Interstitial Photodynamic Therapy-A Focused Review

Abstract

Multiple clinical studies have shown that interstitial photodynamic therapy (I-PDT) is a promising modality in the treatment of locally-advanced cancerous tumors. However, the utilization of I-PDT has been limited to several centers. The objective of this focused review is to highlight the different approaches employed to administer I-PDT with photosensitizers that are either approved or in clinical studies for the treatment of prostate cancer, pancreatic cancer, head and neck cancer, and brain cancer. Our review suggests that I-PDT is a promising treatment in patients with large-volume or thick tumors. Image-based treatment planning and real-time dosimetry are required to optimize and further advance the utilization of I-PDT. In addition, pre- and post-imaging using computed tomography (CT) with contrast may be utilized to assess the response.

Keywords: brain; head and neck; interstitial photodynamic therapy; pancreatic; prostate; treatment planning.

Figure 1

Laser treatment fibers. (A) A typical 600-µm-diameter flat-cut (top), a 0.98-mm-diameter 1-cm cylindrical diffuser fiber emitting red laser light (middle), and an optically transparent plastic catheter with a 2-mm-outer diameter and a 1.45-mm-inner diameter (bottom) that can be used for insertion of cylindrical diffusers [10]; (B) Computer simulation of light propagation from a flat-cut fiber (bottom left), and a 1-cm cylindrical diffuser (bottom right) in a catheter. The black arrows point to the location of the fibers in a 2-cm-diameter spherical geometry with optical properties set to be similar to those measured for 652-nm light in a head and neck tumor by Robinson et al. [12]. A detailed description of the mathematical model and basic assumptions are given in Shafirstein et al. and Oakley et al. [13,14]. In interstitial photodynamic therapy (I-PDT), the light energy density (J/cm²) or light dose is calculated as dose volume histogram (DVH), which is the minimum light dose absorbed in a certain percentage (typically 90%) of the target volume [15].