## 1 Introduction  
Recent advancements in 3D printing technology have enhanced its utility and led to the cost-effective in-house production of customized tools across various fields. In the field of medical physics, there is an increasing number of studies focusing on the printing of imaging and dosimetry phantoms to be used in radiology, radiation oncology, and nuclear medicine departments [1; 2; 3; 4]. It is important for an imaging or dosimetry phantom to mimic the radiological properties of the tissue or tissues that are the subject of interest to perform a particular clinical task. In the context of 3D printing, this goal can be achieved by adjusting the density of the printed part to match the density of the target tissue. This could be achieved by either selecting a printing material with an appropriate density or choosing appropriate printing parameters to adjust the density of the printed object. Fused Deposition Modeling (FDM) is one of the 3D printing technologies that has gained widespread use due to offering users a broad spectrum of printing materials with a wide range of physical properties, which continues to grow over time. This makes FDM technology a major breakthrough for producing a variety of tissue-mimicking radiological phantoms. The radiological properties of commercially available FDM 3D printing filaments have been investigated in many studies by performing computed tomography (CT) scans and reporting the Hounsfield Unit (HU), since it provides a quantitative measure of the X-ray attenuation coefficient, thus allowing for the analysis of tissue equivalency [5; 6; 7; 8; 9; 10]. For a typical body habitus, HU values range from around \(-900\) HU to well above \(+1000\) HU, corresponding to tissues such as the lungs and compact bone, respectively [11]. Notably, [PERSON] et al. conducted an extensive study encompassing a wide array of filaments from different vendors with densities between 0.75 g/cm\({}^{3}\) and 1.70 g/cm\({}^{3}\). The samples, all printed at a maximum achievable material density, yielded a range of HU values, spanning approximately from \(-\)250 to +1000, following a CT scan performed at 120 kVp [12]. This study has proven that it is possible to mimic most of the tissues, except the lungs. On the other hand, even higher HU values have been achieved in different studies experimenting on new commercial filaments and their printing methods [13; 14; 15]. Even further, there are studies that focused on the manufacture of bismuth and barium sulfate-infused Acrylonitrile Butadiene Styrene (ABS) filaments to fabricate very dense materials for radiation protection [16; 17]. On the contrary, despite the abundance of high-density filaments, no filament option exists with a physical density as low as that of the lungs. This has prompted numerous studies focusing on regulating specific printing parameters in FDM printing to reduce the amount of filament deposited per unit volume, thereby decreasing the density of the printed object. Initial efforts have been concentrated on decreasing the infill rate; in other words, increasing the spacing between the printed lines on the axial plane. Unfortunately, this method has yielded unfavorable results, manifesting as increased uncertainties and inhomogeneities at lower infill rates [14; 15; 18; 19; 20; 21; 22]. Several studies that adopted this approach resulted in lung phantoms with unrealistic tissue textures [18; 21; 22; 23; 24]. On the other hand, some recent studies aimed to adjust the density of a printing job via the modulation of the flow rate and print speed [25; 26]. Both parameters were used to govern the printed line width, rather than spacing between the printed lines. This allowed for the subpixel printing of lines and presented much better results in terms of homogeneity and texture control.