Giacomo Reggiori1, Pietro Mancosu2, Natalka Suchowerska3, Francesca Lobefalo1, Antonella Stravato1, Stefano Tomatis1, Marta Scorsetti4. 1. Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy. 2. Medical Physics Service of the Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy. Electronic address: pietro.mancosu@humanitas.it. 3. School of Physics, The University of Sydney, Sydney, Australia; Department of Radiation Oncology, Chris O'Brien Lifehouse, Camperdown, Australia. 4. Department of Radiation Oncology, Humanitas Research Hospital, Rozzano, Milan, Italy.
Abstract
PURPOSE: To characterize the performance of a new unshielded silicon diode (Razor-IBA) for dose measurements in small flattening filter free beams. METHODS: The Razor has an active volume of 0.6 mm in diameter and 20 µm in length. The detector response stability in measured dose, dose rate, dose per pulse, and dark current were evaluated. The detector response in square fields (0.6-5.0 cm) was determined using PDD curves, axial beam profiles and output ratios. The performances were compared to that of the previously available SFD-IBA and PFD-IBA diodes. RESULTS AND DISCUSSION: The Razor short term stability relative to the SFD was much improved (<±0.1% after 1.2 kGy). The linearity was <±1% (0.05-30 Gy range) and the dose rate dependence was <±0.5% (4-24 Gy/min range). The dose per pulse dependence was <±0.7% (0.08-0.21 cGy/pulse range). The PDDs measured with Razor and PFD differed <1%. A larger dark current was observed with increase in dose (0.0025 pA/Gy) compared to the SFD (0.0002 pA/Gy). This characteristic is attributed to an increased concentration of recombination centers. The beam profile showed good agreement with the SFD. Penumbra differences were <±0.3 mm relative to PFD, with a slight overestimation of the tails (<1%), due to the absence of diode shielding. Output ratios were in good agreement for fields up to 5 × 5 cm(2) (<1%). CONCLUSIONS: The Razor diode has the same spatial resolution and performance reliability as its predecessor (SFD), but exhibits the additional advantage of improved stability. These features make the Razor diode detector a good candidate for small field dosimetry.
PURPOSE: To characterize the performance of a new unshielded silicon diode (Razor-IBA) for dose measurements in small flattening filter free beams. METHODS: The Razor has an active volume of 0.6 mm in diameter and 20 µm in length. The detector response stability in measured dose, dose rate, dose per pulse, and dark current were evaluated. The detector response in square fields (0.6-5.0 cm) was determined using PDD curves, axial beam profiles and output ratios. The performances were compared to that of the previously available SFD-IBA and PFD-IBA diodes. RESULTS AND DISCUSSION: The Razor short term stability relative to the SFD was much improved (<±0.1% after 1.2 kGy). The linearity was <±1% (0.05-30 Gy range) and the dose rate dependence was <±0.5% (4-24 Gy/min range). The dose per pulse dependence was <±0.7% (0.08-0.21 cGy/pulse range). The PDDs measured with Razor and PFD differed <1%. A larger dark current was observed with increase in dose (0.0025 pA/Gy) compared to the SFD (0.0002 pA/Gy). This characteristic is attributed to an increased concentration of recombination centers. The beam profile showed good agreement with the SFD. Penumbra differences were <±0.3 mm relative to PFD, with a slight overestimation of the tails (<1%), due to the absence of diode shielding. Output ratios were in good agreement for fields up to 5 × 5 cm(2) (<1%). CONCLUSIONS: The Razor diode has the same spatial resolution and performance reliability as its predecessor (SFD), but exhibits the additional advantage of improved stability. These features make the Razor diode detector a good candidate for small field dosimetry.
Authors: Giordano Biasi; Marco Petasecca; Susanna Guatelli; Ebert A Martin; Garry Grogan; Benjamin Hug; Jonathan Lane; Vladimir Perevertaylo; Tomas Kron; Anatoly B Rosenfeld Journal: J Appl Clin Med Phys Date: 2018-07-12 Impact factor: 2.102