Hyperthermia (HT) is an accepted treatment for recurrent breast cancer which locally heats the tumor to 39–44 °C, and it is a very potent sensitizer for radiotherapy (RT) and chemotherapy. However, currently little is known about how HT with a distinct temperature, and particularly, how the sequence of HT and RT changes the immune phenotype of breast cancer cells. Therefore, human MDA-MB-231 and MCF-7 breast cancer cells were treated with HT of different temperatures (39, 41 and 44 °C), alone and in combination with RT (2 × 5 Gy) in different sequences, with either RT or HT first, followed by the other. Tumor cell death forms and the expression of immune checkpoint molecules (ICMs) were analyzed by multicolor flow cytometry. Human monocyte-derived dendritic cells (moDCs) were differentiated and co-cultured with the treated cancer cells. In both cell lines, RT was the main stressor for cell death induction, with apoptosis being the prominent cell death form in MCF-7 cells and both apoptosis and necrosis in MDA-MB-231 cells. Here, the sequence of the combined treatments, either RT or HT, did not have a significant impact on the final outcome. The expression of all of the three examined immune suppressive ICMs, namely PD-L1, PD-L2 and HVEM, was significantly increased on MCF-7 cells 120 h after the treatment of RT with HT of any temperature. Of special interest for MDA-MB-231 cells is that only combinations of RT with HT of both 41 and 44 °C induced a significantly increased expression of PD-L2 at all examined time points (24, 48, 72, and 120 h). Generally, high dynamics of ICM expression can be observed after combined RT and HT treatments. There was no significant difference between the different sequences of treatments (either HT + RT or RT + HT) in case of the upregulation of ICMs. Furthermore, the co-culture of moDCs with tumor cells of any treatment had no impact on the expression of activation markers. We conclude that the sequence of HT and RT does not strongly affect the immune phenotype of breast cancer cells. However, when HT is combined with RT, it results in an increased expression of distinct immune suppressive ICMs that should be considered by including immune checkpoint inhibitors in multimodal tumor treatments with RT and HT. Further, combined RT and HT affects the immune system in the effector phase rather than in the priming phase.

In order to overcome the limitations of the linear-quadratic model and include synergistic effects of heat and radiation, a novel radiobiological model is proposed. The model is based on a chain of cell populations which are characterized by the number of radiation induced damages (hits). Cells can shift downward along the chain by collecting hits and upward by a repair process. The repair process is governed by a repair probability which depends upon state variables used for a simplistic description of the impact of heat and radiation upon repair proteins. Based on the parameters used, populations up to 4-5 hits are relevant for the calculation of the survival. The model describes intuitively the mathematical behaviour of apoptotic and nonapoptotic cell death. Linear-quadratic-linear behaviour of the logarithmic cell survival, fractionation, and (with one exception) the dose rate dependencies are described correctly. The model covers the time gap dependence of the synergistic cell killing due to combined application of heat and radiation, but further validation of the proposed approach based on experimental data is needed. However, the model offers a work bench for testing different biological concepts of damage induction, repair, and statistical approaches for calculating the variables of state.

Hyperthermia is clinically applied cancer treatment in conjunction with radio- and/or chemotherapy, in which the tumor volume is exposed to supraphysiological temperatures. Since cells can effectively counteract the effects of hyperthermia by protective measures that are commonly known as the heat stress response, the identification of cellular processes that are essential for surviving hyperthermia could lead to novel treatment strategies that improve its therapeutic effects. Here, we apply a meta-analytic approach to 18 datasets that capture hyperthermia-induced transcriptome alterations in nine different human cancer cell lines. We find, in line with previous reports, that hyperthermia affects multiple processes, including protein folding, cell cycle, mitosis, and cell death, and additionally uncover expression changes of genes involved in KRAS signaling, inflammatory responses, TNF-a signaling and epithelial-to-mesenchymal transition (EMT). Interestingly, however, we also find a considerable inter-study variability, and an apparent absence of a ‘universal’ heat stress response signature, which is likely caused by the differences in experimental conditions. Our results suggest that gene expression alterations after heat stress are driven, to a large extent, by the experimental context, and call for a more extensive, controlled study that examines the effects of key experimental parameters on global gene expression patterns.

Time resolved data of DNA damage and repair after radiotherapy elucidates the relation between damage, repair, and cell survival. While well characterized in vitro, little is known about the time-course of DNA damage response in tumors sampled from individual patients. Kinetics of DNA damage after radiotherapy was assessed in eight dogs using repeated in vivo samples of tumor and co-irradiated normal tissue analyzed with comet assay and phosphorylated H2AX (γH2AX) immunohistochemistry. In vivo results were then compared (in silico) with a dynamic mathematical model for DNA damage formation and repair. Maximum %DNA in tail was observed at 15–60 min after irradiation, with a rapid decrease. Time-courses of γH2AX-foci paralleled these findings with a small time delay and were not influenced by covariates. The evolutionary parameter search based on %DNA in tail revealed a good fit of the DNA repair model to in vivo data for pooled sarcoma time-courses, but fits for individual sarcoma time-courses suffer from the heterogeneous nature of the in vivo data. It was possible to follow dynamics of comet tail intensity and γH2AX-foci during a course of radiation using a minimally invasive approach. DNA repair can be quantitatively investigated as time-courses of individual patients by integrating this resulting data into a dynamic mathematical model.

A kinetic bio-mathematical, linear-quadratic (LQ) based model description for clonogenic survival is presented. In contrast to widely used formulations of models, a dynamic approach based on ordinary differential equations for coupling a repair model with a tumour growth model is used to allow analysis of intercellular process dynamics and submodel interference. The purpose of the model formulation is to find a quantitative framework for investigation of tumour response to radiotherapy in vivo. It is not the intention of the proposed model formulation to give a mechanistic explanation for cellular repair processes. This article addresses bio-mathematical aspects of the simplistic kinetic approach used for description of repair. The model formulation includes processes for cellular death, repopulation and cellular repair. The explicit use of the population size in the model facilitates the coupling of the sub-models including aspects of tissue dynamics (competition, oxygenation). The cellular repair is summarized by using a kinetic model for a dose equivalent Γ describing production and elimination of sublethal lesions. This dose equivalent replaces the absorbed dose used in the common LQ- model. Therefore, this approach is called the Γ- LQ- formulation. A comparison with two kinetic radiobiological models (the LPL model of Curtis and the compartmental model of Carlone) is carried out. The resulting differential equations are solved by numerical integration using a Runge-Kutta algorithm. The comparison reveals a good agreement between the Γ- LQ- formulation and the models of Curtis and Carlone under certain, defined conditions: The proposed formulation leads to results which are identical to the model of Carlone over a wide range of investigated biological parameters and different fractionation schemes when using first order repair kinetics. The comparison with experimental data and the LPL- model of Curtis shows a good agreement of the Γ- LQ- formulation using second order repair kinetics over a wide range of dose rate. Over a limited range, the use of second order repair in the Γ- LQ- formulation approximates the same dose rate dependency of clonogenic survival using only one additional parameter to those of the common LQ model. Within the investigated range of parameters, the presented Γ-LQ- formulation may be used to describe the in-vivo tumour response to radiation. The influence of repopulation, oxygenation and other aspects of tissue dynamics may override the differences between the intrinsic radiosensitivity yielded by each of the models. The proposed model formulation can be extended with additional static and dynamic tissue behaviours. This may be useful for the understanding of the reaction of tissues to heat (hyperthermia) or combined anti-cancer treatments (chemo-radiotherapy). Eine kinetische, biomathematische, linear-quadratisch (LQ)-basierte Modellbeschreibung zur Berechnung des Zellüberlebens bei Bestrahlung wird vorgestellt. Im Gegensatz zu weit verbreiteten Modellformulierungen wird eine dynamische, auf gewöhnlichen Differentialgleichungen basierende Beschreibung für die Kopplung eines Zellreparaturmodells mit einem Tumorwachstumsmodell gewählt, welche die Analyse der Dynamik interzellulärer Prozesse und der Wechselwirkung mit gekoppelten Teilmodellen erlaubt. Das Ziel dabei ist das Auffinden einer quantitativen Basis zur Untersuchung des Tumorverhaltens unter Strahlentherapie in vivo. Es wird nicht beabsichtigt, mit der vorgeschlagenen Modellformulierung eine mechanistische Erklärung für die Prozesse der Zellreparatur zu geben. Diese Arbeit beschäftigt sich mit einigen biomathematischen Aspekten einer vereinfachenden Beschreibung der Zellreparatur, welche für ein In-vivo- Modell nützlich sein kann. Die Modellformulierung berücksichtigt Prozesse bezüglich Zelltod, Repopulation und zelluläre Reparatur. Der explizite Gebrauch der Populationsgröße (Anzahl Tumorzellen) im Modell erleichtert die Kopplung mit Teilmodellen zur Beschreibung verschiedener Aspekte der Gewebedynamik (Konkurrenz, Oxygenierung). Die zelluläre Reparatur wird mittels eines kinetischen Modells für ein Dosisäquivalent Γ zusammengefasst, welches die Produktion und Elimination subletaler Schäden beschreibt. Das Dosisäquivalent Γ ersetzt im Prinzip die absorbierte Dosis, wie sie im herkömmlichen LQ- Modell verwendet wird, weshalb die Bezeichnung Γ- LQ- Formulierung gebraucht wird. Es wird ein Vergleich mit zwei kinetischen strahlenbiologischen Modellen (LPL-Modell von Curtis und kompartimentales Modell von Carlone) angestellt. Die resultierenden Differentialgleichungen wurden mittels Runge-Kutta-Verfahren numerisch integriert. Der Vergleich zeigt unter bestimmten, definierten Bedingungen eine gute Übereinstimmung zwischen der vorgeschlagenen, LQ-basierten kinetischen Formulierung und den Modellen von Curtis und Carlone: Über einen großen Wertebereich der Parameter und verschiedenen Fraktionierungsschemata liefert die vorgeschlagene Modellformulierung im Vergleich zum Modell von Carlone identische Ergebnisse, wenn eine Reparaturkinetik erster Ordnung verwendet wird. Über einen begrenzten Bereich der Dosisrate kann mit einer Kinetik zweiter Ordnung und nur einem zum herkömmlichen LQ- Modell zusätzlichen Parameter die Dosisratenabhängigkeit des Zellüberlebens angenähert werden. Reparaturkinetik erster und zweiter Ordnung führten zu einem linear-quadratisch-linearem Verhalten bei den Zellüberlebenskurven, wie dies z.B. von Guerrero and Li beobachtet wurde. Innerhalb des untersuchten Bereichs kann die vorgeschlagene kinetische Modellformulierung potenziell für die Beschreibung der In-vivo-Antwort von Tumoren auf Bestrahlung verwendet werden. Dabei...

During mammography, the thyroid is exposed to scattered radiation from breast tissue and the device. This may increase the risk of radiation induced thyroid cancer. We investigated the scatter radiation exposition of the thyroid and the effect of a tailored thyroid protection in phantom and patient as well as by using Monte Carlo simulation (MCS). The protective effect of a modified thyroid protection, the relevance of the protective effect and acceptance by patients have been investigated. Phantom and patient measurements provided higher values for the surface dose at thyroid position than expected from MCS (phantom 0.32 mGy; patients 0.38 mGy; MCS 0.16 mGy). Phantom measurements indicated scatter contributions from both breast tissue and collimator/tube system. The value found in our patient study is within the range of the literature (0.22–0.39 mGy). The thyroid protection significantly reduced the surface dose but the dose (0.016 mGy) was higher than that expected from the lead equivalent value. However, the impact of the collar to the effective dose was small (< 4%). The collar was not visible on mammograms. Scatter from the collimator/tube system contributed with 50% to the thyroid dose. Due to the relative small fraction of dose deposited in the thyroid when compared to the mean glandular dose to the breast, a collar is not mandatory in general. Not being associated with the risk of obscuring parts of mammograms, such a collar may be used for young women considering their higher radio sensitivity.