A direct comparison of the optically stimulated luminescent properties of BeO and Al2O3 for clinical in-vivo dosimetry

Abstract

Abstract Optically stimulated luminescence dosimetry is a relatively recent field of in-vivo dosimetry in clinical radiotherapy, developing over the last 20 years. As a pilot study, this paper presents a direct comparison between the sensitivity variance with use, stability of measurement and linearity of the current clinical standard Al 2 O 3 :C and a potential alternative, beryllium oxide. A set of ten optically stimulated luminescence dosimeters (OSLD), including five of each type, were used simultaneously and irradiated on a Versa HD linear accelerator. Having similar sensitivity, while Al 2 O 3 :C showed a relatively stable signal response from initial use, BeO was found to have a higher response to the same dose. However, BeO displayed a strong exponential decline from initial signal response following a model of $$Respons{e}_{BeO}=(0.55\pm 0.05){e}^{-\left(0.40\pm 0.05\right)x}+(0.54\pm 0.01)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>R</mml:mi> <mml:mi>e</mml:mi> <mml:mi>s</mml:mi> <mml:mi>p</mml:mi> <mml:mi>o</mml:mi> <mml:mi>n</mml:mi> <mml:mi>s</mml:mi> <mml:msub> <mml:mi>e</mml:mi> <mml:mrow> <mml:mi>BeO</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>0.55</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.05</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mfenced> <mml:mn>0.40</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.05</mml:mn> </mml:mfenced> <mml:mi>x</mml:mi> </mml:mrow> </mml:msup> <mml:mo>+</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>0.54</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> , reaching stability after approximately 10 irradiation cycles. BeO was shown to have potentially higher accuracy than Al 2 O 3 :C, with less variation between individual doses. Both OSLD showed good linearity between 0.2–5.0 Gy. Between these bounds, Al 2 O 3 :C demonstrated a strong linear response following the trend $$Dose_{Al_{2}O_{3}, group(adj)}=(1.00\pm 0.09)x-(0.02\pm 0.04)\,{\text{Gy}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>o</mml:mi> <mml:mi>s</mml:mi> <mml:msub> <mml:mi>e</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:msub> <mml:mi>l</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mo>,</mml:mo> <mml:mi>g</mml:mi> <mml:mi>r</mml:mi> <mml:mi>o</mml:mi> <mml:mi>u</mml:mi> <mml:mi>p</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>a</mml:mi> <mml:mi>d</mml:mi> <mml:mi>j</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>1.00</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.09</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>x</mml:mi> <mml:mo>-</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>0.02</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.04</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:mspace/> <mml:mtext>Gy</mml:mtext> </mml:mrow> </mml:math> , however beyond this showed deviation from linearity, resulting in a measured dose of $$12.0\pm 0.2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>12.0</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.2</mml:mn> </mml:mrow> </mml:math> Gy at 10.0 Gy dose delivery. BeO showed strong linearity across the full examined range of 0.2–10.0 Gy with following a model of $$Dos{e}_{BeO, ind}=(0.98\pm 0.01)x+(0.04\pm 0.01)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>o</mml:mi> <mml:mi>s</mml:mi> <mml:msub> <mml:mi>e</mml:mi> <mml:mrow> <mml:mi>B</mml:mi> <mml:mi>e</mml:mi> <mml:mi>O</mml:mi> <mml:mo>,</mml:mo> <mml:mi>i</mml:mi> <mml:mi>n</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>0.98</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>x</mml:mi> <mml:mo>+</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>0.04</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> Gy with a recorded dose at 10.0 Gy delivery as $$9.9\pm 0.1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>9.9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:math> Gy. In conclusion, BeO does show large variance in sensitivity between individual OSLD and a considerable initial variance and decline in dose–response, however after pre-conditioning and individual normalisation to offset OSLD specific sensitivity BeO provides not only a viable alternative to Al 2 O 3 :C, but potentially provide higher accuracy, precision and reproducibility for in-vivo dosimetry.

Topics & Concepts