Response assessment and outcome of combining immunotherapy and radiosurgery for brain metastasis from malignant melanoma.

BACKGROUND: The optimal sequence of stereotactic radiotherapy (SRT) and immune checkpoint inhibition (ICI) and assessment of response in patients with brain metastases from melanoma remain challenging. METHODS: We reviewed clinical and neuroimaging data of 62 patients with melanoma, including 26 patients with BRAF-mutant tumours, with newly diagnosed brain metastases treated with ICI alone (n=10, group 1), SRT alone or in combination with other systemic therapies (n=20, group 2) or ICI plus SRT (n=32, group 3). Response was assessed retrospectively using response evaluation criteria in solid tumours (RECIST) V.1.1, response assessment in neuro-oncology (RANO) and immunotherapy RANO (iRANO) criteria. MRI follow-up from 43 patients was available for central review. RESULTS: Patients treated with ICI alone showed no objective responses and had worse outcome than patients treated with SRT without or with ICI. RECIST, RANO and iRANO criteria were concordant for complete response (CR) and partial response (PR). RANO called progression earlier than RECIST for clinical deterioration without MRI progression in some patients. Progression was called later when using iRANO criteria because of the need for a confirmatory scan. Pseudoprogression was documented in seven patients: three patients in group 2 and four patients in group 3. Radionecrosis was documented in seven patients: two patients in group 2 and five patients in group 3. Regression of non-irradiated lesions was seen neither in two patients treated with SRT alone nor in five patients treated with SRT plus ICI, providing no evidence for rare abscopal effects. CONCLUSIONS: Pseudoprogression is uncommon with ICI alone, suggesting that growing lesions in such patients should trigger an intervention. Pseudoprogression rates were similar after SRT alone or SRT in combination with ICI. Abscopal effects are rare or do not exist. Response assessment criteria should be considered carefully when designing clinical studies for patients with brain metastases who receive SRT.

Evaluation and validation of the convolution algorithm for Leksell Gamma knife radiosurgery.

The new Leksell Gamma knife convolution algorithm requires evaluation prior to implementation in clinical practice. The superiority of this algorithm, which takes into account tissue electron densities, was evaluated using EBT3 GafChromicTM films within an anthropomorphic phantom. The CIRS anthropomorphic head phantom was chosen for its relevance to validate the convolution algorithm. Absolute dose and dose distributions were measured and compared with the outputs calculated from the Leksell Gamma Plan algorithms (TMR10 and the convolution algorithm). The measured absolute dose and the dose distributions in the homogeneous region of the anthropomorphic phantom were clearly in agreement with the dose distribution computed by the convolution algorithm. In a heterogeneous region where soft tissues contain a medium, such as aluminium, or an air gap, the measured dose profiles drastically changed, and only the convolution algorithm was able to correctly compute the dose to water in water. The convolution algorithm was able to take into account regions with high or very low electron densities such that the measured absolute dose was nearly equal to that computed by the convolution algorithm, with a common accepted dose measurement error of 2%.

MRI assessment of treatment delivery for interstitial photodynamic therapy of high-grade glioma in a preclinical model.

BACKGROUND: High-grade gliomas are primary brain tumors that have shown increasing incidence and unfavorable outcomes. Local control is crucial to the management of this pathology. Photodynamic therapy (PDT), based on the light-induced activation of a photosensitizer (PS), achieves local treatment by inducing selective lesions in tumor tissue. OBJECTIVES: Previous studies have reported the outcomes of PDT for glioblastoma via immunohistological data. Our study aimed to evaluate MRI findings, including diffusion, and perfusion sequences, compared with immunohistological data from the same population to address the efficiency of light fractionation. MATERIALS AND METHODS: Twenty-six "nude" rats grafted with human U87 cells into the right putamen underwent PDT. After PS precursor (5-ALA) intake, an optical fiber was introduced into the tumor. The rats were randomized into the following groups: those without illumination and those that received two or five fractions of light. Treatment effects were assessed with early high-field MRI to measure the volume of necrosis and edema using diffusion and perfusion sequences; the MRI results were compared with immunohistology results, including necrosis and apoptosis markers. RESULTS: Elevated diffusion values were observed on MRI in the centers of the tumors of the treated animals, especially in the 5-fraction group (P < 0.01). Perfusion was decreased around the treatment site, especially in the 5-fraction group (P = 0.024). The MRI findings were consistent with previously published histological data. The median volume of necrosis was significantly different between the sham group and treated groups, 0 mm3 versus 2.67 mm3 , P < 0.001. The same trend was previously observed in histology data when grading the absence or presence of necrosis and when the presence of necrosis was significantly more predominant for the treated group than for the untreated group (P < 001). Additionally, cell death represented by apoptosis marker data (TUNEL method) was significantly higher in the 5-fraction group than in the 2-fraction group (P = 0.01). CONCLUSION: Diffusion and perfusion MRI revealed histological lesions. Interstitial PDT (iPDT) induced specific lesions in the tumor tissue, which were observed with MRI and confirmed by histopathological analysis. Thus, MRI may provide a non-invasive and reliable tool to assess treatment outcomes after PDT. Lasers Surg. Med. 50:460-468, 2018. © 2017 Wiley Periodicals, Inc.

Photodynamic therapy for glioblastoma: A preliminary approach for practical application of light propagation models.

PURPOSE: Photodynamic therapy (PDT) is a promising treatment modality to be added in the management of glioblastoma multiforme (GBM). Light distribution modeling is required for planning and optimizing PDT. Several models have been developed to predict the light propagation inside biological tissues. In the present study, two analytical methods of light propagation emitted from a cylindrical fiber source were evaluated: a discrete and a continuous method. METHODS: The two analytical approaches were compared according to their fluence rate results. Several cylindrical diffuse lengths were evaluated, and the relative deviation in the fluence rates was estimated. Moreover, a sensitivity analysis was conducted to compute the variance of each analytical model. RESULTS: The discrete method provided fluence rate estimations closer to the Monte-Carlo simulations than the continuous method. The sensitivity study results did not reveal significant differences between the variance of the two analytical models. CONCLUSIONS: Although the discrete model provides relevant light distribution, the heterogeneity of GBM tissues was not considered. With the improvement in parallel computing that drastically decreased the computing time, replacing the analytical model by a Monte-Carlo GPU-accelerated code appeared relevant to the GBM case. Nonetheless, the analytical modeling may still function in the optimization algorithms, which might be used in the Photodynamic treatment planning system. Lasers Surg. Med. 50:523-534, 2018. © 2017 Wiley Periodicals, Inc.

A novel device for intraoperative photodynamic therapy dedicated to glioblastoma treatment.

AIM: Photodynamic therapy (PDT) appears to be a valuable new treatment modality for cancer therapy. Studies have reported successful application of PDT for glioblastoma. Here, we introduce a new device dedicated to intraoperative PDT delivered early after fluoro-guided resection combined with a transfer function that determines the treatment time based on the size of the surgical resection cavity. MATERIALS & METHODS: First, we describe the device, which is composed of a trocar, a balloon filled with a diffusing solution, and a fiber guide in which a cylindrical light diffuser is inserted. Ex vivo experiments were performed to measure the fluence rate inside biological tissues. A calibration factor was defined to convert power measurements into fluence rate values. Calf brains were used to simulate light propagation in human brain tissue, and the photosensitizer administration effect on optical properties was discussed. The temperature elevation during illumination was evaluated. RESULTS: Light power was measured in tissues surrounding the device during ex vivo experiments. Using the previously characterized calibration factor, power measurements were converted to fluence rate values to obtain the transfer function. No thermal elevation was observed during a 2-h temperature test, and the impact of protoporphyrin IX on brain optical properties was considered negligible. CONCLUSION: A discussion of experimental precision is presented. The light duration determined by the abacus had a standard deviation of <1 min. This value is weak compared with the total illumination time necessary to treat one patient. The main advantage of our device lies in its straightforward implementation of intraoperative PDT for neurosurgery with acceptable dosimetry and easy treatment time.