The development and characterization of an all-purpose bolus for radiotherapy

Abstract

Objective. The purpose of this study was to develop a new bolus (HM bolus), with tissue equivalence, transparency, reusability, and free shaping at approximately 40 °C for excellent adhesion, and to evaluate the feasibility of clinically using this bolus as an ideal bolus. Approach. We summarized the advantages and disadvantages of existing boluses. To evaluate dose characteristics, a vinyl gel sheet bolus (Gel bolus) and HM bolus placed on a water-equivalent phantom were used to obtain the percent depth dose (PDD) of electron (6 MeV, 9 MeV) and photon (4 MV, 6 MV) beams. The average dose difference of the HM bolus and Gel bolus was calculated. The Gel bolus, a soft rubber bolus (SR bolus), and HM bolus were placed in adherence to a pelvic phantom. CT images taken after shaping and 1, 2, and 3 weeks after shaping were used to evaluate the adhesion and reproducibility using air gap and dice similarity coefficient (DSC). Main results. The average dose difference for electron beams was 0.16% ± 0.79% and photon beams was 0.06% ± 0.34%, both within 1% of the PDD results. The HM bolus showed the same build-up effect and dose characteristics as the Gel bolus. The mean air gap values for the Gel bolus, SR bolus, and HM bolus were 96.02 ± 43.77 cm3, 34.93 ± 21.44 cm3, and 4.40 ± 1.50 cm3, respectively. The mean DSC values compared to initial images for the Gel bolus, SR bolus, and HM bolus were 0.363 ± 0.035, 0.556 ± 0.042, and 0.837 ± 0.018, respectively. Excellent adhesion was observed in the CT simulation and during the treatment period. Significance. The HM bolus has unique features, such as tissue equivalence, transparency, reusability, and free shaping for excellent adhesion, and is thus an ideal bolus for use in clinical cases.

Initial Clinical Experience of a Novel Shapeable Bolus for Radiotherapy in a Patient With a Facial Cutaneous Squamous Cell Carcinoma: A Case Report

“…The thickness of the HM bolus and gel-sheet bolus was 5 mm. Experiments were performed using the same geometry as reported by Nakamura et al [9]. The PDD results are shown in Figure 2, which indicate that the HM bolus agreed with the gel-sheet bolus within 1% of the dose difference.…”

“…We have developed a shapeable soft-rubber bolus and reported its adherence to a head-phantom [8]. Nakamura et al (2023) reported an HM bolus with improved temperature characteristics and transparency, which were limitations of the existing soft-rubber boluses [9]. This report describes the first clinical use of the HM bolus in a patient with a cSCC of the cheek.…”

“…The face is a difficult area for a bolus to adhere to the skin because of its irregular contours. Therefore, several bolus studies have been published [8,9,12,13]. For instance, Park et al reported that a bolus could be fabricated using a three-dimensional (3D) printer [14].…”

“…The ideal bolus should adhere closely to the patient's skin without air gaps. The HM bolus (Hayakawa Rubber Co., Ltd., Hiroshima, Japan) was recently developed by Wakabayashi et al and Nakamura et al [8,9]. The HM bolus has unique features, including tissue equivalence, transparency, and reusability, and it can be easily shaped by hand after warming it to approximately 40 °C, allowing it to adhere closely to the skin.…”

Quantify the Effect of Air Gap Errors on Skin Dose for Breast Cancer Radiotherapy

“…The advantage of these customized 3D printed compensators is that they fit closely with the skin, with very small gaps between them, ensuring that the planned dose is relatively close to the actual dose. 6 However, the downside is the high technical requirements and cost involved. As a result, many hospitals may not have the capacity to provide individual compensators for each patient.…”