A Dosimetric Comparison Study for Blood Irradiation Employing Different Medium and Algorithms in Clinical Linear Accelerator.

Objective: To identify a suitable approach for blood irradiation other than the commonly used water medium and to study the impact of different algorithm dose computations.

Methods: Water is the commonly used medium for blood irradiation. In this study computed tomography scans were taken with locally made blood irradiation phantoms other than water, by using air, rice powder and thermocole using parallel beam for 25 Gy. Plans were recalculated for different algorithms such as collapsed cone (CC), Monte Carlo (MC) and pencil beam (PB). The dose-volume parameters and measured doses were collected and analyzed for each medium and algorithm.

Findings: The monitor unit (MU) for rice powder and water are close (2461±57 and 2469±61, respectively), with a maximum dose of 28.0±1.8 and 28.0±1.9 Gy. The PB algorithm resulted in lower monitor unit values regardless of the medium used, generating values of 2418, 2406, 2382, and 2362 for water, rice powder, air, and Thermocol, respectively. A significant increase in dose was observed irrespective of the medium used when the MC algorithm was employed, with a maximum of 30.26 Gy in rice powder; a smaller dose was used when the CC algorithm was employed, with 26.3 Gy in water medium. The average maximum doses of all groups were equal using the one-way Anova statistical test. Regarding the impact of field size, rice powder appears to have consistent doses across various field sizes, with slight increases as field size grows, which is similar to water.

Novelty/applications: While water is the conventional medium, this study highlights the potential benefits of rice powder, such as eliminating the risks associated with bubble formation and water spillage, which can lead to equipment malfunction and safety hazards. Although previous studies have explored rice powder as a bolus and tissue-equivalent material, this study uniquely applies this knowledge to blood irradiation, an area where rice powder has not been thoroughly investigated.