Physics
Radiotherapy
Radiotherapy is a medical treatment that uses high-energy radiation to target and destroy cancer cells. It is based on the principles of physics, specifically the interaction of radiation with matter. Radiotherapy can be delivered externally using machines like linear accelerators or internally through radioactive implants. The goal is to shrink tumors and prevent cancer from spreading.
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12 Key excerpts on "Radiotherapy"
eBook - ePubNuclear and Radiation Physics in Medicine
A Conceptual Introduction
- Tony Key(Author)
- 2013(Publication Date)
- WSPC(Publisher)
Chapter 4Radiation Therapy4.1 IntroductionPrevious chapters have described the use of radiation as a diagnostic tool. However, in its passage through matter, radiation causes ionization that can damage the cells through which it passes. At the low levels of radiation used in diagnosis, the body can usually repair this damage; at higher levels, illness can result. However, since radiation preferentially destroys cancer cells, which grow at a faster rate and repair themselves less well than do healthy cells, radiation has become a powerful tool in the treatment of cancer.In radiation therapy, the intent is to sterilize or kill the tumour cells while causing minimal damage to adjacent healthy tissues. Many different sources of radiation are used. There are two main methods of delivery of the radiation: teletherapy, where the radiation from X-rays, radioisotopes, or external particle beams (electrons, protons, neutrons, or heavy ions) is directed into the body from the outside, and brachytherapy (the root comes from Greek, meaning short distance), in which a radioisotope is placed on or inside the body, close to the site of the cancerous tissue.Section 4.2 discusses the mechanisms whereby biological cells are damaged by radiation. Section 4.3 shows some basic methods used to calculate the required therapeutic doses from external radiation. Section 4.4 discusses beams of radiation from accelerators and from radioisotopes. Brachytherapy, its uses, and related dose calculations appear in section 4.5 .Chapter 5 provides a short overview of the unavoidably deleterious effects of radiation on healthy cells and the contribution of both diagnostic and therapeutic radiation to the environmental radiation background.4.2 The interaction of radiation with biological cellsX-rays and the emissions from radioactive isotopes (alpha, beta, or gamma rays) ionize the cells through which they pass. (Ionization is the process whereby electrons are removed from an atom or molecule to form an ion or a charged molecule). Alpha particles (nuclei of He atoms, see §3.2.2 ), by virtue of their greater mass and double charge, produce a greater density of ionization than beta particles (electrons or positrons). As a consequence, alpha particles are much more weakly penetrating than beta particles, which in turn are less penetrating than X-ray or gamma ray photons at a given energy. Alpha particles of typical energy are easily stopped by, e.g. a sheet of paper, or human skin; however if they are ingested, their high ionizing ability causes cellular damage to the lungs, which is the main reason smoking causes cancer (see §5.1.2 ). Photons of X- or gamma rays are called indirectly ionizing radiation since they do not directly cause biological damage, but produce energetic electrons via the processes described in §2.3
eBook - PDF- Anthony R. Mundy, John Fitzpatrick, David E. Neal, Nicholas J. R. George, Anthony R. Mundy, John Fitzpatrick, David E. Neal, Nicholas J. R. George(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
27 Radiotherapy: Scientific Principles and Practical Application in Urogical Malignancies Angela Swampillai, Rachel Lewis, Mary McCormack, and Heather Payne Department of Oncology, University College Hospitals, London, U.K. INTRODUCTION Radiotherapy is the therapeutic use of ionizing radi-ation. X rays were first used in the treatment of cancer over 100 years ago by Freund, a German surgeon. Since that time, our understanding of the effects of ionizing radiation on malignant and normal tissues has progressed through the field of radiobiology. In parallel with this, our knowledge of radiation physics has advanced together with significant technological developments in treatment planning and delivery. This chapter outlines the underlying physical and radiobiological principles of Radiotherapy and discusses the scientific practice of Radiotherapy as applied to urological tumors. RADIATION PHYSICS Radiation used therapeutically is called ionizing radi-ation, as it causes its effects through the ionization of intracellular molecules. Ionizing radiation can be clas-sified as electromagnetic or particulate. Electromagnetic Radiation The two types of electromagnetic radiation used in Radiotherapy are X rays and g rays. They are physically identical, but known by different names to distinguish their means of production. g Rays are produced from the nuclear decay of radioactive isotopes. X rays are produced by interactions that occur outside the nucleus. Both types of radiation have short wavelengths, high frequencies and carry high energies that enable them to break chemical bonds and produce biological effects (Fig. 1). The term ‘‘photon’’ is another name that can be used to describe both X rays and g rays. X rays are usually produced artificially by elec-trical means, accelerating electrons to a high energy and then abruptly stopping them in a heavy metal target. Part or all of the kinetic energy of the electrons is converted into X rays.
eBook - PDF- Paola A. Gehrig(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
C hapter 7 Radiation Therapy Hiram A. Gay, Ron R. Allison and Marcus E. Randall Introduction Ionizing radiation has been successfully employed to treat cancer for over a cen tury. The ability to destroy tumor and spare surrounding normal tissue is the essence o f radiation oncology. Radiotherapy plays a critical role in delivering the optimal care for women with gynecologic malignancies. However, the benefits of Radiotherapy can never be realized without the active cooperation between the gynecologic oncologist and radiation oncologist. This chapter aims to review the fundamentals of radiation oncology for medical students and residents so patients can achieve the best outcomes possible; it is divided into three sections: radiation physics, radiobiology and clinical radiation oncology. Physics W h at Is Ion izin g R a d ia tio n ? Unlike other forms o f electromagnetic radiation, such as light, which do not ionize matter, ionizing radiation ultimately creates free radicals which are highly destructive to living tissue. Ionizing radiation is emitted from naturally occurring radioactive isotopes and can also be artificially generated with the use of electricity. Gamma rays, X-rays, beta particles and electrons are types o f radiation that lead to ionization and are often used in clinical radiation oncology. Teletherapy versus B rachytherapy Ionizing radiation used clinically can be separated into two categories: teletherapy and brachytherapy. During teletherapy, the radiation source is at some distance from the target. In contrast, during brachytherapy the radiation source is direedy in or near the target. Brachytherapy relies on radioactive isotopes to generate gamma rays, X-rays and/ or beta particles (electrons) to treat the target. With brachytherapy, one may perma- nendy or temporarily place a radioactive source into a tumor bed or region at risk. Radioactive isotopes o fvarious energies, sizes and shapes have been created for a myriad o f oncologic indications.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
It is also common to combine Radiotherapy with surgery, chemo-therapy, hormone therapy, Immunotherapy or some mixture of the four. Most common cancer types can be treated with Radiotherapy in some way. The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on the tumor type, location, and stage, as well as the general health of the patient. Radiation therapy is commonly applied to the cancerous tumor. The radiation fields may also include the draining lymph nodes if they are clinically or radiologically involved with tumor, or if there is thought to be a risk of subclinical malignant spread. It is necessary to include a margin of normal tissue around the tumor to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, respiration and bladder filling) and movement of external skin marks relative to the tumor position. To spare normal tissues (such as skin or organs which radiation must pass through in order to treat the tumor), shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding, healthy tissue. Brachytherapy, in which a radiation source is placed inside or next to the area requiring treatment, is another form of radiation therapy that minimizes exposure to healthy tissue during procedures to treat cancers of the breast, prostate and other organs. Mechanism of action Radiation therapy works by damaging the DNA of cancerous cells. This DNA damage is caused by one of two types of energy, photon or charged particle. This damage is either direct or indirect ionizing the atoms which make up the DNA chain. Indirect ionization happens as a result of the ionization of water, forming free radicals, notably hydroxyl radicals, which then damage the DNA.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
It is also common to combine Radiotherapy with surgery, chemo-therapy, hormone therapy, Immunotherapy or some mixture of the four. Most common cancer types can be treated with Radiotherapy in some way. The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on the tumor type, location, and stage, as well as the general health of the patient. Radiation therapy is commonly applied to the cancerous tumor. The radiation fields may also include the draining lymph nodes if they are clinically or radiologically involved with tumor, or if there is thought to be a risk of subclinical malignant spread. It is necessary to include a margin of normal tissue around the tumor to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, respiration and bladder filling) and movement of external skin marks relative to the tumor position. To spare normal tissues (such as skin or organs which radiation must pass through in order to treat the tumor), shaped radiation beams are aimed from several angles of exp-osure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding, healthy tissue. Brachytherapy, in which a radiation source is placed inside or next to the area requiring treatment, is another form of radiation therapy that minimizes exposure to healthy tissue during procedures to treat cancers of the breast, prostate and other organs. Mechanism of action Radiation therapy works by damaging the DNA of cancerous cells. This DNA damage is caused by one of two types of energy, photon or charged particle. This damage is either direct or indirect ionizing the atoms which make up the DNA chain. Indirect ionization happens as a result of the ionization of water, forming free radicals, notably hydroxyl radicals, which then damage the DNA.
eBook - PDF- Anthony B. Wolbarst, Robert G. Zamenhof, and William R. Hendee(Authors)
- 2006(Publication Date)
- Medical Physics Publishing(Publisher)
Soon there- after reports began to emerge on how exposure to these new rays caused reddening of the skin, and a number of physicians realized that this was a tool that could, perhaps, cure cancer. 11.1.1 Application of Radiation for Treatment of Disease The first radiation therapy successes were announced as early as 1899. Initially, the unreliability and low radiation output of the radiation production devices meant that nearly all treatments were carried out in multiple fractions. Most of treatments today are still fractionated, but now for radiobio- logical reasons based on extensive observations and clinical experience. Modern fractionation schemes are designed so as to kill the tumor while causing only acceptable damage to surrounding normal tissues. Instead of the 100 fractions spread over 9 months, employed in the first successful cure of a basal-cell carcinoma of the nose, treatment these days is likely to involve 30 fractions over 6 weeks. Advances in medical physics, engineering, and radiation biology have led the evolution of modern radiation therapy. This has given rise to: treatment machines that can deliver radiation dose rapidly and with unprecedented accuracy; imaging modalities that can provide significantly improved diagnosis and localization of cancerous cells; and dosimetric instrumentation, dose calculation algorithms, and treatment planning systems that can optimize the dose distribution, so as to maximize the dose to the tumor while minimizing dose to nearby critical structures. The importance of physics in this field is further reflected by the staffing model used by many modern cancer treatment centers, where there is approximately one medical physics staff for every two radiation oncologists. After a brief historical review, this chapter will present an overview of the state-of-the-art of physics of radiation therapy, both clinical and theoretical; it will also suggest how the field is likely to develop over the next few years.
eBook - ePub- Jeffrey S. Tobias, Daniel Hochhauser(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
5
Radiotherapy
Sources and production of ionizing radiationRadioactive isotopes Artificial production of X-rays and particlesBiological properties of ionizing radiationTumour sensitivity Fractionation and cell deathResponse of biological tissues to radiationNormal tissues Highly radiosensitive tissues Moderately radiosensitive tissues Less radiosensitive tissuesLate sequelae of radiationCarcinogenesis Teratogenicity MutagenicityTechnical aspects of RadiotherapyRadiotherapy planning and treatment techniquesTreatment prescription Maximum, minimum and modal dose Open (direct) and wedged fields Parallel opposed fields Shrinking field technique Systemic irradiation Immobilization devices Conformal and intensitγ-modulated radiation therapyIntegration of Radiotherapy and chemotherapyA recent report from the Royal College of Radiologists (UK) estimated that, taking cancer patients as a whole and assessing the contributions of differing modalities to cure rates, ‘of those cured, 49% are cured by surgery, 40% by Radiotherapy and 11% by chemotherapy’ [1].Ever since the discovery of X-rays by Roentgen in 1895, attempts have been made not only to understand their physical nature but also to use them both in the biological sciences and in a variety of human illnesses. The development of the X-ray tube rapidly led to clinical applications, first as a diagnostic tool and later for therapy in patients with malignant disease. The discovery of radium by Marie and Pierre Curie in 1898 also resulted in the use of radioactive materials for the approach to cancer, since surgery was the only alternative available at that time. Over the past 80 years our understanding of the physical characteristics, biological effects and clinical roles of ionizing radiation has greatly increased. Important articles and papers are listed under Further reading (pages 75–76).
eBook - PDFCancer Nanotechnology
Principles and Applications in Radiation Oncology
- Sang Hyun Cho, Sunil Krishnan, Sang Hyun Cho, Sunil Krishnan(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
Brachytherapy, because of the lower energies of radiation par-ticles, may have greater clinical effectiveness than x-rays used for external beam therapy when combined with nanoparticles 1.4 Radiobiological Basis of Radiation Therapy 1.4.1 What Is Cancer? Tumors occur when a single cell suffers a disruption in its mech-anisms for proliferation and self-elimination. This disruption is caused by a genetic mutation that might be a result of random events during normal cellular replication, but can also be caused by carcinogens such as radiation or cigarette smoke. The malig-nant cells may be immortal or divide many more times than normal cells, and often grow much more rapidly than normal cells. Additionally, they can exhibit abnormal interactions with other cells, allowing them to metastasize and grow in places they would not normally be found. 1.4.2 Role of Radiation Therapy in Cancer Treatments The primary goal of radiation therapy is to kill the cancerous cells. This is achieved by damaging biologically important mol-ecules, particularly deoxyribonucleic acid (DNA). Interestingly, only about one-third of biological damage is caused by the radiation interacting directly with these molecules. The major-ity of damage is achieved when radiation interacts with water which, upon excitation or ionization, transforms into highly reactive chemical species (free radicals) that themselves damage biological molecules. This latter phenomenon is known as indi-rect action and accounts for around two-thirds of the biological damage caused by x-rays. Of particular importance is the fact that indirect action is open to modification by chemical sensitiz-ers or protectors. The sensitivity of cells to radiation is described by four biological processes (known as the four R’s) (Hall 2000): 1.4.2.1 Repair Radiation-induced damage to the DNA can be categorized as DNA protein crosslink, base alterations, single-strand breaks, and double-strand breaks.
eBook - PDFGynaecologic Cancer
A Handbook for Students and Practitioners
- Mohd Rushdan Md Noor, Tay Eng Hseon, Low Jen Hui Jeffrey, Mohd Rushdan Md Noor, Tay Eng Hseon, Low Jen Hui Jeffrey(Authors)
- 2016(Publication Date)
- Jenny Stanford Publishing(Publisher)
Chapter 22 Gynaecologic Cancer: A Handbook for Students and Practitioners Rushdan Noor, Eng Hseon Tay, and Jeffrey Low Copyright © 2014 Pan Stanford Publishing Pte. Ltd. ISBN 978-981-4463-06-5 (Hardcover), 978-981-4463-07-2 (eBook) www.panstanford.com Basic Principles of Radiotherapy 638 Basic Principles of Radiotherapy Introduction Historically, the irst application of radiation for the therapeutic purpose was made in 1896 in Chicago by Grubbe for the treatment of breast cancer and the irst case of the cure of malignant tumour by Radiotherapy alone was reported on a patient with squamous carcinoma of the nose. Radiation therapy is deined as the use of high-energy radiation from X-ray, gamma rays, protons, neutrons, and other sources to kill cancer cells and shrink tumours. Radiation therapy is the most effective non-surgical treatment of cancer. Gynaecologic cancers were among the irst malignancies treated with ionizing radiation more than 100 years ago. It remains an essential component of both as primary treatment and adjuvant post-operative treatment of selected gynaecological malignancies. Radiation therapy can also be palliative in metastatic disease and frequently used to alleviate the symptoms as a result of tumour invasion such as in bone, spine and brain metastases. The most commonly used radiations in clinical practise are X-ray and gamma ray. These two types of radiations are a form of electromagnetic radiation with shorter wavelength than heat and light: also known as the high-energy photon. Both have similar properties but from different origins. Gamma ray originates from the nucleus emitted from a radioisotope, while X-ray originates from outside the nucleus, produced by bombardment of a target by high-speed electrons. Apart from high-energy photon, irradiation can also exist in particulate form (particle radiation) such as electron, proton, neutron and alpha particle.
eBook - PDF- Mitsuru Nenoi(Author)
- 2015(Publication Date)
- IntechOpen(Publisher)
Other proposed approaches include intraoperative irradiation, in which a large dose of external radiation is directed on to the tumor or tumor bed during surgery, thanks to conven‐ tional use of dedicated mobile linear accelerators. Other investigational techniques include the particle beam radiation therapy based on the acceleration of proton or ions to treat localized cancers. The acceleration of these particles requires very sophisticated machines generating modulated or conformal beams to damage tumor cells. Several of these particles, depending on their energy, could produce damage radiobiologically more efficacious than conventional Radiotherapy on both tumor and normal tissues, the latter spared by using very conformal dose distributions. Other recent Radiotherapy modalities are based on radiolabeled antibodies to deliver doses of radiation directly to the cancer site due the presence of tumor-specific antibodies (radioim‐ munotherapy) or in general radionuclides, which thank to their chemical features or their direct injection in the target tissue/tumor bed can target more precisely. The success of this technique will depend upon both the identification of appropriate radioactive substances and the determination of the safe and effective dose of radiation that can be delivered in this way. Scientists are also looking for ways to increase the effectiveness of existing radiation therapy techniques, based on investigational drugs including radiosensitizers, which make the tumor cells more likely to be damaged, radioprotectors, which protect normal tissues from the effects of radiation, or anti-angiogenic drug, interfering with the neo-angiogenic process. Hyperther‐ mia, or the use of heat, is also being studied for its effectiveness in sensitizing tissues to radiation. 3. New methodology in Radiotherapy Radiation therapy (RT) is an integrated part of the modern comprehensive cancer manage‐ ment.
- Angela Newing(Author)
- 1999(Publication Date)
- ICP(Publisher)
Gross damage occurs during cell mitosis and this eventually kills the cell even though it may be capable of a few further divisions. Ionisation occurs in all living tissue, both normal and abnormal, and the success of treatment depends upon recovery of normal tissues and destruction of cancer cells. There will always be a greater number of cancer cells under-going mitotic division than normal cells undergoing division, and therefore a greater probability of killing cancer cells. Radiotherapy must be delivered with great geometrical accuracy and dose fractionation must be correct. The Radiotherapy physicist has three main functions: 1. To ensure that the doses delivered are accurate. 2. To decide on the best combination of radiation fields which will give the highest dose to the tumour volume and the lowest possible to surrounding normal tissue. 3. To advise on appropriate shielding around Radiotherapy installations, and make any necessary radiation protection measurements from time to time. Treatment with Ionising Radiation 61 The Action of Radiation on Tissue Irradiation causes ionisation within cells which can lead to cell death because of damage to the DNA molecules. The interaction with cell processes is extremely complex, and the reader is referred to various works on radiation biology for fuller explanation, (4), but the effectiveness of Radiotherapy treatment depends upon an understanding of radiation damage. The average energy expenditure per ion pair formed in air by X-rays is approximately 34 eV. About half of this is due to ionisation and half to excitation in air atoms. The time scale of the physical interaction resulting in an ionisation event is about 10 13 s and, in human tissue, this initial event is followed by a chemical phase and then a biological one. During the chemical phase of about 10 9 s, short lived free radicals are produced which interact with each other and with the surrounding tissue.
eBook - PDF- Eddy Estlin, Stephen Lowis(Authors)
- 2005(Publication Date)
- Mac Keith Press(Publisher)
Damage to cells is caused by the effect of radio-therapy on DNA, with cell death resulting from DNA strand breaks, apoptosis or necrosis. The interaction of radiation with matter – in particular, living tissue - is a function of the energy of the radiation, the type of radiation (photon, electron, protons, alpha particles), and the tissue itself. For example, a photon with energy between 50 and 550 keV typically produces Compton scattering: a photon interacts with an outer electron of an atom, and transfers part of its energy to that electron. The photon is scattered, and the electron is ejected from the atom, to impart its energy to another atom. The scattered photon, which has a lower energy than the original, may go on to interact with another electron, and may transfer all of its energy, producing a so-called photo-electron. The interaction of photons with matter is infrequent compared to other forms of radiation, and the beam may penetrate to deep within the exposed tissue. The interaction of charged particles – electrons, protons and alpha particles – differs significantly. Electrical interactions with matter are frequent, and result in more complete 163 transfer of energy to the tissue within a shorter interval. Interactions lead to excitation of atoms – promotion of an inner orbital electron to an outer orbit – or ionization, with ejection of an electron from the atom. The absorbed dose of energy per unit mass from Radiotherapy is measured in Grays (1 Gy = 1 Joule/kg), and the amount of energy transferred to a tissue by a radiation beam per unit distance is referred to as the linear energy transfer (LET). Photons have a low LET, are relatively sparing of superficial structures such as skin, and will pene-trate right through the patient. Electrons, protons and alpha particles have a high LET, and deposit their energy within a few centimetres of the skin surface.
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