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Session I.4.13

Part I Review of Fundamentals

Module 4 Sources of Radiation

Session 13 Neutron Production

IAEA Post Graduate Educational CourseRadiation Protection and Safety of Radiation Sources

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Overview

In this Session we will discuss how neutrons are produced and

We will also discuss how neutrons are used for medical neutron therapy

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Neutron Production

Neutrons carry no electrical charge and are thus "neutral"

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Fission

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3He and Neutron Production from Fusion

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Nuclear ReactionsFusion

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Deuterium-TritiumNeutron Generator

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Neutron Production by Spallation

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ISIS NeutronProduction Assembly

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Continuous SpallationNeutron Source

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US SpallationNeutron Source (SNS)

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Neutron Production

(p,n) reactions

(d,n) reactions

(α,n) reactions

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Nuclear ReactionsCharged Particle Bombardment

p + 68Zn 67Ga + 2n

α + 16O 18F + p + n

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Neutron Productionby Various Reactions

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Neutron Production (cont)

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Neutron therapy is a highly effective form of radiation therapy

Long-term experience with treating cancer has shown that certain tumor types are very difficult to kill using conventional radiation therapy

These types are classified as being "radioresistant"

Neutron therapy specializes in treating inoperable, radioresistant tumors occurring anywhere in the body

What is Neutron Therapy?

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Conventional radiation therapy includes photon (X-ray) and electron radiation, which is available at many clinics and hospitals

These beams are produced by electron accelerators or from radioactive sources such as cobalt

Particle therapy includes protons and neutrons, which are generated using proton accelerators

The basic effect of ionizing radiation is to destroy the ability of cells to divide and grow by damaging their DNA strands

What is Neutron Therapy?

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For photon, electron and proton radiation the damage is done primarily by activated radicals produced from atomic interactions

These types of radiation are called low linear-energy-transfer (low LET) radiation

With neutron radiation the damage is done primarily by nuclear interactions

Neutrons are high linear-energy-transfer (high LET) radiation

What is Neutron Therapy?

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If a tumor cell is damaged by low LET radiation it has a good chance to repair itself and continue to grow

With high LET radiation such as neutron radiation, the chance that a damaged tumor cell will repair itself is very small.

Because the biological effectiveness of neutrons is so high, the required tumor dose is about one-third the dose required with photons, electrons or protons

A full course of neutron therapy is delivered in only 10 to 12 treatments, compared to 30 - 40 treatments needed for low LET radiation

What is Neutron Therapy?

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The side effects of fast neutron therapy are similar to those of low LET therapy

Their severity depends on the total dose delivered and the general health of the patient

Effects on normal tissues are minimized by careful computerized treatment planning

What is Neutron Therapy?

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Neutrons were discovered by Sir James Chadwick in 1932

Just six years later, Dr. Robert Stone began clinical trials treating cancer with neutrons produced by E.O. Lawrence's cyclotron in Berkeley, California

These trials were terminated because the cyclotron was needed for the war effort during World War II

Clinical research began again in 1965 when Hammersmith Hospital in London began irradiating patients with neutron beams

History of Neutron Therapy

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By 1969, it was clear that for certain tumors, local control could be achieved using neutron irradiation

Encouraged by these results, the M.D. Anderson Hospital and Tumor Institute in Houston, the Naval Research Laboratory in Washington, D.C., and the University of Washington in Seattle began neutron therapy research

They started treating patients in the early 1970s.

History of Neutron Therapy

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Boron Neutron Capture Therapy (BNCT) is a radiotherapy modality for treating cancerous tumours (e.g. glioma – a cancer of the brain)

It utilizes the reaction between the 10B nucleus and slow (thermal) neutrons:

10B + n 7Li(0.84 MeV) + 4He(1.47 MeV) + γ(0.48 MeV)

The released 7Li atom and alpha-particle (4He) have a total energy of 2.31 MeV which is deposited within the range of approximately 5-9 mm (i.e. at a distance corresponding to about one cell diameter)

Boron Neutron Capture Therapy(BNCT)

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In principle, one boron-neutron interaction liberates enough energy to kill the cell in which the inter-action takes place

The short distance deposition of the released energy spares the surrounding boron-free tissue of the radiation damage

The effect of BNCT is dependent on two preconditions:

the selective accumulation of boron atoms in the target (tumour) rather than in the healthy cells

the tumour site is reached by a sufficient number of neutrons

Boron Neutron Capture Therapy(BNCT)

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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HEAD AND NECK - Salivary glands, tongue, pharynx, oral cavity, nasopharynx, brain tumorsCHEST - Localized tumors of lung, mediastinum, pleura, pericardium

ABDOMEN - Pancreas, colon, bile duct, gallbladder, ampula of vater, peritoneum

PELVIS - Prostate, bladder, uterus, rectosigmoid

EXTREMITIES AND TRUNK - Soft tissue, bone, cartilage

PALLIATIVE - Large tumors and metastasis from neutron-sensitive tumors

Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Medical Neutron Therapy

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Place Country Source Mean Energy (MeV)

Obninsk Russia ReactorGarching Germany Reactor 1.8Chelyabinsk Russia d(0.5) + T 14.3Tomsk* Russia d(14) + Be 5.9Minsk* Belarus d(14) + Be 5.9Essen* Germany d(14.3) + Be 6.0

*Cyclotron

Fast Neutron Therapy Facilities(E < 30 MeV)

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Place Country Source

Orleans France p(34) + BeBeijingº China p(35) + BeDetroit, MI USA d(50) + BeSeattle, WA USA p(50) + BeSeoul+ South Korea p(50) + BeNice+ France p(60) + BeLouvain‑la‑Neuve+ Belgium p(65) + BeBatavia, IL USA p(66) + BeFaure South Africa p(66) + Be

+Not operational at presentºLinac (all other accelerators are cyclotrons)

Fast Neutron Therapy Facilities(E > 30 MeV)

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Neutrons

Although the previous slides have indicated the usefulness of neutron beams for medical therapy, neutrons can also be a nuisance byproduct of medical therapy such as in high energy Linear Accelerator facilities treating patients with high energy photons.

The remaining slides summarize this issue.

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Neutrons

Neutrons are produced by (gamma,n) reactions in high energy linear accelerators (E > 10MV)

Issues are neutron shielding and activation of items in the beam

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Neutron Shielding

Different concept from X-ray shielding

Neutrons scatter more

Attenuation (and scatter) depend VERY strongly on the neutron energy

Best shielding materials contain hydrogen or boron (with high cross sections for thermal neutrons)

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Features of Neutron Shielding

Long maze - many ‘bounces’

Neutron door - typically filled with borated paraffin wax

Care is required as neutrons generate gammas which may require other materials for shielding

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Activation

Neutrons can activate materials High energy linacs are designed around

materials with low activation cross section After high energy photon irradiation, beam

modifiers such as wedges or compensators may become activated

After prolonged use of high energy photons (e.g. for commissioning) it is advisable to let activation products decay prior to entering the room (>10min)

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More Information on Neutrons

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Neutron Evaluation

if the facility has an accelerator with an energy >15 MeV, then radiation scans should include a neutron survey, especially near the entrance to the maze

the survey instrument used for neutrons should be of a suitable type (see, for example, AAPM report 19)

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Where to Get More Information

Cember, H., Johnson, T. E., Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2008)

Martin, A., Harbison, S. A., Beach, K., Cole, P., An Introduction to Radiation Protection, 6th Edition, Hodder Arnold, London (2012)

Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999)

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Where to Get More Information

Dendy, P. P., Heaton, B., et al, Physics for Diagnostic Radiology, CRC Press, London (2011)

International Commission on Radiological Protection, Publication 105, Radiation Protection in Medicine, Ann ICRP 37 (6) (2008)