ESTRO 2024 - Abstract Book

S3265

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

exceeding 10 mm, resulting in large air gap volumes. Additionally, despite good fit, the wax bolus was observed to contain air gaps within the bolus itself, unlike the other boluses.

The TPU and wax boluses had low average Hausdorff distances of 0.63 mm and 0.56 mm for the posterior auricle region, with a value of 1.47 mm for PLA suggesting the rigidity of the PLA bolus could have limited its conformity, compared with the flexibility of TPU. TPU, PLA and dental wax compared similarly for the nasal alar region (0.77 mm, 0.67 mm and 0.59 mm respectively). Vinyl gel performed notably worse for both sites (3.14 mm and 2.27 mm for posterior auricle and nasal alar respectively). The DSCs for the posterior auricle boluses demonstrated greater similarity for TPU, PLA, and wax compared to the vinyl gel sheet (0.87, 0.69, 0.87 and 0.29 respectively), with TPU and dental wax exhibiting greater similarity to the virtual bolus. Likewise, TPU, PLA and wax yielded very similar DSCs for the nasal alar, notably out-performing the vinyl gel. For the film measurements, the vinyl gel bolus generally showed lower surfaces doses compared with the other three boluses. For the posterior auricle surface doses, the TPU bolus displayed the closest agreement with the TPS virtual bolus calculation, with mean dose differences of <1%, while PLA and dental wax demonstrated dose differences within 3%. The 3D printed boluses also demonstrated mean dose differences of <2.5% to TPS dose calculation with the physical boluses, compared with larger mean dose differences of up to 6.4% for the conventional boluses. For the nasal alar region, the dose measurements under the wax displayed the closest agreement to the TPS to within 2% for both virtual and physical bolus dose calculations. Both TPU and PLA displayed higher dose differences of >5% when compared with TPS calculation using virtual bolus. However, these differences reduced significantly when compared with TPS calculation including the physical boluses, most notably with the TPU bolus yielding mean dose differences within 2.1%.

Conclusion:

Contemporary 3D printed boluses designed for an anthropomorphic head phantom demonstrated a comparable fit to wax bolus, and a considerably better fit than vinyl gel sheets. Dosimetric analysis suggests that the TPU and PLA boluses are comparable in performance to the wax bolus, and superior to vinyl gel by minimizing air gaps. which could impact surface dosimetry.

Keywords: 3D-printed bolus, radiochromic film,

References:

[1] Malone C, Gill E, Lott, T, Rogerson, C, Keogh S, et al. Evaluation of the quality of fit of flexible bolus material created using 3D printing technology. J Appl Clin Med Phys. 2022 Mar; 23(3): e13490.

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Poster Discussion