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MOHAMMAD HUSSIEN, NICHOLAS SPYROU & ANDY MA

ANTHROPOMORPHIC VOXEL PHANTOM EFFECTIVE NEUTRON DOSES OUTSIDE A LINAC ROOM. presented on behalf of. MOHAMMAD HUSSIEN, NICHOLAS SPYROU & ANDY MA. by Mary Chin. Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom. PROBLEM STATEMENT.

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MOHAMMAD HUSSIEN, NICHOLAS SPYROU & ANDY MA

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  1. ANTHROPOMORPHIC VOXEL PHANTOM EFFECTIVE NEUTRON DOSES OUTSIDE A LINAC ROOM presented on behalf of MOHAMMAD HUSSIEN, NICHOLAS SPYROU & ANDY MA by Mary Chin Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom

  2. PROBLEM STATEMENT RADIOTHERAPY DELIVERED IN THE ROOM reproduced from Chin MPW 1999 MSc Dissertation, University of Surrey STAFF WORK HERE POSSIBLY PUBLIC AREA WE NEED TO ESTIMATE THE DOSE

  3. CURRENT STANDARDS = HOMOGENEOUS ELLIPSOIDS

  4. Zubal G et al 1994 Med. Phys. 21 299 Alghamdi A A et al 2005 Radiat. Prot. Dosimetry 115606 WE GET TO KNOW NOT ONLY THE EFFECTIVE DOSE, BUT ALSO THE ABSORBED DOSE ORGAN-BY-ORGAN THIS WORK = ANTHROPOMORPHIC PHANTOM

  5. * 252Cf neutron source FIND NEUTRON SPECTRUM AT EACH OF THESE LOCATIONS METHOD: A 2-STAGE SIMULATION STAGE #1 ACTUAL LINAC & PHOTONEUTRON PRODUCTION NOT MODELLED JUSTIFIED IN Chin, Spyrou & Tomlinson 2007 Trans ANS Chin MPW 1999 MSc Dissertation, University of Surrey

  6. 5 4 3 2 • DOSE ESTIMATES AT 5 POSITIONS REPEATED FOR: • ICRP PUBLICATION 60 (1991) • ICRP RECOMMENDATIONS 2005 • ICRP RECOMMENDATIONS 2007 1 METHOD: A 2-STAGE SIMULATION STAGE #2 • SURFACE SOURCE ORIENTATION REPEATED FOR: • LEFT-TO-RIGHT • RIGHT-TO-LEFT • FRONT (ANTERIOR-TO-POSTERIOR) • BACK (POSTERIOR-TO-ANTERIOR) FOUND NEUTRON SPECTRUM

  7. Most significant changes in wT between 1990 and 2007 Gonads from 0.2 to 0.08 Breast from 0.05 to 0.12 Liver, thyroid, bladder & oesophagus from 0.05 to 0.04 Salivary glands introduced at 0.01 Prostate, lymph nodes & gall bladder added to the ‘remainder’ section E = EFFECTIVE DOSE WT = TISSUE WEIGHTING FACTOR WR = RADIATION WEIGHTING FACTOR DT, R = AVERAGE ABSORBED DOSE

  8. E = EFFECTIVE DOSE WT = TISSUE WEIGHTING FACTOR WR = RADIATION WEIGHTING FACTOR DT, R = AVERAGE ABSORBED DOSE THE NEED TO REDUCE WR=5WHEN NEUTRONS INTERACT, CONTRIBUTION FROM SECONDARY PHOTONS INCREASES WITH DECREASING NEUTRON ENERGY Alghamdi A 2006 PhD Thesis University of Surrey • DOSE ESTIMATES AT 5 POSITIONS REPEATED FOR: • ICRP PUBLICATION 60 (1991) • ICRP RECOMMENDATIONS 2005 • ICRP RECOMMENDATIONS 2007 FOR THERMAL NEUTRONS WR = 5 WR = 1 WR = 2.5

  9. PHOTON (TREATMENT) BEAM • NEUTRON CONTAMINATION PHOTONUCLEAR REACTION RADIATION NEUTRON REACTIONS 3.NEUTRON- INDUCED PROMPT RADIATION 4.NEUTRON- INDUCED DELAYED RADIATION ADDITIONAL SHIELDING CONCERNS BUNKER WALL

  10. SPARES HEALTHY TISSUES 6 MV 15 MV MORE PENETRATING FOR HEAD&NECK / SMALL PATIENTS FOR PELVIS / BIG PATIENTS UNWANTED HOT-SPOTS

  11. HENCE ADDITIONAL SHIELDING CONCERNS RADIATION  CONCRETE WALL     PATIENT WE WANT TO TREAT STAFF / PUBLIC WE MUST PROTECT 15 MV MORE PENETRATING IN BODY TISSUES ALSO MORE PENETRATING IN BUNKER WALLS

  12. Organ Absorbed Dose

  13. Organ Absorbed Dose SHIELDED BY

  14. ORGAN SHIELDING EFFECTS BY ANOTHER ORGAN ORGANS ON THE LEFT vs ORGANS ON THE RIGHT ORGANS ON THE ANTERIOR vs ORGANS ON THE POSTERIOR RESULTS CONSISTENT WITH EARLIER FINDINGS Tzortzis M. 2003 MSc Thesis University of Surrey

  15. 5 4 3 2 1 Effective Doses

  16. 5 4 3 2 1 Effective Doses

  17. Comparison between ICRP 1990 and 2007 draft using wR = 1 but different wT 5 4 3 2 1

  18. Comparison between ICRP 1990, 2005 draft and 2007 draft 5 4 3 2 1 WR = 5 FROM 1990 TO 2005 ICRP CHANGED ITS MIND BY 500% FROM 2005 TO 2007 ICRP CHANGED ITS MIND BY 250% QUESTION DO THE REVISIONS MAKE US MORE, OR LESS, CONFIDENT? WR = 2.5 WR = 1

  19. WORST-CASE SCENARIO • linac operates at 4 Gy / min • typical prostate patient receives 2 Gy per visit • 10 patients treated per day on a linac • radiographer works 230 days per year • effective dose per year = 19.17 mSv using current ICRP 1990 (6.78 mSv using 2007 draft) due to neutrons only.

  20. POINTS TO NOTE • no breasts, salivary glands & thymus in the phantom • only one adrenal gland is included in the phantom • a male phantom was used • UK statistics: 9/10 radiotherapy nurses are female • wT for breast increased from 0.05 to 0.12 in 2007 draft

  21. Note RESULTS SHOWN HERE EXCLUDE DELAYED GAMMAS ATOMIC NUMBER LIBRARY SPECIFIER [MCNPX manual] MASS NUMBER MCNPX 2.4.0 DOES NOT SIMULATE DELAYED GAMMAS SIMULATION WAS DONE USING MCNPX 2.4.0 ALTHOUGH IN SOME CASES ARTIFICIAL LINES HAVE BEEN INCLUDED IN THE CROSS SECTIONS BETA VERSIONS 26C/D DO SIMULATE DELAYED GAMMAS HOWEVER, DUE TO MULTIPLE GLITCHES WE FOUND THE CAPABILITY NOT READY FOR OUR USE [Chin & Spyrou 2007. Monte Carlo simulation of (γ, n) and (n, γ) activations: a multi-code comparison with theory. 12th Int Conf Modern Trends in Activation Analysis. Tokyo, ]

  22. ANTHROPOMORPHIC VOXEL PHANTOMS eg. ZUBAL‘s WE KNOW SOME (eg Spyrou et al papers) BUT NOT ALL TEDIOUS SEGMENTATION WORK… ASK KRAMER et al VERY DETAILED INDEED … BUT MONTE CARLO CODES AREN’T GOING TO MAKE MUCH SENSE OUT OF IT EACH TISSUE/ORGAN TYPE MUST BE MAPPED INTO ELEMENTAL (IF NOT ISOTOPIC) COMPOSITION

  23. IN FACT, VOXEL PHANTOMS ARE ROUTINELY USED FOR RADIOTHERAPY PLANNING / VERIFICATION THE ISSUE OF MAPPING CHIN MPW et al 2006 Scientific Computing • INDIVIDUAL PATIENT INSTEAD OF CADAVER / VOLUNTEER • DOSE TO THE INDIVIDUAL PATIENT INSTEAD OF PUBLIC RISK ASSESSMENT • VOXELS ATTRIBUTES: HOUNSFIELD UNITS INSTEAD OF TISSUE / ORGAN TYPES

  24. UK Switzerland Spain Portugal Germany USA Italy BELGIUM MORE MEANINGFUL IN TERMS OF RADIATION PROPERTIES THE ISSUE OF MAPPING BUT NOT AS STRAIGHT-FORWARD AS WE WISHED … • VOXELS ATTRIBUTES: HOUNSFIELD UNITS INSTEAD OF TISSUE / ORGAN TYPES

  25. MATHEMATICAL / MIRD–TYPE PHANTOMS FAITHFUL REPRESENTATION OF THE INDIVIDUAL / VOLUNTEER / CADAVER BEFORE DEBATING ON GENDER / SIZE / ETHNIC DIVERSITIES Downloaded from http://www.internaldosimetry.com WE STILL HAVE A LONG WAY TO GO WE HAVE GONE A LONG WAY ZUBAL / FAX / MAX / … VOXEL PHANTOMS

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