Clinical application of 3D-printed bolus in postmastectomy radiotherapy

To evaluate the fitting accuracy and dose influence of 3D-printed bolus (3DPB) during postmastectomy radiotherapy.

Air gaps were assessed using cone-beam computed tomography (CBCT) images for 27 breast cancer patients who received postmastectomy radiotherapy. Then a CIRS thoracic phantom was used to evaluate the dosimetric effects of different air gap sizes.

In CBCT images of patients, compared with conventional bolus (CB), 3DPB significantly reduced both the maximum and total air gap volumes by an average between 103.04 cm³ and 124.63 cm³, respectively. The average maximum gap height was 0.53 ± 0.20 cm for 3DPB and 2.23 ± 0.41 cm for CB (p<0.05). In the results as obtained from the phantom simulation, as gap height increased from 0.5 cm to 3.5 cm, D95 (dose received by 95% of the target volume) and D98 (dose received by 98% of the target volume) values for the superficial skin zone (SSZ), clinical target volume (CTV), and planning target volume (PTV) all decreased insignificantly. When the gap exceeded 2 cm, dose reductions became more pronounced in SSZ. Similar trends were observed in the CTV and PTV.

For breast cancer radiotherapy patients immobilized using a vacuum bag, as evidenced by the CBCT images and phantom simulation, 3DPB provides a superior anatomical fit, reducing air gaps and associated dose loss in postmastectomy radiotherapy. When the air gap height ≤ 2 cm, dose attenuation with CB remains clinically acceptable, suggesting that 3D printing may not be necessary unless the skin in the gap area is at high risk for recurrence. However, for gaps > 2 cm, the dose reduction becomes significant, warranting the use of 3D-printed boluses to ensure adequate target coverage.