Linac构造与临床关系

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'Linac构造与临床关系'
海外华人医学物理讲师团-放疗物理第二讲(2015)Linac构造与临床关系1. 外形及厂家2. Linac Head 构造2.1) Beam Steering2.2) Flattening Filter2.3) Dual Ionization Chamber2.4) Jaw & EDW2.5) Light Field2.6) MLC and all related issues3. 图像设备(EPID, OBI, CBCT, IsoCai)4. 配件装备(e- app,block, couch)5. 可选设备(SRS Cone, ExacTrac, Gating,etc.)6. 验收(if time allowed) 1.外形及厂家Linac w/ OBLCBCTEPID Linac w/ EPIDLinac (no EPID) Linac (inside) TomoTherapy CyberKnife(mini-linac) Vero (mini-linac)厂家:Varian(瓦里安)45%,Elekta(医科达:+GammaKnife)43%5 Siemens 12.5%,新华(Shinva)12.5%> 东软、大基医疗.Accuray(安科锐:Tomo+CyberKnife), BrainLab(Vero).TPS: Eclipse(Varian), Pinnacle(Philips), iPlan(BrainLab), Monaco(Elekta), XKnife(lntegra), RayStation(RayResearchLab), MultiPlan(CyberKnife), Tomo(Tomo), Oncentra(Elekta), BrachyVisionWariseed(Varian), etc. 2. Linac Head Structure.Suited■vnControlPulsed modulatorFlattening filter? 1花生图■2 Ibra A (3* lUmUrcwtrMtmfcMv?c?<rfUK cxMPatient support assembly (trMtrmnt couch)vacuumPower supplyMlcrowavo power sourcebremsstrahlung photon fluence.scatter more forwarding as energy in creaseFlatteningFilter Free (FFF)Flattening Filter (FF)2.1) Beam Steering:MagnetTop ViewCarousel!旋转木马):Flattening Filter for photon (6X, 10Xz 18X), scattering foil for electron (6e, 9e, 12e# 15ez 18e, 21e), FFF photon (empty).MeVe*e- dualscatteringfoilsBeam Steering example #1:Resultant Dose at D*Solution: adjust the steering of the bending magnets, or the energy of the electron beam, or a combination of both? For any changes made, once profile is flat, must check energv and output! Beam Steering example #2:dose profile at depth 1.5cm (6X photon)Distance from central axis axis (cm)Example: center not aligned perfectly (0.15cm error), not observable on 30cm*30cm profile, but a big impact on SRS profile with 2cm cone size. 2.2) Flattening Filter:FIG. 6.17. An example of beam profiles for two field sizes (10 x 10 cm2 and 30 x 30 cnr) and a 10 MU X ray beam at various depths in water. The central axis close values are scaled by the appropriate PDD value for the two fields.① sop ①>?OHGoal of Flattening Filter:making the profile of each photon energy flat at depth 10cm. Why FFF (Flattening Filter Free)?Less demanding on field junction accuracy for RapidArc/VMAT technique.Field Juntion between FFF beamsField Juntion between FF beams2.3) Dual Ionization Chamber …safety: double check each other (e.g. sealed chamber leaking), backup if another fail.—MU (Monitor Unit): 10cm*10cm field size, 100cm SSD, 1MU gives 1cGy at dmax (e.g. dmax =1.5cm for 6X, 2.5cm for 10X, 3.5cm for 18X).—backscatter effect: (from jaw if Varian Linac, from MLC if Elekta Linac
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Linac 构造 临床 关系
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