Interstitial photodynamic therapy in the canine prostate.
OBJECTIVE
To determine the depth of tissue destruction and the minimum light dose required for necrosis in interstitial photodynamic therapy (PDT), as a prerequisite for the investigational therapy of patients.


METHODS
Seven adult beagle dogs were given 2 mg/kg of the photosensitizer Photofrin intravenously and two controls received none. After 24 h, 450 J/cm of 630 nm wavelength laser light was delivered interstitially to the prostate via a 2 cm long diffuser fibre. Seven single-fibre treatments were performed in five sensitized dogs and two single-fibre treatments in the controls. The two remaining sensitized dogs had two fibres placed 10 mm apart within the prostate to determine the coalescence of PDT lesions. The penetration depth of light was measured in all prostates, and after PDT the extent of necrosis was assessed histologically.


RESULTS
The mean (standard deviation, SD) radius of PDT destruction around each diffuser was 5.3 (1.4) mm and PDT lesions overlapped in prostates treated with two fibres placed 10 mm apart. There was no observable tissue damage in the controls. The mean (SD) minimum light dose required for PDT necrosis was 84 (64) J/cm2. Differences among animals in the light penetration depth were small, with a mean of 2.14 (0.2) mm, and did not correlate with the depth of necrosis (P = 0.07). Bleeding around the optical diffuser fibre impeded light penetration.


CONCLUSIONS
Interstitial PDT in the canine prostate using Photofrin produced modest volumes of tissue necrosis. The minimum light dose required to induce necrosis was variable because bleeding was unpredictable in relation to the optical fibre.
Lee
L K
LK
CRC Department of Experimental Radiation Oncology, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK.
Whitehurst
C
C
Chen
Q
Q
Pantelides
M L
ML
Hetzel
F W
FW
Moore
J V
JV
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017323:Dihematoporphyrin Ether / Q000627:therapeutic use*; D004285:Dogs; D008297:Male; D009336:Necrosis; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D011467:Prostate / Q000473:pathology / Q000528:radiation effects; D011469:Prostatic Diseases / Q000188:drug therapy* / Q000473:pathology
D000970:Antineoplastic Agents; D017319:Photosensitizing Agents; D017323:Dihematoporphyrin Ether