Practical Reference Dosimetry Course April 2015 PRDC Program, at a glance. Version 1.0. Day 1 Day 2 Day 3 Day 4

Transcription

1 Practical Reference Dosimetry Course April 2015 PRDC 2015 Program, at a glance Version 1.0 Day 1 Day 2 Day 3 Day 4 Quantities and Units Free air chambers Uncertainties Brachytherapy traceability Primary standards kv equipment ISO GUM Common errors in Internal Example uncertainty TG-61 framework calcul Recap and summary Break Break Break Break Practical Practical Practical Practical Lunch Lunch Lunch Lunch Calorimetry Ion chamber theory Small fields Equipment for TRS-398 for MV photons Ion chamber types TRS-398 for MV electrons FFF beams Recombin and non-uniformity corrections Assessment 1 Assessment 2 Assessment 3 Practical Break Break Break Break Practical Practical Practical Exam Feedback and close 1 of 6

2 Practical and Hands-On Sessions Practical and hands-on theory: 2 participants per group, 1 supervisor = 8 supervisors. (subject to modific) Practical 1 kv dosimetry using TG-61 Laboratory: RT100 kv output with thin window chamber following TG-61, measure applicator factor and cutout factor 2 Properties of ion chambers Laboratory: Various Ion chamber Sr-90 check in pressure vessel, EPOM demonstr close to source, Jaffe plot for recombin, determine dose error due to temperature lag in phantom not at room temperature 3 Absolute dosimetry and cross-calibr Laboratory: Co-60 teletherapy Thimble chamber calibr, Roos chamber calibr, cross-calibr. Stability in Co-60. Pre-irradi and time to equilibrium. 4 Small field dosimetry Laboratory: Elekta Synergy Linac Small field output factor, daisy chain. Measure with diamond and diode detectors, look up MC correction factors Hands-on theory 1 Investig Fault finding and root cause analysis example of dosimetry error 2 TG Calcul with TG Question sheet 1 and answers 3 Uncertainty calcul 3.1 Calculate uncertainty in a measurement of dose. 3.2 Construct a control chart. 4 TRS-398 calculs 4.1 TRS-398 dose determin (PC simul) 4.2 Question sheet 2 and answers 2 of 6

3 PRDC: Day 1 9:00 0:15 Introduction Welcome and housekeeping Overview 9:15 0:30 Quantities and Units Overview of quantities and units; fluence, kerma, dose and exposure. SI units. Interaction coefficients for photons and electrons. Radi transport. 9:45 0:30 Primary standards Definition of primary standard. Traceability. Free air chambers, calorimeters, Fricke dosimeters. Link to fundamental quantities. 10:15 0:30 Internal measurement framework Internal comparisons; Key Comparison Database (KCDB); degrees of equivalence; origin of dose prescriptions; Reguls, BSS GSR-3 11:05 1:30 Practical session P1 13:45 0:30 Calorimetry Graphite calorimeter: the absorbed dose standard for Co- 60 and MV photons; from calorimetry to chamber calibr; conversion to dose to water; The ARPANSA calibr services. 14:15 0:30 Equipment for Ion chamber types: thimble, parallel-plate, spherical; graphite versus plastic; electrometers and units (nc or Gy); automatic leakage correction; cables and adaptors; water density; water equivalence and various types of solid water; thermometers and barometers; when dosemeters bite; Sr-90 check sources 14:45 0:30 TRS-398 MV photons Choice of chamber for beam quality, PDD and output; effective point of measurement; recombin - the two voltage method and when it breaks down; use of k Q factors; dose to water and dose from a TPS; TG51 versus TRS-398; beam uniformity corrections; cross-calibr 15:45 1:30 Practical session P2 17:15 Close 3 of 6

4 PRDC: Day 2 9:00 0:15 Introduction Recap Day 1 9:15 0:30 Free air chambers Free air chambers as primary standards. Correction factors. The difference between air kerma, exposure and absorbed dose to air. 9:45 0:30 kv dosimetry equipment X-ray tubes; representative spectra and PDDs; inherent filtr, added filtr; applicators; monitor chambers ion chambers; energy response of Farmer and thinwindow chambers 10:15 0:30 TG-61 Air kerma basis for ; differences between IPEMB and TG61 protocols; conversion to absorbed dose to water; in-phantom versus in-air methods; Definition of HVL and BSF; ambiguities in the definitions - different interprets; measuring HVL; filter purity and loc of foils; detector energy response and iterative corrections; 11:05 1:30 Practical session P2 13:45 0:30 Ion chamber theory Bragg-Gray cavity theory. Calcul used in TRS-398 for k Q. Electronic equilibrium. Effect of stem, wall, electrode, volume. Definition of flat energy response. Water and air equivalence; guarding. Choice of voltage. 14:15 0:30 Ion chamber types Common chamber types (thimble, parallel plate, thin window), their strengths and weaknesses. Logic of construction: graphite, aluminium, plastic. Chamber volume. Effective point of measurement. Reference point; resolution; chambers suitable for reference dosimetry and review of McEwen recommends. 14:45 0:30 TRS-398 for MeV electrons 15:45 1:30 Practical session P4 Beam quality determin; why R50?; dose gradients; choice of chamber for beam quality, PDD and output measurements; PDI vs PDD; effective point of measurement; why not use thimble chambers below 10 MeV; why not use parallel plate chambers calibrated in Co-60?; recombin; cross-calibr; use of kq,qint 17:15 Close 4 of 6

5 PRDC: Day 3 9:00 0:15 Introduction Recap Day 2 9:15 0:30 Uncertainties An introduction to the ISO Guide to the Expression of Uncertainty in Measurement; Definitions: accuracy, precision, reproducibility, error, uncertainty; Statistical approach to calculating and combining uncertainties; 9:45 0:30 ISO GUM method Type A and Type B uncertainty assessments; random and systematic uncertainties; the subjective nature of Type B assessments; how to combine and report uncertainties; control charts 10:15 0:30 Example uncertainty calcul Example uncertainty calcul for linac daily output check; how to follow the GUM with minimal effort; calculating the result and expressing it (confidence interval, coverage factor); 11:05 1:30 Practical session P5 13:45 0:30 Small fields Definition of a small field. Volume averaging and spectral differences. Standard methods for IMRT and SRS small field dosimetry. Diamond detectors, diodes and film. 14:15 0:30 FFF beams Dose rates and profiles for common FFF beams. Dealing with increased recombin. Use of TRS-398 and TG-51 for output measurements. Correcting for non-uniformity. Spectral differences across the beam. 14:45 0:30 Recombin and non-uniformity corrections 15:45 1:30 Practical session P6 Types of recombin. Origin and limits of the two voltage method. Jaffe plots. Correction for non-uniform beams, from scans or film. Dose-area-product. 17:15 Close 5 of 6

6 PRDC: Day 4 9:00 0:15 Introduction Recap day 3 9:15 0:30 Brachytherapy Review of output measurements for I-125 and Ir-192. Reference air kerma rate. Primary standards for air kerma and absorbed dose. Recommends for traceability in Australia. 9:45 0:30 Common errors in Air attenu and scatter; electrons produced by cones and cutouts; field size effects, stem leakage, water equivalence of phantoms. Time for thermal equilibrium. Evapor. Pressure at mean sea level. Old equipment. Leakage correction. Use of electrometers in Gy mode. 10:15 0:30 Recap and summary Summary of the presents so far. Key points and take-home messages. 11:05 1:30 Practical session P7 13:45 1:30 Practical session P8 15:45 1:00 Assessment Copies of TRS-398 and TG-61 will be provided. 16:45 0:15 Close Feedback 17:00 Close 6 of 6