Radioactive iodine-125 and palladium-103 decay by X-ray emission and are used in brachytherapy to treat cancer. Consider two patients, one being treated with I-125 and the other with Pd-103. Both receive a total dose of 145 Gy delivered over 10 months. What can be concluded from the data in the table about these treatments?
Note: 1 keV = 1.602 * 10^-¹⁶ J. $\begin{array} { | c | c | c | c | c | } \hline \text { Isotope } & \begin{array} { c } \text { X-ray Energy } \\\text { keV }\end{array} & \begin{array} { c } \mathbf { t } _ { 1 / 2 } \\\text { days }\end{array} & \begin{array} { c } \text { Initial Dose } \\\text { mGy/h }\end{array} & \begin{array} { c } \text { Initial Activity } \\\mathbf { m C i }\end{array} \\\hline \mathrm { L } - 125 & 27 & 60 & 80 & 0.42 \\\hline \mathrm { Pd } - 103 & 21 & 17 & 200 & 1.30 \\\hline\end{array}$
I. The level of radiation is more uniform over the 10 months using I-125.
II. Initially the level of radiation is higher using Pd-103.
III. The density of sites damaged by radiation is higher initially using Pd-103.

Question

Radioactive iodine-125 and palladium-103 decay by X-ray emission and are used in brachytherapy to treat cancer. Consider two patients, one being treated with I-125 and the other with Pd-103. Both receive a total dose of 145 Gy delivered over 10 months. What can be concluded from the data in the table about these treatments?
Note: 1 keV = 1.602 * 10^-¹⁶ J.

\begin{array} { | c | c | c | c | c | } \hline \text { Isotope } & \begin{array} { c } \text { X-ray Energy } \\\text { keV }\end{array} & \begin{array} { c } \mathbf { t } _ { 1 / 2 } \\\text { days }\end{array} & \begin{array} { c } \text { Initial Dose } \\\text { mGy/h }\end{array} & \begin{array} { c } \text { Initial Activity } \\\mathbf { m C i }\end{array} \\\hline \mathrm { L } - 125 & 27 & 60 & 80 & 0.42 \\\hline \mathrm { Pd } - 103 & 21 & 17 & 200 & 1.30 \\\hline\end{array}

I. The level of radiation is more uniform over the 10 months using I-125.
II. Initially the level of radiation is higher using Pd-103.
III. The density of sites damaged by radiation is higher initially using Pd-103.

Quizplus · Accepted Answer

The half-life of I-125 is longer than that of Pd-103, so the level of radiation will be more uniform over the 10 months using I-125. The initial dose rate is higher using Pd-103, so the level of radiation will be higher initially using Pd-103. The density of sites damaged by radiation is proportional to the dose rate, so the density of sites damaged by radiation will be higher initially using Pd-103.

Radioactive Iodine-125 and Palladium-103 Decay by X-Ray Emission and Are