Radiation in Medicine and Biology

Pandit B. Vidyasagar, Sagar S. Jagtap, Omprakash Yemul, Pandit B. Vidyasagar, Sagar S. Jagtap, Omprakash Yemul

• Publisher: Jenny Stanford Publishing
• Year: 2017
• eBook ISBN: 9781351797412
• Edition: 1
• Topic: Medicina
• Subtopic: Biotecnologia in medicina

This book focuses on the conventional and emerging applications of radiations, which include radio waves and ultraviolet and gamma radiations. It discusses new techniques in radiation therapy and the effects of ionizing radiations on biological systems. The applications of radiations in the synthesis and use of nanoparticles along with the effects of hypergravity indicate a new trend. The book offers a concise account of the latest studies carried out so far and shows the new initiatives to be undertaken in the field of medicine and biology. It covers the medical use of radiations, such as ferrous sulfate–benzoic acid–xylenol orange dosimetry, Co-60 tomotherapy, radio-electro-chemotherapy, and fractional radiotherapy, and radiobiological effects, such as the effects of cell phone radiations on human health parameters and the combined effects of radiations and hypergravity on plants.

PART 1

NEW TECHNIQUES IN RADIATION THERAPY

Chapter 1

Generation of Bremsstrahlung Radiation from Different Low- to High-Z Targets for Medical Applications: A Simulation Approach

Bhushankumar Jagnnath Patil,^a Vasant Nagesh Bhoraskar,^b and Sanjay Daga Dhole^b

^aDepartment of Physics, Abasaheb Garware College, Karve Road, Pune, India

^bDepartment of Physics, Savitribai Phule Pune University, Ganeshkhind, Pune, India

[email protected]

When high-energy electrons pass through a target (e–γ target), it generates a cascade shower of bremsstrahlung radiation with continuous energy spectrum shows an end point equal to the electron kinetic energy. A study of bremsstrahlung spectra from 6–18 MeV electron beam on different e–γ targets were carried out using FLUKA simulation. The study includes different materials as bremsstrahlung producing targets with variation of target thickness. The contribution of electrons, positrons and neutrons in the bremsstrahlung dose were calculated for each case and reported in the chapter. The data generated will help researchers and medical physicists to take precise right hand data of flux and energies of bremsstrahlung radiations to be used for desire object in radiation therapy. Moreover, for production of a clinical photon beam (radiotherapy application), the design of accelerator head assembly was optimized using 15 MeV electrons. The e–γ target, primary and secondary collimator, were designed in Monte Carlo based FLUKA code and the corresponding neutron dose equivalent and the gamma dose at the patient plane were estimated at various field sizes. The maximum neutron dose equivalent observed near the central axis of 30 × 30 cm² field and has a value 36.6 mSv/min. This is 0.61% of the central axis photon dose rate of 60 Gy/min. The values fall within the allowed limit by International Electrotechnical Commission (IEC). The dimensions of the collimators and filters were optimized in such a way that the neutron dose equivalent estimated is below the allowed limit in the therapy beam.

1.1 Introduction

1.1.1 Historical Background

In the late 19th century, Roentgen, Becquerel and Curie discovered the X-rays, natural radioactivity, and isolated radium, respectively [1]. However, X-rays were immediately applied to diagnosis and therapy in medicine. These discoveries paved the ways for radiation therapy. Five years after the discovery of radium, it was used for the first time to treat skin cancer. In 1913, Coolidge developed hot cathode X-ray tube, which enables external beam radiotherapy. Around 1920, brachytherapy was widely used to treat accessible tumors with radium needles or tubes [1]. To address the question of radioprotection International Commission on Radiological Protection (ICRP) was created in 1928. Moreover, at the same time the ionizing chamber and Geiger Muller chamber was also discovered to measure the accurate dose received by patients.

Later on, teletherapy unit was designed by using cobalt-60 source of high-energy gamma rays. The Co-60 gamma radiation unit was invented by H. E. Johns in Canada in the early 1950s for radiotherapy. The first telecobalt unit was installed in Hamilton, Canada, and widely used worldwide [1]. The only disadvantage while working with the radioactive sources was to manage the waste. This leads to the replacement of Co-60 teletherapy with a linear accelerator. During the first 50 years of radiotherapy, the technological progress was relatively slow and mainly based on X-ray tubes, Van de Graaff generators, and betatrons. The concurrently developed medical linacs, became the most widely used radiation source in modern radiotherapy. With its compact and efficient design, the linac offers excellent versatility for use in radiotherapy through isocentric mounting and provides either electron or megavoltage X-ray therapy with a wide range of energies [2, 3, 4]. The technology of radiation production has first been aimed to get higher photon and electron beam energies and intensities, and more recently towards computerization and intensity modulated beam delivery [5, 6].

1.1.2 Radiation Therapies for Cancer Diseases

Cells are the basic units of human body; in a normal body, cells grow, divide to make new cells, and die in an orderly way. Cancer begins when genetic changes impair this orderly process and it is because of changes to DNA (deoxyribonucleic acid) of a cell. In a normal cell, when DNA is damaged, the cell either repairs the damage or dies. In cancer cells, the damaged DNA is not repaired, but the cell does not die like it should. Instead, the cell goes on making new cells that the body does not need. These new cells all have the same damaged DNA as the first cell does. Such abnormal cell growth in any part of the body causes cancer. These cells may form a mass called a tumor. As a cancerous tumor grows, the bloodstream or lymphatic system may carry cancer cells to other parts of the body. For most cancers, a biopsy is the only way to make a definite diagnosis. Different types of cancer can behave very differently. For instance, lung cancer and skin cancer are very different diseases. They grow at different rates and respond to different treatments. Therefore, the correct treatment related to type of cancer is more important for cancer patient [7].

There are different ways of cancer treatment. The mostly used cancer treatments are surgery, radiation therapy, and chemotherapy. Surgery is a procedure in which a doctor with special training, called a surgeon, removes cancer from the patient’s body. In radiation therapy, high radiation doses are used to kill cancer cells and shrink tumors. At high doses, radiation kills cancer cells or slows their growth. While in chemotherapy, drugs are usually used to kill cancer cells. Most patients have a combination of treatments, such as surgery with chemotherapy and/or radiation therapy. Radiation may be given before, during, or after surgery. The aim of radiation therapy to use before surgery is to shrink the size of the cancer. It may be used during surgery, so that it goes straight to the cancer without passing through the skin. Radiation therapy used this way is called intraoperative radiation. Sometimes radiation therapy is used after surgery, to kill any cancer cells that may remain or left in the surgical part of the body [7].

There are two main types of radiation therapy: One is an external beam and the other is located internally itself. External beam radiation therapy comes from a machine. Based on the tumor position and size, the type of radiation and the respective energy is decided. Internal radiation therapy is a treatment in which a source of radiation is put inside the patient’s body. The radiation source can be solid or liquid. Internal radiation therapy with a solid source is called brachytherapy. It is used to treat cancers of the head and neck, breast, cervix, prostate, and eye. Liquid forms of internal radiation are most often used to treat thyroid cancer [7].

1.1.3 Today’s Status in the World and India

Presently, there are more than ten thousand of accelerators running all over the world, out of which almost 50% are devoted to the medical applications. The main areas of use are radioisotopes production, radiography, and conventional radiotherapy with electron and photon beams [8]. Electrons and photons were found to be good members of radiation therapy for treating the cancer years ago. This is because of their high penetrability, low linear energy transfer (LET) to exhibit damage to the normal cell, and unique characteristics of dose distribution at depth [9, 10]. With the advent of high-energy linear and circular accelerators, electrons/photons have become a viable option in treating superficial tumors up to the depth of about 5–10 cm [11, 12].

External beam radiation therapy is also carried out with heavier particles such as neutrons produced by neutron generators and cyclotrons; protons produced by cyclotrons and heavy ions (helium, carbon, nitrogen, argon, neon) produced by Van de Graaff, synchrocyclotrons, pelletrons, and synchrotrons. In case of neutrons, the recoils and nuclear disintegration product contributing to the dose are responsible for a high-energy transfer to the biologically active molecules and destroy them in turn. High relative biologi...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Foreword
• Foreword
• Part 1: NEW TECHNIQUES IN RADIATION THERAPY
• Part 2: EFFECTS OF IONIZING RADIATIONS ON BIOLOGICAL SYSTEMS
• Index