Wielheesen, D.H.M.

Steering in locoregional deep hyperthermia: Evaluation of common practice with 3D-planning (Article)

2008-12-22T00:00:00Z

Purpose: In Rotterdam, fifteen years of clinical experience with deep hyperthermia has sublimated in empirical treatment guidelines. In this paper, a hyperthermia treatment planning system (HTPS) is employed to investigate the effect of these guidelines on global power distribution, their effectiveness and the rationale behind each guideline. Materials and methods: Four guidelines were investigated. The first two prescribe steering actions for balancing intraluminal temperatures and alleviating complaints of deep-seated pain or pressure. The third guideline handles superficial complaints of pain or heat sensation. The last guideline states that frequency should be increased from 77 MHz upwards in case of multiple, opposite, painful regions uncontrollable by the previous steering actions. For all steering actions it is assumed that input power is increased until complaints occur. Sigma Hyperplan was used to calculate specific absorption rate (SAR) distributions for five patient models with locally advanced cervical cancer. Absorbed power ratios of different regions of interest were evaluated to illustrate steering efficacy and complaint reduction. Results and conclusions: Phase steering is effective in shifting the central power distribution to the periphery, and is an appropriate method to balance temperatures or to handle deep-seated complaints. Reduction of amplitude is the proper action to alleviate superficial complaints of heat or pressure. Compression of the SAR distribution, mainly in the lateral direction, is predicted with increasing frequency. Hence, for complaints in the lower back or on the sides, a frequency increase should be considered. We conclude that the results of the HTPS are in close agreement with the empirical steering guidelines.

Incidence of acute peripheral neurotoxicity after deep regional hyperthermia of the pelvis (Article)

2008-06-01T00:00:00Z

Background: After observing rather severe acute neurotoxicity in a few patients following deep hyperthermia treatment for a pelvic tumour, we evaluated the incidence of neurotoxicity in all patients treated with deep hyperthermia of the pelvis between June 1990 and April 2004. Materials and methods: Hyperthermia treatment registrations and hospital charts of all 736 patients were reviewed. Differences between the incidence of neurotoxicity in subgroups of patients were evaluated by 2×2 exact tests. Results: Grade 2 or 3 acute neurotoxicity occurred in 2.3% of patients, grade 3 in 0.7%. The duration of symptoms was longer than 3 months in 6 patients (0.8%). Neurological examination in 5 patients showed that the most commonly involved structures are the sacral and lower lumbar nerve roots and the sacral plexus. Acute neurotoxicity occurred only after November 1999 and only in patients treated for primary cervical cancer. Comparison of applied powers and achieved temperatures in patients developing neurotoxicity did not show differences between treatment sessions which resulted in neurotoxicity and sessions not resulting in neurotoxicity. Conclusion: Acute neurotoxicity following hyperthermia for pelvic tumours is a rare complication, but can result in symptoms affecting the activities of daily life. We found no patient, tumour or treatment characteristics predictive for a risk of neurotoxicity.

Benefits of superficial hyperthermia treatment planning: Five case studies (Article)

2007-08-01T00:00:00Z

Purpose: To demonstrate the benefits of treatment planning in superficial hyperthermia. Materials and methods: Five patient cases are presented, in which treatment planning was applied to troubleshoot treatment-limiting hotspots, to select the optimum applicator type and orientation, to assess the risk associated with metallic implants, to assess the feasibility of heating a deeper seated tumour, and to analyse the effective SAR coverage resulting from arrays of multiple incoherent applicators. FDTD simulation tools were used to investigate treatment options, either based on segmented or simplified anatomies. Results: The background, approach and model implementation are presented per case. SAR cross-sections, profiles and isosurfaces are visualized to predict the effective SAR coverage of the target and the location of the maximum power absorption. In addition, the followed treatment strategy and the implications for the clinical treatment are given: for example, higher temperatures, relief of treatment limiting hot-spots or increased power input. Conclusions: Treatment planning in superficial hyperthermia can be applied to improve clinical routine. Its application supports the selection of the optimum technique in non-standard cases, leading to direct benefits for the patient. In addition, treatment planning has shown to be an excellent tool for education and training for hyperthermia technicians and physicians.

Concomitant radiotherapy and hyperthermia for primary carcinoma of the vagina: A cohort study (Article)

2007-07-01T00:00:00Z

Objective: To evaluate the supplementary value of adding hyperthermia to radiotherapy in patients with primary vaginal cancer. Study design: Cohort of 44 patients diagnosed with primary vaginal cancer between 1990 and 2002 was assessed. Survival rates and median survival of patients with primary vaginal cancer undergoing radiotherapy with and without hyperthermia were compared. Hyperthermia was solely added to radiotherapy in case of a tumor size >4 cm in diameter for FIGO stage III disease. Results: The calculated overall 5-year survival of primary vaginal cancer was 63%. In comparison to histologic high grade tumors, higher survival rates for histologic low grade tumors were calculated. For FIGO stage III of disease, the addition of hyperthermia to radiotherapy for tumors >4 cm in diameter resulted similar survival rates and median survival when compared to those achieved by radiotherapy as monotherapy in tumors of <4 cm in diameter. Conclusions: The addition of hyperthermia to radiotherapy might result in better survival rates in primary vaginal cancer for tumors >4 cm in diameter. The supplementary effect of hyperthermia to radiotherapy may be a feasible and beneficial approach in the treatment of vaginal cancer.

Assessment of the local SAR Distortion by Major Anatomical Structures in a Cylindrical Neck Phantom (Article)

2005-03-01T00:00:00Z

The objective of this work is to gain insight in the distortions on the local SAR distribution by various major anatomical structures in the neck. High resolution 3D FDTD calculations based on a variable grid are made for a semi-3D generic phantom based on average dimensions obtained from CT-derived human data and in which simplified structures representing trachea, cartilage, spine and spinal cord are inserted. In addition, phantoms with dimensions equal to maximum and minimum values within the CT-derived data are also studied. In all cases, the phantoms are exposed to a circular coherent array of eight dipoles within a water bolus and driven at 433 MHz. Comparisons of the SAR distributions due to individual structures or a combination of structures are made relative to a cylindrical phantom with muscle properties. The calculations predict a centrally located region of high SAR within all neck phantoms. This focal region, expressed as contours at either 50% or 75% of the peak SAR, changes from a circular cross-section in the case of the muscle phantom to a doughnut shaped region when the anatomical structures are present. The presence of the spine causes the greatest change in the SAR distribution, followed closely by the trachea. Global changes in the mean SAR relative to the uniform phantom are <11%, whilst local changes are as high as 2.7-fold. There is little difference in the focal dimensions between the average and smallest phantoms, but a decrease in the focal region is seen in the case of the largest phantom. This study presents a first step towards understanding of the complex influences of the various parameters on the SAR pattern which will facilitate the design of a site-specific head and neck hyperthermia applicator.