Long duration mild temperature hyperthermia and brachytherapy

Equivalence of cell survival data for radiation dose and thermal dose in ablative treatments: analysis applied to essential tremor thalamotomy by focused ultrasound and gamma knife

Thermal dose and absorbed radiation dose have historically been difficult to compare because different biological mechanisms are at work. Thermal dose denatures proteins and the radiation dose causes DNA damage in order to achieve ablation. The purpose of this paper is to use the proportion of cell survival as a potential common unit by which to measure the biological effect of each procedure. Survival curves for both thermal and radiation doses have been extracted from previously published data for three different cell types. Fits of these curves were used to convert both thermal and radiation dose into the same quantified biological effect: fraction of surviving cells. They have also been used to generate and compare survival profiles from the only indication for which clinical data are available for both focused ultrasound (FUS) thermal ablation and radiation ablation: essential tremor thalamotomy. All cell types could be fitted with coefficients of determination greater than 0.992. As an illustration, survival profiles of clinical thalamotomies performed by radiosurgery and FUS are plotted on a same graph for the same metric: fraction of surviving cells. FUS and Gamma Knife have the potential to be used in combination to deliver a more effective treatment (for example, FUS may be used to debulk the main tumour mass, and radiation to treat the surrounding tumour bed). In this case, a model which compares thermal and radiation treatments is valuable in order to adjust the dose between the two.

Practical considerations for maximizing heat production in a novel thermobrachytherapy seed prototype

PURPOSE

A combination of hyperthermia and radiation in the treatment of cancer has been proven to provide better tumor control than radiation administered as a monomodality, without an increase in complications or serious toxicities. Moreover, concurrent administration of hyperthermia and radiation displays synergistic enhancement, resulting in greater tumor cell killing than hyperthermia and radiation delivered separately. The authors have designed a new thermobrachytherapy (TB) seed, which serves as a source of both radiation and heat for concurrent brachytherapy and hyperthermia treatments when implanted in solid tumors. This innovative seed, similar in size and geometry to conventional seeds, will have self-regulating thermal properties.

METHODS

The new seed's geometry is based on the standard BEST Model 2301(125)I seed, resulting in very similar dosimetric properties. The TB seed generates heat when placed in an oscillating magnetic field via induction heating of a ferromagnetic Ni-Cu alloy core that replaces the tungsten radiographic marker of the standard Model 2301. The alloy composition is selected to undergo a Curie transition near 50 °C, drastically decreasing power production at higher temperatures and providing for temperature self-regulation. Here, the authors present experimental studies of the magnetic properties of Ni-Cu alloy material, the visibility of TB seeds in radiographic imaging, and the ability of seed prototypes to uniformly heat tissue to a desirable temperature. Moreover, analyses are presented of magnetic shielding and thermal expansion of the TB seed, as well as matching of radiation dose to temperature distributions for a short interseed distance in a given treatment volume.

RESULTS

Annealing the Ni-Cu alloy has a significant effect on its magnetization properties, increasing the sharpness of the Curie transition. The TB seed preserves the radiographic properties of the BEST 2301 seed in both plain x rays and CT images, and a preliminary experiment demonstrates thermal self-regulation and adequate heating of a tissue-mimicking phantom by seed prototypes. The effect of self-shielding of the seed against the external magnetic field is small, and only minor thermal stress is induced in heating of the seeds from room temperature to well above the seed operating temperature. With proper selection of magnetic field parameters, the thermal dose distribution of an arrangement of TB and hyperthermia-only seeds may be made to match with its radiation dose distribution.

CONCLUSIONS

The presented analyses address several practical considerations for manufacturing of the proposed TB seeds and identify critical issues for the prototype implementation. The authors' preliminary experiments demonstrate close agreement with the modeling results, confirming the feasibility of combining sources of heat and radiation into a single thermobrachytherapy seed.

The heat shock response: Role in radiation biology and cancer therapy

Since prehistoric times, elevated temperatures have been used to treat cancer in a variety of forms. In modern times (the last 40 years) efforts have concentrated on combining heat with other anti-tumour modalities, principally ionizing radiation and some chemotherapeutic drugs. Despite the emphasis on combined therapy, rodent data relating to heat sensitivity and thermal tolerance development assumed principal importance. These considerations suggested treating at 43 degrees C as a target temperature and fractionation schemes emphasizing thermal tolerance avoidance. Concomitantly crucial data on heat-induced tumour reoxygenation and its temperature dependence were largely ignored. In reality these were unrealistic and undesirable goals. The preponderance of evidence now suggests that lower temperatures (40-42 degrees C) administered more frequently, optimally immediately before and during each administration of ionizing radiation, are likely to yield optimal results. Factoring in trimodality therapy and other combinations of chemotherapeutic drugs will require some modifications of such fractionation schemes.

Present and future technology for simultaneous superficial thermoradiotherapy of breast cancer

This paper reviews systems and techniques to deliver simultaneous thermoradiotherapy of breast cancer. It first covers the clinical implementation of simultaneous delivery of superficial (microwave or ultrasound) hyperthermia and external photon beam radiotherapy, first using a Cobalt-60 teletherapy unit and later medical linear accelerators. The parallel development and related studies of the Scanning Ultrasound Reflector Linear Arrays System (SURLAS), an advanced system specifically designed and developed for simultaneous thermoradiotherapy, follows. The performance characteristics of the SURLAS are reviewed and power limitation problems at high acoustic frequencies (>3 MHz) are discussed along with potential solutions. Next, the feasibility of simultaneous SURLAS hyperthermia and intensity modulated radiation therapy/image-guided radiotherapy (IMRT/IGRT) is established based on published and newly presented studies. Finally, based on the encouraging clinical results thus far, it is concluded that new trials employing the latest technologies are warranted along with further developments in treatment planning.

Magnetic nanoparticle hyperthermia for prostate cancer

Magnetic nanoparticles are increasingly used for clinical applications such as drug delivery, magnetic resonance imaging and magnetic fluid hyperthermia. A novel method of interstitial heating of tumours following direct injection of magnetic nanoparticles has been evaluated in humans in recent clinical trials. In prostate cancer this approach has been investigated in two separate phase I studies, employing magnetic nanoparticle thermotherapy alone and in combination with permanent seed brachytherapy. The feasibility and good tolerability was shown in both trials, using the first prototype of an alternating magnetic field applicator. As with any other heating technique, this novel approach requires specific tools for planning, quality control and thermal monitoring, based on appropriate imaging and modelling techniques. In these first clinical trials a newly developed method for planning and non-invasive calculations of the 3-dimensional temperature distribution based on computed tomography was validated. Limiting factors of the new approach at present are patient discomfort at high magnetic field strengths and irregular intratumoural heat distribution. Until these limitations are overcome and thermoablation can safely be applied as a monotherapy, this treatment modality is being evaluated in combination with irradiation in patients with localised prostate cancer.

Adverse effect of mild temperature hyperthermia combined with hexamethylenetetramine compared to its effect combined with tirapazamine in the treatment of solid tumors

This study aimed to assess the effect on solid tumors of mild temperature hyperthermia (MTH) combined with hexamethylenetetramine (HMTA) or tirapazamine (TPZ). Squamous cell carcinoma (SCC VII) tumor-bearing mice were continuously administered 5-bromo-2'-deoxyuridine (BrdU) to label intratumor proliferating (P) cells. Mice received HMTA or TPZ through intraperitoneal single or subcutaneous continuous administration, with or without MTH (40°C, 60 min), followed or not by γ-ray irradiation or cisplatin treatment. After HMTA or TPZ administration without γ-ray irradiation or cisplatin treatment, immediately after γ-ray irradiation, or 1 h after cisplatin treatment, the response of quiescent (Q) cells was assessed in terms of micronucleus frequency using immunofluorescence staining for BrdU. The response of the total (P + Q) tumor cells was determined based on a comparison with non-BrdU-treated tumors. Without MTH, HMTA and TPZ had a nearly equal radiosensitizing and cisplatin sensitivity-enhancing effect on both total and Q cells. With MTH, radio- and cisplatin-sensitizing effects by HMTA were reduced, particularly in the Q cells. In contrast, the enhancing effects of TPZ were increased, particularly in the Q cells. Continuous administration of HMTA and TPZ resulted in higher radio- and cisplatin-sensitizing effects than intraperitoneal single administration. In terms of tumor cytotoxicity as a whole, including Q cells, the administration of γ-ray irradiation or cisplatin treatment combined with continuous HMTA administration is promising, taking into account the clinical use of HMTA. However, MTH should not be combined with HMTA administration.

Role of nuclear protein denaturation and aggregation in thermal radiosensitization

Hyperthermia at temperatures above 41 degrees C denatures a set of thermolabile cellular proteins located in all parts of the cell. Non-histone nuclear proteins, including those comprising the nuclear matrix, appear to be particularly thermolabile. Heating isolated nuclear matrices of Chinese hamster lung (CHL) V79 cells to 46 degrees C at 1 degree C/min results in approximately 15% denaturation. Protein unfolding during denaturation exposes buried hydrophobic residues, which increases protein-protein interactions and results in the co-aggregation of denatured thermolabile proteins and native, aggregative-sensitive nuclear proteins. This aggregated protein, the majority of which is native, is insoluble and resistant to extraction during isolation of nuclei and is responsible for the increased protein content, usually expressed as an increased protein:DNA ratio, of nuclei isolated from heated cells. A large fraction of the aggregated protein is found to be associated with the nuclear matrix, distributed throughout the fibre network and nucleolus. Three general consequences of nuclear protein denaturation and aggregation of relevance to cellular damage are: (1) protein (enzyme) inactivation, both direct inactivation of thermolabile proteins and indirect inactivation due to co-aggregation; (2) reduced accessibility and altered physical properties of DNA due to masking by aggregated protein; and (3) protein redistribution into and out of the nucleus. Functional impairment of the nucleus appears to be due to one or a combination of these basic mechanisms.

Feasibility of concurrent treatment with the scanning ultrasound reflector linear array system (SURLAS) and the helical tomotherapy system

PURPOSE

To evaluate the feasibility of concurrent treatment with the scanning ultrasound reflector linear array system (SURLAS) and helical tomotherapy (HT) intensity modulated radiation therapy (IMRT).

METHODS

The SURLAS was placed on a RANDO phantom simulating a patient with superficial or deep recurrent breast cancer. A megavoltage CT (MVCT) of the phantom with and without the SURLAS was obtained in the HT system. MVCT images with the SURLAS were obtained for two configurations: (1) with the SURLAS's long axis parallel and (2) perpendicular to the longitudinal axis of the phantom. The MVCT simulation data set was then transferred to a radiation therapy planning station. Organs at risk (OAR) were contoured including the lungs, heart, abdomen and spinal cord. The metallic parts of the SURLAS were contoured as well and constraints were assigned to completely or directionally block radiation through them. The MVCT simulation data set and regions of interest (ROI) files were subsequently transferred to the HT planning station. Several HT plans were obtained with optimization parameters that are usually used in the clinic. For comparison purposes, planning was also performed without the SURLAS on the phantom.

RESULTS

All plans with the SURLAS on the phantom showed adequate dose covering 95% of the planning target volume (PTV D95%), average dose and coefficient of variation of the planning target volume (PTV) dose distribution regardless of the SURLAS's orientation with respect to the RANDO phantom. Likewise, all OAR showed clinically acceptable dose values. Spatial dose distributions and dose-volume histogram (DVH) evaluation showed negligible plan degradation due to the presence of the SURLAS. Beam-on time varied depending on the selected optimization parameters.

CONCLUSION

From the perspective of the radiation dosage, concurrent treatment with the SURLAS and HT IMRT is feasible as demonstrated by the obtained clinically acceptable treatment plans. In addition, proper orientation of the SURLAS may be of benefit in reducing dose to organs at risk in some cases.

Influence of the SURLAS applicator on radiation dose distributions during simultaneous thermoradiotherapy with helical tomotherapy

Simultaneous thermoradiotherapy has been shown to maximize the effect of hyperthermia as a radiation sensitizer in cancer treatment. Here we follow our previous work on feasibility of thermoradiotherapy with the scanning ultrasound reflector linear array system (SURLAS) and TomoTherapy HiArt treatment system, and investigate the influence of the SURLAS hyperthermia applicator on delivered radiation dose with the TomoTherapy. A radiation treatment plan was calculated and the treatment was delivered to a phantom with SURLAS on top simulating the likely clinical setup. Proper positioning of the SURLAS was assisted with a magnetic position-and-orientation tracking device (POTD) and was verified with megavoltage-computed tomography. The delivered dose was measured with an ionization chamber (point measurement) and a radiographic film (2D dose distributions). The planned and delivered point dose data agreed within 0.61% +/- 0.63%. Planar dose data agreed within a dose difference of < or =3% of the maximum dose, and a distance-to-dose-agreement of < or =1 mm. The susceptibility of the delivered radiation dose on correct SURLAS positioning was studied as well. The largest dose discrepancy was measured for a position for which a maximum number of radiation beams intersected the incorrectly positioned SURLAS within one TomoTherapy gantry rotation. The point dose disagreed by 6.14% +/- 0.52%, and 2.25% of pixels of the 2D dose distribution did not pass the 3% dose difference/1 mm distance-to-dose-agreement criteria. Our study showed that correct positioning of the SURLAS applicator had an influence on the delivered radiation dose. Delivered and planned dose distributions were in an excellent agreement when SURLAS was positioned according to the treatment plan. Moving the applicator from its planned position was found to cause a modification of delivered dose distributions. A precise and reproducible positioning of the applicator was assured with a POTD.

[Thermal therapy of prostate cancer using magnetic nanoparticles]

A novel method of interstitial heating using magnetic nanoparticles and a direct injection technique has been evaluated in human cancers in recent clinical trials. In prostate cancer, this approach was investigated in two separate phase-I-studies, employing magnetic nanoparticle thermotherapy alone and in combination with permanent seed brachytherapy. The feasibility and good tolerability was shown in both trials, using the first prototype of a magnetic field applicator. As with any other heating technique, this novel approach requires specific tools for planning, quality control and thermal monitoring, based on appropriate imaging and modelling techniques. In these first clinical trials, a newly developed method for planning and non-invasive calculations of the 3-dimensional temperature distribution based on computed tomography could be validated. Limiting factors of this approach at present are patient discomfort at high magnetic field strengths and suboptimal intratumoral distribution of nanoparticles. Until these limitations will be overcome and thermal ablation can safely be applied as a monotherapy, this treatment modality is being evaluated in combination with irradiation in patients with localized prostate cancer.

Inhibition of repair of radiation-induced damage by mild temperature hyperthermia, referring to the effect on quiescent cell populations

PURPOSE

We evaluated the usefulness of mild temperature hyperthermia (MTH) as an inhibitor of the repair of radiation-induced damage in terms of the responses of the total [= proliferating (P) + quiescent (Q)] and Q cell populations in solid tumors in vivo.

MATERIALS AND METHODS

SCC VII tumor-bearing mice received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all P cells. They then underwent high-dose-rate (HDR) gamma-ray irradiation immediately followed by MTH or administration of caffeine or wortmannin; alternatively, they underwent reduced-dose rate gamma-ray irradiation simultaneously with MTH or administration of caffeine or wortmannin. Nine hours after the start of irradiation, the tumor cells were isolated and incubated with a cytokinesis blocker, and the micronucleus (MN) frequency in cells without BrdU labeling (= Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total tumor cell population was determined using tumors that were not pretreated with BrdU.

RESULTS

In both the total and Q-cell populations, especially the latter, MTH efficiently suppressed the reduction in sensitivity caused by leaving an interval between HDR irradiation and the assay and decreasing the irradiation dose rate, as well as the combination with wortmannin administration.

CONCLUSION

From the viewpoint of solid tumor control as a whole, including intratumor Q-cell control, MTH is useful for suppressing the repair of both potentially lethal and sublethal damage.

Hyperthermia, cisplatin and radiation trimodality treatment: a promising cancer treatment? A review from preclinical studies to clinical application

This review discusses available clinical and experimental data and the underlying mechanisms involved in trimodality treatment consisting of hyperthermia, cisplatin and radiotherapy. The results of phase I/II clinical trials show that trimodality treatment is effective and feasible in various cancer types and sites with tolerable toxicity. Based on these results, phase III trials have been launched to investigate whether significant differences in treatment outcome exist between trimodality and standard treatment. In view of the clinical interest, it is surprising to find so few preclinical studies on trimodality treatment. Although little information is available on the doses of the modalities and the treatment sequence resulting in the largest degree of synergistic interaction, the results from in vivo and in vitro preclinical studies support the use of trimodality treatment for cancer patients. Animal studies show an improvement in treatment outcome after trimodality treatment compared with mono- and bimodality treatment. Studies in different human tumour cell lines show that a synergistic interaction can be obtained between hyperthermia, cisplatin and radiation and that this interaction is more likely to occur in cell lines which are more sensitive to cisplatin.

SURLAS: A new clinical grade ultrasound system for sequential or concomitant thermoradiotherapy of superficial tumors: Applicator description

A new ultrasound applicator with three-dimensional power distribution control was developed for simultaneous thermoradiotherapy. The system was named SURLAS for Scanning Ultrasound Reflector Linear Arrays System. In this paper, the hardware of the first clinical grade SURLAS applicator is described with emphasis on clinically important static acoustic characteristics and on construction aspects not reported before. Functionally, the SURLAS applicator consists of two parallel opposed ultrasound linear arrays aiming their acoustic beams to a V-shape scanning ultrasound reflector, which deflects the beams coming from opposite directions toward the treatment area. The reciprocating motion of the reflector in-between the arrays spreads the ultrasonic energy over the target area scanned. Control of power deposition over the 16 cm by 16 cm treatment window area is achieved by adjusting the power input into the transducer elements of the arrays as a function of the position of the scanning reflector. Furthermore, the arrays operate at significantly different frequencies (1.9 and 4.9 MHz) so that intensity modulation of beams of different frequencies can be exploited to adjust the depth of energy penetration. With this design, external electron or photon beams can be concurrently delivered with hyperthermia by irradiating through the applicator's body. Safety features were implemented into the applicator's design to monitor its performance during operation. A detailed description of the applicator including impedance matching circuits/filters, radiation force balance power measurements, hydrophone pressure field distribution measurements, as well as safety test results are reported.