Assessment of Dosimetric Perturbations In Small Electron Fields Caused By Optically Stimulated Luminescent Dosimeter for In-Vivo Dosimetry
Abstract
Purpose
In-vivo dosimetry in electron radiotherapy ensures accurate plan delivery and patient safety. In hypofractionated treatments such as Boom-Boom radiation (2 Gy in 2 fractions) for indolent B-cell non-Hodgkin lymphomas, the use of small cutout fields increased dose calculation and setup uncertainties, making in-vivo dosimetry valuable. RadPro International GmbH’s myOSLchip offers a practical in-vivo dosimetry solution for its small size and usability. However, the presence of a dosimeter within small electron fields may perturb the delivered dose. This study quantifies the magnitude of dosimetric perturbation introduced by the myOSLchip in clinically relevant small electron fields.
Methods
Measurements were performed in a solid water phantom using an ionization chamber (PTW-31010, 0.125cc) at the nominal depth of maximum dose (dmax) and 90% isodose (d90) depth for 6 MeV and 9 MeV electron beams from a Varian TrueBeam linac. Circular electron cutouts with diameters of 2, 3, 4, and 5 cm were evaluated, along with a 10x10cm2 electron field. For each field size, measurements were acquired under identical conditions with and without a myOSLchip positioned upstream of the measurement location. Relative dose differences were calculated to isolate the dosimeter perturbation caused by the dosimeter.
Results
Dose perturbations were observed for all field sizes, with larger effects at 6 MeV compared to 9 MeV beams. At 6 MeV and the smallest cutout (2cm), dose reductions of 10.4% at dmax and 11.7% at d90 were observed. In the 10x10cm2 field, myOSLchip caused an approximate 7% dose decrease at both depths. For 9 MeV, perturbations were smaller, with a 9% dose reduction at both depths for 2cm cutout and 5-6% reductions for larger cutouts.
Conclusion
This study characterizes the dosimetric perturbation associated with myOSLchip use in small electron fields. An informed understanding of detector-induced dose effects is essential for accurate clinical application of in-vivo dosimetry.