Titania Juang

A Quality Assurance Method that Utilizes 3D Dosimetry and Facilitates Clinical Interpretation

PURPOSE To demonstrate a new three-dimensional (3D) quality assurance (QA) method that provides comprehensive dosimetry verification and facilitates evaluation of the clinical significance of QA data acquired in a phantom. Also to apply the method to investigate the dosimetric efficacy of base-of-skull (BOS) intensity-modulated radiotherapy (IMRT) treatment. METHODS AND MATERIALS Two types of IMRT QA verification plans were created for 6 patients who received BOS IMRT. The first plan enabled conventional 2D planar IMRT QA using the Varian portal dosimetry system. The second plan enabled 3D verification using an anthropomorphic head phantom. In the latter, the 3D dose distribution was measured using the DLOS/Presage dosimetry system (DLOS = Duke Large-field-of-view Optical-CT System, Presage Heuris Pharma, Skillman, NJ), which yielded isotropic 2-mm data throughout the treated volume. In a novel step, measured 3D dose distributions were transformed back to the patients CT to enable calculation of dose-volume histograms (DVH) and dose overlays. Measured and planned patient DVHs were compared to investigate clinical significance. RESULTS Close agreement between measured and calculated dose distributions was observed for all 6 cases. For gamma criteria of 3%, 2 mm, the mean passing rate for portal dosimetry was 96.8% (range, 92.0%-98.9%), compared to 94.9% (range, 90.1%-98.9%) for 3D. There was no clear correlation between 2D and 3D passing rates. Planned and measured dose distributions were evaluated on the patients anatomy, using DVH and dose overlays. Minor deviations were detected, and the clinical significance of these are presented and discussed. CONCLUSIONS Two advantages accrue to the methods presented here. First, treatment accuracy is evaluated throughout the whole treated volume, yielding comprehensive verification. Second, the clinical significance of any deviations can be assessed through the generation of DVH curves and dose overlays on the patients anatomy. The latter step represents an important development that advances the clinical relevance of complex treatment QA.

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.

Evaluation of a dual-arm Archimedean spiral array for microwave hyperthermia

Purpose: This effort describes a third-party performance evaluation of a novel, commercial, dual-armed Archimedean spiral array hyperthermia applicator. The applicator is analysed for its ability to couple efficiently into muscle equivalent phantom loads, operate over a broad bandwidth to help accommodate variable tissue properties and generate predictable and repeatable SAR contours that are adaptable to clinically probable disease shapes. Materials and methods: Characterization of the applicator includes E-field and return-loss measurements in liquid muscle tissue-equivalent phantom, as well as comparison of ‘treatment-planning’ simulations of several possible array SAR patterns with measured SAR from non-coherently driven spiral array antennae. Results: The applicator demonstrates a reasonably low return loss over a large bandwidth and the ability to generate a very uniform heating pattern. Ability to adjust SAR contours spatially to fit specific shapes is also demonstrated. Conclusions: This device should prove a welcome addition to a currently limited set of superficial heating applicators to provide controllable heating of superficial tissue disease.

On the Need for Comprehensive Validation of Deformable Image Registration, Investigated With a Novel 3-Dimensional Deformable Dosimeter

PURPOSE To introduce and evaluate a novel deformable 3-dimensional (3D) dosimetry system (Presage-Def/Optical-CT) and its application toward investigating the accuracy of dose deformation in a commercial deformable image registration (DIR) package. METHODS AND MATERIALS Presage-Def is a new dosimetry material consisting of an elastic polyurethane matrix doped with radiochromic leuco dye. Radiologic and mechanical properties were characterized using standard techniques. Dose-tracking feasibility was evaluated by comparing dose distributions between dosimeters irradiated with and without 27% lateral compression. A checkerboard plan of 5-mm square fields enabled precise measurement of true deformation using 3D dosimetry. Predicted deformation was determined from a commercial DIR algorithm. RESULTS Presage-Def exhibited a linear dose response with sensitivity of 0.0032 ΔOD/(Gy∙cm). Mass density is 1.02 g/cm(3), and effective atomic number is within 1.5% of water over a broad (0.03-10 MeV) energy range, indicating good water-equivalence. Elastic characteristics were close to that of liver tissue, with Youngs modulus of 13.5-887 kPa over a stress range of 0.233-303 kPa, and Poissons ratio of 0.475 (SE, 0.036). The Presage-Def/Optical-CT system successfully imaged the nondeformed and deformed dose distributions, with isotropic resolution of 1 mm. Comparison with the predicted deformed 3D dose distribution identified inaccuracies in the commercial DIR algorithm. Although external contours were accurately deformed (submillimeter accuracy), volumetric dose deformation was poor. Checkerboard field positioning and dimension errors of up to 9 and 14 mm, respectively, were identified, and the 3D DIR-deformed dose γ passing rate was only γ(3%/3 mm) = 60.0%. CONCLUSIONS The Presage-Def/Optical-CT system shows strong potential for comprehensive investigation of DIR algorithm accuracy. Substantial errors in a commercial DIR were found in the conditions evaluated. This work highlights the critical importance of careful validation of DIR algorithms before clinical implementation.

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.

The ACUSITT ultrasonic ablator: the first steerable needle with an integrated interventional tool

Steerability in percutaneous medical devices is highly desirable, enabling a needle or needle-like instrument to avoid sensitive structures (e.g. nerves or blood vessels), access obstructed anatomical targets, and compensate for the inevitable errors induced by registration accuracy thresholds and tissue deformation during insertion. Thus, mechanisms for needle steering have been of great interest in the engineering community in the past few years, and several have been proposed. While many interventional applications have been hypothesized for steerable needles (essentially anything deliverable via a regular needle), none have yet been demonstrated as far as the authors are aware. Instead, prior studies have focused on model validation, control, and accuracy assessment. In this paper, we present the first integrated steerable needle-interventional device. The ACUSITT integrates a multi-tube steerable Active Cannula (AC) with an Ultrasonic Interstitial Thermal Therapy ablator (USITT) to create a steerable percutaneous device that can deliver a spatially and temporally controllable (both mechanically and electronically) thermal dose profile. We present our initial experiments toward applying the ACUSITT to treat large liver tumors through a single entry point. This involves repositioning the ablator tip to several different locations, without withdrawing it from the liver capsule, under 3D Ultrasound image guidance. In our experiments, the ACUSITT was deployed to three positions, each 2cm apart in a conical pattern to demonstrate the feasibility of ablating large liver tumors 7cm in diameter without multiple parenchyma punctures.

Performance evaluation of a conformal thermal monitoring sheet sensor array for measurement of surface temperature distributions during superficial hyperthermia treatments

Purpose: This paper presents a novel conformal thermal monitoring sheet (TMS) sensor array with differential thermal sensitivity for measuring temperature distributions over large surface areas. Performance of the sensor array is evaluated in terms of thermal accuracy, mechanical stability and conformity to contoured surfaces, probe self-heating under irradiation from microwave and ultrasound hyperthermia sources, and electromagnetic field perturbation. Materials and methods: A prototype with 4 × 4 array of fiber-optic sensors embedded between two flexible and thermally conducting polyimide films was developed as an alternative to the standard 1–2 mm diameter plastic catheter-based probes used in clinical hyperthermia. Computed tomography images and bending tests were performed to evaluate the conformability and mechanical stability respectively. Irradiation and thermal barrier tests were conducted and thermal response of the prototype was compared with round cross-sectional clinical probes. Results: Bending and conformity tests demonstrated higher flexibility, dimensional stability and close conformity to human torso. Minimal perturbation of microwave fields and low probe self-heating was observed when irradiated with 915 MHz microwave and 3.4 MHz ultrasound sources. The transient and steady state thermal responses of the TMS array were superior compared to the clinical probes. Conclusions: A conformal TMS sensor array with improved thermal sensitivity and dimensional stability was investigated for real-time skin temperature monitoring. This fixed-geometry, body-conforming array of thermal sensors allows fast and accurate characterization of two-dimensional temperature distributions over large surface areas. The prototype TMS demonstrates significant advantages over clinical probes for characterizing skin temperature distributions during hyperthermia treatments of superficial tissue disease.

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.

A comprehensive investigation of the accuracy and reproducibility of a multitarget single isocenter VMAT radiosurgery technique

PURPOSE Recent trends in stereotactic radiosurgery use multifocal volumetric modulated arc therapy (VMAT) plans to simultaneously treat several distinct targets. Conventional verification often involves low resolution measurements in a single plane, a cylinder, or intersecting planes of diodes or ion chambers. This work presents an investigation into the consistency and reproducibility of this new treatment technique using a comprehensive commissioned high-resolution 3D dosimetry system (PRESAGE(®)∕Optical-CT). METHODS A complex VMAT plan consisting of a single isocenter but five separate targets was created in Eclipse for a head phantom containing a cylindrical PRESAGE(®) dosimetry insert of 11 cm diameter and height. The plan contained five VMAT arcs delivering target doses from 12 to 20 Gy. The treatment was delivered to four dosimeters positioned in the head phantom and repeated four times, yielding four separate 3D dosimetry verifications. Each delivery was completely independent and was given after image guided radiation therapy (IGRT) positioning using Brainlab ExacTrac and cone beam computed tomography. A final delivery was given to a modified insert containing a pin-point ion chamber enabling calibration of PRESAGE(®) 3D data to dose. Dosimetric data were read out in an optical-CT scanner. Consistency and reproducibility of the treatment technique (including IGRT setup) was investigated by comparing the dose distributions in the four inserts, and with the predicted treatment planning system distribution. RESULTS Dose distributions from the four dosimeters were registered and analyzed to determine the mean and standard deviation at all points throughout the dosimeters. A dose standard deviation of <3% was found from dosimeter to dosimeter. Global 3D gamma maps show that the predicted and measured dose matched well [3D gamma passing rate was 98.0% (3%, 2 mm)]. CONCLUSIONS The deliveries of the irradiation were found to be consistent and matched the treatment plan, demonstrating high accuracy and reproducibility of both the treatment machine and the IGRT procedure. The complexity of the treatment (multiple arcs) and dosimetry (multiple strong gradients) pose a substantial challenge for comprehensive verification. 3D dosimetry can be uniquely effective in this scenario.