1H magnetic resonance imaging of normal brain tissue response to photodynamic therapy

Diffusion-weighted MRI for monitoring tumor response to photodynamic therapy

PURPOSE

To examine diffusion-weighted MRI (DW-MRI) for assessing the early tumor response to photodynamic therapy (PDT).

MATERIALS AND METHODS

Subcutaneous tumor xenografts of human prostate cancer cells (CWR22) were initiated in athymic nude mice. A second-generation photosensitizer, Pc 4, was delivered to each animal by a tail vein injection 48 h before laser illumination. A dedicated high-field (9.4 Tesla) small animal MR scanner was used to acquire diffusion-weighted MR images pre-PDT and 24 h after the treatment. DW-MRI and apparent diffusion coefficients (ADC) were analyzed for 24 treated and 5 control mice with photosensitizer only or laser light only. Tumor size, prostate specific antigen (PSA) level, and tumor histology were obtained at different time points to examine the treatment effect.

RESULTS

Treated mice showed significant tumor size shrinkage and decrease of PSA level within 7 days after the treatment. The average ADC of the 24 treated tumors increased 24 h after PDT (P < 0.001) comparing with pre-PDT. The average ADC was 0.511 +/- 0.119 x 10(-3) mm(2)/s pre-PDT and 0.754 +/- 0.181 x 10(-3) mm(2)/s 24 h after the PDT. There is no significant difference in ADC values pre-PDT and 24 h after PDT in the control tumors (P = 0.20).

CONCLUSION

The change of tumor ADC values measured by DW-MRI may provide a noninvasive imaging marker for monitoring tumor response to Pc 4-PDT as early as 24 h.

Photodynamic therapy of established prostatic adenocarcinoma with TOOKAD: a biphasic apparent diffusion coefficient change as potential early MRI response marker

The goal of this study was to examine the use of diffusion-weighted magnetic resonance imaging (DW-MRI) for the assessment of early progression of photodamage induced by Pd-bacteriopheophorbide (TOOKAD)-based photodynamic therapy (PDT). TOOKAD is a novel second-generation photosensitizer for PDT of solid tumors developed in our laboratory and presently under clinical trials for prostate cancer (PC) therapy. Using the subcutaneous human prostate adenocarcinoma WISH-PC14 xenografts in nude mice as a model, a unique biphasic change in the apparent diffusion coefficient (ADC) was observed within the first 24 hours post-PDT, with initial decrease followed by an increase in ADC. Using DW-MRI, this phenomenon enables the detection of successful tumor response to PDT within 7 hours posttreatment. This process was validated by direct, histological, and immunohistochemical examinations and also by evaluation of serum prostate-specific antigen (PSA) levels that decreased significantly already 7 hours posttreatment. In vitro studies of multicellular cell spheroids confirmed a PDT-induced decrease in ADC, suggesting that lipid peroxidation (LPO) significantly contributes to ADC decline observed after PDT. These results demonstrate that TOOKAD-based PDT successfully eradicates prostate adenocarcinoma xenografts and suggests DW-MRI to be useful for the detection of early tumor response and treatment outcome in the clinical setting.

Optimal light dose for interstitial photodynamic therapy in treatment for malignant brain tumors

BACKGROUND AND OBJECTIVE

The primary goal was to determine the maximal tolerable light dose that can be administered to patients undergoing multifiber interstitial photodynamic therapy (PDT) of malignant brain tumors at a fixed dose of photosensitizer.

STUDY DESIGN/MATERIALS AND METHODS

Eighteen patients (12 glioblastomas, 5 anaplastic astrocytoma, and 1 malignant ependymoma) were included in this study. The total light dose delivered to the tumor was divided into three groups of six patients each: 1,500-3,700 J, 3,700-4,400 J, and 4,400-5,900 J.

RESULTS

Five patients (all glioblastomas) demonstrated postoperative permanent neurologic deficits. None of the patients in 1,500-3,700 J, two patients in 3,700-4,400 J, and three patients in 4,400-5,900 J had neurologic deficits. Glioblastomas recurred more often than anaplastic astrocytomas. Increasing the light dose did not make a difference in local/regional control of glioblastomas. Patients with anaplastic astrocytomas survived (mean, 493 days) longer than patients with glioblastomas (mean, 116.5 days) after PDT. Four patients had prolonged survival (more than a year) after PDT.

CONCLUSIONS

Increasing the total light dose delivered to the tumor increases the odds of having a permanent neurologic deficit but does not increase survival or time to tumor progression. There was no difference in local or marginal recurrence with increasing light dose. Recurrent anaplastic astrocytomas tend to do better than recurrent glioblastomas with PDT.

Magnetic resonance imaging evaluation of photodynamic therapy-induced hemorrhagic necrosis in the murine M1 tumor model

Proton magnetic resonance imaging (MRI) and histological methods were used to evaluate photodynamic therapy (PDT)-induced hemorrhagic necrosis in the murine M1 tumor within 72 h of treatment of male DBA/2 mice. The effects of three photosensitizing drugs were investigated: Photofrin (n = 4), Zn (II) phthalocyanine (n = 7) and benzoporphyrin derivative monoacid ring A (n = 11). As noted in previous studies of PDT using MRI, MRI makes possible serial, noninvasive, in vivo observation of tissue response to PDT. Our serial study of MRI and histological data confirms that tumors responded in the same way to PDT treatment using the three photosensitizing drugs: vascular damage followed by hemorrhagic necrosis. Most importantly and unlike previous MRI studies of PDT, we used a very high field magnet that enhanced the effect of magnetic susceptibility on image signal when blood is processed by the body after PDT-induced hemorrhagic necrosis. This last finding demonstrates the utility of high field magnets and the importance of localized, serial experiments in future magnetic resonance studies of PDT.