Radiotherapy toxicity is generally separated into acute toxicity and long-term toxicity Acute toxicity occurs during or shortly after the radiotherapy whereas long-term toxic-ity can manifest itself months to years after the completion of the treatment. Both acute and long-term toxicities show a dose-threshold and therefore fit into the realm ofdeter-ministic responses to radiation (as opposed to cancer development which is considered a stochastic response with no threshold).
It is generally accepted that acute toxicity occurs by direct cytotoxicity to rapidly proliferating normal tissue cells. The exact etiology behind long-term radiotherapy toxicity is somewhat a matter of controversy. The two major theories are (1) that long-term toxicity is caused by the depletion of slowly proliferating stem cells and (2) that long-term damage is related to damage to the vasculature. In actuality, the exact etiology is probably much more complex than our current level ofunderstanding permits, involving depletion ofstem cells, changes in vasculature, and alterations in cellular factors including cytokines, small molecular mediators, and others.
As advances in treatment modalities are made, more focus is shifting to a close examination of quality-of-life issues. They are particularly relevant to radiation therapy since the consequences of toxicity can be debilitating and dramatically affect bodily function. Even when disease is controlled, the short- and long-term effects of radiotherapy can have a significant impact on the quality-of-life. Patients who receive curative radiotherapy for head and neck cancers are often left with a dry mouth and consequently have great difficulty in eating and swallowing. Patients who receive pelvic radiotherapy will in many instances be left with sexual difficulties.
The purpose of this book is to provide a framework for considering normal toxicities when using radiotherapy for cancer treatment. While long-term toxicities often cannot be reversed, approaches have been developed that will permit a reasonable quality of life. Considerations to be made in treatment decisions, approaches to alleviate some consequences of tissue toxicity, and other similar matters are all discussed in the chapters that follow. It is hoped that this will be a guide to the Radiation Oncologist, Medical Oncologist, Oncology Nurses, Radiation Therapists, and all who are involved in treatment of patients with radiation.
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