Advances in breast reconstruction techniques post mastectomy improve patient outcomes, yet treatment complexity increases, especially when ionizing radiation is necessary [1]. Radiation therapy (RT) following a mastectomy often requires precise immobilization for effective dosage delivery, particularly for patients with tissue expanders.
Mastectomy followed by reconstruction is evolving. Tissue expanders are often utilized prior to final reconstructive procedures. However, the presence of high-density materials within expanders can complicate RT due to artifacts in computed tomography (CT) scans and challenges in dose delivery [2]. Effective immobilization is essential for optimal treatment, as movement or shifts can lead to misadministration of the radiation dose, particularly on irradiated skin areas. Traditional bolus materials, which are commonly used to ensure uniform dose distribution, have limitations in adhesion and stability [3], especially when an expander is present.
In this work we describe a case where a novel thermoplastic bolus mask was used to immobilize a breast cancer patient with a tissue expander, ensuring reproducibility and minimizing uncertainty of dose delivery.
A female patient with right breast cancer underwent mastectomy and initial prepectoral reconstruction with a tissue expander. CT imaging of the patient was performed with a Discovery CT 590 scanner, metal artifact reduction was applied to account for high atomic numbers within the tissue expander. Initially, CT scanning and treatment planning were performed in a supine position with the use of a 3 mm bolus placed directly on the skin. The prescribed dose was 40.5 Gy, delivered in 15 fractions. The treatment plan was prepared in the Monaco 6.1.2 system (Elekta, Sweden) with the volumetric modulated arc therapy (VMAT) technique, 6 MV photon beam. The first fraction verification performed with the cone-beam computed tomography (CBCT) revealed positional inconsistencies, likely due to displacement of the expander and inadequate bolus adhesion (Fig. 1A). Consequently, an alternative immobilization method was developed using a thermoplastic mask (Orfit, Belgium) with a bolus integrated internally for enhanced adhesion and stability.
Figure 1.
Cone-beam computed tomography (CBCT) (magenta) compared with computed tomography (CT) (green): A. The first approach (visible air gaps); B. The novel immobilization (great compatibility); C. Individual bolus; D. Thermoplastic mask with the integrated bolus
The custom thermoplastic bolus mask was created embedding the bolus directly underneath the surface of the mask for improved skin adherence (Fig. 1CD). The CT scanning and treatment planning were reperformed under the same conditions as initially. The CBCT scans were performed in each fraction and in-vivo dose measurements [4] were carried out at five points with Gafchromic EBT4 film detectors placed below the mask.
The CBCT verification demonstrated reproducibility in patient positioning, with minimal displacement (Fig. 1B). Average displacements in the Y, X, and Z directions were (−0.05 ± 0.26) cm, (−0.12 ± 0.19) cm, and (0.14 ± 0.16) cm, respectively, with acceptable variability of 0.5 cm across sessions. The variability is consistent with the facility’s Baseline Response Level, which is used during geometric verification, and defined as no less than double the population value of the random patient positioning error and no more than the applied clinical target volume–planning target volume (CTV-PTV) margin (0.5 cm for breast).
Measured doses on the patient skin averaged 2.65 ± 0.03 Gy, showing only a minor deviation (0.92 %) from the planned doses. These results confirmed that the immobilization method provided precise adherence and consistency in dosage delivery.
The innovative use of a thermoplastic mask with an integrated bolus successfully addressed common challenges with tissue expanders in RT, including bolus stability and accurate dose targeting on irradiated skin. This report is based on a single case, and while the results are promising, they require validation in a larger cohort and, ideally, in a controlled, prospective study to assess reproducibility and broader applicability. This approach appears especially beneficial in cases where conventional bolus application is unreliable. The thermoplastic bolus mask enabled effective immobilization, dose accuracy and comfort for the patient, offering a promising approach for similar cases in breast cancer RT with tissue expanders. This method will be integrated into standard practice at our center for patients undergoing similar reconstructive procedures requiring post-mastectomy RT.
Footnotes
Ethics statement: There was full compliance with ethical standards, including informed consent. The patient has provided verbal consent for the publication of this report and any accompanying images.
Conflict of interest: The authors have no relevant financial or non-financial interests to disclose.
Funding: This publication was prepared without any external source of funding.
References
- 1.Socha J. Adjuvant radiation therapy after immediate implant- based breast reconstruction. Nowotwory J Oncol. 2020;70(1):20–25. doi: 10.5603/njo.2020.0004. [DOI] [Google Scholar]
- 2.Palumbo I, Marcantonini M, Scialpi M, et al. Brain natriuretic peptide as a cardiac marker of transient radiotherapy-related damage in left-sided breast cancer patients: A prospective study. Breast. 2016;25(6):45–50. doi: 10.1016/j.breast.2015.10.004. [DOI] [PubMed] [Google Scholar]
- 3.Salagean GAM, Bálint Z, Poortmans P, et al. Can the daily position of bolus material influence radiotherapy treatment? Rep Pract Oncol Radiother. 2024;29(6):732–739. doi: 10.5603/rpor.104013. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Dąbrowski R, Drozdyk I, Kukołowicz P. High accuracy dosimetry with small pieces of Gafchromic films. Rep Pract Oncol Radiother. 2018;23(2):114–120. doi: 10.1016/j.rpor.2018.01.001. [DOI] [PMC free article] [PubMed] [Google Scholar]