Effective atomic number of soft tissue, water and air for interaction of various hadrons, leptons and isotopes of hydrogen

Investigation of the effective atomic number dependency on kinetic energy using collision stopping powers for electrons, protons, alpha, and carbon particles

As an important component in medical applications, dosimetry, and radiotherapy studies, the effective atomic number of body tissue, tissue equivalent substances, and dosimetry compounds are investigated. In this research, considering the Coulomb interaction of charged particles, using the collision stopping power and the NIST library data, the effective atomic number of various materials at different energies is calculated for common radiotherapy particles such as electron, proton, alpha, and carbon ions. Taking into account the direct calculation method based on the collision stopping power, the effective atomic number for electron, proton, alpha, and carbon particles is determined for a group of dosimetry and tissue equivalent materials. Results of the calculations based on the collision stopping power showed that in low kinetic energy, the values of the effective atomic number are equal to the total number of electrons in each molecule of the compound, which is quite justified by the physics of Bethe's formulas.

Dual-Energy Computed Tomography For Differentiation Between Osteoblastic Metastases and Bone Islands

Objective

The objective of our study was to evaluate the utility of Rho/Z on dual-energy computed tomography (DECT) for the differentiation of osteoblastic metastases (OBMs) from bone islands (BIs).

Methods

DECT images of 110 patients with malignancies were collected. The effective atomic number (Z), electron density (Rho), dual energy index (DEI), and regular CT (rCT) values were measured by two observers. Independent-sample t-test was used to compare these values between OBMs and BIs. The diagnostic performance was assessed by receiver operating characteristic (ROC) analysis and the cutoff values were evaluated according to ROC curves.

Results

A total of 205 OBMs and 120 BIs were included. The mean values of Z, Rho, DEI, and rCT of OBMs were significantly lower than those of BIs, whereas the standard deviation values were higher than those of BIs (all p ≤ 0.05). ROC analysis showed that 11.86 was the optimal cutoff value for Z, rendering an area under the ROC curve (AUC) of 0.91, with a sensitivity of 91.2% and a specificity of 82.5%.

Conclusion

DECT can provide quantitative values of Z, Rho, and DEI and has good performance in differentiating between OBMs and BIs.

Effective atomic number and photon buildup factor of bismuth doped tissue for photon and particles beam interaction

Introduction: The doping of high Z nanoparticles into the tumor tissue increases the therapeutic efficiency of radiotherapy called nanoparticle enhanced radiotherapy (NERT). In the present study, we are identifying the effective types of radiation and effective doping concentration of bismuth radiosensitizer for NERT application by analyzing effective atomic number (Zeff) and photon buildup factor (PBF) of bismuth (Bi) doped soft tissue for the photon, electron, proton, alpha particle, and carbon ion interactions.

Material and methods: The direct method was used for the calculation of Zeff for photon and electron beams (10 keV-30 MeV). The phy-X/ZeXTRa software was utilized for the particle beams such as proton, alpha particle, and carbon ions (1-15 MeV). Bismuth doping concentrations of 5, 10, 15, 20, 25 and 30 mg/g were considered. The PBF was calculated over 15 keV-15 MeV energies using phy-X/PSD software.

Results: The low energy photon (<100 keV) interaction with a higher concentration of Bi dopped tissue gives the higher values of Zeff. The Zeff increased with the doping concentration of bismuth for all types of radiation. The Zeff was dependent on the type of radiation, the energy of radiation, and the concentration of Bi doping. The particle beams such as electron, proton, alpha particle, and carbon ion interaction gives the less values of Zeff has compared to photon beam interaction. On the other hand, the photon buildup factor values were decreased while increasing the Bi doping concentration.

Conclusions: According to Zeff and PBF, the low energy photon and higher concentration of radiosensitizer are the most effective for nanoparticle enhanced radiotherapy application. Based on the calculated values of Zeff, the particle beams such as electron, proton, alpha particle, and carbon ions were less effective for NERT application. The presented values of Zeff and PBF are useful for the radiation dosimetry in NERT.