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G C van Rhoon

Publications and source records attributed to G C van Rhoon.

At least 19 recordsLinked to original sources
PubMed2006

Effects of waterbolus size, shape and configuration on the SAR distribution pattern of the Lucite cone applicator.

The effects of waterbolus dimensions and configuration on the effective field size (EFS) of the Lucite cone applicator (LCA) for superficial hyperthermia are presented. The goal of the research is to develop guidelines which mark out a sub-set of optimal LCA-waterbolus set-ups. The effects of variations in (i) waterbolus thickness, (ii) waterbolus area, (iii) waterbolus length/width ratio and (iv) eccentric placement of the applicator have been investigated in an FDTD model study. The prominent effects are verified with IR thermography measurements. An optimal EFS value of 80 cm2 is found for waterbolus area of 200-400 cm2. A small (10 x 10 cm2) waterbolus area restricts the EFS to 25% of the optimal value. The sensitivity to sub-optimal waterbolus area and length/width ratio increases with waterbolus height. Eccentric placement of the LCA near the waterbolus edge reduces the EFS to up to 50% of the optimal value. The IR measurements confirm the model findings. Based on the results, the following guidelines for the clinical application of the LCA have been defined: the waterbolus (i) should extend the LCA aperture at least 2.5 cm, especially at the Lucite windows, and (ii) the height should not exceed 2 cm.

Hyperthermia, Induced↗
PubMed2005

Leg coverage with towels during regional deep hyperthermia treatment and its effect on pelvic temperature and temperature distribution.

INTRODUCTION: The feasibility and its effects on pelvic temperature distribution of covering the legs with towels during the second half of the deep hyperthermia treatment (DHT) is evaluated. PATIENTS AND METHODS: Patients treated with DHT and radiotherapy were randomized to an alternating treatment schedule: 2nd and 4th treatment or 3rd and 5th treatment with the legs covered with towels in the second half of the treatment. Intra-luminal temperatures (vesical, vaginal and rectal) classified as tumour indicative (TI) or tumour contact (TC), oral temperature, applied maximum power and power at the end of the treatment were measured and compared between the two treatment schedules. RESULTS: Fourteen female patients receiving a total of 51 treatments, 24 with and 27 without towels, were included for analysis. The mean intra-luminal, TI and TC temperatures, standard deviation and range for each site were calculated. The applied power was documented. There were no significant differences in any of the measured temperatures. There were no significant differences in the applied power. In only three treatments, the towels were removed preliminarily. CONCLUSION: In the authors' experience, covering the legs with towels during the second half of DHT does not result in significantly higher or more homogeneous pelvic temperatures. There is no indication that the TC and TI temperatures are higher compared to all pelvic temperatures when towels are applied. Regarding the used power, there is no significant decrease with towels placed on the legs. Coverage of the legs does not increase the systemic temperature. Isolating the legs with a water-perfused heater is considered.

Adult↗
PubMed2004

Re-irradiation and hyperthermia for recurrent breast cancer in the orbital region: a case report.

Based on the good results of re-irradiation plus hyperthermia in breast cancer recurrences on the chest wall, it was decided to offer similar treatment to a patient with recurrent metastatic breast cancer in the orbital region. A female patient was diagnosed in 1997 with breast cancer stage T4N0M0. She was treated with six neo-adjuvant chemotherapy courses and mastectomy, followed by hormonal treatment. In December 1998, she was diagnosed with metastatic disease in the medial upper quadrant of the left orbit. This was excised, followed by 40 Gy radiotherapy. Nine months later, the tumour had recurred in the left orbit at the margin of the radiotherapy field. This again was treated with surgery, followed by 30 Gy radiotherapy. Two months thereafter, the eyelid tumour progressed and hormonal therapy was changed, without an effect on the eyelid tumour. Screening gave no evidence of tumour activity elsewhere. The patient preferred treatment with re-irradiation plus hyperthermia to a surgical approach. Eight fractions of 4 Gy were given in 4 weeks, combined with once weekly hyperthermia. One week after treatment, the tumour had regressed completely. The patient died 22 months following treatment. Until last follow-up, a few weeks before death, the patient mentioned a dry left eye for which she used eyedrops, an unchanged vision and no further difficulties. On examination, there was epilation of the eyelids, a slight conjunctival oedema, no subcutaneous fibrosis and no evidence of tumour regrowth. For this patient, a surgical approach would have resulted in loss of the left eye. Toxicity of re-irradiation plus hyperthermia might lead to either a loss of vision or a delayed loss of her left eye due to treatment-induced toxicity. The chosen local treatment resulted in a very good palliative effect, which lasted for the patient's remaining lifetime of 22 months.

Aged↗
PubMed2004

Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia.

The electrical performance of the CFMA-12 operating at 433 MHz is assessed under laboratory conditions using a RF network analyser. From measurements of the scattering parameters of the CFMA-12 on both a multi-layered muscle- and fat/muscle-equivalent phantom, the optimal water bolus thickness, at which the transfer of the energy to the phantom configuration is maximal, is determined to be approximately 1 cm. The SAR distribution of the CFMA-12 in a multi-layered muscle-equivalent phantom is characterized using Schottky diode sheets and a TVS-600 IR camera. From the SAR measurements using the Schottky diode sheets it is shown that the contribution of the E(x) component to the SAR (SAR(x)) is maximal 7% of the contribution of the E(y)component to the SAR (SAR(y)) at different layers in both phantom configurations. The complete SAR distribution (SAR(tot)) at different depths is measured using the power pulse technique. From these measurements, it can be seen that SAR(y)at a depth of 0 cm in the muscle-equivalent phantom represents up to 80% of SAR(tot). At 1 and 2 cm depth, SAR(y) is up to 95% of SAR(tot). Therefore, in homogeneous muscle-equivalent phantoms, E(y) is the largest E-field component and measurement of SAR(y) distribution is sufficient to characterize SAR-steering performance of the CFMA-12. SAR steering measurements at 1 cm depth in the muscle-equivalent phantom show that the SAR maximum varies by 40% (1 SD) around the average value of 38.8 W kg(-1) (range 10-65 W kg(-1)) between single antenna elements. The effective fieldsize (E(50)) varies by 14% (1 SD) around the average value of 19.1 cm(2).

Absorption↗
PubMed2000

Comparison of radiotherapy alone with radiotherapy plus hyperthermia in locally advanced pelvic tumours: a prospective, randomised, multicentre trial. Dutch Deep Hyperthermia Group.

BACKGROUND: Local-control rates after radiotherapy for locally advanced tumours of the bladder, cervix, and rectum are disappointing. We investigated the effect of adding hyperthermia to standard radiotherapy. METHODS: The study was a prospective, randomised, multicentre trial. 358 patients were enrolled from 1990 to 1996, in cancer centres in the Netherlands, who had bladder cancer stages T2, T3, or T4, NO, MO, cervical cancer stages IIB, IIIB, or IV, or rectal cancer stage M0-1 were assessed. Patients were randomly assigned radiotherapy (median total dose 65 Gy) alone (n=176) or radiotherapy plus hyperthermia (n=182). Our primary endpoints were complete response and duration of local control. We did the analysis by intention to treat. FINDINGS: Complete-response rates were 39% after radiotherapy and 55% after radiotherapy plus hyperthermia (p<0.001). The duration of local control was significantly longer with radiotherapy plus hyperthermia than with radiotherapy alone (p=0.04). Treatment effect did not differ significantly by tumour site, but the addition of hyperthermia seemed to be most important for cervical cancer, for which the complete-response rate with radiotherapy plus hyperthermia was 83% compared with 57% after radiotherapy alone (p=0.003). 3-year overall survival was 27% in the radiotherapy group and 51% in the radiotherapy plus hyperthermia group. For bladder cancer, an initial difference in local control disappeared during follow-up. INTERPRETATION: Hyperthermia in addition to standard radiotherapy may be especially useful in locally advanced cervical tumours. Studies of larger numbers of patients are needed for other pelvic tumour sites before practical recommendations can be made.

Aged↗
PubMed1999

Comparison of the clinical effectiveness of the 433 MHz Lucite cone applicator with that of a conventional waveguide applicator in applications of superficial hyperthermia.

PURPOSE: This report presents the final stage of our program to improve the quality of our superficial hyperthermia treatments. We have already demonstrated that the Lucite cone applicator (LCA), our technically improved water-filled, wave-guide applicator (WGA), is superior to the conventional WGA. The main objective of the present study was to investigate whether the technical improvements of a WGA were reflected in an improved clinical performance, e.g., a better temperature distribution. METHODS AND MATERIALS: Power and temperature analyses were performed retrospectively on 128 treatments of superficially located tumors (less than 4 cm depth). Twenty-three patients were treated alternately with a WGA setup and a LCA setup. RESULTS: The average power level per antenna in an array was 48 W and 62 W for the WGA and LCA respectively. The average invasively measured temperatures increased by 0.27 degrees C when the LCAs were used. The temperature difference between the center and the periphery of an antenna, averaged over the complete array of antennae, was 0.43 degrees C using WGAs and -0.05 degrees C using LCAs indicating a more uniform heating. The T90 of the invasively measured temperatures remained unchanged (WGA: 39.4 degrees C versus LCA: 39.5 degrees C). CONCLUSION: The LCA is now our standard applicator for superficial hyperthermia treatments as it is technically and clinically proven to be superior to the WGA.

Analysis of Variance↗
PubMed1999

[Hyperthermia in combination with radiotherapy].

The clinical application of hyperthermia in the treatment of oncological patients is based on a strong biological rationale: hyperthermia is an effective cell-killing agent, the effects of which can be induced selectively in tumour tissue. The mechanism of action of hyperthermia is complementary to that of radiotherapy (and chemotherapy). Furthermore, hyperthermia enhances the effects of radiotherapy (and of chemotherapy). In the approximately 20 years that hyperthermia was clinically investigated, much progress was made in the techniques of application. The clinical results achieved so far show that the therapeutic gain by adding hyperthermia can indeed be substantial.

Combined Modality Therapy↗
PubMed1999

[Re-irradiation with hyperthermia in patients with recurrent breast cancer].

In the Daniel den Hoed Cancer Centre in Rotterdam, the Netherlands, patients with recurrent breast cancer within a previously irradiated area, are treated by application of hyperthermia in addition to reirradiation. In this development, the following issues are important: (a) the choice of an effective and tolerable reirradiation schedule; (b) the establishment of the limitations of the hyperthermia techniques available; (c) the finding that additional hyperthermia has to be applied to the total tissue volume at risk for tumour recurrence; (d) the assessment of the value of additional hyperthermia by a randomised study. With the reirradiation schedule of 8 x 4 Gy and the hyperthermia application technique at present available, local control is achieved in 76% of the patients for a median duration of 32 months. The probability of local control is related to tumour size. The treatment is tolerated well, with acceptable toxicity. In patients with recurrent breast cancer in a previously irradiated area, combined reirradiation and hyperthermia is very effective, well tolerated and little toxic.

Aged↗
PubMed1999

Reirradiation combined with hyperthermia in recurrent breast cancer results in a worthwhile local palliation.

Both experimental and clinical research have shown that hyperthermia (HT) gives valuable additional effects when applied in combination with radiotherapy (RT). The purpose of this study was evaluation of results in patients with recurrent breast cancer, treated at the Daniel den Hoed Cancer Center (DHCC) with reirradiation (re-RT; eight fractions of 4 Gy twice weekly) combined with HT. All 134 patients for whom such treatment was planned were included in the analysis. The complete response rate in 119 patients with macroscopic tumour was 71%. Including the 15 patients with microscopic disease, the local control rate was 73%. The median duration of local control was 32 months, and toxicity was acceptable. The complete response (CR) rate was higher, and the toxicity was less with the later developed 433-MHz HT technique compared with the 2450-MHz technique used initially. With this relatively well-tolerated treatment, palliation by local tumour control of a worthwhile duration is achieved in the majority of patients. The technique used for hyperthermia appeared to influence the achieved results. The value of HT in addition to this re-RT schedule has been confirmed by a prospective randomized trial in a similar patient group. In The Netherlands, this combined treatment is offered as standard to patients with breast cancer recurring in previously irradiated areas.

Adenocarcinoma↗
PubMed1999

A phase I/II study of combined weekly systemic cisplatin and locoregional hyperthermia in patients with previously irradiated recurrent carcinoma of the uterine cervix.

We investigated the feasibility and the anti-tumour activity of weekly cisplatin and the simultaneous application of local hyperthermia in patients with a pelvic recurrence of cervical cancer in previously irradiated area. Dose levels of cisplatin 60 mg m(-2), 70 mg m(-2) and 80 mg m(-2) were studied. Treatment objective of hyperthermia was the achievement of a tumour temperature of > or = 42 degrees for 60 min, during cisplatin administration. The protocol advised six weekly cycles of combined treatment. Nineteen patients, median age 47 years (range 26-71), were treated. A total of 89 cycles of combined treatment were administered. Even at the highest dose level of cisplatin, 80 mg m(-2) weekly, no dose-limiting toxicity was observed. Leucocytopenia at scheduled retreatment resulted in 1 or 2 weeks postponement in five cases. Neurotoxicity and renal toxicity were mild or absent. Maximum tumour temperatures achieved ranged 39.7-43.6 degrees C, mean 41.6+/-0.7 degrees C. All 19 patients were evaluable for response. One patient achieved a complete response that lasted 20 months, and nine patients achieved a partial response for a median duration of 6 months (range 4-50+ months), for an overall response rate of 53%. One patient subsequently underwent salvage surgery and currently remains free of disease at 4 years. We found that this combined hyperthermia-dose-intensive cisplatin regimen was well-tolerated. The true impact of the combination of cisplatin and locoregional hyperthermia can only be answered in a randomized study. Nonetheless, based on existing data on the poor efficacy of cisplatin in pelvic recurrent cervical cancer, we believe that the combined modality approach of weekly hyperthermia plus dose-intensive cisplatin is an attractive regimen, particularly if subsequent salvage surgery is available.

Adult↗
PubMed1998

Practical limitations of interstitial thermometry during deep hyperthermia.

PURPOSE: Intratumor thermometry during hyperthermia treatment is considered important for several reasons. The morbidity that we experienced from interstitially placed catheters in deep-seated tumors gave reason to weigh the advantages and disadvantages against each other. METHODS AND MATERIALS: The available thermometry in 215 patients treated with hyperthermia for deep-seated tumors was analyzed with the aim to evaluate practically feasible intratumor measurements. The influence of intratumor measurements on the treatment procedure was assessed. RESULTS: Total 120 catheters were placed interstitially in 78 patients. Over the years, the percentage of patients with interstitial thermometry decreased considerably. Forty-nine catheters could remain in place during the whole hyperthermia treatment series. The remaining catheters had to be removed for more or less severe complications, including one fatal event. In fact, the interstitial catheters caused the most severe treatment-related morbidity. During 188 of the total 859 treatments, at least one interstitial catheter was available for thermometry. Per treatment with catheter(s) in situ, the average number of intratumor measurement sites was 6.9. The value of interstitial thermometry for power steering during treatment, to both optimize intratumor temperature distribution and prevent toxicity, appeared limited. The mean volume of the tumors with interstitial thermometry was 314 cm3, SD 325. In relation to the large tumor volumes, the thermal dose parameters calculated from the available data is considered to be of limited value. CONCLUSION: In view of the possible severe complications and the limited clinical value of the information achieved by interstitially placed thermometry catheters, interstitial thermometry was not found to routinely benefit the individual patient.

Catheters, Indwelling↗
PubMed1998

Quantitative evaluation of 2 x 2 arrays of Lucite cone applicators in flat layered phantoms using Gaussian-beam-predicted and thermographically measured SAR distributions.

SAR distributions from four different E-field-orientated 2 x 2 arrays of incoherently driven Lucite cone applicators (LCAs) were investigated. The LCAs operated at 433 MHz with an aperture of 10.5 cm x 10.5 cm each. Two techniques were used to obtain SAR distributions in flat layered phantoms: Gaussian beam (GB) predictions and thermographical (TG) imaging. The GB predictions showed that the effective field size of the different array configurations varied by up to 3%. The TG-measured SAR distribution showed significant deviations from the GB-predicted SAR distributions (maximum 34.6%). The difference between GB-predicted and TG-measured SAR levels (averaged per 10% GB-predicted SAR intervals) equalled less than 11.3% for the parallel E-field orientated array and respectively 15.1% for the clockwise-orientated array. When antennae in the clockwise-orientated array were more widely spread (array aperture 23 cm x 23 cm) in order to diminish their mutual interactions, these differences decreased to 12.4%. However, the overall difference within the 50% SAR or higher range decreased from 14% to 9%. The results lead us to conclude that LCAs can be used clinically and their antenna interactions are not considered to be a problem under clinical conditions.

Humans↗
PubMed1996

Radiotherapy with or without hyperthermia in the treatment of superficial localized breast cancer: results from five randomized controlled trials. International Collaborative Hyperthermia Group.

PURPOSE: Claims for the value of hyperthermia as an adjunct to radiotherapy in the treatment of cancer have mostly been based on small Phase I or II trials. To test the benefit of this form of treatment, randomized Phase III trials were needed. METHODS AND MATERIALS: Five randomized trials addressing this question were started between 1988 and 1991. In these trials, patients were eligible if they had advanced primary or recurrent breast cancer, and local radiotherapy was indicated in preference to surgery. In addition, heating of the lesions and treatment with a prescribed (re)irradiation schedule had to be feasible and informed consent was obtained. The primary endpoint of all trials was local complete response. Slow recruitment led to a decision to collaborate and combine the trial results in one analysis, and report them simultaneously in one publication. Interim analyses were carried out and the trials were closed to recruitment when a previously agreed statistically significant difference in complete response rate was observed in the two larger trials. RESULTS: We report on pretreatment characteristics, the treatments received, the local response observed, duration of response, time to local failure, distant progression and survival, and treatment toxicity of the 306 patients randomized. The overall CR rate for RT alone was 41% and for the combined treatment arm was 59%, giving, after stratification by trial, an odds ratio of 2.3. Not all trials demonstrated an advantage for the combined treatment, although the 95% confidence intervals of the different trials all contain the pooled odds ratio. The greatest effect was observed in patients with recurrent lesions in previously irradiated areas, where further irradiation was limited to low doses. CONCLUSION: The combined result of the five trials has demonstrated the efficacy of hyperthermia as an adjunct to radiotherapy for treatment of recurrent breast cancer. The implication of these encouraging results is that hyperthermia appears to have an important role in the clinical management of this disease, and there should be no doubt that further studies of the use of hyperthermia are warranted.

Breast Neoplasms↗
PubMed1995

Thermal enhancement of both tumour necrosis factor alpha-induced systemic toxicity and tumour cure in rats.

In vitro and in vivo studies have suggested synergistic anti-tumour activity of combined hyperthermia and tumour necrosis factor alpha (TNF-alpha). However, some studies indicated an increased systemic toxicity of TNF by additional hyperthermia. The aim of this study was to obtain starting dosages for a clinical phase I study on the application of deep local hyperthermia and systemic TNF. We investigated the effect of local hyperthermia on the toxicity and efficacy of systemic TNF. Rats (Wag/Rij) carrying a subcutaneously transplanted osteosarcoma in the hind leg received a single intravenous dose of recombinant human (rh) TNF-alpha, either at normothermia or at hyperthermia, by positioning the tumour bearing hind leg in a water bath of 43 degrees C. Dose-effect curves for lethality and tumour cure were established and LD50 and TCD50 values were calculated. Systemic toxicity was increased by local hyperthermia. The LD50 values (+/- s.e.) were 1088 (+/- 61) micrograms kg-1 at normothermia and 205 (+/- 23) micrograms kg-1 at hyperthermia, resulting in a thermal enhancement ratio (TER) of 5.3. Following normothermia, tumour cures were observed at TNF concentrations of 1000-1300 micrograms kg-1, while this was observed at doses of 50-300 micrograms kg-1 when combined with hyperthermia (TCD50 values of 1211 and 188 micrograms kg-1 respectively), resulting in a TER of 6.4. Systemic toxicity and anti-tumour activity of TNF are both increased by local hyperthermia. A safe starting dose for the combined clinical treatment would be 10% of the dose of TNF-alpha that has been recommended for phase II studies on intravenous bolus administration of TNF-alpha at normothermia. In view of the large variability in tumour sensitivity for TNF-alpha, the clinical usefulness of this combined treatment modality has to be determined.

Animals↗
PubMed1994

Radio-frequency ring applicator: energy distributions measured in the CDRH phantom.

SAR distributions were measured in the CDRH phantom, a 1 cm fat-equivalent shell filled with an abdomen-equivalent liquid (sigma = 0.4-1.0 S m-1; dimensions 22 x 32 x 57 cm) to demonstrate the feasibility of the ring applicator to obtain deep heating. The ring electrodes were fixed in a PVC tube; diameter 48 cm, ring width 20 cm and gap width between both rings 31.6 cm. Radio-frequency energy was fed to the electrodes at eight points. The medium between the electrodes and the phantom was deionised water. The SAR distribution in the liquid tissue volume was obtained by a scanning E-field probe measuring the E-field in all three directions. With equal amplitude and phase applied to all feeding points, a uniform SAR distribution was measured in the central cross-section at 30 MHz. With RF energy supplied to only four adjacent feeding points (others were connected to a 50 omega load), the feasibility to perform amplitude steering was demonstrated; SAR values above 50% of the maximum SAR were measured in one quadrant only. SAR distributions obtained at 70 MHz showed an improved focusing ability; a maximum at the centre exists for an electric conductivity of the abdomen-equivalent tissue of 0.6 and 0.4 S m-1.

Electromagnetic Fields↗
PubMed1992

Experimental assessment of electrical impedance imaging for hyperthermia monitoring.

Two experimental studies are presented that attempt to assess the use of electrical impedance tomography (EIT) to map thermal changes deep in the body. The first was a joint study between our group in Sheffield and the Daniel den Hoed Cancer Center in Rotterdam, funded by the COMAC-BME Hyperthermia project. Phantom and in vivo experiments were conducted with a deep heating ring-capacitive hyperthermia device; the results highlighted some of the inherent problems (electromagnetic interference, nonuniform sensitivity) that remain to be solved for this application. The second experimental study involved heating the stomachs of volunteers by pumping known quantities of liquid (a salt/glucose solution, conductivity 5 mS) at controlled temperatures (25, 37 and 47 degrees C) in and out of the stomach via a nasogastric tube. Results indicated that the level of thermal change induced by these liquids could be reproducibly measured by impedance imaging. Both studies were a further step in assessing the capabilities of EIT for noninvasive monitoring of deep body hyperthermia. The results are encouraging and indicate the value of continued development of EIT for non-invasive thermometry.

Electric Conductivity↗