**5. Conclusions**

Dose localization within an arteriole wall could be achieved using 1.0–1.5 MeV proton beams. Alpha particles with energies below 3 MeV will not penetrate the arteriole wall. The arteriole wall is disrupted, with minimal dose to surrounding tissue, by alpha particles in the 4–5 MeV energy range. Sufficient absorbed dose to disrupt vessels with wall thicknesses between 20

12C ions with energies below about 20 MeV do not penetrate the arteriole wall, and 20–50 MeV ions will deposit sufficient energy into a range of vessel wall thicknesses in the 20–100 μm range to produce vascular disruption. Selective arteriole wall disruption is achieved using 25–30 MeV 12C ions. However, the generation of 12C, 20Ne, and 40Ca ions is a more significant

20Ne ions below 30 MeV do not penetrate the arteriole wall. 20Ne ions in the range of 50–110 MeV will be sufficient to reach the range of vessel wall thicknesses addressed in this chapter. Arteriole wall disruption with minimal dose to surrounding tissue is achieved using 50–70 MeV 20Ne ions. In a similar manner, 40Ca ions require 150–200 MeV to selectively disrupt the arteriole

**Table 2** illustrates that photon energies in the range of 15–50 keV can deposit the requisite absorbed dose to disrupt an arteriole wall. Significant dose is also deposited in the 20–100 μm

Internal radiation-generating devices can also be developed to emit low-energy electrons. Electrons present a concern because their bremsstrahlung radiation can irradiate healthy tissue beyond the target volume. However, low-energy electrons preferentially irradiate the arteriole wall with minimal bremsstrahlung. **Table 3** summarizes the range and bremsstrah-

**Electron energy (keV) Range in water (μm) Fraction of electron energy converted** 

He, 12C, 20Ne, and 40Ca ions achieve

**into bremsstrahlung**

and 100 μm can be delivered by alpha particles having energies below 8 MeV.

technical challenge than producing lighter ions in a first generation IRGD.

wall and 100–300 MeV 40Ca ions penetrate vessel wall thicknesses of 10–75 μm.

lung production for 20–85 keV electrons impinging on the arteriole wall.

 6.79 5.26 × 10−5 10.6 6.57 × 10−5 15.1 7.89 × 10−5 20.3 9.20 × 10−5 26.1 1.05 × 10−4 39.6 1.31 × 10−4 55.1 1.58 × 10−4 72.6 1.84 × 10−4 91.8 2.10 × 10−4 102 2.23 × 10−4

**Table 3.** Vascular disruption by low-energy electrons from an internal radiation-generating device.

range by the 15–50 keV photons. However, protons and 4

better dose localization.

226 Radiotherapy

Internal radiation-generating devices and microspheres loaded with alpha-emitting radionuclides preferentially deposit dose in the target tissues while minimizing the dose delivered to healthy tissue. This selective deposition minimizes stray dose and limits the side effects that often accompany radiotherapy procedures. The microsphere approach can be realized in the near term, but an internal radiation-generating device relies on technology that is not currently available. Additional research is required to develop the techniques proposed in this chapter into practical radiotherapy protocols.
