Patient positioning in deep hyperthermia:influences of inaccuracies, signal correction possibilities and optimization potential

\u3cp\u3eIn this deep hyperthermia study, the robustness of SAR (specific absorption rate) patterns to patient-position variations is assessed, as well as the possibilities to correct for improper positioning and the benefits of non-standard positions. With a finite element model, the SAR distributions were predicted for ten patients at 33 positions. Position sensitivity is assessed for both SAR-focus steering, i.e. settings based on a calculated focus in a cylindrical patient representation, and HTP (hyperthermia treatment planning)-guided steering, i.e. model-based optimization of the SAR distribution. Position inaccuracies of less than 1 cm do not significantly affect SAR patterns. For SAR-focus steering, the SAR maximum is not always at the desired focus location, especially in the Y (anterior/posterior)- and Z (axial)-directions. For a maximum shift of 5 cm in all directions, both SAR-focus steering and HTP-guided steering are suitable to correct for improper positioning up to the level that none of the investigated positions appears preferable. Current positioning precision is sufficient in the X (right-left)-direction, but precision measurements are needed to reach the desired accuracy in the Y-direction. In the Z-direction, a cranial shift of the applicator is predicted to be beneficial. If the position is known accurately, correction of the treatment setting is possible without loss of heating efficiency. Additionally, no preferable positions exist.\u3c/p\u3

Benefit of replacing the Sigma-60 by the Sigma-Eye applicator : a Monte Carlo-based uncertainty analysis

\u3cp\u3eBACKGROUND AND PURPOSE: To investigate the clinical benefit of replacing the BSD-2000 Sigma-60 with the Sigma-Eye applicator, taking into account effects of uncertainties in tissue and water bolus parameters.\u3c/p\u3e\u3cp\u3ePATIENTS AND METHODS: For 20 patients, specific absorption rate (SAR) and temperature distributions were calculated and optimized, based on computed tomography (CT) scans in treatment position. The impact of uncertainties on predicted distributions was studied using a Monte Carlo uncertainty assessment.\u3c/p\u3e\u3cp\u3eRESULTS: Replacing the Sigma-60 by the Sigma-Eye applicator resulted in a higher SAR in the tumor [on average a decrease of the hotspot tumor quotient (HTQ) by 24%; p < 0.001], and higher temperatures (T90: +0.4°C, p < 0.001; T50: +0.6°C, p < 0.001) using literature values and SAR optimization. When temperature optimization (T90) was used, a larger average increase was found (T90: +0.7°C, p < 0.001; T50: +0.8°C, p < 0.001). When taking into account uncertainties, a decrease of 23% in median HTQ (p < 0.001) and an increase in T50 and T90 of 0.4°C (p < 0.001) could be demonstrated.\u3c/p\u3e\u3cp\u3eCONCLUSION: Based on this uncertainty analysis, significant and clinically relevant improvements in HTQ and tumor temperature were achieved when replacing the Sigma-60 by the Sigma-Eye applicator.\u3c/p\u3

EMF dose in patients and medical staff during hyperthermia treatment of cancer

\u3cp\u3eAt the Erasmus Medical Center, we apply hyperthermia treatments (HT) of cancer in the pelvic area using an electromagnetic applicator installed in a Faraday shielded treatment room. Consequently, medical staff and accompanying persons are exposed to electromagnetic fields (EMF) during treatment. In the past, procedures were defined based on measurements defining compliant areas where the fields are expected to be below the exposure guidelines. Today, advanced electromagnetic models enable more precise dose assessment in the human anatomy and better evaluation of the procedures. The objective of this study was to investigate theoretically if the exposure of medical staff and accompanying persons is compliant to the guidelines when adhering to the procedures. Therefore, the whole-body averaged (SAR\u3csub\u3ewb\u3c/sub\u3e) and spatial-averaged (SAR\u3csub\u3e10g\u3c/sub\u3e) specific absorption rate was assessed numerically in whole-body models of the patient, medical staff and an accompanying person. We found that predicted fields can exceed the exposure guidelines ten fold. However, the basic restrictions on SAR\u3csub\u3ewb\u3c/sub\u3e and SAR\u3csub\u3e10g\u3c/sub\u3e are not exceeded for workers, but SAR\u3csub\u3ewb\u3c/sub\u3e can exceed the guideline by a factor of two for accompanying persons that are in close vicinity of the applicator. In conclusion, adhering to the procedures defined in the early nineties is effective in keeping the exposure in medical staff and accompanying persons compliant to the exposure guidelines.\u3c/p\u3

Implementation of treatment planning in the routine clinical procedure of regional hyperthermia treatment of cervical cancer:an overview and the Rotterdam experience

\u3cp\u3ePURPOSE: This manuscript provides an overview in the field of hyperthermia treatment planning (HTP) in cervical cancer. Treatment planning techniques: The workflow of an HTP assisted treatment generally consists of patient imaging, tissue segmentation, model generation, electromagnetic (EM) and thermal calculations, optimisation, and clinical implementation. A main role in HTP is played by numerical simulations, for which currently a number of software packages are available in hyperthermia. To implement these simulations, accurate applicator models and accurate knowledge of dielectric and thermal parameters is mandatory. Model validation is necessary to check if this is implemented well. In the translation from HTP models to the clinic, the main aspect is accurate representation of the actual treatment situation in the HTP models. Accurate patient positioning and organ-specific segmentation can be helpful in minimising the differences between model and clinic.\u3c/p\u3e\u3cp\u3eSTEERING STRATEGIES: In the clinic, different approaches are possible: simple, i.e. target centre point (TCP) steering, often called 'target steering', or only pretreatment planning versus advanced, i.e. active HTP guided steering or image guided hyperthermia by non-invasive thermometry (NIT). The Rotterdam experience: To illustrate the implementation of HTP guided steering, the Rotterdam approach of complaint adaptive steering is elaborated, in which optimisation is adapted with increased constraints on tissues with heat-induced discomfort.\u3c/p\u3e\u3cp\u3eCONCLUSIONS: Many publications on HTP show that HTP can be considered a feasible method to optimise and control a hyperthermia treatment, with the objective to enhance treatment quality and documentation. Ultimately, after overcoming the various uncertainties, this may lead to dose prescription.\u3c/p\u3

Challenges of the clinical application of hyperthermia for head and neck tumors

\u3cp\u3eIntroducing hyperthermia in a clinical setting requires primarily the focused effort of a dedicated and highly motivated multi-disciplinary team that minimally consists of a medical/radiation oncologist, a physicist and a hyperthermia technician. In early days application of hyperthermia was mainly applied following an experience and expertise based procedure. The rapid evolutions of modern technology, like hyperthermia treatment planning and non-invasive thermometry enables new advanced methods for controlled delivery of hyperthermia. However, new advanced methods bring also new demands to the clinical staff involved. A very interesting problem is already the definition of the target for hyperthermia. A secondary challenge is to assure that what we predicted by treatment planning is also what we deliver to the patient. Solutions to these challenges are possible but come step by step. Some of these steps in the development of the HyperCollar system as used for hyperthermia treatment of head and neck tumors are reported.\u3c/p\u3

Clinical integration of software tool VEDO for adaptive and quantitative application of phased array hyperthermia in the head and neck

\u3cp\u3eBACKGROUND AND PURPOSE: In Rotterdam, patient-specific hyperthermia (HT) treatment planning (HTP) is applied for all deep head and neck (H&N) HT treatments. In this paper we introduce VEDO (the Visualisation Tool for Electromagnetic Dosimetry and Optimisation), the software tool required, and demonstrate its value for HTP-guided online complaint-adaptive (CA) steering based on specific absorption rate (SAR) optimisation during a H&N HT treatment.\u3c/p\u3e\u3cp\u3eMATERIALS AND METHODS: VEDO integrates CA steering, visualisation of the SAR patterns and mean tumour SAR (SAR(target)) optimisation in a single screen. The pre-calculated electromagnetic fields are loaded into VEDO. During treatment, VEDO shows the SAR pattern, overlaid on the patients' CT-scan, corresponding to the actually applied power settings and it can (re-)optimise the SAR pattern to minimise SAR at regions where the patient senses discomfort while maintaining a high SAR(target).\u3c/p\u3e\u3cp\u3eRESULTS: The potential of the quantitative SAR steering approach using VEDO is demonstrated by analysis of the first treatment in which VEDO was used for two patients using the HYPERcollar. These cases show that VEDO allows response to power-related complaints of the patient and to quantify the change in absolute SAR: increasing either SAR(target) from 96 to 178 W/kg (case 1); or show that the first SAR distribution was already optimum (case 2).\u3c/p\u3e\u3cp\u3eCONCLUSION: This analysis shows that VEDO facilitates a quantitative treatment strategy allowing standardised application of HT by technicians of different HT centres, which will potentially lead to improved treatment quality and the possibility of tracking the effectiveness of different treatment strategies.\u3c/p\u3

Simulation techniques in hyperthermia treatment planning

\u3cp\u3eAbstract Clinical trials have shown that hyperthermia (HT), i.e. an increase of tissue temperature to 39-44 °C, significantly enhance radiotherapy and chemotherapy effectiveness [1]. Driven by the developments in computational techniques and computing power, personalised hyperthermia treatment planning (HTP) has matured and has become a powerful tool for optimising treatment quality. Electromagnetic, ultrasound, and thermal simulations using realistic clinical set-ups are now being performed to achieve patient-specific treatment optimisation. In addition, extensive studies aimed to properly implement novel HT tools and techniques, and to assess the quality of HT, are becoming more common. In this paper, we review the simulation tools and techniques developed for clinical hyperthermia, and evaluate their current status on the path from 'model' to 'clinic'. In addition, we illustrate the major techniques employed for validation and optimisation. HTP has become an essential tool for improvement, control, and assessment of HT treatment quality. As such, it plays a pivotal role in the quest to establish HT as an efficacious addition to multi-modality treatment of cancer.\u3c/p\u3