Perspectives on interstitial photodynamic therapy for malignant tumors

Abstract

Significance: Despite remarkable advances in the core modalities used in combating cancer, malignant diseases remain the second largest cause of death globally. Interstitial photodynamic therapy (IPDT) has emerged as an alternative approach for the treatment of solid tumors.

Aim: The aim of our study is to outline the advancements in IPDT in recent years and provide our vision for the inclusion of IPDT in standard-of-care (SoC) treatment guidelines of specific malignant diseases.

Approach: First, the SoC treatment for solid tumors is described, and the attractive properties of IPDT are presented. Second, the application of IPDT for selected types of tumors is discussed. Finally, future opportunities are considered.

Results: Strong research efforts in academic, clinical, and industrial settings have led to significant improvements in the current implementation of IPDT, and these studies have demonstrated the unique advantages of this modality for the treatment of solid tumors. It is envisioned that further randomized prospective clinical trials and treatment optimization will enable a wide acceptance of IPDT in the clinical community and inclusion in SoC guidelines for well-defined clinical indications.

Conclusions: The minimally invasive nature of this treatment modality combined with the relatively mild side effects makes IPDT a compelling alternative option for treatment in a number of clinical applications. The adaptability of this technique provides many opportunities to both optimize and personalize the treatment.

Keywords: dosimetry; interstitial photodynamic therapy; photosensitizers; solid tumors.

Fig. 1

IPDT framework comprising four stages: initial profiling, pretreatment planning, treatment delivery and real-time feedback, and posttreatment outcome assessment.

Fig. 2

(a) Six-fiber IPDT system with diagnostic and treatment capability: top panels present diagnostic mode (left) and treatment mode (right) of operation; bottom panels depict the diagrams of fiber arrangement for the diagnostic (left) and therapeutic mode (right). Reproduced with permission from Ref. , courtesy of SPIE and OSA. (b) IPDT setup with real-time spectroscopic monitoring for brain tumors. Inset shows a photograph of the clinical setting during IPDT procedure. Reproduced with permission from Ref. , courtesy of Wiley. (c) IPDT prostate treatment: guidance with TOOGUIDE software (left), dedicated laser generator (middle), and preoperative view of vascular-targeted photodynamic therapy in action (right). Reproduced with permission from Ref. , courtesy of Springer Nature (based on CC BY license).

Fig. 3

Illustration of dose plan for focal prostate PDT, in which the right posterior side of the prostate is targeted using seven bare fibers as sources. The dose unit is $\mathrm{J}/{\mathrm{cm}}^2$. The upper chart shows the DVH with the dose threshold indicated at $20\mathrm{J}/{\mathrm{cm}}^2$. The images show the isodose curves overlaid on US images and segmentations of prostate (in red), urethra (in yellow), and rectum (in brown). The lower right chart shows the total light illumination time durations per fiber.