Monitoring the effect of mild hyperthermia on tumour hypoxia by Cu-ATSM PET scanning

Biological modeling in thermoradiotherapy: present status and ongoing developments toward routine clinical use

Biological modeling for anti-cancer treatments using mathematical models can be very supportive in gaining more insight into dynamic processes responsible for cellular response to treatment, and predicting, evaluating and optimizing therapeutic effects of treatment. This review presents an overview of the current status of biological modeling for hyperthermia in combination with radiotherapy (thermoradiotherapy). Various distinct models have been proposed in the literature, with varying complexity; initially aiming to model the effect of hyperthermia alone, and later on to predict the effect of the combined thermoradiotherapy treatment. Most commonly used models are based on an extension of the linear-quadratic (LQ)-model enabling an easy translation to radiotherapy where the LQ model is widely used. Basic predictions of cell survival have further progressed toward 3 D equivalent dose predictions, i.e., the radiation dose that would be needed without hyperthermia to achieve the same biological effect as the combined thermoradiotherapy treatment. This approach, with the use of temperature-dependent model parameters, allows theoretical evaluation of the effectiveness of different treatment strategies in individual patients, as well as in patient cohorts. This review discusses the significant progress that has been made in biological modeling for hyperthermia combined with radiotherapy. In the future, when adequate temperature-dependent LQ-parameters will be available for a large number of tumor sites and normal tissues, biological modeling can be expected to be of great clinical importance to further optimize combined treatments, optimize clinical protocols and guide further clinical studies.

Positron emission tomography to assess hypoxia and perfusion in lung cancer

In lung cancer, tumor hypoxia is a characteristic feature, which is associated with a poor prognosis and resistance to both radiation therapy and chemotherapy. As the development of tumor hypoxia is associated with decreased perfusion, perfusion measurements provide more insight into the relation between hypoxia and perfusion in malignant tumors. Positron emission tomography (PET) is a highly sensitive nuclear imaging technique that is suited for non-invasive in vivo monitoring of dynamic processes including hypoxia and its associated parameter perfusion. The PET technique enables quantitative assessment of hypoxia and perfusion in tumors. To this end, consecutive PET scans can be performed in one scan session. Using different hypoxia tracers, PET imaging may provide insight into the prognostic significance of hypoxia and perfusion in lung cancer. In addition, PET studies may play an important role in various stages of personalized medicine, as these may help to select patients for specific treatments including radiation therapy, hypoxia modifying therapies, and antiangiogenic strategies. In addition, specific PET tracers can be applied for monitoring therapy. The present review provides an overview of the clinical applications of PET to measure hypoxia and perfusion in lung cancer. Available PET tracers and their characteristics as well as the applications of combined hypoxia and perfusion PET imaging are discussed.

Simultaneous radiotherapy and superficial hyperthermia for high-risk breast carcinoma: a randomised comparison of treatment sequelae in heated versus non-heated sectors of the chest wall hyperthermia

PURPOSE

In vitro data demonstrate that heat-induced radiosensitisation is maximised if hyperthermia and radiotherapy are given simultaneously, with the radiation fraction delivered midway through a hyperthermia session, rather than sequentially. The long-term normal tissue toxicity of full-dose simultaneous thermoradiotherapy is unknown.

MATERIALS AND METHODS

Patients with locally advanced breast cancer (T3, T4 or more than three involved nodes or local recurrence), no prior radiotherapy, received between four and eight sessions of simultaneous thermoradiotherapy. Hyperthermia always included the primary tumour site. In addition an electively heated sector (EHS) was included. The EHS was randomised to either medial or lateral to the tumour site, with the other side an irradiated but unheated control. As per our usual practice, patients received surgery and/or chemotherapy prior to radiotherapy. Radiation doses were 46-50 Gy followed by a boost of ≤16 Gy at 1.8-2 Gy per fraction. EHS and control sectors received the same dose.

RESULTS

A total of 57 evaluable cases with average follow-up of 79 months experienced two local and two nodal recurrences. There was no significant difference in ≥grade 2 toxicity for heated versus control sectors (LR χ(2 )= 0.78, p = 0.38) with no relationship between number of hyperthermia sessions and toxicity (LR χ(2 )= 2.90, p = 0.09).

CONCLUSIONS

Simultaneous full-dose thermoradiotherapy for breast cancer is feasible and well tolerated, with no significant difference in late toxicity between electively heated and unheated control sectors. All patients had hyperthermia to the primary tumour site with excellent local control.

The promise and pitfalls of positron emission tomography and single-photon emission computed tomography molecular imaging-guided radiation therapy

External beam radiation therapy procedures have, until recently, been planned almost exclusively using anatomic imaging methods. Molecular imaging using hybrid positron emission tomography (PET)/computed tomography scanning or single-photon emission computed tomography (SPECT) imaging has provided new insights into the precise location of tumors (staging) and the extent and character of the biologically active tumor volume (BTV) and has provided differential response information during and after therapy. In addition to the commonly used radiotracer (18)F-fluoro- 2-deoxyD-glucose (FDG), additional radiopharmaceuticals are being explored to image major physiological processes as well as tumor biological properties, such as hypoxia, proliferation, amino acid accumulation, apoptosis, and receptor expression, providing the potential to target or boost the radiation dose to a biologically relevant region within a tumor, such as the most hypoxic or most proliferative area. Imaging using SPECT agents has furthered the possibility of limiting dose to functional normal tissues. PET can also portray the distribution of particle therapy by displaying activated species in situ. With both PET and SPECT imaging, fundamental physical issues of limited spatial resolution relative to the biological process, partial volume effects for quantification of small volumes, image misregistration, motion, and edge delineation must be carefully considered and can differ by agent or the method applied. Molecular imaging-guided radiation therapy (MIGRT) is a rapidly evolving and promising area of investigation and clinical translation. As MIGRT evolves, evidence must continue to be gathered to support improved clinical outcomes using MIGRT versus purely anatomic approaches.

The effect of mild temperature hyperthermia on tumour hypoxia and blood perfusion: relevance for radiotherapy, vascular targeting and imaging

Clinically achievable mild temperature local hyperthermia (<43 degrees C) has been demonstrated to be an effective adjuvant to radiotherapy in pre-clinical and clinical studies. In this article, we briefly review the recent progress in the following areas: (1) the effect of mild temperature hyperthermia (MTH) on tumour hypoxia and blood perfusion as assessed by dual marker immunohistochemistry (IHC); (2) the kinetics of MTH induced changes in tumour hypoxia; (3) the potential role of heat-induced tumour reoxygenation on radio- and chemo-sensitisation; (4) the potential role of MTH in combination with vascular targeting agents (VTAs) on tumour response; and (5) non-invasive detection of changes in tumour oxygenation and blood perfusion. It is shown that MTH, by itself or in combination with VTAs, leads to changes in tumour perfusion and oxygenation with potential for radio- and chemo-sensitisation.

Imaging tumour physiology and vasculature to predict and assess response to heat

The vascular supply of tumours and the tumour microenvironment both play an important role when tumours are treated with hyperthermia. Blood flow is one of the major vehicles by which heat is dissipated thus the vascular supply will influence the ability to heat the tumour. It also influences the type of microenvironment that exists within tumours, and it is now well-established that cells existing in areas of oxygen deficiency, nutrient deprivation and acidic conditions are more sensitive to the effect of hyperthermia. The vascular supply and microenvironment are also affected by hyperthermia. In general, mild heat temperatures transiently improve blood flow and oxygenation, while higher hyperthermia temperatures cause vascular collapse and so increase the adverse microenvironmental conditions. Being able to image these vascular and microenvironmental parameters both before and after heating will help in our ability to predict and assess response. Here we review the various techniques that can be applied to supply this information, especially using non-invasive imaging approaches.

PET of hypoxia and perfusion with 62Cu-ATSM and 62Cu-PTSM using a 62Zn/62Cu generator

OBJECTIVE

Copper-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) and copper-pyruvaldehyde-bis(N4-methylthiosemicarbazone) (Cu-PTSM) are being studied as potential markers of hypoxia and perfusion, respectively. The use of short-lived radionuclides (e.g., 62Cu) has advantages for clinical PET, including a lower radiation dose than long-lived radionuclides and serial imaging capability. A 62Zn/62Cu microgenerator and rapid synthesis kits now provide a practical means of producing 62Cu-PTSM and 62Cu-ATSM on-site. Tumors can be characterized with 62Cu-PTSM, 62Cu-ATSM, and 18F-FDG PET scans during one session. We present the initial clinical data in two patients with lung neoplasms.

CONCLUSION

Hypoxia and perfusion are important parameters in tumor physiology and can have major implications in diagnosis, prognosis, treatment planning, and response to therapy. We have shown the feasibility of performing 62Cu-ATSM and 62Cu-PTSM PET together with FDG PET/CT during a single imaging session to provide information on both perfusion and hypoxia and tumor anatomy and metabolism.

Cu-ATSM: a radiopharmaceutical for the PET imaging of hypoxia

Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone), Cu-ATSM, labeled with a positron emitting isotope of copper ((60)Cu, (61)Cu, (62)Cu or (64)Cu) has been shown, in vitro and in vivo, to be selective for hypoxic tissue. In silico studies have explored the mechanism of its hypoxia selectivity, and clinical studies with this agent have shown non-invasive imaging data that is predictive of a cancer patients' response to conventional therapy. This Perspective discusses the evolution of Cu-ATSM, how its selectivity can be improved upon, and where this metal-ligand platform could be taken in the future.

Clinical Trials in a Molecular World

New therapies aimed at molecular abnormalities are often more efficacious and less toxic than nontargeted therapies; however, with current technology, major treatment decisions are being made with inadequate data. This problem needs to be fixed by molecular imaging technology, enabling he noninvasive establishment of the presence of a molecular target, its spatial distribution and heterogeneity, and how this changes over time. This article discusses the status of molecular imaging in clinical trails today, and looks forward to what physicians would like it to become.