**1. Introduction**

A significant issue associated with existing radiotherapy approaches is that agents that deliver dose to tumor cells also irradiate healthy tissue [1–6]. Short-term as well as long-term detriments can appear following radiotherapy procedures. These effects occur when healthy tissue outside the target volume is irradiated and affect the patient's subsequent recovery and quality of life. For example, short-term detriments (e.g., incontinence and erectile dysfunction) occur following prostate cancer therapy [7]. Long-term effects include secondary cancers and cardiovascular disease [8]. In view of these detriments, alternative therapy approaches that preferentially deliver dose to the target tissue are of interest and should be investigated.

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This chapter considers two approaches that have the potential to significantly minimize the dose to healthy tissue while maximizing the dose delivered to the target tissue. The first technique utilizes internal radiation-generating devices that are in their conceptual development phase, and the second is an enhancement of the 90Y microsphere approach that has been successfully utilized to treat liver cancers by disrupting the tumor's vasculature.

Heavy ions, neutrons, protons, and other radiation types have numerous applications for treating a variety of cancers [1–3, 6, 9–14]. To date, these techniques have focused on beams originating outside the body. These external beams selectively irradiate the tumor mass, but still deliver some dose to healthy tissue. This chapter investigates the possibility of using radiation-generating devices that would be implanted within a tumor to preferentially irradiate its volume and develops their requisite characteristics to permit the selective irradiation of tumors. These devices are postulated to have a size on the order of 10−6 m [1–3, 6].

Microspheres offer a unique approach that has the potential to impact tumor cells by disrupting their vascular structure. A number of authors [15, 16] have proposed a therapy approach that prevents the development of the tumor's vascular supply. Vascular disruption agents incorporate both chemotherapy [17, 18] as well as radiotherapy [18–27]. Radiotherapy vascular disruption techniques utilizing 90Y microspheres, including anti-angiogenic and radioembolization therapies, are used to treat liver cancers [18–23]. Other radionuclides (e.g., 32P) are under investigation, but radiation types other than high-energy beta particles are not under active consideration [22].
