3D-printed bolus ensures the precise postmastectomy chest wall radiation therapy for breast cancer

Application of 3D printing for personalized boluses in radiotherapy: a systematic review

The goal of this study was to evaluate the current literature covering the topic of 3D-printed radiotherapy boluses in the context of fabrication methods, materials, and clinical outcomes. This systematic review followed the PRISMA 2020 guidelines. Data were extracted for authors, publication details, application type, printing technique and materials, study type, radiation type, reported outcomes and implementation difficulties. The search yielded 161 articles, 52 of which met the inclusion criteria. Publications on 3D printing for customized boluses have increased since 2014, with the most articles from the United States (21%). Most studies (80.8%) focused on manufacturing custom boluses and testing 3D printing materials, whereas 19.2% explored creating molds for boluses. CT scans were the primary method for defining the bolus area (88.6%). The publications included three study types: dosimetric evaluations, evaluations with anthropomorphic phantoms, and clinical case studies. Fused Deposition Modeling (FDM) was the most common printing technique (88.1%), with Polylactic Acid (PLA) being the most frequently used material (57.1%). Challenges included ensuring proper fit, assessing material properties, and managing printing time. The outcomes of this review suggest that 3D printing technology holds significant promise for improving radiotherapy by creating custom-fit boluses. 3D-printed boluses demonstrated notable advantages, such as improved dose distribution, better bolus conformity, and reduced setup times. However, several limitations have been identified, including considerable variability in study designs, making it challenging to draw generalized conclusions. Some studies had small sample sizes or did not clearly report methodological details. Addressing these issues will help to optimize technology's implementation.

Additive manufacturing of patient specific bolus for radiotherapy: large scale production and quality assurance

Bolus is commonly used to improve dose distributions in radiotherapy in particular if dose to skin must be optimised such as in breast or head and neck cancer. We are documenting four years of experience with 3D printed bolus at a large cancer centre. In addition to this we review the quality assurance (QA) program developed to support it. More than 2000 boluses were produced between Nov 2018 and Feb 2023 using fused deposition modelling (FDM) printing with polylactic acid (PLA) on up to five Raise 3D printers. Bolus is designed in the radiotherapy treatment planning system (Varian Eclipse), exported to an STL file followed by pre-processing. After checking each bolus with CT scanning initially we now produce standard quality control (QC) wedges every month and whenever a major change in printing processes occurs. A database records every bolus printed and manufacturing details. It takes about 3 days from designing the bolus in the planning system to delivering it to treatment. A 'premium' PLA material (Spidermaker) was found to be best in terms of homogeneity and CT number consistency (80 HU +/- 8HU). Most boluses were produced for photon beams (93.6%) with the rest used for electrons. We process about 120 kg of PLA per year with a typical bolus weighing less than 500 g and the majority of boluses 5 mm thick. Print times are proportional to bolus weight with about 24 h required for 500 g material deposited. 3D printing using FDM produces smooth and reproducible boluses. Quality control is essential but can be streamlined.

Individualized 3D-printed bolus promotes precise postmastectomy radiotherapy in patients receiving breast reconstruction

Purpose

To evaluate the efficacy and safety of 3D-printed tissue compensations in breast cancer patients receiving breast reconstruction and postmastectomy radiotherapy (PMRT).

Methods and materials

We enrolled patients with breast cancer receiving breast reconstruction and PMRT. The dose distribution of target and skin, conformability, and dose limit of organs at risk (OARs) were collected to evaluate the efficacy of the 3D-printed bolus. Radiation Therapy Oncology Group (RTOG) radiation injury classification was used to evaluated the skin toxicities.

Results

A total of 30 patients diagnosed between October 2019 to July 2021 were included for analysis. Among all the patients, the 3D-printed bolus could ensure the dose coverage of planning target volume (PTV) [homogeneity index (HI) 0.12 (range: 0.08-0.18)], and the mean doses of D99%, D98%, D95%, D50%, D2% and Dmean were 4606.29cGy, 4797.04cGy, 4943.32cGy, 5216.07cGy, 5236.10cGy, 5440.28cGy and 5462.10cGy, respectively. The bolus demonstrated an excellent conformability, and the mean air gaps between the bolus and the chest wall in five quadrants were 0.04cm, 0.18cm, 0.04cm, 0.04cm and 0.07cm, respectively. In addition, the bolus had acceptable dosage limit of OARs [ipsilateral lung: Dmean 1198.68 cGy, V5 46.10%, V20 21.66%, V30 16.31%); heart: Dmean 395.40 cGy, V30 1.02%, V40 0.22%; spinal cord planning risk volume (PRV): Dmax 1634 cGy] and skin toxicity (grade 1, 76.0%; grade 2, 21.0%; grade 3, 3.3%).

Conclusion

The 3D-printed bolus offers advantages in terms of dose uniformity and controllable skin toxicities in patients receiving breast reconstruction and PMRT. Further research is needed to comprehensively evaluate the effectiveness of the 3Dprinted bolus in this patient subset.