Principles and Instruments of Rditi ThRadiation Therapym99.nthu.edu.tw/~s9962554/hhpeng/slide/20110516_Radiotherapy.pdf · 一般治療儀器種類 ... Wedge Filter • 視治療計畫決定使用哪一類wedge

放射治療原理技術及儀器放射治療原理技術及儀器Principles and Instruments of

R di ti ThRadiation Therapy

彭旭霞

國立清華大學生醫工程與環境科學系國立清華大學生醫工程與環境科學系

1

什麼是放射治療?• Radiation Therapy = Radiotherapy• 俗稱: 電療 (誤用)俗稱: 電療 (誤用)

- 治療原理為”輻射”, 並非”電”治療儀器需用大量用電- 治療儀器需用大量用電

• 放射治療原理• 相關儀器相關儀器

2

治療機制

• damaging the DNA of cancerous cells• X-ray (煞車效應)• Electron beam• 放射核種

3

原子核的中子質子比

Stable nuclei

遠離穩定區的核種- 遠離穩定區的核種皆傾向產生衰變

愈大需要愈多的- Z愈大, 需要愈多的中子才能穩定

4

Isodose curve

• SSD: source to surface distance• SAD: source to axis distance

- distance from the source to axis of gantryg yrotation (isocenter)

5

Dose profile at depth: Co60

6

Isodose curveIsodose curveSSD SAD

7

percentage depth dose

100dD

8

1000

d

d

D

Central axis depth dose distribution

9

Initial dose b ild pInitial dose buildup

• Kerma- Energy transferred from photons to directly ionizing electrons

- decrease with increased depthp- decrease with decreased photon energy fluence

• Absorbed dose- increase with increased depth (high-speed e- ejected)- decrease with decreased photon energy fluencep gy- depth with max. absorbed dose: ~ electron range in mediummedium

10

Initial dose buildupp

11

一般治療儀器種類

• Kilovoltage: 現在較少見- 1950s 之前常用- ~300 kVp X-rayp y- 用途: superficial skin lesion

• Linear Accelerator (Linac): 現在最常用• Linear Accelerator (Linac): 現在最常用• Co-60: 現今多用於頭部治療

12

Linear Accelerator (Linac)

• 現在最常見• 高頻電磁波: 加速電子• 治療機頭模式

- 高速電子: 表淺腫瘤高速電子撞擊靶產生X ray: 深部腫瘤- 高速電子撞擊靶產生X-ray: 深部腫瘤

13

Linac

14

Typical medical Linac

15

Linac

• Electron gun: produce electrons (~ 50 keV)• Accelerator structure

- high vacuumg- copper tube with copper discs/ diaphragms

e-: gain energy from sinusoidal electric field- e : gain energy from sinusoidal electric field• e- pencil beam: 3 mm in diameter• Bent beam: high-energy linac

- 避免過長的accelerator tube

16

Linac: Magnetron/Klystron

• Produce microwave• ~3000 MHz• Central cathode• Outer anode with resonant cavity

• Magnetron: 多用於low-energy linac (< 6 MV)• Klystron: 多用於 high-energy linac

17


18


• cathode- heated by inner filament- thermionic emission: generate electronsg

• Static magnetic filed + pulsed DC electric field• Static magnetic filed + pulsed DC electric field- electrons: complex spiral toward resonant cavities- radiating energy in the form of microwaves

19

Linac: Treatment head (兩種模式)

20X-ray therapy mode Electron therapy mode

放射治療技術及儀器

• Treatment Simulation• 3D Conformal Radiation Therapy (CRT)3D Conformal Radiation Therapy (CRT)• Intensity-Modulated Radiation Therapy (IMRT)

P t B Th• Proton Beam Therapy• Brachytherapy (近接治療)

21

Treatment Simulation• purpose

- diagnostic x-ray tubediagnostic x ray tube- 複製/模擬治療儀器:

t i h i l ti l tigeometric, mechanical, optical properties- display treatment field- confirm: field, shielding blocks…

22

Treatment Simulation• Treatment simulation

- radiographic simulatorradiographic simulator- CT simulator

23

Radiographic simulator

24基本上長得與治療儀器相似

Treatment: Portal Image

25Digital Reconstructed Radiography (DRR)

CT Simulator

26

Wedge Filter• Modify isodose distribution (beam-modifying) • Progressive decrease of intensity across beam• Isodose curve tilt toward thin end

27Wedge filter Isodose curve

Wedge Filter• 視治療計畫決定使用哪一類wedge filter

Individualized wedge Universal wedge

28

(thin edge align with field border) (center of wedge at beam axis)

Wedge Filter• 觀察wedge filter改變isodose curve

Without wedge With wedge29

Without wedge With wedge

Field Shaping

• Custom block• Multileaf collimator

30

Custom Blocking• Lipowitz metal (品名: Cerrobend)• Lipowitz metal (品名: Cerrobend)

- 50% bismuth, 26.7% lead, 13.3% tin, 10% cadmium)low melting point: 70 oC (lead: 327 oC)- low melting point: 70 oC (lead: 327 oC)

- density = 9.4 g/cm3 (~83% of lead)

31

Custom Blocking

block for head & neckblock for head & neck

32Simulating on a film Positive block for lung

Multileaf Collimator• 一樣是為了blocking/field shaping• 優點

- 自動化減少Cerrobend製作- 減少Cerrobend製作

- 縮短setup time• 不適用

- 很小的區域- 島狀區域

• 進階版: CRT IMRT (後面會再提到)33

• 進階版: CRT, IMRT (後面會再提到)

Multileaf Collimator

Collimator + accelerator

治療位置

34

Compare physical penumbra

Cerrobend blockMultileaf collimator

35

Tissue CompensatorIrregular or sloping surface: skew isodose curve• Irregular or sloping surface: skew isodose curve

• ~ 20 cm away from patient’s skin

Compensator

Irregular surface

36

Tissue Compensator

• 用styrofoam (聚苯乙烯泡沫塑料) 做出模型料) 做出模型

• 再填充tissue-equivalentmaterialmaterial - 相同effective atomic number- 相同electron density相同electron density

37

Patient Setup位置與進行 i l ti 相同• 位置與進行simulation相同

• 雷射定位床與治療機頭可調整角度• 床與治療機頭可調整角度

38

Bite block system整個療程分好幾次• 整個療程分好幾次

• 每次位置都要固定f• for head and neck immobilization

固定角度咬合物咬合物

硬式底盤

39

Brachytherapy近接治療• 近接治療

• 放射核種• 放置入體內某一段時間

40

Brachytherapy

Interstitial and intra-cavitary therapy41

Brachytherapy: Cs-137

Isodose curveautoradiography

42

Isodose curveautoradiography

Brachytherapy: Pd-103

Seed source

43

Brachytherapy: Afterloading

Smaller cervixLarger cervix

44

Smaller cervix(overdose)

Larger cervix(underdose)

下週

• IMRT• Co-60

45

還有什麼沒提到?

• Measure absorbed dose• Dose distribution and scatter analysis• Details in treatment planningp g• Quality assurance• Treatments for different diseases• Treatments for different diseases• Radiobiology• …

46

Conformal Radiotherapy (CRT)• 順形治療• 通常是3D: 需要3D imaging information (CT, MRI, US,

SPECT, PET)• purpose p p

- maximize tumor control probability (TCP)- minimize normal tissue complication pprobability (NTCP)

• Limitation: knowledge of tumor extentg- clinical tumor volume (CTV)- Imaging system: gross tumor volume (GTV)Imaging system: gross tumor volume (GTV)

47

Conformal Radiotherapy (CRT)

• Requests- treatment planning- treatment deliveryy- quality assurance

• 與一般非CRT之區別?- field- beam arrangementg

48

Ex.: Image fusion: CT+MRI

CT MRI red: CT; green: MRI

特殊設計的治療計畫: image fusion

CT MRI red: CT; green: MRI

特殊設計的治療計畫: image fusion

49

Intensity Modulated Radiotherapy (IMRT)

• Intensity-modulated system- compensatorp- wedge- transmission blocktransmission block- dynamic jaw- moving barmoving bar- multileaf collimator (MLC)- tomotherapy collimatortomotherapy collimator- scanned elementary beams of variable intensity

• Dynamic (modern) intensity modulation?• Dynamic (modern) intensity modulation?- last five 50

Required systems

• Conventional linear accelerator• Computer treatment-planning system with

IMRT software• Beam delivery system: nonuniform fluences

• Request: 與CRT相似

51

Multileaf intensity-modulating collimator

52

Two banks of 20 leaves each

Intensity modulation profile

Method#1 Method#2

Blue: fluence profileRed: measured dose

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Ex.: thyroid tumor

Concave-shaped target Transverse view

54

Critical: spinal cord spinal cord: min. dose

Quality assurance (QA):Quality assurance (QA): routine mechanical check

Abnormal conditionAbnormal condition

55Normal condition

201 cobalt-60 sources

• 用途: 腦部腫瘤• 優點: simple setup• 限制

- small field size (max. 18 mm)(several isocenters可擴展治療區域)(several isocenters可擴展治療區域)

- 治療部位

56

201 cobalt-60 sources

k iγ - knife γ - knife unit

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Documents

Principles and Instruments of Rditi ThRadiation Therapym99.nthu.edu.tw/~s9962554/hhpeng/slide/20110516_Radiotherapy.pdf · 一般治療儀器種類 ... Wedge Filter • 視治療計畫決定使用哪一類wedge