Stereotactic body radiotherapy of central lung tumours using a 1.5 T MR-linac: First clinical experiences.

Background: MRI-guidance may aid better discrimination between Organs at Risk (OARs) and target volumes in proximity of the mediastinum. We report the first clinical experiences with Stereotactic Body Radiotherapy (SBRT) of (ultra)central lung tumours on a 1.5 T MR-linac. Materials and Methods: Patients with an (ultra)central lung tumour were selected for MR-linac based SBRT treatment. A T2-weighted 3D sequence MRI acquired during free breathing was used for daily plan adaption. Prior to each fraction, contours of Internal Target Volume (ITV) and OARs were deformably propagated and amended by a radiation oncologist. Inter-fractional changes in volumes and coverage of target volumes as well as doses in OARs were evaluated in offline and online treatment plans. Results: Ten patients were treated and completed 60 Gy in 8 or 12 fractions. In total 104 fractions were delivered. The median time in the treatment room was 41 min with a median beam-on time of 8.9 min. No grade ≥3 acute toxicity was observed. In two patients, the ITV significantly decreased during treatment (58 % and 37 %, respectively) due to tumour shrinkage. In the other patients, 81 % of online ITVs were within ±15 % of the volume of fraction 1. Comparison with the pre-treatment plan showed that ITV coverage of the online plan was similar in 52 % and improved in 34 % of cases. Adaptation to meet OAR constraints, led to decreased ITV coverage in 14 %. Conclusions: We describe the workflow for MR-guided Radiotherapy and the feasibility of using 1.5 T MR-linac for SBRT of (ultra) central lung tumours.

[Chronic radiation enteritis after irradiation of the lesser pelvis: surgical (im)possibilities]. / Chronische radiatie-enteritis na bestraling op het kleine bekken: chirurgische (on)mogelijkheden.

Three women aged 74, 59 and 36 years, had chronic complaints of abdominal pain, nausea, vomiting and diarrhoea, 1 to 8 years after radiotherapy for pelvic malignancies. Mechanical ileus due to fibrotic adhesions was found to be the cause; all three patients recovered after one or more operations. The prevalence of chronic radiation injury correlates with both radiation factors (volume) and patient characteristics. If possible, tumour recurrence needs to be excluded. Chronic intermittent ileus is the predominant symptom of chronic radiation injury. It often occurs within 2 years, but sometimes as long as 10 to 20 years after radiotherapy. Resection is warranted when short segments are affected. In other cases an intestinal bypass or stoma is the treatment of choice.

The learning curve in prostate seed implantation.

OBJECTIVE: To describe the learning curve in prostate seed implantation, according to the experience with two groups of 100 patients. MATERIAL AND METHODS: A perineal, ultrasound-guided implantation technique with manual afterloading was used in all patients. Of a total of 255 patients treated over the period 1989 through 1998, the results of the first hundred patients were compared in relation to the last hundred patients. In the first group single seeds were used, while in the second group RAPID Strands were applied. RESULTS: Although there is a difference in the follow-up period, a significant difference is found in disease-free survival between the two groups. PSA progression was noticed in 39% of patients in the first group and in 12% in the other group. The strongest prognostic factor, however, is the initial PSA value. Toxicity is relatively low, though higher in the second group. CONCLUSIONS: The results obtained in the second hundred patients are in agreement with data from literature. Differences in outcome between the two groups are, however, not only explained by differences in technique, but also by selection and total number of implanted seeds.

Regional hyperthermia of pelvic tumours using the Utrecht 'Coaxial TEM' system: a feasibility study.

Between August 1989 and July 1992 a total of 22 patients (64 treatments) with inoperable or recurrent deep seated pelvic tumours were treated with regional hyperthermia and radiotherapy. The 70 Mhz Coaxial TEM applicator with its characteristic open waterbolus was used as heating device. The main objective of this pilot study was to evaluate the feasibility, toxicity and temperature data. The results showed that the major treatment limiting factors were insufficient power and systemic stress. Local pain was observed in only 10% of all treatments. Most of the treatments resulted in elevated systemic temperatures with the overall mean maximum oesophagus temperature reaching 38.9 +/- 0.7 degrees C, however, in only 6% of these treatments this was found to be treatment limiting. From the measured data the following intratumoral temperatures were calculated: T90 = 39.9 +/- 1.0 degrees C; T50 = 40.7 +/- 1.0 degrees C; T10 = 41.4 +/- 1.0 degrees C. In addition, the overall mean average normal tissue temperatures were determined: Trectum = 40.8 +/- 0.7 degrees C; Tvagina = 41.3 +/- 0.9 degrees C; Turethra = 40.8 +/- 0.9 degrees C. The temperatures in normal tissue were frequently higher than in tumour, indicating that a large volume was heated. The open waterbolus allows strong cooling, but the strategy was changed during the study: higher systemic temperatures were allowed to improve the pelvic temperatures. This pilot study proved that the open waterbolus is clinically a success, because it offers patient comfort and SAR-steering by patient repositioning, and that regional hyperthermia with the Coaxial TEM is feasible.