Avoiding Pitfalls in Thermal Dose Effect Relationship Studies: A Review and Guide Forward

Simple Summary Hyperthermia, heating tumours to 39-44 degrees C, is a therapy used for cancer treatment. The temperature measured during treatment can be used to obtain the thermal dose delivered to the patient, and this can be correlated with the treatment outcome or toxicity (thermal dose effect relationship). While some clinical studies have found a correlation between thermal dose and treatment outcome or toxicity, others have not. In this review, we assessed the literature to understand possible differences in the hyperthermia treatment characteristics that could have impacted the results of the published studies. We found that fundamental information was not or not uniformly reported in the clinical studies investigating thermal dose relationships. Based on this, we propose definitions and reporting guidelines that have the biggest potential to solve the identified pitfalls. We hope that by standardising the reporting of hyperthermia treatment characteristics, progress in thermal dose effect relationships will be made. The challenge to explain the diffuse and unconclusive message reported by hyperthermia studies investigating the thermal dose parameter is still to be unravelled. In the present review, we investigated a wide range of technical and clinical parameters characterising hyperthermia treatment to better understand and improve the probability of detecting a thermal dose effect relationship in clinical studies. We performed a systematic literature review to obtain hyperthermia clinical studies investigating the associations of temperature and thermal dose parameters with treatment outcome or acute toxicity. Different hyperthermia characteristics were retrieved, and their influence on temperature and thermal dose parameters was assessed. In the literature, we found forty-eight articles investigating thermal dose effect relationships. These comprised a total of 4107 patients with different tumour pathologies. The association between thermal dose and treatment outcome was the investigated endpoint in 90% of the articles, while the correlation between thermal dose and toxicity was investigated in 50% of the articles. Significant associations between temperature-related parameters and treatment outcome were reported in 63% of the studies, while those between temperature-related parameters and toxicity were reported in 15% of the studies. One clear difficulty for advancement is that studies often omitted fundamental information regarding the clinical treatment, and among the different characteristics investigated, thermometry details were seldom and divergently reported. To overcome this, we propose a clear definition of the terms and characteristics that should be reported in clinical hyperthermia treatments. A consistent report of data will allow their use to further continue the quest for thermal dose effect relationships.