RESUMO

Uniform light fluence distribution for patients undergoing photodynamic therapy (PDT) is critical to ensure predictable PDT outcomes. However, current practice when delivering intrapleural PDT uses a point source to deliver light that is monitored by seven isotropic detectors placed within the pleural cavity to assess its uniformity. We have developed a real-time infrared (IR) tracking camera to follow the movement of the light point source and the surface contour of the treatment area. The calculated light fluence rates were matched with isotropic detectors using a two-correction factor method and an empirical model that includes both direct and scattered light components. Our clinical trial demonstrated that we can successfully implement the IR navigation system in 75% (15/20) of the patients. Data were successfully analyzed in 80% (12/15) patients because detector locations were not available for three patients. We conclude that it is feasible to use an IR camera-based system to track the motion of the light source during PDT and demonstrate its use to quantify the uniformity of light distribution, which deviated by a standard deviation of 18% from the prescribed light dose. The navigation system will fail when insufficient percentage of light source positions is obtained (<30%) during PDT.

Assuntos

RESUMO

Successful outcome of Photodynamic therapy (PDT) depends on accurate delivery of prescribed light dose. A quality assurance program is necessary to ensure that light dosimetry is correctly measured. We have instituted a QA program that include examination of long term calibration uncertainty of isotropic detectors for light fluence rate, power meter head intercomparison for laser power, stability of the light-emitting diode (LED) light source integrating sphere as a light fluence standard, laser output and calibration of in-vivo reflective fluorescence and absorption spectrometers. We examined the long term calibration uncertainty of isotropic detector sensitivity, defined as fluence rate per voltage. We calibrate the detector using the known calibrated light fluence rate of the LED light source built into an internally baffled 4″ integrating sphere. LED light sources were examined using a 1mm diameter isotropic detector calibrated in a collimated beam. Wavelengths varying from 632nm to 690nm were used. The internal LED method gives an overall calibration accuracy of ±4%. Intercomparison among power meters was performed to determine the consistency of laser power and light fluence rate measured among different power meters. Power and fluence readings were measured and compared among detectors. A comparison of power and fluence reading among several power heads shows long term consistency for power and light fluence rate calibration to within 3% regardless of wavelength. The standard LED light source is used to calibrate the transmission difference between different channels for the diffuse reflective absorption and fluorescence contact probe as well as isotropic detectors used in PDT dose dosimeter.

RESUMO

Accurate light dosimery is critical to ensure consistent outcome for pleural photodynamic therapy (pPDT). Ellipsoid shaped cavities with different sizes surrounded by turbid medium are used to simulate the intracavity lung geometry. An isotropic light source is introduced and surrounded by turbid media. Direct measurements of light fluence rate were compared to Monte Carlo simulated values on the surface of the cavities for various optical properties. The primary component of the light was determined by measurements performed in air in the same geometry. The scattered component was found by submerging the air-filled cavity in scattering media (Intralipid) and absorbent media (ink). The light source was located centrally with the azimuthal angle, but placed in two locations (vertically centered and 2 cm below the center) for measurements. Light fluence rate was measured using isotropic detectors placed at various angles on the ellipsoid surface. The measurements and simulations show that the scattered dose is uniform along the surface of the intracavity ellipsoid geometries in turbid media. One can express the light fluence rate empirically as ϕ =4S/As *Rd/(1 - Rd), where Rd is the diffuse reflectance, As is the surface area, and S is the source power. The measurements agree with this empirical formula to within an uncertainty of 10% for the range of optical properties studied. GPU voxel-based Monte-Carlo simulation is performed to compare with measured results. This empirical formula can be applied to arbitrary geometries, such as the pleural or intraperitoneal cavity.

RESUMO

Uniform delivery of light fluence is an important goal for photodynamic therapy. We present summary results for an infrared (IR) navigation system to deliver light dose uniformly during intracavitory PDT by tracking the movement of the light source and providing real-time feedback on the light fluence rate on the entire cavity surface area. In the current intrapleural PDT protocol, 8 detectors placed in selected locations in the pleural cavity monitor the light doses. To improve the delivery of light dose uniformity, an IR camera system is used to track the motion of the light source as well as the surface contour of the pleural cavity. A MATLAB-based GUI program is developed to display the light dose in real-time during PDT to guide the PDT treatment delivery to improve the uniformity of the light dose. A dualcorrection algorithm is used to improve the agreement between calculations and in-situ measurements. A comprehensive analysis of the distribution of light fluence during PDT is presented in both phantom conditions and in clinical cases.

RESUMO

The goal of this study was to develop and improve an infrared (IR) navigation system to deliver light dose uniformly during intracavitory PDT by tracking the movement of the light source and providing real-time feedback on the light fluence rate on the entire cavity surface area. In the current intrapleural PDT protocol, several detectors placed in selected locations in the pleural cavity monitor the light doses. To improve the delivery of light dose uniformity, an IR camera system is used to track the motion of the light source as well as the surface contour of the pleural cavity. Monte-Carlo simulation is used to improve the calculation algorithm for the effect of light that undergoes multiple scattering along the surface in addition to an improvement of the direct light calculation using an improved model that accounts for the anisotropy of the light from the light source.

RESUMO

Determination of optical properties (absorption (µa) and scattering (µs') coefficients) in human tissue is important when it comes to accurate calculation of fluence rate in and around tissue area. ALA application to the tissue induces production of protoporphyrin IX when activated by red light. Changes in the tissue optical properties can send information such as treatment outcome and tissue drug concentration. Patients in this study were treated with PDT for head and neck mucosal dysplasia. They were enrolled in a phase I study of escalating light doses and oral ALA with 60mg/kg. Red light at 630nm was administered to the tumor from a laser. The light dose was escalated from 50-200J/cm2 with a measured fluence rate at tissue surface of 100mW/cm2. We developed a light detection device for the purpose of determining optical properties in vivo using the semi-infinite method. The light detection device consists of two parallel, placed 5mm apart. In one of the catheters a 2 mm long linear diffusing light source is placed while in the second catheter, a calibrated isotropic detector is placed. The detector is scanned along the length of the light source containing catheter. Scans are done with the device placed on the treatment area (tumor) and on the normal tissue. Optical properties were measured in-vivo before and after PDT delivery for both normal tissue and tumor.

RESUMO

In-vivo light dosimetry for patients undergoing photodynamic therapy (PDT) is critical for predicting PDT outcome. Patients in this study are enrolled in a Phase I clinical trial of HPPH-mediated PDT for the treatment of non-small cell lung cancer with pleural effusion. They are administered 4mg per kg body weight HPPH 48 hours before the surgery and receive light therapy with a fluence of 15-45 J/cm2 at 661 and 665nm. Fluence rate (mW/cm2) and cumulative fluence (J/cm2) are monitored at 7 sites during the light treatment delivery using isotropic detectors. Light fluence (rate) delivered to patients is examined as a function of treatment time, volume and surface area. In a previous study, a correlation between the treatment time and the treatment volume and surface area was established. However, we did not include the direct light and the effect of the shape of the pleural surface on the scattered light. A real-time infrared (IR) navigation system was used to separate the contribution from the direct light. An improved expression that accurately calculates the total fluence at the cavity wall as a function of light source location, cavity geometry and optical properties is determined based on theoretical and phantom studies. The theoretical study includes an expression for light fluence rate in an elliptical geometry instead of the spheroid geometry used previously. The calculated light fluence is compared to the measured fluence in patients of different cavity geometries and optical properties. The result can be used as a clinical guideline for future pleural PDT treatment.

RESUMO

This study examines the light fluence (rate) delivered to patients undergoing pleural PDT as a function of treatment time, treatment volume and surface area. The accuracy of treatment delivery is analyzed as a function of the calibration accuracies of each isotropic detector and the calibration integrating sphere. The patients studied here are enrolled in a Phase I clinical trial of HPPH-mediated PDT for the treatment of non-small cell lung cancer with pleural effusion. Patients are administered 4mg per kg body weight HPPH 24-48 hours before the surgery. Patients undergoing photodynamic therapy (PDT) are treated with light therapy with a fluence of 15-60 J/cm2 at 661nm. Fluence rate (mW/cm2) and cumulative fluence (J/cm2) is monitored at 7 different sites during the entire light treatment delivery. Isotropic detectors are used for in-vivo light dosimetry. The anisotropy of each isotropic detector was found to be within 15%. The mean fluence rate delivery and treatment time are recorded. A correlation between the treatment time and the treatment volume is established. The result can be used as a clinical guideline for future pleural PDT treatment.

RESUMO

In-vivo light dosimetry for patients undergoing photodynamic therapy (PDT) is one of the critical dosimetry quantities for predicting PDT outcome. This study examines the relationship between the PDT treatment time and thoracic treatment volume and surface area for patients undergoing pleural PDT. In addition, the mean light fluence (rate) and its accuracy were quantified. The patients studied here were enrolled in Phase II clinical trial of Photofrin-mediated PDT for the treatment of non-small cell lung cancer with pleural effusion. The ages of the patients studied varied from 34 to 69 years old. All patients were administered 2mg per kg body weight Photoprin 24 hours before the surgery. Patients undergoing photodynamic therapy (PDT) are treated with laser light with a light fluence of 60 J/cm2 at 630nm. Fluence rate (mW/cm2) and cumulative fluence (J/cm2) was monitored at 7 different sites during the entire light treatment delivery. Isotropic detectors were used for in-vivo light dosimetry. The anisotropy of each isotropic detector was found to be within 30%. The mean fluence rate deliver varied from 37.84 to 94.05 mW/cm2 and treatment time varied from 1762 to 5232s. We found a linear correlation between the total treatment time and the treatment area: t (sec) = 4.80 A (cm2). A similar correlation exists between the treatment time and the treatment volume: t (sec) = 2.33 V (cm3). The results can be explained using an integrating sphere theory and the measured tissue optical properties assuming that the saline liquid has a mean absorption coefficient of 0.05 cm-1. Our long term accuracy studies confirmed light fluence rate measurement accuracy of ±10%. The results can be used as a clinical guideline for future pleural PDT treatment.

RESUMO

The object of this study is to develop optimization procedures that account for both the optical heterogeneity as well as photosensitizer (PS) drug distribution of the patient prostate and thereby enable delivery of uniform photodynamic dose to that gland. We use the heterogeneous optical properties measured for a patient prostate to calculate a light fluence kernel (table). PS distribution is then multiplied with the light fluence kernel to form the PDT dose kernel. The Cimmino feasibility algorithm, which is fast, linear, and always converges reliably, is applied as a search tool to choose the weights of the light sources to optimize PDT dose. Maximum and minimum PDT dose limits chosen for sample points in the prostate constrain the solution for the source strengths of the cylindrical diffuser fibers (CDF). We tested the Cimmino optimization procedures using the light fluence kernel generated for heterogeneous optical properties, and compared the optimized treatment plans with those obtained using homogeneous optical properties. To study how different photosensitizer distributions in the prostate affect optimization, comparisons of light fluence rate and PDT dose distributions were made with three distributions of photosensitizer: uniform, linear spatial distribution, and the measured PS distribution. The study shows that optimization of individual light source positions and intensities are feasible for the heterogeneous prostate during PDT.