Evaluation of Light Fluence Distribution Using an IR Navigation System for HPPH-mediated Pleural Photodynamic Therapy (pPDT)

Abstract

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.

Figure 1.

Modified endotracheal (ET) tube fitted with a laser fiber inside 0.01% intralipid is used as treatment delivery wand. A stainless steel rod fit with a custom-shaped 360 degree 9-reflective ball mount was attached to the side of the treatment delivery wand to aid the determination of laser source position.

Figure 2.

Laser source positioning calibration devices are used to determine the shift between the laser source position inside the ET tube and the tip of the stainless steel rod. The device is composed of 4 poles positioned at equal distances (5 cm) from the central pole, which holds an isotropic detector. Light fluence rate was measured at these 4 positions plus another 4 positions when the 4-cm ET tube filled with 0.1% intralipid was in contact with the detector at front, back, right, left positions.

Figure 3.

Detector positions inside a patient’s pleural cavity contour determined from raw data.

Figure 4.

Time and distance from the center of effective data (i.e., none of the reflective markers are blocked during PDT treatment) acquired throughout the entire course of PDT treatment of a representative patient (Case No. 013).

Figure 5.

Measured (blue solid line) light fluence data over the course of treatment along with calculated (red ‘x’) light fluence using the direct component plotted for 7 detector locations (Case No. 013): (a) anterior chest wall (ACW), (b) apex, (c) anterior sulcus (AS), (d) posterior chest wall (PCW), (e) pericardium (Peri), (f) posterior mediastinum (PM), and (g) posterior sulcus (PS).

Figure 6.

Measured (blue solid line) light fluence data over the course of treatment along with calculated (red ‘x’) light fluence using the direct component with fixed scattered light plotted for 7 detector locations (Case No. 013): (a) anterior chest wall (ACW), (b) apex, (c) anterior sulcus (AS), (d) posterior chest wall (PCW), (e) pericardium (Peri), (f) posterior mediastinum (PM), and (g) posterior sulcus (PS).

Figure 7.

Measured (blue solid line) light fluence data over the course of treatment along with calculated (red ‘x’) light fluence using the direct component with fixed scattered light and the dual correction method plotted for 7 detector locations (Case No. 013): (a) anterior chest wall (ACW), (b) apex, (c) anterior sulcus (AS), (d) posterior chest wall (PCW), (e) pericardium (Peri), (f) posterior mediastinum (PM), and (g) posterior sulcus (PS).

Figure 8.

Fluence distribution map for a representative patient (Case No. 013). The 3D geometry is unwrapped and displayed on a 2D surface plot. Locations of 7 isotropic detectors are indicated by ‘x’ symbols.

Figure 9.

Fluence distribution for all patients along the z-axis (depth) for each angular location. The mean is shown in a solid black line and the standard deviation is indicated by the grey shaded area. Uniformity is calculated as percent variation and summarized for each patient in Table 5.