Radiotherapy new materials and FFF

Transcription

1 Radiotherapy new materials and FFF Debbie Peet Head of Radiation Protection Department of Medical Physics

2 Contents Building materials Basic bunker design FFF IPEM75 update

3 Shielding materials Concrete (poured) Earth (not covered) Steel Lead Magnetite concrete Laminated barriers Forster Sandwich (covered at previous IPEM meeting) Concrete blocks High density blocks from chapter content IPEM 75 rewrite

4 Concrete

5 Transmission curves - concrete NCRP49 Handbook of Radiological Protection

6 Transmission curves - concrete Nelson and LaRiviere Health Physics NCRP151

7 Concrete Tenth Value Layers 6MV 10MV 15MV IPEM75 Primary Secondary NCRP151 6MV 10MV 15MV Primary Secondary

8 Magnadense (IPEM meeting 2007) High grade natural aggregate Physical density 3800kg/m3 MagnaDense MagnaDense is a high grade aggregate manufactured from the natural iron oxide Magnetite. Mined and processed at our own group resources in the north of Sweden ensures a long-term, reliable source of consistent quality material. MagnaDense product uses With its high density MagnaDense is used as loose ballast or as aggregate to produce high density concrete which is easily produced and placed using standard equipment. Minelco LKAB minerals

9 Used in walls (IPEM meeting 2007)

10 Magnadense- broad beam transmission 6MV 10MV 15MV Primary Secondary Scaled from density and concrete TVL 6MV 10MV 15MV Primary Secondary Jones Peet and Horton Health Physics

11 Leeds (IPEM RT meeting 2009)

12 Equivalent thicknesses (IPEM75) 6MV 10MV 15MV Steel Primary Secondary Lead Primary Secondary

13 NCRP 151 TVLs steel and lead 6MV 10MV 15MV Steel Primary Lead Primary

14 Poured concrete vs concrete blocks

15 Poured concrete vs concrete blocks Information from Nelco Worldwide

16 Concrete vs High density Material Information from Veritas Radiation Shielding Systems

17 Concrete vs High density Material Information from Veritas Radiation Shielding Systems

18 Blocks

19 Separate concrete pours

20 Bracknell Pictures supplied by Nelco

21 An aside about surveys Access High dose rates Instrumentation Rain

22 Calculation points Point 1 2 Position Distance from source (m) Outer Wall (Left) Control Room (Right) Wall Thickness (m)

23 Calculation parameters Workload: X-ray energy: Dose rate: Dose per patient IMRT factor 60 patients/day 10MV photons 6 1m 3 Gy/patient x3 for 20% of patients Or: Workload: 40 pts per day No of patients per day at each energy: conventional therapy 30/70/10% at 6/10/15MV Proportion of patients undergoing IMRT: 50% Dose per patient: 3Gy IMRT factor: 3 Dose rate at isocentre for each X-ray energy for conventional therapy: 6Gy/min. Dose rate at isocentre for IMRT: 4 Gy/min or up to 24Gy/min FFF (6 and 10MV only)

24 Other calculation parameters Occupancy factors Orientation factors and 180 degree gantry angles

25 Typical calculation to calculate barrier thickness Dose per annum at calculation point (unattenuated) Required attenuation to meet annual dose constraint (0.3mSv per annum) Calculate thickness required of chosen construction material

26 Typical calculation to calculate impact of barrier thickness Calculation Point Thickness of Attenuation factor Position concrete (mm) 1 - primary x 10-6 barrier 2 - primary x 10-6 barrier 3 secondary x 10-5 barrier 4- primary barrier x secondary barrier x 10-1

27 Calculation parameters Workload: X-ray energy: Dose rate: Dose per patient IMRT factor 60 patients/day 10MV photons 6 1m 3 Gy/patient x3 for 20% of patients Or: Workload: 40 pts per day No of patients per day at each energy: conventional therapy 30/70/10% at 6/10/15MV Proportion of patients undergoing IMRT: 50% Dose per patient: 3Gy IMRT factor: 3 Dose rate at isocentre for each X-ray energy for conventional therapy: 6Gy/min. Dose rate at isocentre for IMRT: 4 Gy/min or up to 24Gy/min FFF (6 and 10MV only)

28 FFF

29 New bunkers and old bunkers Varian max 24Gy/min Elekta max 22Gy/min

30 Compliance with IRR99 Design Survey (easier when IDRs are higher) Environmental Monitoring very tricky but very common?pointless Other means..

31 Dose Washing Model bunker Take beam data Project onto barriers Calculate attenuation Sum all doses 3 months later. Huge input from Gavin Alexander

32 Early results no attenuation

33 Bunker model

34 Projections onto walls

35 Dose on each surface

36 Ceiling Outer wall Floor Operator wall

37 Ceiling Outer wall Floor Operator wall

38 Annual dose on surfaces Room Operator wall (Sv) Outer wall (Sv) Ceiling (Sv) Floor (Sv) e e e 3 9.8e e e 2 4.0e e e 3 4.1e e e 3 Checking by Rupert Larkin

39 What next Model other bunkers (almost done) Include rotational therapy Include FFF data from clinical sites Model FFF

40 IPEM75 rewrite 1 The Design & Procurement Process incorporate Chapters 1, 2 & 3 of IPEM Report 75 but in a 2 The Design of Radiotherapy Facilities current context. 3 Radiation Protection Requirements Regulations /BSS 4 Design Criteria for Linear Accelerator Bunkers 4.1 Equipment & Current Radiotherapy Practice Conformal IMRT VMAT FFF Techniques SRS (head & body) TBI Respiratory gating 4.2 Shielding Materials 5 Dose and Doserate Calculations 6 Methods Modelling x-ray photons Modelling neutrons Visualisation of fluxes 7 LinAc Bunker Detail Design Construction details Room furniture and engineering controls Control rooms Specialist applications : tomotherapy gamma knife and Cyberknife 9 Kilovoltage & Supervoltage Therapy 10 Brachytherapy 11 Introduction to Shielding for Particle Therapy 12 Radiation Surveys 13 Appendices - Data and Tables Review of existing physical data Physical data for new materials 14 References 15 Glossary 16 Index

41 Acknowledgements Pat Horton Bracknell / Reading - John Crossman and Nelco Veritas Minelco Leeds - Peter Bownes and Peter Howells BIR working party Colin Martin Dave Sutton and Jerry Williams Colleagues at Guildford Gavin Alexander Rupert Larkin

42 References Radioactive Substances Advisory Committee (1971). Handbook of radiological protection data, part 1 data. London: HMSO NCRP (1976). NCRP Report 49 Structural shielding design and evaluation for medical use of x rays and gamma rays of energies up to 10 MeV,: National Council on Radiation Protection and Measurements. Bethesda (USA) Nelson and LaRiviere Primary and leakage radiation calculations at 6, 10 and 25MeV Health Physics (1984) NCRP (2005) NCRP Report 151 Structural Shielding Design and evaluation for megavoltage X and gamma-ray radiotherapy facilities for Medical X-Ray Imaging Facilities: National Council on Radiation Protection and Measurements Bethesda USA IPEM (1998) IPEM Report No 75 The Design of Radiotherapy Treatment Room Facilities, IPEM, York Jones M R, Peet D J and Horton P W (2009) Attenuation Characteristics of MagnaDense High-density Concrete at 6, 10 and 15MV for use in radiotherapy bunker design. Health Physics 96(1) Sutton DG, Williams JR Martin CJ & Peet D (2012) Application of the constraint on instantaneous dose rate in the UK Approved Code of Practice 249 is inappropriate for radiology. J. Radiol. Prot. 32 (2012)