Computational fluid dynamics powered treatment planning to improve temperature predictions for bladder hyperthermia

This dissertation investigates the role of computational fluid dynamics (CFD) for simulating hyperthermia treatments, in particular of urinary bladder tumours.
Hyperthermia treatment, i.e., heating a tumour (area) to 40–44 °C, is given to enhance the effectiveness of radiotherapy and/or chemotherapy. It has shown good clinical results for many tumour sites, including bladder tumours. Reliable analysis of a treatment (plan) requires accurately knowing the target temperature. So-called treatment planning software is used to simulate temperature distributions in tissue during treatment, but does not, so far, comprise CFD software for modelling fluid volumes. This leads to potentially large errors, especially when evaluating bladder treatments.
Therefore, a CFD module capable of modelling convective flow was developed and added to the treatment planning system. Phantom experiments showed the accuracy to be better than 0.1 °C. Retrospective analysis of actual bladder hyperthermia treatments showed that the CFD module reduced the median error in reconstructed steady state temperature from −3.7 °C to −0.6 °C. The measured temperature in the bladder lumen was shown to be strongly correlated to the clinically relevant bladder wall temperature, indicating the practical usefulness of bladder lumen measurements.
An air pocket in the bladder—present in all studied patients—leads to lower minimum temperatures, reducing expected therapeutic effect, and to higher maximum temperatures, increasing risk of complications. The effect size is strongly patient dependent.
Like the bladder, the brain comprises relevant fluid volumes, especially after brain tumour excision. Simulation of a treatment with a novel paediatric brain applicator shows acceptable treatment plans may be feasible, but require fluid modelling for accurate assessment. A greatly simplified fluid model may yield useful results with significantly less computation time.
Thus, this dissertation made an important step in adding and assessing CFD for hyperthermia treatment planning.