Fermilab Neutron Therapy Facility Medical Control System

Kevin Ramkissoon

North Carolina Central University

Durham, North Carolina

Project Supervisor:

Thomas Kroc

Neutron Therapy Facility

Fermi National Accelerator

July 2001

Contents

I. Introduction

Making Neutrons – Beam Delivery

II. Theory

Radiation Therapy

Why Neutron Therapy?

III. NTF Computer System

Microcomputer Calibration System

NTF Patient Treatment Application

IV. Program Development

jCVS

Forte for Java

V. Summary

VI. Acknowledgements

VII. References

VIII. Appendix

Abstract

Radiation therapy is just one form of treatment used in the ongoing fight against cancer. There are a number of different types of radiation therapy with varying modes of action and effectiveness. What holds true for all forms is that in working with radiation there must be mechanisms in place to ensure not only the safety of the medical and technical personnel but the patients as well. At the Neutron Therapy Facility (NTF) at Fermi National Accelerator Laboratory (FNAL) this involves constant monitoring of all conditions that have a bearing on the source, delivery, intensity and placement of the particle beam that is the source of radiation used in treatment. This is all done in order to maximize the positive and minimize the negative effects of the radiation treatment. This paper presents an overview of the Neutron Therapy Facility and provides a look at the new, Java based, patient treatment application programs currently under development.

Introduction

Established in June, 1975, the Neutron Therapy Facility (NTF) at Fermi National Accelerator Laboratory is one of only seven facilities in the world that carry out research and treatment in high linear-energy-transfer (high LET) radiation cancer therapy.

NTF utilizes fast (high energy) neutron beams to carry out radiation treatments on patients. Since 1976, more than three thousand patients have been treated at the facility.

Making Neutrons - Beam Delivery

Fermi National Accelerator Laboratory (Fermilab) operates the most powerful particle accelerator in the world. The 1000GeV proton accelerator at Fermilab consists of four individual accelerators operating series. The first three form what is called the “injector” and serve to fill the vacuum chamber of the main accelerator with tightly bunched groups of 8GeV protons. The main ring in turn increases the energy of the protons for use in high-energy physics experiments. While protons are being accelerated in the main ring, NTF extracts protons from the linear accelerator (Linac) [fig.1], the second in the cycle.

The first accelerator in the cycle, a Cockcroft-Walton [fig. 2] and the first three sections of the nine-section Linac are used to accelerate protons to 66MeV. The protons then drift through tank 4 of the Linac and are extracted between sections 4 and 5 using two bending magnets [fig. 3]; the first bending the beam through 58° and the second through 32º. Seven quadrupole magnets and beam position monitoring systems then focus the beam onto a beryllium target. This collision creates the neutrons with the desired energy for utilization in the treatment of patients.

Theory

Radiation Therapy

Radiation therapy refers to the treatment of diseases using penetrating beams of radiation. This encompasses electromagnetic radiation, such as photons (x-rays and gamma rays); and particulate radiation (electrons, protons, neutrons, alpha particles, and beta particles) all of which are forms of ionizing radiation.

The desired effect of ionization radiation in cancer therapy is to damage the DNA strands of cancer cells hence impairing the cells’ ability to grow and divide. Atomic interactions resulting from the use of photons, electrons and protons result in the production of activated radicals that are responsible for causing structural damage to cells. These types of radiation are called low linear-energy-transfer (low LET) radiation and often result in damage to a cell’s DNA that is repairable.

Neutrons interact with matter in a variety of ways depending on their velocity and the nature of the target. Scattering (elastic and inelastic), absorption, and capture by nuclei, which results in the production of new elements, may occur. The most fundamental difference between neutron and electromagnetic radiation is the mechanism by which the incident radiation interacts with matter. X-rays are scattered by the electrons surrounding atomic nuclei, but the charge neutral neutrons are scattered by the nucleus itself. For this reason, neutrons have very different radiobiological properties. The interaction with atomic nuclei via the short-ranged nuclear force is the mechanism by which damage to cell’s DNA structures is accomplished.

Unlike photons, neutrons are a form of high linear-energy-transfer radiation (high LET). In the human body, elastic collisions of neutrons with carbon (C), oxygen (O) or other heavier nuclei cause the nuclei to recoil. Elastic scattering of neutrons with hydrogen nuclei causes the protons to recoil violently. Since the mass of the proton and other nuclei is so much greater than that of the electron, when they recoil they generate a much denser ion path that results in more damage to tissue. Once slowed by these elastic collisions, the neutrons are easily captured. High LET radiation usually results in irreparable damage to the exposed cells.

Why Neutron Therapy?

Radio-sensitivity is a term used to reflect how susceptible a cell, cancerous or healthy, is to radiation-induced damage. Cells that divide frequently tend to be radiosensitive and are more affected by radiation. Cellular radio-sensitivity depends on many factors including the size and complexity of intracellular targets (DNA), the integrity of enzyme systems involved in the processes of DNA replication and repair; and certain biochemical factors; most notably oxygen tension, which affects the number and mobility of activated secondary radicals.

Advantages of Neutron Therapy:

i. The biological effectiveness of neutrons is not affected by the growth stage of tumor cells. Most other forms of radiation are more effective on cells that are actively reproducing and on those that divide more rapidly than normal. They are less effective on cells that are in the resting phase or divide slowly.

ii. The higher biological effectiveness of neutrons results in a required dose that is about one-third the dose required with photons, electrons or protons.

iii. Fewer treatments (10-12) over a shorter period of time (~ 4 weeks) are necessary with the high LET neutron therapy as compared with the different forms of low LET radiation (30-40 over 6-8 weeks).

iv. The damage done to the cell DNA structure is often irreparable permanently halting cell reproduction and tumor growth.

v. Unlike low LET radiation neutrons do not depend on the presence of oxygen to be effective. This is especially critical when considering large tumors that do not have good blood, and hence oxygen supply.

vi. Unlike other forms of radiation therapy neutrons are relatively harmless unless at low energies and unless captured. This is exploited in minimizing unwanted damage to the skin and tissue along the path of the beam and in the vicinity of the tumor.

NTF Computer System

NTF relies on an extensive network of computer systems [fig. 4], manual and electronic devices in order to ensure the safe delivery of the correct amount of radiation to patients.

The set of programs constituting the Patient Treatment Application, a part of the medical microcomputer system, which together with the beam line microcomputer form the Microcomputer Calibration System, serve a crucial role in the everyday functions of the facility.

The Microcomputer Calibration System

The Microcomputer Calibration System consists of the “Beam Line” and the “Medical” microcomputers.

The beam line microcomputer, among other functions:

i. Monitors atmospheric pressure

ii. Reads voltages from ionization chamber current integrators

iii. Closes and opens reed relays used to discharge the integrator capacitors

iv. Measures time

The medical microcomputer, among other functions:

i. Measures temperature where required

ii. Sends instructions to the beam line microcomputer

iii. Receives information on timing, voltages, pressure etc from the beam line microcomputer

iv. Performs arithmetic functions

v. Displays the information needed by the medical physicists and radiation therapy technologists

NTF Patient Treatment Application

The NTF Patient Treatment Application includes two calibration programs, the Ionization Chamber Calibration and Neutron Beam Transmission Chamber Calibration programs; and a Patient Treatment Program. These three are instrumental in ensuring that the right dosage is administered to the patient.

The Ionization Chamber Calibration is done with respect to Colbat-60 (60Co) in a Cesium-137 (137Cs) source and the calibration page transfers its results directly to the Neutron Beam Transmission Chamber Calibration program. These calibrations are carried out before each day of therapy begins. At midnight, both programs have the calibration constants erased and require a full recalibration procedure.

Program Development

A number of factors were considered in choosing Java as the development language for this project. Java’s robust versatility, its memory management abilities, support for multithreaded programming and the fact that it is platform-neutral all influenced this decision. Another motivating factor for the use of Java is the recent implementation of jCVS at the laboratory.

jCVS

JCVS is a CVS client package written entirely in Java. CVS, an acronym for "Concurrent Versions System” is a source control/revision control tool designed to keep track of source changes made by groups of developers working on the same files, allowing them to stay in sync with each other as each individual chooses.

JCVS provides a complete CVS client/server protocol package that allows any Java program to implement the complete suite of CVS operations. JCVS provides a Swing based client that provides a commercial quality GUI client and provides a servlet that allows any servlet-enabled web server to present any CVS repository on the internet for browsing and download.

Forte for Java

Forte for Java Community Edition was chosen as the development environment for this project. Available as freeware from Sun Microsystems, Forte was chosen because it has:

i. an interface that provides developer tools, such as an application browser, Java language source editor, debugger, compiler and online help.

ii. a framework source code based on open Application Programming Interfaces (APIs) which serves as code templates and greatly reduces coding time. The framework source code is modular, allowing editor plug-in, compiler and RTE (executor) among other tools.

iii. a debugger that includes conditional breakpoints, breakpoint logging, an evaluator, code stepping and watches for finding and fixing bugs. It also provides simultaneous multi-process debugging, thus simplifying development of partitioned applications.

Summary

Limited testing has determined that the new calibration and patient treatment programs in their current stage of development successfully perform many of the duties of the system programs currently in use by NTF. These include the obtaining of raw data from the beam line microcomputer and the calculation of critical values necessary for administering treatment to patients. Further development and extensive testing is necessary before the new Java-based programs can be utilized with full confidence by NTF in its everyday operations.

Acknowledgements

I would like to thank the following people for lending their time and knowledge toward the completion of this project:

v Thomas Kroc

v Arlene Lennox

v Robert Florian

v Gordon Holmblad

I would also like to thank Elliot McCrory, Dianne Engram, Dr. Davenport, Chandra Bhat, Carmenita Moore and Summer Internship in Science and Technology (SIST) committee members for the invaluable research opportunity, their support and mentorship.

References

“Computing Concepts with Java 2 Essentials” 2^nd Edition, Cay Horstmann

John Wiley & Sons Inc. (2000)

“Java 2: The Complete Reference” 4^th Edition, Herbert Schildt

Osborne/McGraw-Hill (2001)

“Radiation Dosimetry Vol. I” 2^nd Edition, Attix, Roesch & Tochilin

Academic Press

“Radiation Oncology -Technology and Biology” Mauch & Loeffler

WB Saunders Company

Appendix

Fig. 1- Linear Accelerator (Linac)

Fig. 2 - Cockcroft-Walton

Fig. 3 - Linac showing bending magnets between tanks 4 and 5

Patient Treatment Application

Test Run Screens

Sun Microsystems’ Forte for Java Community Edition v. 2.0 was the development environment utilized in the upgrade of the patient treatment program. Forte for Java, release 2.0 requires the Java[tm] 2 Platform, Standard Edition, v. 1.3 (J2SE[tm] 1.3)

Editing: Screenshot of the Forte Editing workspace

Debugging: Screenshot of the Forte Debugger workspace

One of the many error message notifications encountered during program development

Execution: Screenshot of the Forte Running workspace

NTF Patient Treatment Application

Title Panel: This is the first screen displayed when the system program is executed

The tabs give the user easy access to the required calibration and treatment

panels.

Cs-137 Calibration Panel: This is the first page to be executed by the user. It provides a continuous real-time monitoring of chamber parameters, calculates G-Gamma and passes the value to the Neutron Calibration page.