Development of micro-collimators for highly precise irradiation of ophthalmic tumours with I-125 brachytherapy eye applicators
Final Report Abstract
The aim of the project was the development and dosimetry of small beam-shaping components (micro-collimators) for integration into brachytherapy applicators with the photon emitter I-125 for radiotherapy of eye tumors. Alignment of the radiation to the target volume (tumor) and protection of healthy areas should improve the therapy result. The size of the elements was adapted to the cylindrical enclosed emitters ("seeds", 4.5mm long, Ø 0.8mm). Micro-collimators had a lamellar structure consisting of absorber layers (gold foil) 10-25 µm thick and radiationpermeable layers (silicone, Histoacryl) ≥100 µm thick. The first focus of the project was the development of a method for manufacturing microcollimators that is reproducible under clinical conditions. First, gold foil and thin layers of silicone, made thinner by the addition of toluene and evenly distributed by centrifugal force, were alternately layered on top of each other in rotary coaters. A lack of layer adhesion in these sandwich structures led to delamination during subsequent cutting processes. Laser-cut openings in the gold foil increased adhesion by bridging between the silicone layers, but were too complex to manufacture. Mixtures of silicone and metal powder instead of the gold foil were too viscous to work with. However, stable, reproducible sandwich structures could be created from gold foils to which a thin layer of Histoacryl paper of a defined thickness was glued. After hardening, the paper was completely saturated with Histoacryl and the blank formed into a sandwich structure by folding and stacking. After wetting with water, the Histoacryl hardened in the paper. This stable construction could easily be further processed into various collimators, adapted to the intended use in an eye applicator. The second part of the project covered the dosimetry of micro-collimators in a newly developed automated water phantom by means of plastic scintillator detectors made of polyethylene naphthalate. There was satisfactory agreement between the measurement results and GEANT4-based simulation calculations Micro-collimators with a good collimating effect could be arranged in a set up in order to form the desired beam geometries. However, a high degree of collimation was associated with a dose rate reduction higher than expected and, thus, unacceptably long application times. For clinical practice, the overall seed activity in such applicators would have to be significantly increased. At the current time, however, the additional costs are not covered by the therapy proceeds. Therefore, as a result of the project, only simplified beam-shaping elements have been put into clinical use to date.
Publications
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DGMP/DPG-Webinar Konstruktion und Vermessung von Mikrokollimatoren für die Augentumor-Brachytherapie. 06. Juli in Berlin
C. Scharmberg
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Mikrokollimatoren für den Einsatz in der Therapie hochprominenter Augentumoren. DGMP Abstractband
C. Scharmberg, M. Eichmann, W. Sauerwein & D. Flühs
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Design of a precise scintillation dosimetry system for the measuring of microcollimators. DGMP Abstractband
C. Scharmberg, M. Eichmann, Ch. Rütten, B. Spaan & D. Flühs
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Vermessung von Mikrokollimatoren mit einem hochpräzisen PEN-basierten Dosimetriesystem. DGMP Abstractband
C. Scharmberg, D. Flühs, C. Rütten, V. Handrick & B. Spaan
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Untersuchung von verschiedenen Mikrokollimatoren für den Einsatz in der Brachytherapie. DGMP Abstractband
A. L. Borghoff, C. Scharmberg, D. Flühs & B. Spaan
