Quantum mechanics

Engineering

Photodetector

Photocurrent

Materials science

Radiation

Nuclear physics

Dosimetry

Linearity

Physics

Irradiation

Optics

Photodiode

Absorbed dose

Electronic engineering

Sensitivity (control systems)

Dosimeter

Dark current

Medicine

Nuclear medicine

Optoelectronics

Medical Physics

Purpose The response to radiation typically used in radiotherapy treatments has been experimentally evaluated for three samples of two phototransistors (BPW85B and OP505A) and two PIN photodiodes types (VTB8440BH and BPW34S). Methods To that end, a staggered irradiation cycle has been applied which included dose rate values from 0.81 to 4.87 cGy/s, achieving a total absorbed dose of 21.4 Gy. The samples have been irradiated with a linear accelerator and the relations between the induced photocurrent and the average and instantaneous dose rates, and between the accumulated charge and the absorbed dose, have been determined. The radiation‐induced output currents were measured by means of an external interface of the devices to a previously designed readout unit. Results Experimental results of Si PIN photodiode BPW34S have shown a sensitivity of (13.9 ± 0.5) nC/cGy, slight sensitivity dependence on dose rate, and a high linearity of the current with the average and instantaneous dose rate, requiring only 10 V of reverse bias voltage. This device thermal drift has characterized and modeled for temperature effect compensation. Conclusions Silicon PIN photodiode BPW34S, previously tested for X‐rays and Co‐60 gamma ray source, can also be a reliable candidate for dose rate and absorbed skin dose determination in typical radiotherapy treatments irradiations. A low sensitivity loss below 2% up to 21.4 Gy has been measured, allowing its use as an affordable reusable skin dosimeter. Moreover, no significant difference has been observed between its response to dose‐per‐pulse and changing pulse repetition frequency in terms of sensitivity and dependence with dose‐rate value.

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy