Workload implications for clinic workflow with implementation of three-dimensional printed customized bolus for radiation therapy: A pilot study

Abstract

Bolus is commonly used in radiation therapy to improve radiation dose distribution to the target volume, but commercially available products do not always conform well to the patient surface. Tumor control may be compromised, particularly for superficial tumors, if bolus does not conform well and air gaps exist between the patient surface and the bolus. Three-dimensional (3D) printing technology allows the creation of highly detailed, variable shaped objects, making it an attractive and affordable option for customized, patient-specific bolus creation. The use of 3D printing in the clinical setting remains limited. Therefore, the objective of this study was to assess the implications on time and clinical fit using a workflow for 3D printing of customized bolus in companion animals with spontaneous tumors treated with radiation therapy. The primary aim of this study was to evaluate the time required to create a clinical 3D printed bolus. The secondary aims were to evaluate the clinical fit of the bolus and to verify the skin surface dose. Time to segmentation and 3D printing were documented, while the clinical fit of the bolus was assessed in comparison to the bolus created in the treatment planner. The mean and median time from segmentation to generation of 3D printed boluses was 6.15 h and 5.25 h, respectively. The 3D printed bolus was significantly less deviated from the planned bolus compared to the conventional bolus (p = 0.0078) with measured dose under the bolus within 5% agreement of expected dose in 88% of the measurements. Clinically acceptable 3D printed customized bolus was successfully created for treatment within one working day. The most significant impact on time is the 3D printing itself, which therefore has minimal implications on personnel and staffing. Quality assurance steps are recommended when implementing a 3D printing workflow to the radiotherapy clinic.

Fig 1

Photographs of the commercially available skinless bolus (A and B) in place prior to treatment compared to the customized 3D bolus in the dame dog (C and D).

Fig 2. Correlation of time required to 3D print bolus to bolus volume.

The hours required to generate 3D printed bolus was significantly correlated to the size of the bolus.

Fig 3. Spatial accuracy of 3D bolus placement compared to the planned bolus.

The planned bolus is in yellow while the PTV is in red where visible. Images demonstrate the planned bolus (left), 3D generated bolus on the CBCT (middle) and conventional bolus on the CBCT (right). (A) Axial images demonstrate bolus for Case 7, which was the largest mean surface deviation for the conventional bolus (far right) compared to the planned bolus. The conventional bolus is outlined in green here to demonstrate its location external to the planned bolus. (B) Bolus for Case 14, which demonstrated the smallest mean surface deviation for the conventional bolus. (C) Bolus for Case 9, which generated a poor fit with both 3D printed bolus and conventional bolus due to a large number of mobile skin folds.

Fig 4. Mean surface deviation in the treatment bolus compared to the planning bolus.

The mean surface deviation in the 3D bolus or the conventional bolus is presented for each case as the mean deviation in mm with the standard deviation (SD).