Characterization of a non-contact imaging scintillator-based dosimetry system for total skin electron therapy

Abstract

Surface dosimetry is required for ensuring effective administration of total skin electron therapy (TSET); however, its use is often reduced due to the time consuming and complex nature of acquisition. A new surface dose imaging technique was characterized in this study and found to provide accurate, rapid and remote measurement of surface doses without the need for post-exposure processing. Disc-shaped plastic scintillators (1 mm thick × 15 mm ) were chosen as optimal-sized samples and designed to attach to a flat-faced phantom for irradiation using electron beams. Scintillator dosimeter response to radiation damage, dose rate, and temperature were studied. The effect of varying scintillator diameter and thickness on light output was evaluated. Furthermore, the scintillator emission spectra and impact of dosimeter thickness on surface dose were also quantified. Since the scintillators were custom-machined, dosimeter-to-dosimeter variation was tested. Scintillator surface dose measurements were compared to those obtained by optically stimulated luminescence dosimeters (OSLD). Light output from scintillator dosimeters evaluated in this study was insensitive to radiation damage, temperature, and dose rate. Maximum wavelength of emission was found to be 422 nm. Dose reported by scintillators was linearly related to that from OSLDs. Build-up from placement of scintillators and OSLDs had a similar effect on surface dose (4.9% increase). Variation among scintillator dosimeters was found to be 0.3 ± 0.2%. Scintillator light output increased linearly with dosimeter thickness (~1.9 × /mm). All dosimeter diameters tested were able to accurately measure surface dose. Scintillator dosimeters can potentially improve surface dosimetry-associated workflow for TSET in the radiation oncology clinic. Since scintillator data output can be automatically recorded to a patient medical record, the chances of human error in reading out and recording surface dose are minimized.

Technical Note: Quality assurance and relative dosimetry testing of a 60Co total body irradiator using optical imaging

“…Furthermore, the intensified camera used during this study has maximum detection efficiency in the wavelength band of EJ‐200 scintillator emission (400–500 nm) thereby suppressing and enhancing detection of Cherenkov and scintillation signal, respectively. Previous studies have demonstrated the feasibility of conducting surface dosimetry, treatment QA, and radiation field verification by capturing light emission from plastic scintillator targets during linear accelerator (linac)‐based radiotherapy . Thus, the optical imaging methods described in this study could also be adapted for use in linac TBI QA testing.…”

“…In turn, workflow time can be minimized and there exists the possibility for reducing human error by automating data processing and analysis. There also exists the possibility of utilizing this system for patient imaging by incorporation of a modified version of a previously described equalized background subtraction method …”

“…There also exists the possibility of utilizing this system for patient imaging by incorporation of a modified version of a previously described equalized background subtraction method. [13][14][15] ACKNOWLEDGMENTS This work was sponsored by NIH grants R44 CA199836, R01 EB023909, and P30 CA023106.…”

“…Previous studies have shown that optical imaging of scintillator light emission can be used to measure surface dose in both phantoms and patients undergoing radiotherapy. [13][14][15] These served as motivation for adapting scintillator imaging for use in 60 Co irradiator commissioning and QA. Ionization chambers (IC), optically stimulated luminescence detectors (OSLD), and other standard dosimeters are used when evaluating the performance of a 60 Co irradiator.…”

“…Previous studies have shown that optical imaging of scintillator light emission can be used to measure surface dose in both phantoms and patients undergoing radiotherapy . These served as motivation for adapting scintillator imaging for use in 60 Co irradiator commissioning and QA.…”