Abstract
This work aims to provide a comparison between two important detectors (Pinpoint and Semiflex) that are frequently used in radiation dosimetery in radiotherapy. This is carried out through the employment of both detectors in a quantitative estimation of the change in out-of-field dose with important dosimetric parameters such as field size (from 5×5cm2 to 30×30cm2) and depth (from 1.5cm to 30cm) at two different energies (6MV and 15MV) and two different collimator angles (0–90°). The change in out-of-field dose with Source-Skin-Distance (SSD) from 80 to 115cm is also studied using both detectors. Results show that, the Pinpoint and Semiflex detectors both reported an increase in out-of-field dose with field size, depth, energy and SSD. In almost all measurements, Pinpoint detector reported considerably higher out-of-field dose values compared to Semiflex. For 6MV and 0° collimator angle, the out-of-field dose at field size of 30×30cm2 and at a depth of 1.5cm is 7.3% for Pinpoint detector compared to 4.3% for Semiflex. At collimator angle of 90°, the out-of-field dose is 6.5% for Pinpoint detector compared to 5.5% for semiflex. The out-of-field dose for a depth of 30cm and field size of 10×10cm is 7.9% for Pinpoint detector compared to 5.9% for Semiflex. For 15MV and 0° collimator angle, the out-of-field dose at field size of 30×30cm2 and at a depth of 1.5cm is 7.5% for Pinpoint detector compared 5.1% for Semiflex. At 6MV, field size of 10×10cm2 and depth of 1.5cm, the out-of-field dose at SSD 115cm is 3.7% for Pinpoint detector compared to 3.4% for Semiflex. The considerably higher out-of-field dose values reported by Pinpoint detector compared to Semiflex may be attributed to the relatively higher sensitivity of Pinpoint detector for low doses (such as out-of-field doses). Therefore, for reliable out-of-field dose measurements a Pinpoint detector is highly recommended.
•The out-of-field dose is measured using Pinpoint and Semiflex detectors.•This is carried out at different dosimetric parameters (field size, depth, energy, collimator angle and at different SSD).•The out-of-field dose increased with all of the given parameters using both detectors.•Pinpoint detector is found to be much more sensitive than Semiflex in out-of-field dose measurements.