Scintillation dosimetry array based on air core technology

Full text: Our aim is to improve the safety and quality of high precision radiotherapy using small radiation fields. Commercially available dosimeters are challenged in fields smaller than 10 mm, introducing a new uncertainty. Our strategy was to develop and test an array of scintillation detectors, based on air core technology (HE-FODTM) excluding Cerenkov background. Two prototype arrays were constructed with different levels of spatial resolution. The first consisted of seven BC400 scintillation elements, each a cube of 2 mm side length, with a centre to centre separation of 4 mm. An array of 2 mm square air core waveguides were custom cut from commercially available PMMA sheets with sufficient optical quality to produce efficient light transport. The second array used sixteen I mm side length scintillator elements coupled to I mm square waveguides. The HE-FOD array was exposed parallel and perpendicular to a 6 MV photon beam (Varian Novalis TX), measuring the beam profile and percentage depth dose. The scintillation light was detected using a photomultiplier array. Both arrays characterised the beam for a range of field sizes. Dose measurements were possible with a time resolution of 0.1 s, sufficient for characterising dynamic fields in SRT. The I mm array was found to be particularly useful for fields less than 10 mm, as it measures in-field and penumbral regions using a single exposure. Higher spatial resolution was achieved by displacing the array to give interpolated measurements. Monte Carlo simulations confirmed the water equivalence of the array. HE-FOD arrays provide real-time monitoring of dynamic stereotactic fields with high spatial resolution.