The Physics of Modern Brachytherapy for Oncology PDF

Preface

This Physics of Modern Brachytherapy for Oncology is the most comprehensive brachytherapy textbook for physicists that has so far been written and intentionally includes chapters on basic physics that are necessary for an understanding of modern brachytherapy. The book therefore stands alone as a total reference book, with readers not having to consult other texts to obtain information on the basics, which are presented in Chapter 2 through Chapter 4 and are set out in a logical fashion starting with quantities and units, followed by basic atomic and nuclear physics.

It was only after the development of the atomic bomb in the Manhattan project in the late 1940s that the peaceful uses of ionizing radiation (other than radium and radon) were harnessed in medicine. This led to the introduction of ⁶⁰cobalt and ¹³⁷cesium in the late 1950s and these radionuclides replaced radium for the manufacture of tubes and needles and ¹⁹⁸gold seeds replaced the radon seeds. However, there was still a problem with the tubes and needles because a sufficiently high specific activity could not be achieved and thin malleable wire sources were impossible to make using ⁶⁰Co and ¹³⁷Cs. This was eventually overcome in the early 1960s by initially using ¹⁸²tantalum wire and later ¹⁹²iridium wire, with the latter being the standard brachytherapy source today not only for use with the Paris system but also in the form of miniature sources for use with high dose rate (HDR) afterloading machines. With radium and ¹³⁷Cs only, low dose rate (LDR) brachytherapy could be performed, again because of specific activity limitations. ⁶⁰Co was first used for HDR afterloaders but was too expensive because of the need for regular source replacements and for extended radiation protection infrastructure. ¹⁹²Ir was a cheaper option. Work continues on possibilities for the use of new radionuclides such as ²⁴¹americium, ¹⁶⁹ytterbium and ¹⁴⁵samarium, but currently the three mainstay radionuclides are ¹⁹²Ir, ¹²⁵iodine and ¹⁰³palladium. This is reflected in the contents of Chapter 5 and Chapter 6.

Dosimetry is an essential part of brachytherapy physics and has been from the earliest days when the first measurements were made by Marie Curie using the piezo electrometer designed by Pierre Curie and his brother Jacques. However, international agreement on radium dosimetry units took many years and, for example, the roentgen unit of exposure was not recommended by the ICRU as a unit of measurement for both x-rays and radium gamma rays until 1937. Previously there was a differentiation between x-ray roentgens and gamma ray roentgens. Also, prior to 1937, more than 50 proposals for radiation units had been made, depending not only on the ionization effect, but also on, for example, silver bromide photographic film blackening, fluorescence and skin erythema. The latter formed the basis of the radium dosage system developed by the physicist Edith Quimby at Memorial Hospital, New York.

The most popular unit used was the milligram-hour, which was merely the product of the milligrams of radium and the duration of the treatment. For radon, the analogous unit was millicurie-destroyed since radon had a half-life of only some 3.5 days. However, the best experimental results were made using ionization chambers, particularly those developed in the late 1920s by the physicist Rolf Sievert of the Radiumhemmet in Stockholm, who was also responsible for the Sievert integral. Source calibration and dosimetry protocols are considered in Chapter 7 and Chapter 8. Monte Carlo aided and experimental dosimetry, including gel dosimetry, which has only been available in the last decade, are the topics in Chapter 9 and Chapter 10.