Two for every 500 patients simulated annually staff (brachytherapy) As neededTreatment aid As needed, usually one per 300-400 patients treated annuallyNurse One per center for up to 300 patients treated annually and an

additional one per 300 patients treated annuallySocial worker As needed to provide serviceDietitian As needed to provide servicePhysical therapist As needed to provide serviceMaintenance engineer/electronics technician

On per 2 megavoltage units or 1 megavoltage unit and a simulator if equipment serviced in-house

Physics staffingPhysics staffing

EquipmentEquipment

1. External Beam Units

2. Brachytherapy Sources

3. Simulator

Dosimetric accuracyDosimetric accuracyAccuracy of approximately 5% in dose delivery

Uncertainties in equipment calibration, treatment planning, and patient setup

Further reduction in dose accuracy limit will be not only very difficult but probably of marginal value

Equipment specificationsEquipment specifications

Justification of need

Market evaluation of different makes and models

Checks of vendors’ business relations and service record

Calling up users for their opinions

Writing bid specifications

Making final evaluation

Doing price negotiation

Acceptance testingAcceptance testing

To satisfy all the specifications and criteria contained in the purchase contract

To perform all the tests in accordance with the company’s procedure manual

Any equipment to be used for patients must be tested to ensure that it meets its performance specifications and safety standards

Linear acceleratorLinear accelerator

Installation, acceptance testing, commisioning

Commission: the machine tested to be acceptable and sufficient data have been acquired to permit treatment planning and dose calculations for patient treatments

Linear acceleratorLinear accelerator: Radiation survey: Radiation survey

To evaluate the exposure levels outside the room will not exceed permissible limits, considering the dose rate output, machine on time, use factors and occupancy factors for the surrounding areas

A calibration of the machine output (cGy/MU)

Radiation protection surveyHead leakage

Area survey

Tests of interlocks, warning lights, and emergency switches

Linear accelerator: Jaw symmetryLinear accelerator: Jaw symmetry

Jaw symmetryA machinist’s dial indicator

The symmetry error of collimator jaw: typically less than 1 mm

http://www.gwrauto.com/phoenix/brake_tools.html

Linear accelerator: Linear accelerator: CoincidenceCoincidence

Collimator axis, light beam axis and cross-hairs

The light field edges

The intersection of diagonals and the position of cross-hair images

Light beam with x-ray beamAAPM guidelines 3% (2%)

Mechanical IsocenterMechanical Isocenter

The intersection point of the axis of rotation of the collimator and the axis of rotation of the gantry

Collimator rotation2 mm diameter circle

Gantry rotation±1 mm

Radiation IsocenterRadiation Isocenter

Collimator2 mm diameter circle

Treatment table 2 mm diameter circle

Gantry 2 mm diameter circle

Multiple Beam Alignment Multiple Beam Alignment CheckCheck

Focal spot displacement

Asymmetry of collimator jaws

Displacement in the collimator rotation axis or the gantry rotation axis

The split-field test

1 2 1 2

X-ray Beam PerformanceX-ray Beam Performance

EnergyA central axis depth dose distribution

A suitable ion chamber in a water phantomSmall chamber (<3 mm)

For a larger chamber, the depth dose curve should be shift to the left (toward the source) by 3/4r.

Suitable depths for comparing depth dose ratios are 10 and 20 cm.

1010, 100 cm SSD, and 10 cm depth ±2%

Field flatnessThe variation of dose relative to the central axis over the central 80% of the field size at 10 cm depth

< ±3%

Within the region extending up to 2 cm from the field edge at a 10 cm depth

+3% ~ -5%

The diagonal flatness extending up to 2.8 cm from the 50% isodose curve in a plane at a 10 cm depth

+4% ~ -6%

X-ray Beam PerformanceX-ray Beam Performance

X-ray Beam PerformanceX-ray Beam Performance

Field symmetryTo fold the profile at the field center and the two halves of the profiles to be compared

< 2% at any pair of points

Electron Beam PerformanceElectron Beam Performance

EnergyTG-25

Rp (Ep)0=C1+C2Rp+C3Rp2

< ±0.5 MeV

Flatness and symmetryTG-25

flatness±5% (± 3%)

symmetry < 2%

Monitor chambersMonitor chambers

Linearity

As a function of dose rate

Special operating conditionsTotal body irradiation

Total skin irradiation

Arc rotation

Long-term stability check

WedgesWedges

1010

±2°

Miscellaneous ChecksMiscellaneous Checks

Isocenter shift with couch motion up and down < ±2 mm

ODI < ±2 mm

Field size indicators < ±2 mm

Gantry angle and collimator angles < 1º

Laser lights aligned with the isocenter < ±2 mm

Tabletop sag with lateral or longitudinal travel under a distributed weight of 180 lb < 0.5 cm

SimulatorSimulator

Checking of the geometric and spatial accuracies

Performance evaluation of the x-ray generator and the associated imaging system

Table 17.5

BrachytherapyBrachytherapyIntracavitary sources and applicators

Source identityPhysical length, diameter, serial No.

Source uniformity and symmetryThe superposition of the autoradiograph and transmission radiograph

Source calibrationA well ionization chamber 5%

Applicator evaluationOrthogonal radiographsThe ease of source loading and removal

Remote Afterloaders (1)Remote Afterloaders (1)

Operational testing of the afterloading unit

Radiation safety check of the facility

Checking of source calibration and transport

Checking of treatment planning software

Table 17.6

Remote Afterloaders (2)Remote Afterloaders (2)

Source positioningThe position of dummy sources and radioactive sources should correspond within ±1 mm.

Source calibrationA well ionization chamber

A cylindrical lead insert for a conventional well ionization chamber for calibrating HDR sources

Cylindrical ion chamberA free air geometryAn interpolative method of obtaining exposure calibration factor

CommissioningCommissioning

After all the necessary beam data have been acquired and adopted, the machine can be released or commissioned for clinical use.

Commissioning Data for a Linear AcceleratorCommissioning Data for a Linear AcceleratorData Description

Calibration Dose per MU calibration of all modalities and energies according to current protocol (TG21)

Depth dose Central axis depth dose distribution for all modalities and energies, sufficient number of FS to allow interpolation of data and all available electron cones

Profiles Tranverse, longitudinal, and diagonal dose profiles for all modalities and energies at dmax for electrons and selected depths for photons; all cones for electrons and selected FS for photons

Isodose distribution

Isodose curves for all modalities and energies, all cones for electrons and selected FS for photons, all wedge filters for selected field sizes

Output factors Sc,p, Sc, and Sp factors as a function of FS for all photon energies: output factors for all electron energies, cones, and standard inserts; tray transmission factors and wedge transmission factors

Off-axis ratios A table of off-axis ratios for all photon energies as a function of distance from central axis; these data may be obtained from those profiles for a 4040 cm field at selected depths

Inverse square law

Verification of inverse square law for all photon energies,virtual source position for all electron energies, and effective SSD for all electron energies and cones

TPR/TMR Direct measurement of TPRs/TMRs for all photon energies and selected FS and depths for verification of values calculated from percent depth doses

Surface and buildup dose

For all photon energies and selected FS, percent surface dose for all electron energies for a 1010 cm cone

Treatment planning system

Beam data input, generation, and verification of central axis percent depth dose and TPR/TMR tables; sample isodose curves for unwedged, wedged, asymmetric and blocked fields; sample isodose curves for multiple field plans using rectangular and elliptical contours; electron beam depth dose data, isodose curves on rectangular and circular contours

Special dosimetry

Data for special techniques such as total body irradiation, total skin irradiation, stereotactic radiosurgery, intraoperative electron therapy, etc

Periodic QA of Linear AcceleratorPeriodic QA of Linear AcceleratorFrequency Procedure Tolerence (±)

Daily X-ray output constancy 3%

Localization lasers 2 mm

Operational parameters recorded

Biweekly Electron output constancy 3%

Weekly Light/radiation field coincidence 3 mm

X-ray flatness and symmetry 3%

Electron flatness and symmetry 3%

Monthly X-ray output calibration 2%

X-ray energy 2% in fepth dose (2% in ionization ratio)

Electron energy 3 mm in R80 (2 mm in Rp)

Optical distance indicator 2 mm

Field size indicators 2 mm

Gantry angle indicator 1°

Collimator angle indicator 1°

Cross-hair centering 1 mm

Annually Full calibration 2%

Isocenter shift

Collimator rotation 2 mm diameter

Gantry rotation 2 mm diameter

Couch rotation 2 mm diameter

Couch vertical travel 2 mm

Tabletop sag 2 mm

Periodic QA of SimulatorsPeriodic QA of SimulatorsFrequency Procedure Tolerance (±)

Daily Localization lasers 2 mm

Weekly Light/radiation field coincidence 2 mm

Monthly ODI 2 mm

FS indicator 2 mm

Gantry angle indicator 1º

Collimator angle indicator 1º

Cross-hair centering 1 mm

Annually Isocenter shift

collimator rotation 2 mm diameter

gantry rotation 2 mm diameter

Couch rotation 2 mm diameter

couch vertical travel 2 mm

Tabletop sag 2 mm

依游離輻射防護法第十七條第三項規定訂定之 自中華民國九十四年七月一日施行

輻射醫療曝露品質保證標準醫用直線加速器 含鈷六十放射性物質之遠隔治療機 含放射性物質之遙控後荷式近接治療設備

輻射醫療曝露品質保證組織與專業人員設置及委託相關機構管理辦法

設有醫用直線加速器者，應置二人。超過一部者，每增加一部，應增置一人。 設有含放射性物質之遙控後荷式近接治療設備者，應置一人。

項次 校驗項目 結果或誤差容許值

A1-1 定位雷射 小於二毫米

A1-2 光學距離指示器 小於二毫米

A1-3 治療室門連鎖 功能正常

A1-4 視聽監視器 功能正常

A1-5 光子輸出劑量 小於百分之三

醫用直線加速器每日品質保證作業項目醫用直線加速器每日品質保證作業項目結果或容許誤差結果或容許誤差

醫用直線加速器每月品質保證作業項目結果或容許誤差醫用直線加速器每月品質保證作業項目結果或容許誤差 項次 校驗項目 結果或誤差容許值 A2-1 光子輸出劑量 小於百分之二 A2-2 緊急關閉按鈕 功能正常 A2-3 楔形濾器、電子錐連鎖裝置 功能正常 A2-4 電子輸出劑量 小於百分之二 A2-5 光子射束中心軸於治療深度之劑量參數 每一點小於百分之二 A2-6 電子射束中心軸於治療深度之劑量參數 每一點小於百分之二或於

治療深度內小於二毫米 A2-7 光子平坦性 小於基準直百分之二 A2-8 電子平坦性 小於基準直百分之三 A2-9 光子對稱性 小於百分之三 A2-10 電子對稱性 小於百分之三 A2-11 光照野與輻射照野一致性 小於二毫米 A2-12 旋轉臂及準直儀角度指示器 數位式小於零點五度；機

械式小於一度 A2-13 十字交叉線中心位置 小於直徑二毫米圓形範圍 A2-14 照野指示器 小於二毫米 A2-15 準直儀對稱性 小於二毫米

醫用直線加速器每年品質保證作業項目結果或容許誤差醫用直線加速器每年品質保證作業項目結果或容許誤差項次 校驗項目 結果或誤差容許值

A3-1 光子輸出劑量 小於百分之二A3-2 緊急關閉按鈕 功能正常A3-3 楔形濾器、電子錐連鎖裝置 功能正常A3-4 電子輸出劑量 小於百分之二

A3-5 光子射束中心軸於治療深度之劑量參數 每一點小於百分之二

A3-6 電子射束中心軸於治療深度之劑量參數 每一點小於百分之二或於治療深度內小於二毫米

A3-7 光子平坦性 小於基準直百分之二A3-8 電子平坦性 小於基準直百分之三A3-9 光子對稱性 小於百分之三

A3-10 電子對稱性 小於百分之三

A3-11 光照野與輻射照野一致性 小於二毫米或靶至量測距離之百分之一

A3-12 旋轉臂及準直儀角度指示器 數位式小於零點五度；機械式小於一度

A3-13 十字交叉線中心位置 小於直徑二毫米圓形範圍

A3-14 照野指示器 小於二毫米

A3-15 準直儀對稱性 小於二毫米

醫用直線加速器每年品質保證作業項目結果或容許誤差醫用直線加速器每年品質保證作業項目結果或容許誤差A3-16 準直儀機械旋轉中心 小於直徑二毫米圓形範圍

A3-17 旋轉臂機械旋轉中心 小於直徑二毫米圓形範圍

A3-18 治療床機械旋轉中心 小於直徑二毫米圓形範圍

A3-19 準直儀輻射旋轉中心 小於直徑二毫米圓形範圍

A3-20 旋轉臂輻射旋轉中心 小於直徑二毫米圓形範圍

A3-21 治療床輻射旋轉中心 小於直徑三毫米圓形範圍

A3-22 區域監測器 功能正常

A3-23 治療床垂直升降之線性 小於百分之二

A3-24 光子照野因子 小於百分之二

A3-25 電子錐因子 小於百分之二

A3-26光子或電子射束中心軸百分深度劑量比，組織與空氣比 小於百分之二

A3-27 穿透因子 小於百分之二

A3-28 楔形濾器穿透因子 小於百分之二

A3-29 監測游離腔之線性 小於百分之二

A3-30 安全連鎖 ( 含門、緊急停止與臨時中斷 ) 功能正常

遙控後荷式近接治療設備每日品質保證作業項目結果或容許誤差遙控後荷式近接治療設備每日品質保證作業項目結果或容許誤差

項次校驗項目 結果或誤差容許值

B1-1輻射安全系統確認、警示系統、視聽監測器系統、安全連鎖 ( 含門、緊急停止與臨時中斷 )

功能正常

B1-2 檢視輻射源治療管線完整性 功能正常

遙控後荷式近接治療設備每月質保證作業項目結果或容許誤差遙控後荷式近接治療設備每月質保證作業項目結果或容許誤差

項次 校驗項目 結果或誤差容許值

B2-1輻射安全系統確認、警示系統、視聽監測器系統、安全連鎖 ( 含門、緊急停止與臨時中斷 )

功能正常

B2-2 備用電池狀況 功能正常

B2-3 檢視輻射源導線完整性 功能正常

B2-4 輻射源速率 啟動輻射源由原點至最遠距離之時間誤差為小於一秒

B2-5輻射源強度（每月、每年為計算值，換輻射源為實測值） 小於百分之一

B2-6 輻射源停留位置 小於一毫米

B2-7 輻射源停留時間 每分鐘小於一秒

遙控後荷式近接治療設備每年質保證作業項目結果或容許誤差遙控後荷式近接治療設備每年質保證作業項目結果或容許誤差

項次 校驗項目 結果或誤差容許值

B3-1輻射安全系統確認、警示系統、視聽監測器系統、安全連鎖 ( 含門、緊急停止與臨時中斷 )

功能正常

B3-2 檢視裝療器及裝療管完整性 功能正常

B3-3輻射源擦拭試驗測試值（擦拭面積至少一百平方厘米） 小於七十四貝克

Thanks for your attention!!Thanks for your attention!!