Most photosensitizers absorb light at a specific wavelength which produces maximal photodynamic effect and can be delivered from a laser directed along optical fibres. The use of fibres has allowed treatment of both superficial lesions, and interstitial treatments, as the fibres can be inserted directly to the target organ. The patient is placed in the lithotomy position, under general anaesthetic, in a darkened operating theatre with eye and skin protection. The optical fibres are inserted transperineally using a brachytherapy template on a stepper device, guided with transrectal ultrasound imaging (see Fig. 21.1). Fibres may be either bare ended, with light directly emitted from the end of the fibre, or cylindrical, with a diffusing end. For bare-ended fibres, light is distributed in all directions from the end of the fibre, like a torch or flashlight, and the light dose is measured in J/cm². The dose from the active length of cylindrical fibres is measured in J/cm, comparable to a ‘strip light’. Bare-ended fibres allow light delivery along a given length at the distal end of the fibre and can be used for superficial treatments using endoscopic access to hollow organs or on the skin itself. Cylindrical diffusers are more commonly used for treatments in solid organs, such as the prostate.

In preclinical studies, optical fibres were also inserted either with an open technique at laparotomy. Although technically feasible for human treatments, open fibre insertion would be inappropriate considering the other available options (transurethral/transperineal). In animal studies, the transurethral approach was associated with urethral strictures and has not been clinically evaluated for use in treatment of prostate cancer (Selman and Keck 1994). In current clinical trials, treatment is delivered using a transperineal template and transrectal ultrasound guidance.

Treatment planning may be either done prior to treatment with a ‘rule-based’ approach or with a ‘real-time’ approach during treatment itself, using feedback from light, drug and oxygen measurements (Moore et al. 2011). With individualised pretreatment planning, account can be made for anatomical variations, with predetermination of the number and position of treatment fibres and light characteristics. The first reported clinical demonstration of patient-specific treatment planning for photodynamic therapy was in the TOOKAD study of recurrent prostate cancer (Davidson et al. 2009). The largest studies of this vascular-targeted PDT for prostate cancer used MR imaging to determine prostate anatomy prior to treatment, with subsequent planning of fibre placement. A retrospective review of patients treated with the water-soluble WST-11 was used to produce a model for treatment planning, with demonstration of correlation between the treatment plan and posttreatment MR imaging (Betrouni et al. 2011). In the TOOKAD study currently underway, a study committee remotely determines the treatment plan, which is sent to the treating centres prior to the scheduled treatment.

Pretreatment planning has some disadvantages, including the anatomical deformation due to the effect of the rectal ultrasound probe and intra-operative swelling of the prostate due to fibre insertion and treatment effect. Even for a pretreatment MR-based plan, it may well be necessary to alter the grid positions and add or exclude light delivery fibres once the prostate is seen under real-time ultrasound guidance.

Canine studies have demonstrated the feasibility of real-time treatment planning modified according to light dose received (Jankun et al. 2005), and it has been reported in a small cohort of patients (Swartling et al. 2010

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