BACKGROUND

Lack of an ideal detector for small field dosimetry has led to the development of many new types of detectors. Recent studies have shown that plastic scintillation detectors (PSDs) provide favorable dosimetric characteristics, such as minimal volume averaging and fluence perturbation effects, real time response rates, high signal to noise ratio (SNR), and independence to temperature, energy spectrum, dose rate, and irradiation direction, in the field of small field dosimetry, largely due to their small size and water-equivalent composition materials, which eliminates the need for certain correction factors.

PURPOSE

The goal of this study was to evaluate a new 0.5 × 0.5 mm PSD (called in this study Medscint0.5), with detailed uncertainty analysis, for its suitability in small field dosimetry and in comparison, to other commercially available PSDs.

METHODS

This detector characterization was performed for small field output factors, pre- and post- irradiation leakage, short-term repeatability, angular dependency, dose rate and energy dependency, dose response linearity, and temperate dependency. The small field output factors measured with this detector were also evaluated to determine if any correction factors were needed for extremely small fields.

RESULTS

The Medscint0.5 showed negligible leakage (< 0.1%) and short-term repeatability (< 0.1% response deviations), similar to other commercially available PSDs. It also demonstrated comparable dose rate (< 0.47%) and dose response linearity (< 0.73%) to an ion chamber. Moreover, it also showed excellent angular (< 0.30%) and temperature independence (< 0.38%) relative to other commercially available PSDs. Stereotactic cone factor measurements showed good agreement (< 1.10%) with MC for all SRS cone sizes for both 6 and 10 MV FFF beams. The total uncertainty for absolute dosimetry using this detector was found to be ∼1.1% at one standard deviation from the mean. The uncertainty can be reduced to 0.8% at one standard deviation when this detector is used for relative small field dosimetry, that is, field output measurements.

CONCLUSION

The latest small size Medscint0.5 detector is suitable for small field dosimetry with its unique advantage in measuring field output factors without need of any correction factor even in measuring small circular fields down to 4 mm diameter.