Radiological, dosimetric and mechanical properties of a deformable breast phantom for radiation therapy and surgical applications

Abstract

The displacement of tumor bed walls during oncoplastic breast surgery (OBS) decreases the accuracy of using surgical clips as the sole surrogate for tumor bed location. This highlights the need for better communication of OBS techniques to radiation oncologists. To facilitate OBS practice and investigate clip placement reliability, a realistic silicone-based breast phantom was constructed with components emulating a breast parenchyma, epidermis, areola, nipple, chest wall, and a tumor. OBS was performed on the phantom and surgical clips were placed to mark the tumor bed. The phantom was imaged with CT, MRI, and ultrasound (US). The parenchyma's signal-to-noise ratio (SNR) and clips to parenchyma's contrast-to-noise ratio (CNR) were measured. The phantom's CT Hounsfield Unit (HU), relative electron density (RED), and mass density were determined. 6 and 10 MV photon beam attenuation measurements were performed in phantom material. The Young's Modulus and ultimate tensile strength (UTS) of the phantom parenchyma and epidermis were measured. Results showed that the breast phantom components were visible on all imaging modalities with adequate SNR and CNR. The phantom's HU is 130±10. The RED is 0.983. Its mass density is 1.01±0.01 g cm −3 . Photon attenuation measurements in phantom material were within 1% of those in water. The Young's Moduli were 13.4±4.2 kPa (mechanical) and 30.2±4.1 kPa (US elastography) for the phantom parenchyma. The UTS' were 0.05±0.01 MPa (parenchyma) and 0.23±0.12 MPa (epidermis). We conclude that the phantom's imaging characteristics resemble a fibroglandular breast's and allow clear visualization of high-density markers used in radiation therapy. The phantom material is suitable for dose measurements in MV photon beams. Mechanical results confirmed the phantom's similarity to breast tissue. The phantom enables investigation of surgical clip displacements pre-and post-OBS, and is useful for radiation therapy quality assurance applications.

Dosimetric considerations for moldable silicone composites used in radiotherapy applications

“…Moreover, in the Monaco TPS, the relative mass collisional stopping power for a medium, $$( {\frac{{{S_{{\rm{col}}}}}}{\rho }} )_{w{\rm{ater}}}^{{\rm{med}}}$$, is calculated as a function of mass density using equations applicable over variable ranges of mass densities, where $$( {\frac{{{S_{{\rm{col}}}}}}{\rho }} )_{{\rm{water}}}^{{\rm{med}}}$$ = 1.000 between the range of 0.98 < ρ < 1.02 24 . This is not entirely accurate since, as determined previously, 5 $$( {\frac{{{S_{{\rm{col}}}}}}{\rho }} )_{{\rm{water}}}^{{\rm{silicone}}}$$ is 0.948 for 6 MV photon beams. Silicone has a mean excitation energy that is ∼25% higher than water's (see data provided in Table 3) which in turn lowers the mass stopping power for silicone relative to water.…”

“…Radiotherapy treatments are often prescribed with different types of bolus material to increase dose at the skin surface and/or compensate for missing tissue 1–3 . There are several characteristics that bolus materials must fulfill, 4 many of which can be met by certain moldable silicone (MS) composites 5 . These materials can have similar mass densities as water's, and can also be manufactured to have similar tactile properties as human tissue's by modifying silicone formulations.…”

“…1 , 2 , 3 There are several characteristics that bolus materials must fulfill, 4 many of which can be met by certain moldable silicone (MS) composites. 5 These materials can have similar mass densities as water's, and can also be manufactured to have similar tactile properties as human tissue's by modifying silicone formulations.…”

Low-Cost and Easily Fabricated Ultrasound-Guided Breast Phantom for Breast Biopsy Training

“…A silicone-based breast phantom was constructed with components emulating a breast parenchyma/chest wall (silicone rubber mixed with agricultural grade silicone oil), epidermis (mesh fabric layer applied with silicone rubber), areola/nipple (epidermis mixture and a silicone baby bottle nipple as the mold) and a tumor (marble) [32].…”

“…This type of phantoms is currently not well studied in terms of its tunability of acoustic and mechanical properties and a way to make it a multilayer structure. Gelatin-agar- [25][26][27], paraffin-gel wax- [28], PVC- [29][30][31] and silicone rubber-based [32] phantoms are considered as more advanced types of phantoms that can closely resemble acoustic and mechanical properties of human tissues. These phantoms are adjustable in terms of acoustic and mechanical properties and capable of being made in a multilayer structure.…”