Implementation of 3D printing in photon, electron radiotherapy and brachytherapy

Abstract

Use of three-dimensional (3D) printing in radiotherapy remains limited despite being available for over 20 years. This thesis focused on three studies which investigated the efficacy and feasibility of implementing 3D printing in both brachytherapy and teletherapy including electron and photon therapy for cervix and breast cancer respectively. Firstly, VeneziaTM and GenevaTM are two commercially available applicators targeted to treat all stages of cervix and vaginal vault recurrent corpus cancer. For cases with extensive parametrium and vaginal involvement or if the uterus is too short or long, modified applicator using 3D printing can be made patient specifically to increase tumour’s coverage. In Chapter 2 and 3, we described the use of redesigned 3D-printed applicators and recruited 10 patients with cervix or uterine cancers with vaginal vault recurrence. Our results demonstrated that the new design significantly increased the dose of gross tumour volume, high and intermediate risk clinical target volumes by 11.7%, 8.0% and 19.4%, respectively. Secondly, sequential electron radiotherapy after tangential photon radiotherapy acts as a boost for the surgical bed after lumpectomy for breast cancer patients and is widely used for its easy delivery. However, poor target conformity has made electron boost less favourable. In Chapter 4, we evaluated the feasibility of 3D-printed patient specific modulated electron bolus (MEB) in terms of dosimetric comparison from the 27 left breast cancer patients we recruited. We demonstrated that left lung and heart statistically significant decreases in percentage volume when receiving more than 5 Gy, 10 Gy, 20 Gy, 30 Gy, and mean dose ranges from 3.6% to 44.4% for MEB plans versus conventional plans. The maximum dose of left anterior descending artery and ribs decreased by 5.6% and 6.1%, respectively. Conformity index improved by 19.9% and the monitor units statistically significantly increased by 6.0% using MEB. Thirdly, simultaneous integrated boost for breast cancer patients is another method to deliver dose to the boost volume after lumpectomy for breast cancer patients. Asian women tumours are shallowly located due to relatively smaller breasts, thereby requiring bolus to increase the near surface dose. Traditionally, oncologists would locate the tumour to delineate the bolus size according to surgical reports and scar location and send patient to undergo computed tomography (CT) with the bolus for treatment planning. However, the scar location does not represent the exact boost volume location, insufficient bolus size resulting in insufficient dose coverage to planning target volume occurs frequently, thereby requiring re-CT and re-bolus. In Chapter 5, tailor-made 3D-printed patient-specific bolus were made and applied for 20 breast cancer patients. The results revealed the mean boost target coverage had increased statistically significantly by 20.1% without increasing any organs at risk dose when compared to using traditional dental wax bolus. To conclude, 3D printing is feasible to use in brachytherapy and teletherapy for both electron and photon therapies since the quality of the treatment delivery is improved with increased dose to target volumes. The last study mentioned the potential of reducing the need of re-CT and achieved time savings for patient and oncologists.