Semiconductor dosimetry in modern external-beam radiation therapy

Abstract

Semiconductor dosimeters are ubiquitous in modern external-beam radiation therapy. They possess key features. The response, electronically available in real time, is stable and linear with absorbed dose for given irradiation conditions; the radiation-sensitive volume can be rather small in size, while retaining mechanical strength and high sensitivity. We describe three common semiconductor dosimeters: diodes, metal-oxide-semiconductor field-effect transistors and diamonds. We discuss in detail their operation principles and applications in modern external-beam radiation therapy, primarily with megavoltage photon beams. We also explore their use in proton and heavy ion therapy, and in experimental radiotherapy techniques such as synchrotron-based micro-beam radiation therapy.

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

“…Commonly used dosimeters in small fields are small volume ionization chambers [10], radiochromic films [11], silicon diodes [12], and diamond detectors [13,14] reports operation principles of solid-state dosimeters and their applications in modern radiation therapy with X-Ray beams while [15] describes the advantages and potential drawbacks of each kind of dosimeter available for small field dosimetry. Pointlike detectors are usually used for small field relative dosimeters, while taking into account variations in space and time of the beam spectrum 1D-2D detectors are desirable [14]. Radiochromic films could be a valid choice for small field dosimetry because they are almost tissue equivalent and have little energy dependence, high spatial resolution, dose rate independence, and no angular dependence.…”

“…Moreover, the sensitivity degradation with an accumulated dose can be controlled [18] and to some extent the dose per pulse dependence too [18][19][20]. Readers can learn more about the accumulated dose and dose rate topics in [14]. Moreover, silicon detector signal suffers from directional dependence which is important in measuring beam profiles and PDDs [21].…”

“…In small field applications, in the absence of equilibrium, unshielded diodes are used since the effect of spectral changes is less important than the volume averaging [22]. Furthermore, new generation silicon dosimeters present improved stability, dose linearity and radiation hardness [14]. Thanks to its material properties, diamonds get quite close to satisfying almost all ideal dosimeter requirements.…”

“…The first studies describing the proprieties of chemical vapor deposition (CVD) and the high-pressure high temperature (HPHT) diamond detectors and their performances as dosimeters are reported in the literature [26,27]. Finally, [14,15] report further developments in diamond detectors and their applications related to small field dosimetry. Compared to the abovementioned papers, this manuscript draws attention to radiotherapy applications of single and poly-crystalline CVD diamond dosimeters, focusing on their performance under photon MegaVoltage beams.…”

Radiation and Spontaneous Annealing of Radiation-sensitive Field-effect Transistors with Gate Oxide Thicknesses of 400 and 1000 nm

“…Radiation-sensitive field-effect transistors (known as RADFETs or pMOS dosimeters) can be used as radiation dosimeters for applications such as space, the nuclear industry, and radiotherapy. (1)(2)(3)(4)(5)(6)(7) RADFETs have a small sensor element of less than 1 × 1 mm 2 and allow realtime dose measurement in vivo, which is especially important for radiotherapy. A RADFET can be used as a wireless dosimeter, permanently implanted in vivo.…”