Clinical Dosimetry Measurements In Radiotherapy

While radiation dosimetry is no longer the ¿hot topic¿ of research that it once was, new treatment modalities still have challenges to be solved and detector systems are constantly being developed. But as a relatively mature subject, there is no widely used current book devoted to clinical dosimetry. A primary purpose of producing this Summer School was to create such a text to help in the education of clinical physicists who had not had access to the forefront research into understanding radiation dosimetry. Making sure the dose delivered to the patient is what it should be is one of the most important jobs medical physicists have. There are many aspects to doing this, but at the core, the radiation must be accurately measured. One of the original major tasks of the AAPM was to establish methods which its members could use to reliably carry out this task, and it has been highly successful. There have been clinical dosimetry protocols and formalisms for brachytherapy dosimetry developed, calibration laboratories accredited, and a myriad of task group reports produced on different dosimetry techniques and delivery modalities

This book provides a first comprehensive summary of the basic principles, instrumentation, methods, and clinical applications of three-dimensional dosimetry in modern radiation therapy treatment. The presentation reflects the major growth in the field as a result of the widespread use of more sophisticated radiotherapy approaches such as intensity-modulated radiation therapy and proton therapy, which require new 3D dosimetric techniques to determine very accurately the dose distribution. It is intended as an essential guide for those involved in the design and implementation of new treatment technology and its application in advanced radiation therapy, and will enable these readers to select the most suitable equipment and methods for their application. Chapters include numerical data, examples, and case studies.

This study guide will be a reliable support and easy-to-use source of information for students in the fields of dosimetry, physics, radiation oncology, and therapy as they progress through the educational levels in preparation for board examinations. The theoretical and practical knowledge gained by students on previous courses or in clinical settings is reinforced by means of almost 1200 questions and accompanying detailed analytical answers. In order to cater for the needs of all students, the questions are arranged according to three levels of difficulty. The level 1 questions are mainly intended for those hoping to pass the Medical Dosimetrist Certification Board (MDCB) exam but will also be beneficial for Medical Physics candidates taking written exams and for Radiation Oncology residents. The level II questions are in general clinically related and will be relevant for any student, while the level III questions are advanced and are especially suitable for American Board of Radiology candidates or those taking equivalent exams elsewhere in the world. The study guide is broken down into different subject areas, with provision of multiple questions and answers on each subject. In addition, the mathematical and physics questions include brief explanations of how the student can solve each problem. At the end of the guide, three practice tests are included with the same number of questions as are found in the MDCB exam. These tests will help students to test their knowledge and improve their test-taking speed.

Practical clinical dosimetry is a fundamental step within the radiation therapy process and aims at quantifying the absorbed radiation dose within a 1-2% uncertainty. To achieve this level of accuracy, corrections are needed for calibrated and air-filled ionization chambers, which are used for dose measurement. The procedures of correction are based on cavity theory of Spencer-Attix and are defined in current dosimetry protocols. Energy dependent corrections for deviations from calibration beams account for changed ionization chamber response in the treatment beam. The corrections applied are usually based on semi-analytical models or measurements and are generally hard to determine due to their magnitude of only a few percents or even less. Furthermore the corrections are defined for fixed geometrical reference-conditions and do not apply to non-reference conditions in modern radiotherapy applications. The stochastic Monte Carlo method for the simulation of radiation transport is becoming a valuable tool in the field of Medical Physics. As a suitable tool for calculation of these corrections with high accuracy the simulations enable the investigation of ionization chambers under various conditions. The aim of this work is the consistent investigation of ionization chamber dosimetry in photon radiation therapy with the use of Monte Carlo methods. Nowadays Monte Carlo systems exist, which enable the accurate calculation of ionization chamber response in principle. Still, their bare use for studies of this type is limited due to the long calculation times needed for a meaningful result with a small statistical uncertainty, inherent to every result of a Monte Carlo simulation. Besides heavy use of computer hardware, techniques methods of variance reduction to reduce the needed calculation time can be applied. Methods for increasing the efficiency in the results of simulation were developed and incorporated in a modern and established Monte Carlo simulation environment.