Not all 3D-printed bolus is created equal: Variation between 3D-printed polylactic acid (PLA) bolus samples sourced from external manufacturers.

INTRODUCTION: Polylactic acid (PLA) is a promising material for customised bolus 3D-printing in radiotherapy, however variations in printing techniques between external manufacturers could increase treatment uncertainties. This study aimed to assess consistency across various 3D-printed PLA samples from different manufacturers. METHODS: Sample prints of dimensions 5 × 5 × 1 cm with 100% infill were acquired from multiple commercial 3D-printing services. All samples were CT scanned to determine average Hounsfield unit (HU) values and physical densities. The coefficient of equivalent thickness (CET) was obtained for both photons and electrons and dose attenuation compared to TPS calculations in Elekta Monaco v5.11. RESULTS: Some samples showed warped edges up to 1.5 mm and extensive internal radiological defects only detectable with CT scanning. Physical densities ranged from 1.06 to 1.22 g cm-3 and HU values ranged from -5.1 to 221.0 HU. Measured CET values varied from 0.95 to 1.17 and TPS dose calculations were consistent with the variation in CET. Electron R50 and R90 shifted by up to 2 mm for every 1 cm of printed bolus, a clinically significant finding. Photon surface dose varied by up to 3%, while depth doses were within 1%. CONCLUSIONS: 3D-printed PLA can have considerable variability in density, HU and CET values between samples and manufacturers. Centres looking to outsource 3D-printed bolus would benefit from clear, open communication with manufacturers and undertake stringent QA examination prior to implementation into the clinical environment.

Serum procollagen 1 amino-terminal propeptide (P1NP) in prostate cancer: pitfalls of its use as an early surrogate marker for bone metastasis.

INTRODUCTION: Procollagen 1 amino-terminal propeptide (P1NP) is a bone formation marker and has been shown to have a strong association with the extent of bone metastases (BM) in patients with advanced prostate cancer. More recently, its levels were found to be affected by androgen deprivation therapies and bisphosphonates. We investigated the role of P1NP as a surrogate marker of sub-radiological skeletal metastases in prostate cancer patients with biochemical failure (BF). METHODS: BePrepared is a prospective longitudinal substudy of RADAR trial in which serial P1NPs were collected at regular intervals for 123 patients who had completed RADAR protocol treatment. RESULTS: There was no trend identified in P1NP levels prior to diagnosis of BM. We found that there was no difference in P1NP concentrations at the time of diagnosis of BM in the group that developed BM compared with P1NP levels in groups with only nodal metastases or BF. In the group of patients who did not experience BF, P1NP was affected by previous luteinizing hormone-releasing hormone-agonist and bisphosphonate therapy. Hence, patients who received an 18-month course of androgen deprivation without bisphosphonates had significantly higher P1NP values than patients with shorter androgen deprivation therapy (ADT) course combined with a course of bisphosphonates. CONCLUSION: P1NP is not a sensitive serum marker of early BM in high-risk prostate cancer patients with BF and low prostate-specific antigen levels as its levels are affected by prior history of bone remodelling therapies such as ADT and bisphosphonates.