Spectrum of secondary radiation from the hydroxyapatite-wollastonite marker for pre-irradiation marking

   Objective. To determine the potential for generating secondary radiation on a hydroxyapatite-wollastonite graft, which has the potential to be used as a marker for postoperative pre-irradiation marking.

   Materials and methods. During the simulation of a radiotherapy session, the spectrum of secondary radiation generated on the hydroxyapatite-wollastonite graft and polyacrylamide was studied. Polyacrylamide, composed of basic chemical elements similar to those in human soft tissues, was used as an equivalent. Hydroxyapatite-wollastonite was obtained by plasma-reactive sintering of Ca₃(Si₃O₉) powder mixed with reactive components (CaO and CaHPO₄HAP). The simulation of radiotherapy was conducted using a TrueBeam Linear Accelerator, developed by Varian Medical Systems, utilizing photon energy of 6 mega-electron volts (MeV) with a portable lead block shield and an aperture of 10 mm in diameter for irradiation. An SKS-50M gamma spectrometer with a high-purity germanium detector was used to record the photon distribution. Instrument readings were summarized in increments of 50 kilo-electron volts (keV) within the range of 0 to 2650 keV and presented graphically. Three measurements were taken in each range, after which the arithmetic mean and mean deviation were calculated. The significance of differences between means was determined using Student's t-test.

   Results. The secondary radiation from the studied samples in the range of 51–100 keV showed minor differences: hydroxyapatite-wollastonite produced 23.18 ± 2.57 pulses/second compared to polyacrylamide at 21.57 ± 2.37 pulses/second, while at energies of 101–150 keV, hydroxyapatite-wollastonite yielded 21.18 ± 2.51 pulses/second versus polyacrylamide at 22.9 ± 2.41 pulses/second. However, these differences were not statistically significant.

   Conclusion. The graft of hydroxyapatite-wollastonite micro-particles is considered to be a promising material for precise postoperative/pre-irradiation marking during treatment planning and does not require recalculation of radiation dose.

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