Imaging and dosimetry for radium-223: the potential for personalized treatment

Abstract

Radium-223 (²²³Ra) offers a new option for the treatment of bone metastases from prostate cancer. As cancer treatment progresses towards personalization, the potential for an individualized approach is exemplified in treatments with radiotherapeutics due to the unique ability to image in vivo the uptake and retention of the therapeutic agent. This is unmatched in any other field of medicine. Currently, ²²³Ra is administered according to standard fixed administrations, modified according to patient weight. Although gamma emissions comprise only 1% of the total emitted energy, there are increasing reports that quantitative imaging is feasible and can facilitate patient-specific dosimetry. The aim of this article is to review the application of imaging and dosimetry for ²²³Ra and to consider the potential for treatment optimization accordingly, in order to ensure clinical and cost effectiveness of this promising agent.

Figure 1.

Radiopharmaceutical treatments of bone metastases. ²²³Ra, radium-223; ¹⁵³Sm EDTMP, samarium-153 ethylenediamine tetra(methylene phosphonic acid); ⁸⁹Sr, strontium-89. Adapted from Rojas et al.

Figure 2.

Energy spectrum for radium-223 (acquired for a standard, using medium-energy collimators on a Philips Forte camera).

Figure 3.

Anterior scans of radium-223 at days 0, 1, 2, 3 and 6 following administration of 55 kBq/kg.

Figure 4.

Absorbed doses delivered to bone surfaces from six patients treated twice with 55 kBq kg⁻¹ radium-223 with a 6-week interval.

Figure 5.

Incidence of bone sarcomas as a function of the absorbed dose to the skeleton. Adapted from Rowland.