Purpose: This study aimed to dosimetrically compare the technique of three-dimensional conformal radiotherapy (3D CRT), which is a traditional prophylactic cranial irradiation method, and the intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques used in the last few decades with the dynamic conformal arc therapy (DCAT) technique.
Methods: The 3D CRT, VMAT, IMRT, and DCAT plans were prepared with 25 Gy in 10 fractions in a Monaco planning system. The target volume and the critical organ doses were compared. A comparison of the body V₂, V₅, and V₁₀ doses, monitor unit (MU), and beam on-time values was also performed.
Results: In planned target volume of the brain (PTV_Brain), the highest D99 dose value (P<0.001) and the most homogeneous (P =0.049) dose distribution according to the heterogeneity index were obtained using the VMAT technique. In contrast, the lowest values were obtained using the 3D CRT technique in the body V₂, V₅, and V₁₀ doses. The MU values were the lowest when DCAT (P =0.001) was used. These values were 0.34% (P =0.256) lower with the 3D CRT technique, 66% (P =0.001) lower with IMRT, and 72% (P =0.001) lower with VMAT. The beam on-time values were the lowest with the 3D CRT planning (P<0.001), 3.8% (P =0.008) lower than DCAT, 65% (P =0.001) lower than VMAT planning, and 76% (P =0.001) lower than IMRT planning.
Conclusions: Without sacrificing the homogeneous dose distribution and the critical organ doses in IMRTs, three to four times less treatment time, less low-dose volume, less leakage radiation, and less radiation scattering could be achieved when the DCAT technique is used similar to conventional methods. In short, DCAT, which is applicable in small target volumes, can also be successfully planned in large target volumes, such as the whole-brain.

Purpose: In this study, the dosimetric characteristics of lung stereotactic body radiotherapy (SBRT) plans using the new Halcyon system were analyzed to assess its suitability.
Methods: We compared the key dosimetric parameters calculated for the Halcyon SBRT plans with those of a conventional C-arm linear accelerator (LINAC) equipped with a high-definition multileaf collimator (HD-MLC)—Trilogy Tx. A total of 10 patients with non-small-cell lung cancer were selected, and all SBRT plans were generated using the RapidArc technique.
Results: Trilogy Tx exhibited significant superiority over Halcyon in terms of target dose coverage (conformity index, homogeneity index, D_{0.1 cc}, and D_95%) and dose spillage (gradient). Trilogy Tx was more efficient than Halcyon in the lung SBRT beam delivery process in terms of the total number of monitor units, modulation factor, and beam-on time. However, it was feasible to achieve a dose distribution that met SBRT plan requirements using Halcyon, with no significant differences in satisfying organs at risk dose constraints between both plans.
Conclusions: Results confirm that Halcyon is a viable alternative for performing lung SBRT in the absence of a LINAC equipped with HD-MLC. However, extra consideration should be taken in determining whether to use Halcyon when the planning target volume setting is enormous, as in the case of significant tumor motions.