A technique for combining microwave hyperthermia with intraluminal brachytherapy of the oesophagus

Biological cell survival mapping for radiofrequency intracavitary hyperthermia combined with simultaneous high dose-rate intracavitary irradiation

We examined the best way to combine recently developed radiofrequency intracavitary hyperthermia with simultaneous high dose-rate intracavitary brachytherapy in an original experimental model. Temperature distribution was measured with an experimental phantom which was immersed in a water bath with the temperature controlled at 37 degrees C. Radiation dose distribution was calculated with a treatment-planning computer. Cell survival was measured by colony assay with HeLa-TG cells in vitro. Radiation dose response at 1 - 7 Gy and time response with hyperthermia in the range of 40 - 46 degrees C were estimated. Radiation dose-response curves in simultaneous treatment with hyperthermia for 30 min at 37 to 46 degrees C were estimated and the surviving fractions in combined treatment were plotted against temperature. For intracavitary radiation alone, cell survival rates increased with increasing distance from the source. For intracavitary hyperthermia alone, the maximum temperature was observed at a depth of 13 mm from the surface of the applicator under suitable treatment conditions. Homogeneous cell killing from the surface of the applicator to a tumor depth of 13 mm was observed under a specific treatment condition. Our experimental model is useful for evaluating the best simultaneous combined treatment.

Quantification of the 3-D electromagnetic power absorption rate in tissue during transurethral prostatic microwave thermotherapy using heat transfer model

Experiments were performed in a tissue microwave-equivalent phantom gel to quantitatively examine the volumetric heating produced by a microwave antenna with a peripheral cooling system for the transurethral prostatic thermotherapy. Based on previous research, expression for the specific absorption rate (SAR) of microwave energy in the gel was extended to three dimensions, which includes its dependence on radial, angular, and axial direction. A theoretical heat transfer model was developed to study the temperature distribution in the gel by introducing this proposed SAR expression. The parameters in this expression and the convection coefficient due to the chilled water running around the antenna were determined using a least-square residual fit of the theoretical temperature predictions to the experimentally measured steady-state temperature field within the gel. The analytical expression of the three-dimensional SAR distribution obtained in this study will help provide a better understanding of the microwave heating pattern in the prostatic tissue and, thus, to aid in designing improved applicators. It can also be used in the future as an accurate input to heat transfer models which predict temperature distributions during the transurethral microwave thermotherapy.

A pilot study of intracavitary hyperthermia combined with radiation in the treatment of oesophageal carcinoma

Twenty-five patients with primary squamous cell carcinoma of the oesophagus were treated with intracavitary hyperthermia combined with external beam radiation and intraluminal radiation at Nanjing Jinling Hospital, China. External beam radiation was given with a 6-MV X-ray; 1.8-2.0 Gy per fraction and five fractions per week; this brought the total dose to 60 Gy. Two weeks later, hyperthermia was applied with 915 MHz microwave intracavitary applicators, which were designed at the City of Hope. Temperature measurements were obtained while moving fibreoptic temperature sensors at 1.0 cm intervals in each of the six peripheral channels of the applicator. Hyperthermia was applied for 1 h before and after the intraluminal radiation. Intraluminal radiation was provided by low dose-rate iridium-192 ribbons in the same intracavitary applicator, giving 30 Gy at 0.75 cm from the applicator surface. The 3-month post-treatment responses showing complete response, partial response, no change and progressive disease were 60% (15/25), 24% (6/25), 8% (2/25) and 8% (2/25) respectively. The median follow-up time was 17 months (range 4-29 months). The 1- and 2-year overall survival rates were 72% (18/25) and 32% (8/25) respectively, and disease-free survival rates were 47 and 30% respectively. The median overall survival and disease-free survival periods were 17 and 10 months respectively. Fourteen patients had local recurrence (either at the primary site or in the lymph node) or had local progression, and five developed metastases. The median duration of the onset of local recurrence or of local progression was 9.5 months (range 0-20 months); the median of distant metastases was 8 months (range 2-16 months). Seventeen patients died. Of these, 15 died of cancer: six with local recurrence alone, four with local progression primary cancer alone, three with distant metastases alone, and two with both local and distant failure. Two patients with complete response of the primary disease died of other diseases. The toxicity was mild. According to the mucous reaction scoring criteria of the Radiation Therapy Oncology Group, the acute toxicity grades I, II, III and IV were 0% (0/25), 20% (5/25), 48% (12/25) and 32% (8/25) respectively. The major late complication was a mild oesophagus fibrosis and difficult swallowing. No serious side effects (grade IV), fistulas or perforations were seen. These results indicate that this method is safe and feasible for treating oesophageal carcinoma.

Advanced esophageal carcinoma

From 1976 until 1990 a total of 212 patients with squamous cell carcinoma of the thoracic esophagus were referred for surgical treatment. Resectability was 84.1% (161 of 191). Actuarial 5-year survival in patients with negative lymph nodes was 51.2% versus 12.4% in lymph node-positive patients. Therefore advanced carcinoma was defined to compromise all patients with involved regional (N1) or distal lymph nodes (M+Ly) as well as patients with T4 tumors or solid organ metastasis (M+org) irrespective of their lymph node status. Comparing complete (R0) versus incomplete (R1-R2) resections for stage III and IV carcinoma revealed 20% and 0% five-year survivals, respectively. There was no 5-year survival in the stage IV group. When excluding solid organ metastasis, the median survival shifted from 8.5 months after incomplete (R1-R2) to 20 months after complete (R0) resection. In 1991 three-field lymphadenectomy was initiated that included bilateral cervical lymphadenectomy. Thirty-seven patients have been treated so far (23 squamous cell carcinoma, 14 adenocarcinomas). Cervical lymph nodes were positive in 24.3% with an incidence up to 28.5% for distal-third carcinoma. Subsequently, 6 patients (16%) moved from M0 to M+Ly status. Our results confirm the key role of surgery not only in improving survival and locoregional tumor control but in refining the accuracy of staging advanced carcinomas provided complete resection is possible.(ABSTRACT TRUNCATED AT 250 WORDS)

Transurethral microwave hyperthermia for benign prostatic hyperplasia: the Leuven clinical experience

Local microwave hyperthermia, delivered transurethrally or transrectally, is a new treatment modality for benign prostatic hyperplasia. We started transurethral application, delivering 915-MHz microwaves at the prostatic urethra using a helical microwave antenna incorporated in a Foley catheter. This hyperthermia was given without a urethral surface cooling system. Thermophysical testing of the applicator proved therapeutic efficacy in vitro and in vivo. Pathologic studies demonstrated hyperthermia-induced lesions in the periurethral prostatic tissues and permitted us to hypothesize a working mechanism of transurethral hyperthermia. Clinical Phase I and II studies showed clinical efficacy in patients with urinary retention or prostatism secondary to benign hyperplasia, especially in bilobar or trilobar prostatic configurations. While awaiting results of further pathologic and thermophysical experimental work and ongoing Phase II and III studies, we consider transurethral hyperthermia an investigational but promising conservative treatment modality for benign prostatic hyperplasia.

Heating pattern of helical microwave intracavitary oesophageal applicator

Helical microwave intracavitary oesophageal (HMIO) applicators were designed to operate at frequencies of 433 MHz and 915 MHz. Heating patterns were studied within muscle-equivalent phantom by thermographic camera and fibreoptic thermometers. The results showed that frequency significantly influenced the microwave heating pattern. The 433 MHz applicator had a single power deposition region, the longitudinal specific absorption rate (SAR) distribution appeared to be nearly even, and the maximum SAR value occurred close to the centre of the active length of the applicator. The 915 MHz applicator had two power deposition regions, the peak SAR values occurred at about 1/4 and 3/4 of the active length respectively. The radial SAR distribution suggested that there is no obvious difference between the 433 MHz and 915 MHz applicators in that the average radial penetration of 50% surface SAR (RP50) was about 0.65 cm. It was also shown that power deposition was axially symmetric for both 433 MHz and 915 MHz HMIO applicators. It is shown that better impedance matching is more important for intracavitary hyperthermia than for external hyperthermia. Choosing HMIO applicators in clinical practice is also discussed.

The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities

The results of a simulation study and subsequent experimental verification on the feasibility of using electrically focused arrays for intracavitary ultrasound hyperthermia are presented. The relative acoustic pressure fields from these cylindrical phased arrays were calculated for different dimensions and acoustic parameters to determine relevant design criteria. A thermal model based on the bioheat transfer equation was used to compute the resulting steady-state temperature distributions in tissue for various array configurations. This study has shown that cylindrical arrays of a practical size (75 mm long, 15 mm OD), resonating at 0.5 MHz with individual elements that are 1.5-mm wide, can preferentially heat regions that are between 20 and 50 mm from the surface of the array. In addition, it was shown that the temperature distribution can be further controlled by varying the focal position within the target volume, producing heated regions up to 40 mm wide. If practical constraints (i.e. number of amplifiers available or minimum element size attainable) become a limiting factor, arrays with wider elements would also be functional, but with certain restrictions applied to their flexible heating patterns. Thus, these electrically focused ultrasound arrays appear to offer a significant improvement over the existing intracavitary hyperthermia methods by producing a deeper and more controlled energy deposition.

Heating characteristics of a helical microwave applicator for transurethral hyperthermia of benign prostatic hyperplasia

A new applicator for intraurethral hyperthermic treatment of benign prostatic hyperplasia is described. The applicator uses an insulated helical antenna wound on the outer surface of a silicone urological (Foley) balloon catheter. The balloon catheter assures rapid and reproducible localization of the antenna in the prostatic urethra. Two small cannulae are fixed to the exterior surface of the applicator. One holds a temperature control sensor at a fixed location, the other is used to map temperature along the applicator. Two-dimensional SAR and steady-state temperature distributions measured in a plane tangent to the applicator in a tissue-equivalent phantom are presented, as well as longitudinal temperature distributions measured in situ at the applicator-urethral interface. Prostatic temperatures were also measured intraoperatively. The applicator appears to be capable of elevating temperature to greater than 42 degrees C in a cylindrically symmetric volume of about 4 cm length and about 0.5 cm radial penetration surrounding the antenna. The heating characteristics of this applicator are similar to an earlier design that employed an array of three dipoles. The helical applicator is narrower, more flexible and simpler to use than the earlier design.

Transurethral microwave hyperthermia for benign prostatic hyperplasia: preliminary clinical and pathological results

Transurethral microwave hyperthermia is a new conservative treatment modality for benign prostatic hyperplasia. We treated 15 patients with 915 MHz. microwaves delivered transurethrally by a helical applicator. Of the patients 12 showed substantial objective and subjective improvement of obstructive outflow parameters. Significant improvement in objective study parameters included increased mean flow rate (p less than 0.00021), decreased mean residual volume (p less than 0.00001) and decreased mean prostatic volume (p less than 0.0077). Analysis of patterns of failure showed chronic bladder atony, prostate asymmetry and middle lobe configuration as important factors that could explain the failure of hyperthermia in 3 patients. Toxicity was mild, consisting of bladder spasms, perineal pain, dysuria and hematuria. Hyperthermia-induced pathological changes in prostatic tissues, causing periurethral shrinking and secondary dilatation of the prostatic urethra, are described. The reported clinical results of this phase I study are preliminary due to the short followup. A phase II study to optimize transurethral hyperthermia currently is underway. A phase III study is to be phased in comparing hyperthermia with transurethral resection of the prostate.

Thermoradiotherapy of patients with locally advanced carcinoma of the rectum

The effectiveness of local hyperthermia was investigated in 56 patients with locally advanced carcinoma of the rectum (T4N0M0). All received combined heat and radiation therapy as a pre-operative treatment. The control group consisted of 59 patients with the same stage of disease as those who were only irradiated. Both groups of patients underwent the same surgical procedure. The total tumour dose of ionizing radiation was 40 Gy in 10 fractions, three times a week. The tumour was heated four or five times to a maximum of 42-43 degrees C by electromagnetic waves with a frequency of 905 MHz before irradiation. Each heating session lasted 60 min. Patients were selected on the principle of randomization: 16.1% of patients (n = 9; n: actual number of patients) showed complete response and 53.6% (n = 30) showed significant regression of the primary tumour compared with 1.7% (n = 1) and 33.9% (n = 20) in the control group, respectively. The differences were significant (p less than 0.05). It was found that thermoradiotherapy allowed the 5-year survival rate of patients to increase up to 35.6% (n = 12) compared with 6.6% (n = 7) in the control group (p less than 0.05).