Hyperthermia Treatment Planning Including Convective Flow in Cerebrospinal Fluid for Brain Tumour Hyperthermia Treatment Using a Novel Dedicated Paediatric Brain Applicator

Abstract

Hyperthermia therapy (40–44 °C) is a promising option to increase efficacy of radiotherapy/chemotherapy for brain tumours, in particular paediatric brain tumours. The Chalmers Hyperthermia Helmet is developed for this purpose. Hyperthermia treatment planning is required for treatment optimisation, but current planning systems do not involve a physically correct model of cerebrospinal fluid (CSF). This study investigates the necessity of fluid modelling for treatment planning. We made treatments plans using the Helmet for both pre-operative and post-operative cases, comparing temperature distributions predicted with three CSF models: a convective “fluid” model, a non-convective “solid” CSF model, and CSF models with increased effective thermal conductivity (“high-k”). Treatment plans were evaluated by T90, T50 and T10 target temperatures and treatment-limiting hot spots. Adequate heating is possible with the helmet. In the pre-operative case, treatment plan quality was comparable for all three models. In the post-operative case, the high-k models were more accurate than the solid model. Predictions to within ±1 °C were obtained by a 10–20-fold increased effective thermal conductivity. Accurate modelling of the temperature in CSF requires fluid dynamics, but modelling CSF as a solid with enhanced effective thermal conductivity might be a practical alternative for a convective fluid model for many applications.

Heating technology for malignant tumors: a review

“…Nevertheless, results demonstrated that the degree of control was sufficient for the tumor sites involved, which included bladder, superficial tumors and deep-seated pelvic tumors. Unmet clinical needs are progressing toward more challenging tumor sites such as brain, deep-seated head and neck tumors and peritoneal metastases [94,[422][423][424]. As a result, there is a trend toward device designs providing greater spatial control of the energy deposition to ensure that SAR and temperature distributions in tissues reliably match with rigorous treatment plans to achieve effective treatment of challenging tumor sites, while sparing adjacent critical structures.…”

“…applicators for brain tumors [422] and H&N tumors [121,330,331] based on MW technology, as well as US or MR guided HIFU devices, both for hyperthermia and for thermal ablation. A design challenge for most of these devices is matching the technical and clinical performance of the device with the oncological requirements for the specific site, e.g., the target volume size for gastrointestinal tumors and the need to spare surrounding normal tissue for brain tumors.…”

Technical developments for MR-based electrical property mapping

“…A dedicated modelling approach was adopted for the bladder. Recent studies have shown that modelling fluid convection has a large impact on the final temperature distribution, yielding more accurate hyperthermia treatment planning [200,249,250,272]. However, modelling convective heat transfer is computationally time-consuming at this moment, which makes it impractical for routine clinical use.…”

“…A practical and time-efficient alternative is to increase the effective thermal conductivity of the fluid. This strategy was shown to approximate the thermal effect of fluid dynamics fairly well [250,272]. We included this strategy to account for convective heat transfer in the urinary bladder, which we modelled to have zero perfusion and thermal conductivity 10 times higher than the literature value [200,250,272].…”

“…urine and cerebrospinal fluid, are present in the heated region, convection will influence the temperature distribution. Schooneveldt et al developed convective fluid models of the bladder [200,249] and cerebrospinal fluid [250] to accurately represent the fluid dynamics during hyperthermia. In the bladder, for example, more realistic and homogeneous temperatures were predicted by the complete fluid thermodynamic model.…”