Comparison of intra-luminal versus intra-tumoural temperature measurements in patients with locally advanced prostate cancer treated with the coaxial TEM system: Report of a feasibility study

Abstract

A study was performed on regional hyperthermia for patients with locally advanced prostate carcinoma. The primary objective was to analyse the thermometry data with an emphasis on the possibility of replacing invasive thermometry by tumour-related intra-luminal thermometry. Fourteen patients were treated with a combination of conformal external beam radiotherapy (70 Gy) and hyperthermia. Hyperthermia was delivered using the Coaxial TEM system, one treatment per week, to a total of five treatments. Thermometry was performed in bladder, urethra, rectum and esophagus. Invasive thermometry in the prostate was carried out during one or two treatments for each patient by placing transperineally a central and a peripheral catheter. Heterogeneous temperature distributions were measured in the prostate. The mean average invasive temperature range was 1.1°C. Due to the temperature heterogeneity and a limited number of thermometry sensors (mean 7, range 2-13), large variability between treatments and patients existed regarding achieved temperatures and dose. The mean invasive T90 was 40.2±0.6°C and T50 was 40.8±0.6°C. The mean Cummin 790>40.5°C per treatment was 22 (range 0-50). Importantly, intra-luminal temperatures did not reliably predict invasively measured temperatures. Invasive thermometry, therefore, remains compulsory to calculate a thermal dose for an individual patient. Changes in temperature during treatment, measured by the urethral sensors, corresponded well with changes in temperature measured by the individual invasive sensors. Similar comparison of rectal temperature changes with intra-prostatic temperature changes was not as predictive. The similarity in temperature changes between the urethral and interstial sites, suggests that urethral temperatures are sufficient for treatment optimization. The SAR profile did not correspond with the temperature profile indicating heterogeneous perfusion. Although regional hyperthermia in combination with external beam radiotherapy for locally advanced prostate carcinoma is clinically feasible, the question on the importance of invasive thermometry remains.