Exradin W1 plastic scintillation detector for in vivo skin dosimetry in passive scattering proton therapy.

In vivo skin dosimetry is desirable in passive scattering proton therapy because of the possibility of high entrance dose with a small number of fields. However, suitable detectors are needed to determine skin dose in proton therapy. Plastic scintillation detectors (PSDs) are particularly well suited for applications in proton therapy because of their water equivalence, small size, and ease of use. We investigated the utility of the Exradin W1, a commercially available PSD, for in vivo skin dosimetry during passive scattering proton therapy. We evaluated the accuracy of the Exradin W1 in six patients undergoing proton therapy for prostate cancer, as part of an Institutional Review Board-approved protocol. Over 22 weeks, we compared in vivo PSD measurements with in-phantom ionization chamber measurements and doses from the treatment planning system, resulting in 96 in vivo measurements. Temperature and ionization quenching correction factors were applied on the basis of the dose response of the PSD in a phantom. The calibrated PSD exhibited an average 7.8% under-response (±1% standard deviation) owing to ionization quenching. We observed 4% under-response at 37 °C relative to the calibration-temperature response. After temperature and quenching corrections were applied, the overall PSD dose response was within ±1% of the expected dose for all patients. The dose differences between the PSD and ionization chamber measurements for all treatment fields were within ±2% (standard deviation 0.67%). The PSD was highly accurate for in vivo skin dosimetry in passively scattered proton beams and could be useful in verifying proton therapy delivery.

Alsanea F ，Wootton L ，Sahoo N ，Kudchadker R ，Mahmood U ，Beddar S ... -  《-》

Passively scattered proton beam entrance dosimetry with a plastic scintillation detector.

Wootton L ，Holmes C ，Sahoo N ，Beddar S ... -  《-》

Characterization of the exradin W1 plastic scintillation detector for small field applications in proton therapy.

Hoehr C ，Lindsay C ，Beaudry J ，Penner C ，Strgar V ，Lee R ，Duzenli C ... -  《-》

Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry.

Small field dosimetry has been an active area of research for over a decade. It is now known that large dosimetric errors can be introduced if proper detectors or correction factors are not used. The International Atomic Energy Agency (IAEA) through the technical report series No. 483 provides guidelines for small field dosimetry procedures as well as correction factors for most detectors available in the market. The plastic scintillator detector (PSD) Exradin W1 has been found to have a correction factor close to unity; however, it is not designed for beam scanning. To overcome this limitation, the new PSD Exradin W2 has been developed to be used as a scanning as well as a relative dosimeter. Characterization of this detector in small field dosimetry is presented in this study. A 6 MV beam from a Varian-Edge linac was used to collect data for the characterization of a W2 detector. Cerenkov light ratio (CLR) is corrected through a separate new electrometer system that comes with the W2 detector. The parameters investigated include the dose and dose rate linearity, beam profiles, percent depth dose (PDD), field output factors, and temperature response. The results were compared with Gafchromic film (EBT-3 film) for beam profiles. The field output factor and temperature response were compared to the Exradin W1 detector. The dose linearity measured with 600 MU/min dose rate showed minimal variations (<0.5%) even for small MU, and similar results were seen for dose rate linearity. The comparison of field output factors between the W2 and W1 showed small differences for various depth and field sizes. The temperature response showed small variation when the temperature was varied from 6 ∘ C to 50 ∘ C . The slope was - 0.0017 / ∘ C and - 0.0016 / ∘ C for the W2 and the W1 detector, respectively. The differences in profiles are 0.5% in umbra and penumbra region for 1 × 1 cm 2 field size when compared to the EBT-3 film profile. The W2 scintillator detector showed similar dosimetric and temperature properties to the W1 scintillator detector. The main advantage of the W2 detector among other plastic scintillators is the beam scanning capabilities that, combined with its correction factor of 1.0, make it an ideal detector for commissioning of SRS and SBRT techniques.

Galavis PE ，Hu L ，Holmes S ，Das IJ ... -  《-》

Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector.

Pasquino M ，Cutaia C ，Radici L ，Valzano S ，Gino E ，Cavedon C ，Stasi M ... -  《-》