Heating characteristics of a 434 MHz transurethral system for the treatment of BPH and interstitial thermometry

Blood flow and oxygenation status of prostate cancers

Hypoxia is a characteristic of many solid tumors, can lead to the development of an aggressive phenotype and acquired treatment resistance, and is an independent, adverse prognostic indicator. In this literature review, we show that hypoxia is also a typical feature in prostate cancer (PC), the most commonly diagnosed cancer among men in most western countries. Data on blood flow (a major determinant of oxygenation status in malignancies) and on the oxygenation status (as assessed by O(2)-sensitive electrodes) are presented. Where possible, data on prostate cancers are compared to normal prostate (NP) tissue and benign prostate hyperplasia (BPH). The average blood flow rate in NP is 0.21 vs. 0.28 mL/g/min in BPH. Blood flow in PC is approximately three times higher than in NP (mean flow: 0.64 mL/g/min) and shows pronounced intra- and inter-tumor variability. Despite relatively high flow rates in PC, the overall mean pO(2) in cancers is 6 mmHg compared to 26 mmHg in NP. As was the case with blood flow, tissue oxygenation was extremely heterogeneous with no clear dependency on a series of tumor (Gleason score, clinical size, androgen deprivation) and patient characteristics (serum PSA levels, age).

Prostate perfusion in patients with locally advanced prostate carcinoma treated with different hyperthermia techniques

PURPOSE

We determined prostate perfusion in 18 patients with locally advanced prostate carcinoma treated with a combination of external beam irradiation and regional (10) or interstitial (8) hyperthermia.

MATERIALS AND METHODS

Perfusion values were calculated from temperature elevations due to constant applied power and from transient temperature measurements after a change in applied power. Student's t test was used for comparing perfusion values with time and in the 2 groups.

RESULTS

At the start of regional hyperthermia treatment mean estimated perfusion plus or minus standard deviation was 10 +/- 8 ml./100 gm. per minute. At the end of treatment mean perfusion was increased to 14 +/- 2 ml./100 gm. per minute (p <0.01). Achieved thermal parameters were a mean temperature of at least 40.3C +/- 0.6C in 90% of the prostate, 40.9C +/- 0.6C in 50% and a mean maximum temperature of 41.6C +/- 0.6C. At the end of interstitial hyperthermia treatment estimated mean perfusion was 47 +/- 5 ml./100 gm. per minute, which was significantly different compared with the end of regional hyperthermia (p < 0(-7) ). Mean temperature was at least 39.4C +/- 0.9C in 90% of the prostate and 41.8C +/- 1.6C in 50%, while mean maximum temperature was 53.1C +/- 6.3C. Systemic temperature increased during regional hyperthermia up to 38.6C, whereas during interstitial hyperthermia body temperature was not elevated.

CONCLUSIONS

During interstitial hyperthermia perfusion values are higher than during regional hyperthermia. Hyperthermia causes increased prostate perfusion.

Three-dimensional controlled interstitial hyperthermia combined with radiotherapy for locally advanced prostate carcinoma--a feasibility study

PURPOSE

To perform a feasibility study of three-dimensional spatially controlled interstitial hyperthermia for locally advanced prostate cancer.

METHODS AND MATERIALS

Twelve patients with prostate cancer (T3NxM0) were treated with conventional external beam radiotherapy and one interstitial hyperthermia treatment. Hyperthermia was delivered with the 27-MHz multielectrode current source (MECS) interstitial hyperthermia technique on an outpatient basis. Guided by transrectal ultrasonography, 12 catheters (range 7-16) were placed in the prostate through a template. Two electrodes per probe were inserted. Thermometry (average 100 sensors) was performed from within the probes for online temperature control. Additional thermometry was done in the prostate, rectum, urethra, and bladder. Reconstruction was done by sonography. Prostate perfusion was estimated from the thermal decay at the end of treatment. The full three-dimensional temperature distribution was calculated.

RESULTS

No toxicities greater than Grade 2 were recorded. A learning curve for implantation, position verification, reconstruction, and temperature simulation was experienced. Perfusion was 47 mL/100 g/min (range 30-65). The average measured temperature was T(90) (90% of the prostate reached a temperature of at least:) 39.9 degrees C and T(50) 44.1 degrees C. The average calculated temperatures were lower: T(90), 39.4 degrees C and T(50), 41.8 degrees C, because the entire prostate was taken into account. The tumor temperatures were T(90), 40.7 degrees C and T(50), 43.0 degrees C. The bladder and rectal temperatures were below the safety limits.

CONCLUSION

Multielectrode-current-source interstitial hyperthermia is technically feasible and well tolerated. It was not possible to achieve the goal temperature of 42-43 degrees C because of high perfusion and implantation limitations.

Determination and validation of the actual 3D temperature distribution during interstitial hyperthermia of prostate carcinoma

To determine the thermal dose of a hyperthermia treatment, knowledge of the three-dimensional (3D) temperature distribution is mandatory. The aim of this paper is to validate an interstitial hyperthermia treatment planning system with which the full 3D temperature distribution can be obtained in individual patients. Within a phase I study, 12 patients with prostate cancer were treated with interstitial hyperthermia using our multi electrode current source interstitial hyperthermia treatment (MECS IHT) system. The temperature distribution was measured from within the heating devices and by additional thermometry. The perfusion level was estimated and the heating implant reconstructed. The steady-state temperature distribution was calculated using our interstitial hyperthermia treatment planning system. The simulated temperature distribution was validated by individually comparing the measured and simulated thermo-sensors, both for the thermometry integrated with the heating applicators and the additional thermometry. The entire procedure was also performed on a no-flow agar-agar phantom. It was shown that the calculated temperature distribution of an individual patient during MECS interstitial hyperthermia is very heterogeneous. The validation indicates that the calculated temperature elevations match the measurements within approximately 1 degrees C. Possible improvements are more precise reconstruction, incorporation of discrete vasculature and using a temperature-dependent, heterogeneous perfusion distribution. Further technical improvements of the MECS-IHT system may also result in better temperature calculations.

Optimizing transurethral microwave thermotherapy: a model for studying power, blood flow, temperature variations and tissue destruction

OBJECTIVE

To examine the role of microwave power and blood flow on temperature variations and tissue destruction in the prostate, using a theoretical model of transurethral microwave thermotherapy (TUMT), and thus compare fixed-energy TUMT with no intraprostatic temperature monitoring (constant microwave power applied over a fixed period) with 'feedback' TUMT in which the microwave power is adjusted according to the monitored intraprostatic temperature.

MATERIALS AND METHODS

The temperature distribution in the prostate was modelled for a typical TUMT catheter at various blood flow rates. The volume of tissue destroyed was simultaneously calculated from cell survival data after thermal exposure. The calculated quantity of tissue destroyed at the different microwave power levels and blood flow rates was used to describe qualitatively the simulated treatments.

RESULTS

Treatment monitoring and consistency were better during feedback TUMT than fixed-energy TUMT, in that the former compensated for variations in blood flow rate. The modelled values agreed with observations during real TUMT.

CONCLUSIONS

Blood flow rate is a key factor in the outcome of TUMT. Only by measuring intraprostatic temperature is it possible to compensate for the large variations in prostatic blood flow and obtain consistent treatment results. Repeated interruptions prompted by high rectal temperatures should be minimized and preferably avoided, as the quantity of tissue destroyed is then greatly reduced, and in extreme cases the treatment is totally ineffective.