Simultaneous ThermoBrachytherapy: Electromagnetic Simulation Methods for Fast and Accurate Adaptive Treatment Planning.

Ioannis Androulakis,Inger-Karine K Kolkman-Deurloo,Gerard C Van Rhoon,Rob M C Mestrom,Miranda E M C Christianen

doi:10.3390/s22041328

Abstract

The combination of interstitial hyperthermia treatment (IHT) with high dose rate brachytherapy (HDR-BT) can improve clinical outcomes since it highly enhances the efficiency of cell kill, especially when applied simultaneously. Therefore, we have developed the ThermoBrachy applicators. To effectively apply optimal targeted IHT, treatment planning is considered essential. However, treatment planning in IHT is rarely applied as it is regarded as difficult to accurately calculate the deposited energy in the tissue in a short enough time for clinical practice. In this study, we investigated various time-efficient methods for fast computation of the electromagnetic (EM) energy deposition resulting from the ThermoBrachy applicators. Initially, we investigated the use of an electro-quasistatic solver. Next, we extended our investigation to the application of geometric simplifications. Furthermore, we investigated the validity of the superpositioning principle, which can enable adaptive treatment plan optimization without the need for continuous recomputation of the EM field. Finally, we evaluated the accuracy of the methods by comparing them to the golden standard Finite-Difference Time-Domain calculation method using gamma-index analysis. The simplifications considerably reduced the computation time needed, improving from >12 h to a few seconds. All investigated methods showed excellent agreement with the golden standard by showing a >99% passing rate with 1%/0.5 mm Dose Difference and Distance-to-Agreement criteria. These results allow the proposed electromagnetic simulation method to be used for fast and accurate adaptive treatment planning.

Highlights

In the treatment of prostate cancer, interstitial high dose rate brachytherapy (HDR-BT)is commonly used either as monotherapy or in combination with external beam radiotherapy [1]
The benefit of using interstitial hyperthermia together with interstitial brachytherapy has been shown in vivo [10], while clinical studies have shown good heating characteristics in sequential HDR-BT and IHT prostate cancer treatment [11]
About the effect of distance between electrodes, we see that the larger distance between row 2 and 3 in the y axis of Figure 4e–h compared to Figure 4a–d, leads to a drop in specific absorption rate (SAR), while the shorter distance between rows 1 and 2 in the x-axis leads to a higher SAR density

Summary

Introduction

In the treatment of prostate cancer, interstitial high dose rate brachytherapy (HDR-BT)is commonly used either as monotherapy (mainly for low and favorable intermediaterisk prostate cancer) or in combination with external beam radiotherapy (in high-risk prostate cancer) [1]. In the treatment of prostate cancer, interstitial high dose rate brachytherapy (HDR-BT). Attempts to deliver an adequate radiation dose to the target in these ultrahypofractionated treatments have increased stress on the neighboring organs at risk (OAR), and so far, attempts to go to a single fraction monotherapy treatment have shown discouraging results [3,4]. Whether simultaneous RT+HT is superior over sequential RT+HT depends on the ability to preferentially deliver the RT and HT to the target, aiming at achieving maximum protection of the healthy surrounding tissue and OAR. The benefit of using interstitial hyperthermia together with interstitial brachytherapy has been shown in vivo [10], while clinical studies have shown good heating characteristics in sequential HDR-BT and IHT prostate cancer treatment [11]

Methods

Results

Discussion

Conclusion