Jaime L. Schlorff

Conformal microwave array (CMA) applicators for hyperthermia of diffuse chest wall recurrence

Purpose: This article summarises the evolution of microwave array applicators for heating large area chest wall disease as an adjuvant to external beam radiation, systemic chemotherapy, and potentially simultaneous brachytherapy. Methods: Current devices used for thermotherapy of chest wall recurrence are reviewed. The largest conformal array applicator to date is evaluated in four studies: (1) ability to conform to the torso is demonstrated with a CT scan of a torso phantom and MR scan of the conformal water bolus component on a mastectomy patient; (2) specific absorption rate (SAR) and temperature distributions are calculated with electromagnetic and thermal simulation software for a mastectomy patient; (3) SAR patterns are measured with a scanning SAR probe in liquid muscle phantom for a buried coplanar waveguide CMA; and (4) heating patterns and patient tolerance of CMA applicators are characterised in a clinical pilot study with 13 patients. Results: CT and MR scans demonstrate excellent conformity of CMA applicators to contoured anatomy. Simulations demonstrate effective control of heating over contoured anatomy. Measurements confirm effective coverage of large treatment areas with no gaps. In 42 hyperthermia treatments, CMA applicators provided well-tolerated effective heating of up to 500 cm2 regions, achieving target temperatures of Tmin = 41.4 ± 0.7°C, T90 = 42.1 ± 0.6°C, Tave = 42.8 ± 0.6°C, and Tmax = 44.3 ± 0.8°C as measured in an average of 90 points per treatment. Conclusion: The CMA applicator is an effective thermal therapy device for heating large-area superficial disease such as diffuse chest wall recurrence. It is able to cover over three times the treatment area of conventional hyperthermia devices while conforming to typical body contours.

Multilayer conformal applicator for microwave heating and brachytherapy treatment of superficial tissue disease

Purpose: The purpose of this study was to construct and perform preliminary functionality evaluations of a multilayer conformal applicator with provisions for thermal monitoring, tight conformity and simultaneous microwave heating and brachytherapy treatment of large-area contoured surfaces. Materials and methods: The multilayer conformal applicator consists of thermal monitoring catheters for fibre-optic monitoring of skin temperatures, a waterbolus, a PCB microwave antenna array, a dielectric spacer for brachytherapy considerations, brachytherapy catheters for delivering HDR radiation and an inflatable air bladder for improving conformity to contoured surfaces. The applicator also includes an elastic attachment structure to hold the applicator securely in place on the patient. The conformity of the applicator to irregular surfaces was evaluated through CT imaging of the applicator fitted onto a life-sized human torso phantom. The fluid flow dynamics of the waterbolus, which impact the effectiveness of temperature control, were evaluated with thermometry during a 19°C step change temperature of the circulating water. Results: CT imaging showed improved conformity to the torso phantom surface following the application of gentle inward pressure from inflating the outer air bladder. Only a small number of 1–5 mm sized air gaps separated the conformal applicator and tissue surface. Thermometry testing of the bolus fluid flow dynamics demonstrated temperature uniformity within ±0.82°C across a 19 × 34 × 0.6 cm area bolus and ±0.85°C across a large 42 × 32 × 0.6 cm area bolus. Conclusion: CT scans of the applicator confirmed that the applicator conforms well to complex body contours and should maintain good conformity and positional stability even when worn on a mobile patient. Thermometry testing of two different waterbolus geometries demonstrated that uniform circulation and temperature control can be maintained throughout large, complex bolus shapes.

Progress on system for applying simultaneous heat and brachytherapy to large-area surface disease (Invited Paper)

Laboratory experiments have shown that thermal enhancement of radiation response increases substantially for higher thermal dose (approaching 100 CEM43) and when hyperthermia and radiation are delivered simultaneously. Unfortunately, equipment capable of delivering uniform doses of heat and radiation simultaneously has not been available to test the clinical potential of this approach. We present recent progress on the clinical implementation of a system that combines the uniform heating capabilities of flexible printed circuit board microwave array applicators with an array of brachytherapy catheters held a fixed distance from the skin for uniform radiation of tissue <1.5 cm deep with a scanning high dose rate (HDR) brachytherapy source. The system is based on the Combination Applicator which consists of an array of up to 32 Dual Concentric Conductor (DCC) apertures driven at 915 MHz for heating tissue, coupled with an array of 1 cm spaced catheters for HDR therapy. Efforts to optimize the clinical interface and move from rectangular to more complex shape applicators that accommodate the entire disease in a larger number of patients are described. Improvements to the system for powering and controlling the applicator are also described. Radiation dosimetry and experimental performance results of a prototype 15 x 15 cm dual-purpose applicator demonstrate dose distributions with good homogeneity under large contoured surfaces typical of diffuse chestwall recurrence of breast carcinoma. Investigations of potential interaction between heat and brachytherapy components of a Combination Applicator demonstrate no perceptible perturbation of the heating field from an HDR source or leadwire, no perceptible effect of a scanning HDR source on fiberoptic thermometry, and <0.5% variation of radiation dose delivered through the CMA applicator. By applying heat and radiation simultaneously for maximum synergism of modalities, this dual therapy system should expand the number of patients that can benefit from effective thermoradiotherapy treatments.

Construction of a Conformal Water Bolus Vest Applicator for Hyperthermia Treatment of Superficial Skin Cancer

Large area chestwall recurrence of breast carcinoma can be treated with moderate temperature hyperthermia in combination with radiation or chemotherapy. For diffuse chestwall disease, hyperthermia is best delivered with a conformal microwave array (CMA) applicator using a temperature-controlled water bolus designed specifically to fit complex contours and maintain contact with the tissue surface to prevent air gaps which distort the microwave power deposition pattern. In order to maintain the desired temperature range of 41-45 ° C during local hyperthermia treatments, it is necessary to have an effective fluid flow system to serve as a buffer and prevent overheating of skin, which can lead to small blisters or, in rare cases, deeper burns. The fluid flow dynamics of a vest shaped open water bag design is evaluated with thermometry during a step temperature change of circulating water. The data confirm the feasibility of uniform circulation and temperature control throughout complex bolus shapes. This water bolus design should improve temperature uniformity of current treatments for superficial tissue disease.

Thermal characteristics of thermobrachytherapy surface applicators for treating chest wall recurrence.

The aim of this study was to investigate temperature and thermal dose distributions of thermobrachytherapy surface applicators (TBSAs) developed for concurrent or sequential high dose rate (HDR) brachytherapy and microwave hyperthermia treatment of chest wall recurrence and other superficial diseases. A steady-state thermodynamics model coupled with the fluid dynamics of a water bolus and electromagnetic radiation of the hyperthermia applicator is used to characterize the temperature distributions achievable with TBSAs in an elliptical phantom model of the human torso. Power deposited by 915 MHz conformal microwave array (CMA) applicators is used to assess the specific absorption rate (SAR) distributions of rectangular (500 cm(2)) and L-shaped (875 cm(2)) TBSAs. The SAR distribution in tissue and fluid flow distribution inside the dual-input dual-output (DIDO) water bolus are coupled to solve the steady-state temperature and thermal dose distributions of the rectangular TBSA (R-TBSA) for superficial tumor targets extending 10-15 mm beneath the skin surface. Thermal simulations are carried out for a range of bolus inlet temperature (T(b) = 38-43 degrees C), water flow rate (Q(b) = 2-4 L min(-1)) and tumor blood perfusion (omega(b) = 2-5 kg m(-3) s(-1)) to characterize their influence on thermal dosimetry. Steady-state SAR patterns of the R- and L-TBSA demonstrate the ability to produce conformal and localized power deposition inside the tumor target sparing surrounding normal tissues and nearby critical organs. Acceptably low variation in tissue surface cooling and surface temperature homogeneity was observed for the new DIDO bolus at a 2 L min(-1) water flow rate. Temperature depth profiles and thermal dose volume histograms indicate bolus inlet temperature (T(b)) to be the most influential factor on thermal dosimetry. A 42 degrees C water bolus was observed to be the optimal choice for superficial tumors extending 10-15 mm from the surface even under significant blood perfusion. Lower bolus temperature may be chosen to reduce the thermal enhancement ratio (TER) in the most sensitive skin where maximum radiation dose is delivered and to extend the thermal enhancement of radiation dose deeper. This computational study indicates that well-localized elevation of tumor target temperature to 40-44 degrees C can be accomplished by large surface-conforming TBSAs using appropriate selection of coupling bolus temperature.

Combination applicator for simultaneous heat and radiation

We present the development of operator and patient friendly conformal applicators that can deliver moderate temperature hyperthermia simultaneously with radiation in superficial tissue overlying contoured anatomy. This applicator combines the uniform heating capabilities of large area conformal microwave array (CMA) flexible printed circuit board applicators with a patient interface (coupling bolus) that facilitates positioning of brachytherapy sources at a fixed distance (e.g. 1.5 cm) from the skin. A customized inverse treatment planning program (IPSA) was used to optimize spacing of a parallel array of source catheters and separation distance from skin, and to characterize the effects of bolus thickness and conformal array curvature on radiation dose uniformity. Performance of a 15 cm/spl times/15 cm combination applicator was evaluated in flat and contoured homogenous muscle tissue models. Results demonstrate effective heating and radiation distributions to 1-1.5 cm depth and out to the periphery of the array. This applicator should prove useful for treatment of diffuse chestwall disease located over contoured anatomy that is difficult to treat with external beam radiation. By applying heat and radiation simultaneously for maximum synergism of modalities, this device should expand the number of patients that can benefit from effective thermoradiotherapy for superficial disease.

Radiation Dosimetry of a Conformal Heat-brachytherapy Applicator

The purpose of this paper is to report the radiation dosimetric characteristics of a new combination applicator for delivering heat and radiation simultaneously to large area superficial disease <1.5 cm deep. The applicator combines an array of brachytherapy catheters (for radiation delivery) with a conformal printed circuit board microwave antenna array (for heat generation), and a body-conforming 5–10 mm thick temperature-controlled water bolus. The rationale for applying both modalities simultaneously includes the potential for significantly higher response rate due to enhanced synergism of modalities, and lower peak toxicity due to temporal extension of heat and radiation induced toxicities. Treatment plans and radiation dosimetry are calculated with IPSA (an optimization tool developed at UCSF) for 15 × 15 cm2 and 35 × 24 cm2 applicators, lesion thicknesses of 5 to 15 mm, flat and curved surfaces, and catheter separation of 5 and 10 mm. The effect on skin dose of bolus thickness and presence of thin copper antenna structures between radiation source and tissue are also evaluated. Results demonstrate the ability of the applicator to provide conformal radiation dose coverage for up to 15 mm deep target volumes under the applicator. For clinically acceptable plans, tumor coverage is > 98%, homogeneity index > 0.95 and the percentage of normal tissue irradiated is < 20%. The dose gradient at the skin surface varies from 3 to 5 cGy/mm depending on bolus thickness and lesion depth. Attenuation of the photon beam by the printed circuit antenna array is of the order 0.25% and secondary electron emissions are absorbed completely within 5 mm of water bolus and plastic layers. Both phenomena can then be neglected in dose calculations allowing commercial software to be used for treatment planning. This novel applicator should prove useful for the treatment of diffuse chestwall disease located over contoured anatomy that may be difficult to treat with single field external beam therapy. By delivering heat and radiation simultaneously, increased synergism is expected with a TER in the range of 2–5. Lowering radiation dose by an equivalent factor may produce lower radiation toxicity with similar efficacy, while preserving the option of subsequent retreatment(s) with thermoradiotherapy in order to further extend patient survival.

Progress on conformal microwave array applicators for heating chestwall disease

Previous studies have reported the computer modeling, CAD design, and theoretical performance of single and multiple antenna arrays of Dual Concentric Conductor (DCC) square slot radiators driven at 915 and 433 MHz. Subsequently, practical CAD designs of microstrip antenna arrays constructed on thin and flexible printed circuit board (PCB) material were reported which evolved into large Conformal Microwave Array (CMA) sheets that could wrap around the surface of the human torso for delivering microwave energy to large areas of superficial tissue. Although uniform and adjustable radiation patterns have been demonstrated from multiple element applicators radiating into simple homogeneous phantom loads, the contoured and heterogeneous tissue loads typical of chestwall recurrent breast cancer have required additional design efforts to achieve good coupling and efficient heating from the increasingly larger conformal array applicators used to treat large area contoured patient anatomy. Thus recent work has extended the theoretical optimization of DCC antennas to improve radiation efficiency of each individual aperture and reduce mismatch reflections, radiation losses, noise, and cross coupling of the feedline distribution network of large array configurations. Design improvements have also been incorporated into the supporting bolus structure to maintain effective coupling of DCC antennas into contoured anatomy and to monitor and control surface temperatures under the entire array. New approaches for non-invasive monitoring of surface and sub-surface tissue temperatures under each independent heat source are described that make use of microwave radiometry and flexible sheet grid arrays of thermal sensors. Efforts to optimize the clinical patient interface and move from planar rectangular shapes to contoured vest applicators that accommodate entire disease in a larger number of patients are summarized. By applying heat more uniformly to large areas of contoured anatomy, the CMA applicator resulting from these enhancements should expand the number of patients that can benefit from effective heating of superficial disease in combination with radiation or chemotherapy.

Design of a water coupling bolus with improved flow distribution for multi-element superficial hyperthermia applicators

A water bolus used in superficial hyperthermia couples the electromagnetic (EM) or acoustic energy into the target tissue and cools the tissue surface to minimise thermal hotspots and patient discomfort during treatment. Parametric analyses of the fluid pressure inside the bolus computed using 3D fluid dynamics simulations are used in this study to determine a bolus design with improved flow and surface temperature distributions for large area superficial heat applicators. The simulation results are used in the design and fabrication of a 19 × 32 cm prototype bolus with dual input-dual output (DIDO) flow channels. Sequential thermal images of the bolus surface temperature recorded for a step change in the circulating water temperature are used to assess steady state flow and surface temperature distributions across the bolus. Modelling and measurement data indicate substantial improvement in bolus flow and surface temperature distributions when changing from the previous single input–single output (SISO) to DIDO configuration. Temperature variation across the bolus at steady state was measured to be less than 0.8°C for the DIDO bolus compared to 1.5°C for the SISO water bolus. The new DIDO bolus configuration maintains a nearly uniform flow distribution and low variation in surface temperature over a large area typically treated in superficial hyperthermia.

Progress on ThermoBrachytherapy Surface Applicator for Superficial Tissue Disease

This work reports the ongoing development of a combination applicator for simultaneous heating of superficial tissue disease using a 915 MHz DCC (dual concentric conductor) array and High Dose Rate (HDR) brachytherapy delivered via an integrated conformal catheter array. The progress includes engineering design changes in the waterbolus, DCC configurations and fabrication techniques of the conformal multilayer applicator. The dosimetric impact of the thin copper DCC array is also assessed. Steady state fluid dynamics of the new waterbolus bag indicates nearly uniform flow with less than 1°C variation across a large (19×32cm) bolus. Thermometry data of the torso phantom acquired with computer controlled movement of fiberoptic temperature probes inside thermal mapping catheters indicate feasibility of real time feedback control for the DCC array. MR (magnetic resonance) scans of a torso phantom indicate that the waterbolus thickness across the treatment area is controlled by the pressure applied by the surrounding inflatable airbladder and applicator securing straps. The attenuation coefficient of the DCC array was measured as 3± 0.001% and 2.95±0.03 % using an ion chamber and OneDose™ dosimeters respectively. The performance of the combination applicator on patient phantoms provides valuable feedback to optimize the applicator prior use in the patient clinic.