From Simulation to Surgery: Comprehensive Validation of an Optical Sensor for Monitoring Focal Laser Ablation of Solid Organ Tumors

Focal laser ablation (FLA) is a minimally invasive procedure where a laser fiber, integrated into a catheter, is inserted into the tumor to treat it via thermal coagulation. FLA eliminates the need for tumor excision, thus reducing complications compared to conventional surgical approaches. However, its widespread adoption is hindered by the absence of reliable monitoring techniques to ensure complete coagulation of cancerous tissue while avoiding damage to surrounding healthy structures. This paper addresses a critical challenge in the FLA of solid organ tumors: the lack of an accurate, affordable, and real-time monitoring system.

Existing monitoring methods, such as MRI thermometry and thermal probes, have substantial limitations. MRI thermometry is expensive and requires specialized equipment, limiting its accessibility for widespread use. Thermal probes, though inexpensive and simple, only provide point measurements, making precise control over the ablation zone difficult. Moreover, these methods rely on the Arrhenius thermal damage model, which requires challenging tissue-specific calibration, introducing errors in tissue damage prediction. Therefore, a reliable, cost-effective solution that doesn’t depend on temperature or tissue-specific models is needed.

To address this issue, the paper introduces a novel optical sensor for real-time monitoring of FLA. The sensor uses light to monitor changes in the optical properties of the tissue as it transitions from its native to coagulated state. By placing the optical probe at the boundary of the ablation zone, the sensor detects changes in light intensity caused by the coagulation process, signaling when to terminate the laser. This ensures the creation of an accurate ablation zone, preventing undertreatment or overtreatment of the tumor.

The optical sensor was validated through three stages: Monte Carlo simulations, ex vivo studies, and clinical trials.

1. Monte Carlo Simulations: The authors conducted simulations to model how the optical sensor performs across different tissues, including prostate, liver, and brain. The simulations showed that the sensor could detect the coagulation boundary in these tissues without requiring specific tissue calibration, demonstrating its versatility and robustness.
2. Ex Vivo Studies: The sensor was then tested in ex vivo bovine liver tissue. During these studies, laser ablation was performed with real-time sensor data guiding the termination of laser exposure. The resulting ablation zones were measured using immunohistochemistry and were found to closely match the planned size, with a radial error of less than 1 mm, showcasing precise control over the ablation zone.
3. Clinical Trials: Finally, the sensor was tested in a clinical trial for prostate cancer treatment with the induced ablation zone measured on post-operative MRI. The results demonstrated that the optical sensor could consistently differentiate between undertreatment, complete treatment, and overtreatment. In contrast, an adjacent thermal sensor was unable to provide such feedback as the prediction strongly depended on the chosen tissue calibration properties

In conclusion, the optical sensor offers several advantages over traditional methods. It does not require tissue-specific calibration, making it simpler and more reliable. It also provides real-time, accurate monitoring of the ablation zone, ensuring complete coagulation of the tumor while minimizing damage to surrounding tissues. This technology has the potential to improve the accuracy, affordability, and accessibility of FLA for tumor treatment.