Dosimetric Comparison of Photon Beams Using CIRS Thorax Phantom to Evaluate Monaco Radiotherapy Treatment Planning System

Abstract

In three inhomogeneous mediums, the performance of different algorithms for Flattening Filter Free (FFF) photon beams and flattening filter (FF) photon beams was evaluated in this research work. The performance of the algorithms used for dose calculations is constantly being investigated, as an incorrect dose calculation could result in radiation dosage delivery uncertainty. Algorithms for any newer technology radiation generating equipment, such as the Linear Accelerator (LINAC), must be verified to be sure enough about the real amount of dose delivered. As radiotherapy consists of several processes, the most important of which are imaging, contouring, planning, verification, delivery, and follow-up.

 Algorithms contribute to one of the potential sources of radiation delivery uncertainty [1]. For the various aspects relevant to proper dose calculation, these algorithms fundamentally take care of the various anatomical and compositional variations (i.e. inhomogeneity) of individual patients. The importance of precise dose estimations may be seen in the fact that the data for these algorithms is taken from a homogenous static water phantom, which is not reflective of the true patient composition [2]. In the presence of inhomogeneity such as tissue bone junction, air cavity, and air soft tissue border/junction, the factor of uncertainty in dose calculation in flattened beam taking care of scattered and leakage radiation becomes larger compared to homogeneous static water phantom setup used in extraction of commissioning data for the Treatment Planning System (TPS). Due to their obvious features, such as higher dose rate of the LINAC, which reduces treatment time, recently released flattening filter free linear accelerators are become popular. The treatment site, such as lung cancer, is constantly changed by breathing and other actions, which might lead to dose delivery uncertainty [3]. Due to the high dose rate, the FFF beam technology reduces treatment time and helps in dose delivery with greater precision and accuracy. Despite their popularity, FFF beams have raised concerns about dose calculation accuracy, particularly in inhomogeneous media and body structures. FFF beams have been studied in a limited span compared to FF beams for performance evaluation in various media and densities [4]. As a result, the goal of this research was to compare the performance of various algorithms for flattening filter free photon beams and filter beams in inhomogeneities [4].

The CIRS phantom (Model 002LFC, computerised imaging reference Systems Inc., Norfolk, Virginia) was employed in this study to assess algorithm performance and dose delivery accuracy. Dose assessments in three density locations, namely bone, lung, and tissue, were performed using interchangeable solid water inserts to assess the calculation accuracy of different algorithms. In this present study ionization chambers was employed for the point dose measurements. The sensitive volume of chamber is 0.6 cc (TM30013) (PTW, Freiburg, Germany) connected to PC electrometer (Sun Nuclear Corporation). The chamber is designed for the absolute and depth dose measurements suitable for the energy range from Co-60 to 50 MV photons and 6 to 50 MeV electrons.

 In the present study, authors attempted to sought some performance assessment of the popular TPS algorithms keep the prime attention specially for FFF beams which are lashed with the unique advantages in terms of high dose rate helping in minimisation of the deteriorating impact of motion on radiotherapy delivery and its outcomes. Both the, FF and FFF photon, beams were analysed for their accuracy in dose calculation in different mediums. For both FF and FFF photon beams, the accuracy of dose calculation algorithms was tested in a variety of materials covering practically the entire density spectrum, including lung, water, and bone. In lung, water, and bone mediums, both FF and FFF beams functioned differently. The evaluation of algorithms was carried out using an anthropomorphic phantom that represented the average human thorax; thus, these findings may assist in the selection of an appropriate algorithm for specific clinical settings in terms of beam energy type (FF or FFF) and radiation delivery site tumour. The findings could also suggest the need for stress to be invested in daily QA procedures, depending on the location of the tumour and the photon beam(s) employed in radiotherapy. It may also be concluded that radiation distribution in the lung and other low-density clinical situations is complicated and difficult, especially with FFF beams. As a result, one must find a compromise between radiation delivery speed and motion management and precision.