Components of a hyperthermia clinic: Recommendations for staffing, equipment, and treatment monitoring

Abstract

Like other technically sophisticated medical endeavours, a hyperthermia clinic relies on skilled staffing. Physicians, physicists and technologists perform multiple tasks to ensure properly functioning equipment, appropriate patient selection, and to plan and administer this treatment. This paper reviews the competencies and tasks that are used in a hyperthermia clinic.

• Clinical hyperthermia
• quality assurance

Introduction

The original version of the following document was prepared by the authors, for the US Society for Thermal Medicine (STM). Some of us have since found it helpful in justifying staffing needs and other support for our hyperthermia clinics. We have opted, therefore, to publish it for the benefit of the general community. The guidelines are primarily in reference to traditional hyperthermia (localised delivery of thermal doses equivalent to about 40–44 °C × 1 h per session) as an adjunct to radiotherapy and/or chemotherapy (including hyperthermia-mediated drug release or targeting). There is a wide range of approaches to hyperthermia and treatment goals. Therefore, the recommendations discussed in this document should be viewed as general guidelines and should not be construed in any manner as a basis for establishing legal standards of care. Furthermore, they are not intended to apply to the practice of other types of thermotherapy such as thermal ablation, cryotherapy, or whole body hyperthermia.

The major emphasis in this document is the competencies and tasks that might be provided by the personnel (physicians, physicists, and technologists) in a hyperthermia clinic. As such this document is intended to supplement and complement quality assurance standards and procedures published by other organisations such as the Radiation Therapy Oncology Group (RTOG) [1–4], the European Society for Hyperthermic Oncology (ESHO) [5–8], and others [9–20].

The STM is not a credentialing organisation. However, as a scientific body with an interest in promoting and improving the clinical application of hyperthermia, we have delineated herein the critical components of a clinical hyperthermia programme. The basic suggested competencies and equipment operation guidelines listed here are also intended to assist us in our educational mission, providing a syllabus for courses to be given online and at hyperthermia workshops and conferences. We also hope that these guidelines will be helpful for healthcare providers, especially those new to the hyperthermia field, in deciding how to staff, equip and maintain a hyperthermia clinic.

Guidelines

1. Recommended competencies for hyperthermia

1. Physicists (also known as, for example, medical physicists, biomedical/clinical engineers, hyperthermia physicist).

1. Physicists providing hyperthermia (thermal therapy) services should have a solid understanding of energy deposition into, transfer within, and interaction of heating fields with various human tissues, tissue interfaces and coupling media, for all typical hyperthermia energy sources (ultrasound, radiofrequency, microwave, thermal conduction), especially those being used clinically at his/her institution. This includes an understanding of lateral uniformity and depth of penetration of energy deposition, what temperature/volume distribution is feasible with each device, what factors can degrade that performance.

2. Physicists should know how to measure heating patterns (or specific absorption rate – SAR) produced by hyperthermia devices using homogeneous phantoms for both obtaining clinical data for treatment planning of special cases and for ongoing quality control/assurance.

3. Physicists must be trained on the use and quality assurance of hyperthermia systems before initiating independent clinical activity.

4. Physicists should understand the paramount importance of quality assurance in thermal therapy; they should be familiar with existing literature on this topic, as well as with specific equipment manufacturer recommendations. They should incorporate as much of this understanding as is reasonably possible into clinical practice, keeping a balance between minimising risks to patients and costs in terms of time and resources. The physicist should develop quality assurance (QA) procedures for spot checks, and daily, monthly, quarterly and yearly QA and related performance evaluations.

5. Physicists should also be fully able to operate the equipment in both QA and treatment modes and they should be comfortable with administering treatments to patients. If the system includes a computerised treatment planning system (TPS), the physicist should be knowledgeable of the capabilities and limitations of the TPS. If the system includes a feedback temperature control system, the physicist should understand the operation of the algorithm and devise ways to test it prior to clinical use. The physicist is responsible for acceptance testing and commissioning of all clinical thermal therapy devices, TPS, feedback temperature control, and related hyperthermia equipment.

6. Physicists should have a practical understanding of the characteristics of temperature distributions in vivo, and the main physical and physiological factors affecting them. Physicists should know how to interpret and deliver thermal therapy prescriptions. They should also understand and calculate commonly used thermal dose parameters from treatment temperature data.

7. Physicists should understand the principles of thermometry, including methods to minimise interactions with heating equipment and trade-offs for optimum placement of thermal sensors for monitoring thermal treatments.

8. Physicists should understand the principles of thermal biology, including the biological mechanisms by which hyperthermia contributes to cytotoxicity, for tumours and normal tissue.

9. Prior to treatment, the physicist should review set-up configuration, device appropriateness, and thermometry needs with the treating physician and technologist.

10. During a course of treatments, the physicist should review thermal dose delivery and, if pre-treatment thermal dose targets are not being met, review options for set-up modification with the physician. It may be necessary for a physicist to be present in the treatment room for complex set-ups, such as some regional hyperthermia treatments.

11. Both physicists and physicians should know what constitutes appropriate and suitable documentation for billing hyperthermia procedures.

1. Physicians

1. Treating physicians should have an understanding of the energy deposition pattern of hyperthermia devices, particularly those available at his/her facility. This includes an understanding of lateral uniformity and depth of penetration of energy deposition, what temperature/volume distribution is feasible with each device, what factors can degrade that performance.

2. Physicians should have knowledge of the biological mechanisms by which hyperthermia can eradicate tumour cells. This includes an understanding of direct thermal cytotoxicity, heat-induced radiosensitisation, other mechanisms of synergy with radiation, and interactions with chemotherapy. The physician should also know how these effects depend on temperature, duration of heating, and sequencing of hyperthermia with other modalities. Physicians should learn the most commonly used thermal dose parameters such as equivalent minutes at 43 °C and T₉₀ and how they relate to clinical outcome.

3. Morbidity: Physicians should know what the potential morbidities are from hyperthermia with the devices available at his/her facility, what technical and patient specific factors can increase the risk of morbidity, what interventions can be taken to reduce the risk of toxicity, what interventions can be taken to enhance patient comfort during a hyperthermia treatment (without increasing the risk of toxicity), and what measures are appropriate for managing toxicity when it occurs.

4. Case selection: Physicians should know what the potential benefit is in terms of disease response and long-term control that may accrue from hyperthermia, what the most appropriate tumours are for treatment, and what clinical presentations are least likely to benefit from treatment with the devices that the physician has available.

5. Physicians should understand the indications for and where to place interstitial thermometry sensors appropriate for the tumour being treated and the device used.

6. Physicians should understand the limitations and usefulness of surface thermometry relative to the disease site and equipment used.

7. The treating physician should work in concert with the hyperthermia physicist and treating technologist, supporting efforts to make hyperthermia treatment delivery as safe and reliable as possible.

8. Prior to treatment, the physician should specify tumour thermal dose objectives and normal tissue constraints, and place interstitial thermal sensors. The physician should also review positioning of surface sensors with the technologist and physicist prior to treatment.

9. During a course of treatments, a physician should see the patient in regular check-up visits. If thermal dose objectives are not being achieved, the physician should review options for set-up modification with the physicist. During each treatment session a physician should be available. It may be necessary for a physician to be present in the treatment room for complex set-ups or medically stressful treatments, such as some regional hyperthermia treatments.

10. Both physicists and physicians should know what constitutes appropriate and suitable documentation for billing hyperthermia procedures.

1. Technologists

1. Technologists should have an understanding of sterile procedures and should be able to assist the physician in the placement of thermometry probes.

2. Technologists should understand the working principles of thermometry probes appropriate for the hyperthermia devices at their institution. Technologists may place surface sensors as directed by the physician and physicist.

3. The technologist should be trained to properly install or load the appropriate applicator and set up the hyperthermia apparatus for subsequent treatment.

4. Technologists should be able to properly couple a treatment applicator to the patient, including, where appropriate, applicator gel and/or supplementary bolus bags.

5. Hyperthermia equipment operations: The technologist should be able to set up a computer data acquisition program for treatment, know how to adjust treatment parameters, and shut down treatment normally and quickly in case of an emergency.

6. Monitor and maintain treatments: The technologist should be able to achieve and maintain temperatures for the hyperthermia treatment according to the prescribed dose, including adjustments to applicator position and applied power as necessary to accommodate changes in patient position, tolerance, or physiological response to treatment. The technologist should know how to adjust the treatment parameters so that maximum temperatures are not exceeded, and know how to adjust treatment parameters rapidly and appropriately in response to patient symptoms and responses. At least one member of the treatment team should be in the room with the patient at all times during administration of hyperthermia.

2. Hyperthermia applicators

1. Performance and maintenance/QA

1. Physicists are responsible for acceptance testing of devices based on benchmarks agreed upon with the vendor before the purchase of the system. Similar benchmarks for non-commercial devices should be established as part of an application for any required regulatory approval such as an Investigational Device Exemption (IDE; USA) or Conformité Européenne (CE) mark (European Union).

2. Physicists are responsible for commissioning of devices. Commissioning should be understood as the performance of tests and data collection necessary for the effective and safe operation of devices. For example, the determination of the 25% and 50% SAR contours at 1 and 2 cm deep in a homogeneous muscle equivalent phantom for a 915 MHz microwave applicator for various coupling media; including, for example, the determination of power limits, output power versus console setting linearity, efficiency, stray radiation.

3. Physicists are responsible for establishing a quality assurance programme (QAP) for thermal therapy devices used clinically at their institution [1–13,15–20]. An effective QAP is one that balances the probability of risks to patients, with reasonable costs. The physicist should develop QA procedures for daily, monthly, quarterly and yearly QA tests.

4. Physicists shall oversee that clinical equipment receives appropriate periodic maintenance by the manufacturer. If repairs are needed, the physicist is responsible for releasing a repaired system back into clinical use.

5. Physicists are responsible for providing training regarding the capabilities, limitations and proper use of clinical heating equipment to physicians, other physicists in training, and technologists.

6. All of the above tasks should be adequately documented in a logbook located visibly near the equipment or in an electronic medical record system readily accessible to personnel assessing or utilising the equipment. Records should be kept for at least seven years including after decommissioning the system.

1. Safety and appropriate uses

1. Every medical device has been approved for specific indications and clinical scope by the appropriate government regulatory body, such as the Food and Drug Administration (FDA) in the USA. Physicians and physicists should learn and understand under what circumstances the thermal therapy devices at their institution were approved for clinical use by local regulations and the manufacturer.

3. Thermometry

1. Devices

Although the field of non-invasive thermometry is progressing rapidly and especially in the area of magnetic resonance image-based techniques, there are no FDA-approved (commercial) non-invasive thermometry systems available today. Therefore, this standard only deals with invasive thermometry probes/sensors and surface thermometry. However, the spirit of the standard can be applied to any forthcoming thermometry.

Invasive thermometry requires insertion of a sensor directly into tissue, or indirectly by first inserting a catheter into tissue and then inserting the temperature sensor into the catheter. The most common devices are thermocouples, thermocouple needles with single or multiple sensors, thermistors and other temperature-dependent resistance sensors, and fibre-optic sensors. Each of these sensors has advantages and disadvantages mostly depending on the type of the energy source, diameter of the probe, the possible number of sensors per probe, and cost. The hyperthermia physicists should know and understand the characteristics (spatial and temperature resolutions, temporal response, working temperature range, calibration requirements and stability, potential artefacts, thermal smearing effects, electromagnetic/ultrasonic interferences) and limitations of the thermometry systems available at his/her institution.

1. Performance and maintenance/QA

The thermometry system is to be acceptance-tested and commissioned by the physicist along with all other clinical hyperthermia equipment. There is extensive literature documenting how to test and perform quality assurance for clinical hyperthermia thermometers [14,21–29]. The physicist should develop calibration procedures, each to be performed periodically to ensure nominal accuracy and precision of ±0.2 °C. Temperature probes/sensors experience considerable mechanical stress during treatments and QA procedures, so it is important to verify the integrity of these probes visually and electrically before each treatment.

1. Safety and appropriate uses

Physicists should know what the most appropriate thermometry sensor is for the energy source in their clinical hyperthermia system. Only appropriate sensors should be employed once their calibration is established and their potential artefacts and limitations have been evaluated. Needle sensors, which are directly inserted into tissues, need to be sterilised as per manufacturer recommendations to avoid damage. Sensors to be inserted into catheters need to be cleaned after each use. Therefore, it is paramount for physicists to routinely check the thermometry probes due to their heavy use and handling.

4. Components of hyperthermia treatment planning

At present the analogue of a radiation therapy isodose distribution computation is not a routinely performed service for hyperthermia, although some facilities have developed planning systems. The following are recommendations that should be considered in developing or using hyperthermia treatment planning systems. The underlying goal of these recommendations is to provide information analogous to radiation therapy isodose computations.

1. The plan may consist of computation of either SAR distribution or equilibrium temperature distribution. In either case, the energy deposition pattern should be computed using patient specific radiographic information. If an equilibrium temperature distribution is computed, the assumptions made in estimating local perfusion and tissue properties need to be well documented.

2. In general, it is recommended that tissue heterogeneity be included in a hyperthermia treatment planning computation system, since heterogeneity can have a much greater effect on hyperthermia than it does in radiation therapy. An exception would be small volume, carefully confined heating configurations – e.g. many brachytherapy and some superficial hyperthermia scenarios. For brachytherapy hyperthermia planning, the analogue of what is done for radiation therapy implants is recommended: radiographic characterisation of the actual configuration of the implant, rather than assuming a geometrically perfect placement.

3. Patient specific computation utilising radiographic information from the patient himself/herself is preferred, preferably with the device or a mock-up in place. Device output categorisation for a generic geometry and tissue distribution, while better than no planning, does not produce accurate SAR or temperature distribution planning.

4. If it is not technically feasible to obtain treatment planning images with the treatment device (or mock-up) coupled to the patient, then the treatment process should include monitoring checks to make certain that the patient is coupled to the treatment device in a manner consistent with the plan.

5. Treatment planning systems can be useful to guide and improve treatment delivery. However, care-givers must understand that patient–device coupling and tissue responses (such as perfusion) can vary during a session and between sessions, and therefore temperature still needs to be adequately monitored each session. Hyperthermia treatment planning systems therefore will not have the precision of radiation therapy planning systems. It is important to know both the utility and limitations of a thermal planning system.

Declaration of interest

Paul Turner is Chief Technology Officer and a stockholder of BSD Medical Corporation. William Nau is a principal research and development engineer at Covidien. The other authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.