Session Item

For creating adapted to clinical user applicator library (Oncentra Brachy 4.6 treatment planning system, Flexitron afterloading machine) to collect data about behaviour/traveling position of the Ir-192 radiation source inside source guiding channel of most questionable Ring Applicator Ø 26 mm.

Technique of autoradiography, when X-ray film have been used to visualize actual position of the radiation source inside the applicator source travel path, in direction parallel to tandem (“z-coordinate”, Fig., Z+), in this case do not applicable for technical reason. Thus for the solving this problem the manipulation/handling with dummy source inside source travel cavity/path is one approach to get information about source position traveling through. For this purpose the dummy source cable was installed into extended/modified Source Position Simulator Set instead of dummy/check cable. Step size of the dummy moving was 1 cm. The fluoroscopic images of the source inside applicator channel in different dwell positons was analysed using standard measuring tools. For the point of origin/beginning of “z-coordinate” was taken the centre of source travel channel Ø 3 mm (Fig., Z=0, 3) and the positive direction of “z-coordinate” it was taken direction of the applicator tandem. Special care was undertaken (using angle indicators) to adjust angle of the fluoroscopic image direction view to be parallel to plate of ring applicator fixation.

Figure.   Flexitron Ring Applicator Ø 26 mm, Side View, „Z-coordinate“of dummy source dwell positions. 1,2 – “300 mm” dwell position of the dummy source for Measurement type 1 and type 2, respectively.  3 - Source travel path cavity, diameter 3 mm.

On the figure the curves 1 and 2 correspond to two types/groups of obtained measurements: 1- moving of dummy source into last distal position “300 mm” with Z= ~+0,5 mm;  2 - dummy source, spontaneously, moving into last distal position “300 mm” with Z= ~-0,4 mm; For start dwell positions inside ring (“240-260” positions) these curves almost coincide between each other, but for distal dwell positions (“270-300”) they, unexpectedly, differs by ~1mm. Z-coordinate for library applicator in dwell position “300” close to Measurement 1 result and in dwell position “270” close to Measurement 2. For dwell positions “240-260” library Z-coordinate differ from our measurement by ~0,5 mm.

For all dwell positions inside Ring Applicator Ø 26 mm library “z-coordinates” don’t differ from our measurement more than 1 mm (i.e. gives contribution ≤5% difference in dose at 4 cm distance), which can  be evaluated/valued as small rate. So, for creating adapted to clinical user Ring Aapplicator library the “z-coordinates” of source dwell positions, at the first stage, can be copied from library data.