| Summary: | To monitor patient-surface dose in intensity-modulated radiation therapy (IMRT), developed a novel capacitor dosimeter with a disposable USB-A mini-substrate consisting of a 0.22 μF capacitor and a silicon X-ray diode (Si-XD). The capacitor dosimeter consisted of a USB-A mini-substrate and a microcomputer dock. The capacitor in the substrate was charged to 3.30 V using the dock before 4 MV X-ray irradiation. The charging voltage was reduced by photocurrents flowing through the Si-XD during irradiation. After which the substrate was re-inserted into the dock, and the discharging voltage was measured. A Farmer-type ionization chamber (N30013, PTW) was used to convert the discharging voltages into absorbed dose (Gy). The IMRT study was performed using a custom-made head-neck phantom. The decrease in the charging voltage was found to be proportional to the X-ray dose, and the calibrated dose corresponded well to those obtained using the ionization chamber. The surface dose measured on the head-neck phantom were equivalent to those obtained from a treatment planning system. An inexpensive dosimeter with Si-XDs was developed, as a promising too. The results suggest for monitoring patient-surface dose during radiation therapy.
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