Akke Bakker

Quality assurance guidelines for superficial hyperthermia clinical trials: I. Clinical requirements

Abstract Quality assurance guidelines are essential to provide uniform execution of clinical trials and treatment in the application of hyperthermia. This document provides definitions for a good hyperthermia treatment and identifies the clinical conditions where a certain hyperthermia system can or cannot adequately heat the tumour volume. It also provides brief description of the characteristics and performance of the current electromagnetic (radiative and capacitive), ultrasound and infra-red heating techniques. This information helps to select the appropriate heating technique for the specific tumour location and size, and appropriate settings of the water bolus and thermometry. Finally, requirements of staff training and documentation are provided. The guidelines in this document focus on the clinical application and are complemented with a second, more technical quality assurance document providing instructions and procedure to determine essential parameters that describe heating properties of the applicator for superficial hyperthermia. Both sets of guidelines were developed by the ESHO Technical Committee with participation of senior STM members and members of the Atzelsberg Circle.

Thermal dosimetry for bladder hyperthermia treatment. An overview

Abstract The urinary bladder is a fluid-filled organ. This makes, on the one hand, the internal surface of the bladder wall relatively easy to heat and ensures in most cases a relatively homogeneous temperature distribution; on the other hand the variable volume, organ motion, and moving fluid cause artefacts for most non-invasive thermometry methods, and require additional efforts in planning accurate thermal treatment of bladder cancer. We give an overview of the thermometry methods currently used and investigated for hyperthermia treatments of bladder cancer, and discuss their advantages and disadvantages within the context of the specific disease (muscle-invasive or non-muscle-invasive bladder cancer) and the heating technique used. The role of treatment simulation to determine the thermal dose delivered is also discussed. Generally speaking, invasive measurement methods are more accurate than non-invasive methods, but provide more limited spatial information; therefore, a combination of both is desirable, preferably supplemented by simulations. Current efforts at research and clinical centres continue to improve non-invasive thermometry methods and the reliability of treatment planning and control software. Due to the challenges in measuring temperature across the non-stationary bladder wall and surrounding tissues, more research is needed to increase our knowledge about the penetration depth and typical heating pattern of the various hyperthermia devices, in order to further improve treatments. The ability to better determine the delivered thermal dose will enable clinicians to investigate the optimal treatment parameters, and consequentially, to give better controlled, thus even more reliable and effective, thermal treatments.

Improving hyperthermia treatment planning for the pelvis by accurate fluid modeling.

PURPOSE Hyperthermia is an established (neo)adjuvant treatment modality for a number of pelvic malignancies. Optimal treatment of these tumors requires robust treatment planning, but up until now, the urinary bladder was not modeled accurately, making current simulations less reliable. The authors improved the dielectric and thermophysical model of the urinary bladder in their treatment planning system, and showed the improvements using phantom experiments. METHODS The authors suspended a porcine bladder in muscle tissue equivalent gel and filled it with 120 ml 0.9% saline. The authors heated the phantom during 15 min with their deep hyperthermia device, using clinical settings, and measured the temperature both inside and outside the bladder. The authors simulated the experiment, both using the clinically used treatment planning system, and using the improved model featuring correct dielectric properties for the bladder content and an enhanced thermophysical model, enabling the simulation of convection. RESULTS Although the dielectric changes have an impact throughout the phantom, the dominant effect is a higher net heat absorption in the bladder. The effects of changing the thermophysical model are limited to the bladder and its surroundings, but result in a very different temperature profile. The temperatures predicted by the simulations using the new bladder model were in much better agreement with the measurements than those predicted by currently used treatment planning system. CONCLUSIONS Modeling convection in the urinary bladder is very important for accurate hyperthermia treatment planning in the pelvic area.

Feasibility of on-line temperature-based hyperthermia treatment planning to improve tumour temperatures during locoregional hyperthermia

Abstract Background: The effectiveness of hyperthermia is strongly dependent on the achieved tumour temperatures. Phased-array systems allow flexible power steering to realise good tumour heating while avoiding excessive heating in normal tissue, but the limited quantitative accuracy of pre-treatment planning complicates realising optimal tumour heating. On-line hyperthermia treatment planning could help to improve the heating quality. This paper demonstrates the feasibility of using on-line temperature-based treatment planning to improve the heating quality during hyperthermia in three patients. Methods: Hyperthermia treatment planning was performed using the Plan2Heat software package combined with a dedicated graphical user interface for on-line application. Electric fields were pre-calculated to allow instant update and visualisation of the predicted temperature distribution for user-selected phase-amplitude settings during treatment. On-line treatment planning using manual variation of system settings for the AMC-8 hyperthermia system was applied in one patient with a deep-seated pelvic melanoma metastasis and two cervical cancer patients. For a clinically relevant improvement the increase in average target temperature should be at least 0.2 °C. Results: With the assistance of on-line treatment planning a substantial improvement in tumour temperatures was realised for all three patients. In the melanoma patient, the average measured target temperature increased from 38.30 °C to 39.15 °C (i.e. +0.85 °C). In the cervical cancer patients, the average measured target temperature increased from 41.30 °C to 42.05 °C (i.e. +0.75 °C) and from 41.70 °C to 42.80 °C (i.e. +1.1 °C), respectively. Conclusion: On-line temperature-based treatment planning is clinically feasible to improve tumour temperatures. A next, worthwhile step is automatic optimisation for a larger number of patients.

Improved temperature monitoring and treatment planning for loco-regional hyperthermia treatments of Non-Muscle Invasive Bladder Cancer (NMIBC)

Introduction– Hyperthermia is a cancer treatment that increases the effectiveness of radiotherapy or chemotherapy by heating the tumor area to 41-43°C. Recently, a multi-center phase III randomized clinical trial comparing adjuvant treatment of NMIBC using Mitomycin C with and without loco-regional hyperthermia has started. This invites careful consideration of the bladder as a treatment site. Optimal treatment and quality control requires reliable thermometry and accurate hyperthermia treatment planning. This study aims to improve the current standard in both areas.

Analysis of clinical data to determine the minimum number of sensors required for adequate skin temperature monitoring of superficial hyperthermia treatments

Abstract Purpose: Tumor response and treatment toxicity are related to minimum and maximum tissue temperatures during hyperthermia, respectively. Using a large set of clinical data, we analyzed the number of sensors required to adequately monitor skin temperature during superficial hyperthermia treatment of breast cancer patients. Methods: Hyperthermia treatments monitored with >60 stationary temperature sensors were selected from a database of patients with recurrent breast cancer treated with re-irradiation (23 × 2 Gy) and hyperthermia using single 434 MHz applicators (effective field size 351–396 cm2). Reduced temperature monitoring schemes involved randomly selected subsets of stationary skin sensors, and another subset simulating continuous thermal mapping of the skin. Temperature differences (ΔT) between subsets and complete sets of sensors were evaluated in terms of overall minimum (Tmin) and maximum (Tmax) temperature, as well as T90 and T10. Results: Eighty patients were included yielding a total of 400 hyperthermia sessions. Median ΔT was <0.01 °C for T90, its 95% confidence interval (95%CI) decreased to ≤0.5 °C when >50 sensors were used. Subsets of <10 sensors result in underestimation of Tmax up to −2.1 °C (ΔT 95%CI), which decreased to −0.5 °C when >50 sensors were used. Thermal profiles (8–21 probes) yielded a median ΔT < 0.01 °C for T90 and Tmax, with a 95%CI of −0.2 °C and 0.4 °C, respectively. The detection rate of Tmax ≥43 °C is ≥85% while using >50 stationary sensors or thermal profiles. Conclusions: Adequate coverage of the skin temperature distribution during superficial hyperthermia treatment requires the use of >50 stationary sensors per 400 cm2 applicator. Thermal mapping is a valid alternative.

The effect of air pockets in the urinary bladder on the temperature distribution during loco-regional hyperthermia treatment of bladder cancer patients

Abstract Purpose: Loco-regional hyperthermia combined with mitomycin C is used for treatment of nonmuscle invasive bladder cancer (NMIBC). Air pockets may be present in the bladder during treatment. The aim of this study is to quantify the effect of air pockets on the thermal dose of the bladder. Methods: We analysed 16 patients treated for NMIBC. Loco-regional hyperthermia was performed with the in-house developed 70 MHz AMC-4 hyperthermia device. We simulated treatments with the clinically applied device settings using Plan2Heat (developed in-house) including the air pockets delineated on CT scans made following treatment, and with the same volume filled with urine. Temperature distributions simulated with and without air pockets were compared. Results: The average air and fluid volumes in the bladder were 6.0 ml (range 0.8 − 19.3 ml) and 183 ml (range 47–322 ml), respectively. The effect of these air pockets varied strongly between patients. Averaged over all patients, the median bladder wall temperature (T50) remained unchanged when an air pocket was present. Temperature changes exceeded ±0.2 °C in, on average, 23% of the bladder wall volume (range 1.3–59%), in 6.0% (range 0.6–20%) changes exceeded ±0.5 °C and in 3.2% (range 0.0–7.4%) changes exceeded ±1.0 °C. There was no correlation between the differences in temperature and the air pocket or bladder volume. There was a positive correlation between air pocket surface and temperature heterogeneity. Conclusion: Presence of air causes more heterogeneous bladder wall temperatures and lower T90, particularly for larger air pockets. The size of air pockets must therefore be minimized during bladder hyperthermia treatments.

Predictive value of simulated SAR and temperature for changes in measured temperature after phase-amplitude steering during locoregional hyperthermia treatments

Abstract Introduction: On-line adaptive hyperthermia treatment planning can be useful to suppress treatment limiting hot spots and improve tumor temperatures during locoregional hyperthermia. This requires adequate prediction of changes in heating patterns after phase-amplitude steering. We investigated the predictive value of simulated SAR and temperature for changes in measured temperature after phase-amplitude steering during locoregional hyperthermia. Methods: All treatment sessions of 75 patients with pelvic malignancies treated between September 2013 and March 2018 were evaluated. Phase-amplitude adaptations during the 60 min steady-state period were analyzed. Treatment planning was performed using Plan2Heat, based on CT scans with (thermometry) catheters in the vagina, rectum, and bladder in situ. The predicted SAR and temperature along the thermometry tracks were extracted from the simulated distributions. Correlations between changes in average measured temperature and the simulated SAR and temperature were evaluated for single phase-amplitude steering events, unaccompanied by other (steering) actions. Results: A total of 67 phase-amplitude steering events were suitable for analysis. Simulated changes in both SAR and temperature correlated with the measured temperature changes. For the vagina, R2 = 0.44 and R2 = 0.55 for SAR and temperature, respectively. For the rectum, these values were 0.53 for SAR and 0.66 for temperature. Correlations for the bladder were weaker: R2 = 0.15 and R2 = 0.14 for SAR and temperature, respectively. This can be explained by convection in the bladder fluid, unaccounted for by present treatment planning. Conclusion: Treatment planning can predict changes in an average temperature after phase-amplitude steering. This allows on-line support with phase-amplitude steering to optimize hyperthermia treatments.

A flexible 70 MHz phase-controlled double waveguide system for hyperthermia treatment of superficial tumours with deep infiltration

Abstract Purpose: Superficial tumours with deep infiltration in the upper 15 cm of the trunk cannot be treated adequately with existing hyperthermia systems. The aim of this study was to develop, characterise and evaluate a new flexible two-channel hyperthermia system (AMC-2) for tumours in this region. Materials and methods: The two-channel AMC-2 system has two horizontally revolving and height adjustable 70 MHz waveguides. Three different interchangeable antennas with sizes 20 × 34, 15 × 34 and 8.5 × 34 cm were developed and their electrical properties were determined. The performance of the AMC-2 system was tested by measurements of the electric field distribution in a saline water filled elliptical phantom, using an electric field vector probe. Clinical feasibility was demonstrated by treatment of a melanoma in the axillary region. Results: Phantom measurements showed a good performance for all waveguides. The large reflection of the smallest antenna has to be compensated by increased forward power. Field patterns become asymmetrical when using smaller top antennas, necessitating phase corrections. The clinical application showed that tumours deeper than 4 cm can be heated adequately. A median tumour temperature of 42 °C can be reached up to 12 cm depth with adequate antenna positioning and phase-amplitude steering. Conclusions: This 70 MHz AMC-2 waveguide system is a useful addition to existing loco-regional hyperthermia equipment as it is capable of heating axillary tumours and other tumours deeper than 4 cm.

OC-0548: Hyperthermia treatment planning in the pelvis using thermophysical fluid modelling of the bladder

Conclusion: Proton-beam grids with 3 mm beam elements produce dose distributions in water for which the grid pattern is preserved down to large depths. PBGT could be carried out at proton therapy centers, equipped with spot-scanning possibilities, using existing tools. However, smaller beams than those currently available could be advantageous for biological reasons. With PBGT, it is also possible to create a more uniform target dose than what has been possible to produce with photon-beam grids. We anticipate that PBGT could be a useful technique to reduce both shortand longterm side effects after radiotherapy.