Transrectal implantation and stability of gold markers in prostate bed for salvage radiotherapy of macroscopic recurrences

Exploratory models comparing ethiodized oil-glue and gold fiducials for bladder radiotherapy image-guidance

Background and purpose

Image-guidance with fiducials has been shown to improve pelvic radiotherapy outcome. However, bladder fiducials using ethiodized oil (EO) alone can disperse widely, and gold causes Computed Tomography scan (CT) metal artifacts. The study's purpose was to investigate the ability to deliver EO-tissue glue fiducials and compare them to gold for bladder radiotherapy image guidance.

Materials and methods

A fluid-filled porcine bladder model was used to assess the ability to cystoscopically inject visible EO glue fiducials into the submucosa. We then transferred the bladders into a porcine pelvis for imaging and compared them to gold fiducials using CT, Cone Beam CT (CBCT), and kilovoltage (KV) planar views. A tissue-equivalent phantom was utilized to analyze the CT number Hounsfield Unit (HU) characteristics and artifacts of the glue and gold fiducials. Percentile ranges and normal tissue voxel percentages of the subsequent CT number voxel histogram from a 2 cm sphere surrounding the fiducial was used to characterize the artifact.

Results

We successfully delivered all EO glue fiducials into the porcine bladders as discrete fiducials. They were well seen on CT, CBCT, and KV imaging. The glue fiducials had lower CT number values, but less CT number spread of the voxel percentile ranges consistent with the diminished contrast and less artifact than gold. The glue fiducial types had similar CT number characteristics.

Conclusion

This study has shown that EO glue fiducials can be delivered with online visualization qualities comparable to gold fiducials without metal-related artifacts.

Role of fiducial markers in the assessment of prostate bed motion in post-prostatectomy patients treated with volumetric modulated arc therapy

Aim:

Accurate localisation of target position is crucial when using techniques with sharp dose fall off such as volumetric modulated arc therapy (VMAT). Gold seed fiducial markers have been used for target localisation in image-guided radiation therapy for various tumors including intact prostate cancers. However, their role for target localisation in post-prostatectomy radiotherapy is unclear. This study was undertaken to determine the feasibility and effectiveness of gold seed fiducial markers in patients undergoing prostate bed VMAT.

Materials and methods:

The institutional radiation oncology database was used to analyse the treatment data of 18 post-prostatectomy patients with implanted gold seed fiducial markers. The shifts of the fiducial markers were reviewed, tabulated and statistically analysed.

Results:

Three hundred and eighty-six orthogonal pair images for 18 patients were reviewed. Specifically, the average gold seed fiducial shifts were 0·34 cm in the superior–inferior (S/I) axis (0·31 SD), 0·31 cm (0·29 SD) in the anterior–posterior (A/P) axis and 0·28 cm (0·25 SD) in the lateral axis (R/L). As a result, the 95% probability of fiducial marker displacement was 0·96 cm in the S/I, 0·89 cm in the A/P and 0·78 cm in the R/L axes. The most frequent shifts occurred in the inferior, left and posterior directions. The percentage of shifts more than 0·5 cm were 19·74, 21·56 and 12·47% for the S/I, A/P and R/L axes, respectively.

Conclusion:

In the absence of fiducial markers, non-uniform planning target volume (PTV) margins of 1 cm for S/I, 9 mm for A/P and 8 mm for the lateral direction are necessary for target localisation in post-prostatectomy radiotherapy. By improving prostate bed localisation, gold seed fiducial markers can decrease PTV margins, reduce normal tissue radiation exposure and allow for dose-escalated and/or hypofractionated radiotherapy to be considered in appropriate clinical scenarios.

Stereotactic Re-irradiation for Local Recurrence in the Prostatic Bed After Prostatectomy: Preliminary Results

Objectives: To report the preliminary results of salvage re-irradiation in the prostatic bed after radical prostatectomy and salvage external beam radiation therapy (EBRT) using robotic stereotactic body radiation therapy (SBRT) with Cyberknife® for local recurrence of prostate cancer.

Materials and Methods: Retrospective monocentric analysis was performed on patients treated with SBRT for isolated macroscopic recurrence in the prostatic bed. All patients had radical prostatectomy and salvage or adjuvant EBRT. Local recurrence was documented using magnetic resonance imaging (MRI) and positron emission tomography (PET). Biochemical recurrence was defined as 2 rises in prostate-specific antigen (PSA) of ≥ 0.2 ng/mL above nadir. Internal gold fiducials were used for the tracking of tumor motion during SBRT. The prescription dose was 36 Gy in 6 fractions for all patients. Toxicity was scored according to the CTCAE v4.0.

Results: Between July 2011 and November 2017, 12 patients were treated with SBRT for prostatic bed recurrence with a median follow-up of 34.2 (range, 3.5–64.4) months. Isolated non-metastatic recurrence in the prostatic bed was seen at MRI and PET imaging. Two patients were treated with 6 months androgen deprivation therapy (ADT) concomitant with re-irradiation. The median planning target volume was 4.5 cm³ (range, 1.2–13.3). A PSA decrease after SBRT was found in 10 (83%) patients. The 1 and 2 years biochemical recurrence-free survival rates were 79 and 56%, respectively. Biochemical recurrence was observed for 6 patients (50%) after a median time of 18 (4-42) months. Toxicity showed: 3 patients (25%) with grade 1 cystitis and 1 patient (8%) with acute grade 2 proctitis at 4 months. One patient (13%) had grade 1 cystitis at 12 months.

Conclusion: Re-irradiation for local recurrence in the prostatic bed using Cyberknife® after surgery and salvage or adjuvant EBRT is well-tolerated and associated with 2 years biochemical recurrence-free survival rates of 56%. Longer follow-up and larger series are necessary.

The Effect of Electrode Topography on the Magnetic Properties and MRI Application of Electrochemically-Deposited, Synthesized, Cobalt-Substituted Hydroxyapatite

Magnetic nanoparticles are used to enhance the image contrast of magnetic resonance imaging (MRI). However, the development of magnetic nanoparticles with a low dose/high image contrast and non-toxicity is currently a major challenge. In this study, cobalt-substituted hydroxyapatite nanoparticles deposited on titanium (Ti-CoHA) and cobalt-substituted hydroxyapatite nanoparticles deposited on titanium dioxide nanotubes (TNT-CoHA) were synthesized by the electrochemical deposition method. The particle sizes of Ti-CoHA and TNT-CoHA were 418.6 nm and 127.5 nm, respectively, as observed using FE-SEM. It was shown that CoHA can be obtained with a smaller particle size using a titanium dioxide nanotube (TNT) electrode plate. However, the particle size of TNT-CoHA is smaller than that of Ti-CoHA. The crystal size of the internal cobalt oxide of CoHA was calculated by using an XRD pattern. The results indicate that the crystal size of cobalt oxide in TNT-CoHA is larger than that of the cobalt oxide in Ti-CoHA. The larger crystal size of the cobalt oxide in TNT-CoHA makes the saturation magnetization (Ms) of TNT-CoHA 12.6 times higher than that of Ti-CoHA. The contrast in MRIs is related to the magnetic properties of the particles. Therefore, TNT-CoHA has good image contrast at low concentrations in T₂ images. The relaxivity coefficient of the CoHA was higher for TNT-CoHA (340.3 mM^-1s^-1) than Ti-CoHA (211.7 mM^-1s^-1), and both were higher than the commercial iron nanoparticles (103.0 mM^-1s^-1). We showed that the TNT substrate caused an increase in the size of the cobalt oxide crystal of TNT-CoHA, thus effectively improving the magnetic field strength and MRI image recognition. It was also shown that the relaxivity coefficient rose with the Ms. Evaluation of biocompatibility of CoHA using human osteosarcoma cells (MG63) indicated no toxic effects. On the other hand, CoHA had an excellent antibacterial effect, as shown by E. coli evaluation, and the effect of TNT-CoHA powder was higher than that of Ti-CoHA powder. In summary, TNT-CoHA deposited electrochemically on the TNT substrates can be considered as a potential candidate for the application as an MRI contrast agent. This paper is a comparative study of how different electrode plates affect the magnetic and MRI image contrast of cobalt-substituted hydroxyapatite (CoHA) nanomaterials.

A Comparative Study on the Direct and Pulsed Current Electrodeposition of Cobalt-Substituted Hydroxyapatite for Magnetic Resonance Imaging Application

Hydroxyapatite has excellent biocompatibility and osteo-conductivity and, as the main inorganic component of human bones and teeth, is commonly used for bone repair. Its original characteristics can be changed by metal ion substitution. Cobalt ions can act as hypoxia-inducible factors and accelerate bone repair. At the same time, cobalt has paramagnetic properties and is often used in the study of medical imaging and target drugs. Through the introduction of cobalt ions, the unique hydroxyapatite has better biological activity and positioning of medical images. Herein, cobalt-substituted hydroxyapatite (CoHA) was synthesized on the surface of a titanium plate by electrochemical deposition and changes in the power output mode to explore the impact on CoHA. Electrochemical deposition with a pulse current significantly improved the productivity and uniformity of CoHA on the surface of titanium. CoHA show paramagnetic characteristics by a superconducting quantum interference device (SQUID). Resulting smaller particle size and circular morphology improves the magnetic strength of CoHA. Magnetic resonance imaging (MRI) of CoHA showed significant image contrast effect at low concentrations. The calculated particle relaxation rate was higher than other common MRI contrast agents. Biocompatibility of CoHA powder was evaluated using the human osteosarcoma cell line (MG63) which confirmed that CoHA is not cytotoxic and can promote cell growth and extracellular matrix mineralization. With the release of cobalt ions, CoHA was found to be significantly good in repression E. coli indicating about than 95% reduction in bacterial growth. The as-synthesized CoHA has a low degree of crystallinity, highly sensitive image contrast effect, and good bioactivity, and may have potential applications in bone repair and MRI.