Iterative time-reversal for multi-frequency hyperthermia

Abstract

Time-reversal (TR) is a known wideband array beam-forming technique that has been suggested as a treatment planning alternative in deep microwave hyperthermia for cancer treatment. While the aim in classic TR is to focus the energy at a specific point within the target, no assumptions are made on secondary lobes that might arise in the healthy tissues. These secondary lobes, together with tissue heterogeneity, may result in hot-spots (HSs), which are known to limit the efficiency of the thermal dose delivery to the tumor. This paper proposes a novel wideband TR focusing method that iteratively shifts the focus away from HSs and towards cold-spots from an initial TR solution, a procedure that improves tumor coverage and reduces HSs. We verify this method on two different applicator topologies and several target volume configurations. The algorithm is deterministic and runs within seconds, enabling its use for real-time applications. At the same time, it yields results comparable to those obtained with global stochastic optimizers such as Particle Swarm.

Microwave Imaging of the Neck by Means of Artificial Neural Networks for Tumor Detection

“…In these kinds of tumors, i.e., supraglottic laryngeal carcinoma [18] and thyroid cancer [19], the cross section can be approximated as a circular inclusion [64]. Also in previous works [65]- [67], the tumor is simulated like a circle. Tumors such as thyroid cancers [18], [64], neck sarcomas or cervical lymph node metastases [20] are nodular, being approximately spherical, with a radius in the range 3-5 mm, located up to 3 cm below the skin surface [68]- [70].…”

“…To reproduce in an accurate way the dielectric properties of the tumor, the results obtained in [66] are followed. For most neck tumors, the relative dielectric properties are relatively high, and in the considered frequency band are on average around 𝜀 𝑟 ≈ 59 and 𝜎 ≈ 0.9 [S/m], depending on the type and staging, as can be derived by MRI and as usually modeled in numerical studies in the field of microwave hyperthermia [14], [17], [65], [67]. For this reason, by also taking into account a possible variability of such parameters, the dielectric properties of the simulated tumor model were chosen in the range between 55 and 65 for the relative dielectric permittivity, whilst the electrical conductivity lies within [0.5, 1] S/m.…”

Suitability of eigenvalue beam‐forming for discrete multi‐frequency hyperthermia treatment planning

“…TR beam‐forming is a promising approach in this respect; however, current forms 24 lack the ability to properly control hot‐spot formation. Recent and ongoing work is aiming at improving TR‐based UWB HTP by means of iterative hot‐spot suppression and cold‐spot coverage 16 . Stochastic optimization, usually implemented via particle swarm (PS), is computationally demanding already in the single‐frequency setting.…”

Radiobiological Evaluation of Combined Gamma Knife Radiosurgery and Hyperthermia for Pediatric Neuro-Oncology

“…Moreover, the presence of electrically highly conductive cerebrospinal fluid (CSF) leads to considerable absorption of EM radiation, thereby making CSF more susceptible to the emergence of treatment-limiting hot spots. However, recently published numerical studies [25][26][27][28][29] suggest that the intracranial heating with those innovative approaches is feasible. A particularly unique approach is a helmet-like configuration that utilises UWB antennas, allowing for better focusing with fewer antennas than standard annular-phased-array applicators [30].…”