Authors (including presenting author) :
Kwok PW(1), Lau CT(1), Tai KK(1), Lee WY (1),Tin WY(1)
Affiliation :
(1) Department of Clinical Oncology, Tuen Mun Hospital
Introduction :
Boluses are used in radiotherapy to overcome skin-sparing effect of high-energy photon radiotherapy. Conventional workflow of using material such as dental wax or Superflab® as bolus involves estimating the required bolus size and shape by clinicians before planning CT. It has several disadvantages, including potential erroneous estimation of the bolus required, resulting in over- or under-dosing of skin tissue; poor conformity resulting in air gaps between bolus and patient’s surface; and is labour-intensive and time-consuming. An unfit bolus may require a second moulding and CT, causing inconvenience to patient, and potentially delaying radiotherapy treatment.
3D-printing technology enables individualized bolus to be produced after planning CT. A pilot programme was launched in Tuen Mun Hospital to use 3D-printed bolus for radiotherapy. We report nine successful cases of radiotherapy treatment using 3D-printed boluses in our centre.
Objectives :
To assess the feasibility, dosimetric and treatment outcome of 3D-printed bolus in radiotherapy.
Methodology :
Patients were selected for 3D-printed bolus if they would otherwise require remoulding (e.g., patients with unsatisfactory conventional boluses, or the use of bolus had not been anticipated beforehand).
Patients were selected for 3D-printed bolus if they would otherwise require remoulding (e.g., patients with unsatisfactory conventional boluses, or the use of bolus had not been anticipated beforehand).
After the planning CT, an estimated virtual bolus was generated based on the planning target volume (PTV) and dosimetric need. Bolus was then 3D-printed with polylactic acid (PLA) or thermoplastic polyurethane (TPU) and applied to patient. The position of the bolus was re-verified by another CT, which is then matched to planning CT for evaluation. Patients were treated with 3D-printed boluses and followed up in clinic during and after treatment to evaluate toxicities. Treatment and dosimetric outcomes with 3D-printed bolus were collected and analysed.
Result & Outcome :
Nine patients (five breast cancer patient, one soft tissue sarcoma patient, one anal canal cancer patient, one orbital MALToma patient, and one glottic cancer patient) were selected to receive radiotherapy treatment with 3D-printed bolus based on their dosimetric need. Six had conventional bolus prepared and were found unsatisfactory, and three were not anticipated to require bolus. Satisfactory dosimetric outcome was achieved with new 3D-printed bolus. The new 3D-printed bolus produced better coverage in terms of V100% compared to conventional bolus (mean V100% 98.2%±1.5% (SD) vs. 91.3%±7.5%) and similar Dmax (mean Dmax 107.1%±1.9% vs 107.4%±1.8%). During clinical follow up, there were no excessive acute toxicities observed.
Conclusion
This project marks the first public oncology centre in Hong Kong to utilise 3D-printed bolus for radiotherapy treatment. The preliminary results of 3D-printed bolus were encouraging. 3D-printed bolus provided good dosimetric outcome with no apparent additional skin toxicities. It has the potential to mitigate the common problems with conventional boluses, in particular under-coverage of PTV and patient’s inconvenience for re-moulding. Future research is needed to further explore additional potential benefits of 3D-printed bolus, including better conformity to patient’s body contour, reducing air gaps, cost- and labour-saving, etc.
A second phase of the pilot programme is proposed with a new workflow to mitigate the need of conventional boluses. We plan to continue incorporate 3D-printed boluses into routine clinical practice and apply to more oncology patients in our centre.
