Aims To retrospectively evaluate the quality of fit of 3D printed bolus over four different treatment sites to determine whether certain sites favor a 3D printed approach and if the quality of fit changes over the course of treatment. Materials and methods A retrospective analysis of the first 60 cases treated using 3D printed bolus in our radiotherapy center was undertaken. All boluses were printed using flexible thermoplastic polyurethane (TPU) material. We developed a system of rating the quality of fit using four quality categories. The analysis of 60 patients consisted of a review of a total 627 treatment fractions for head and neck (H&N), scalp, pelvis, and extremity treatment sites. Results Out of 627 fractions evaluated, 75.1% were rated either “good” or “excellent”, 20.6% were rated as “acceptable” and 4.3% were rated “poor”. H&N, scalp, and extremity treatment regions were found to favor a 3D printed approach. However, pelvis cases had a higher proportion of “acceptable” and “poor” ratings. Trend analysis showed no notable change in the quality of 3D printed bolus fit over the course of treatment, except for pelvis cases which tended to change categories more than other treatment sites. Conclusion This evaluation demonstrates that 3D printed bolus, created using semi‐flexible materials such as TPU, is an effective and practical bolus choice for radiotherapy. In particular, using a 3D printed approach for H&N, scalp, and extremities was found to have a highly conformal fit.

(a) The add-on microMLC system in combination with our LINAC has been commissioned to be used for clinical purposes and showed good agreement with published results for different ,MLC types. (b) This work has lead to the recommendation that leaves should be recalibrated after ten static beams or after each dynamic arc.

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