First report on the use of a thinner 125I radioactive seed within 20-gauge needles for permanent radioactive seed prostate brachytherapy: Evaluation of postimplant dosimetry and acute toxicity

Mathematical modeling and computer simulation of needle insertion into soft tissue

In this study we present a kinematic approach for modeling needle insertion into soft tissues. The kinematic approach allows the presentation of the problem as Dirichlet-type (i.e. driven by enforced motion of boundaries) and therefore weakly sensitive to unknown properties of the tissues and needle-tissue interaction. The parameters used in the kinematic approach are straightforward to determine from images. Our method uses Meshless Total Lagrangian Explicit Dynamics (MTLED) method to compute soft tissue deformations. The proposed scheme was validated against experiments of needle insertion into silicone gel samples. We also present a simulation of needle insertion into the brain demonstrating the method's insensitivity to assumed mechanical properties of tissue.

Effectiveness and safety of a robot-assisted 3D personalized template in 125I seed brachytherapy of thoracoabdominal tumors

PURPOSE

This research aims to evaluate the effectiveness and safety of a robot-assisted 3D personalized template in 125I seed brachytherapy of thoracoabdominal tumors.

MATERIAL AND METHODS

Forty-three patients with different tumors were involved in this research between 2013 and 2015. They were all eligible to 125I seed implantation based on robot-assisted 3D personalized template. Meanwhile, 51 patients with similar tumors, which were treated with a conventional coplanar template, were involved for comparison. Follow-up was carried out after the surgery to evaluate the therapeutic efficacy, including overall survival (OS) of the patient and local control (LC) of the tumor. Complications were also summarized to evaluate the safety. Besides, statistical analysis was achieved to investigate possible factors associated with the result.

RESULTS

In the robot-assisted 3D personalized template-guided brachytherapy, the median target volume treated by the prescription dose (V100) was 95.3% (range, 92.4-109.8), and the median dose administered to 90% of the target volume (D90) was 126.1 Gy (range, 114.2-132.0), improved 5% and 8% compared with the conventional template-guided brachytherapy, respectively. The median OS was 30 months (95% CI: 19.4-40.6) and the rates of 2-year OS and LC were 58.1% and 86.0%, respectively. The median OS was prolonged 10 months and the 2-year OS and LC were improved 18.9% and 23.3% compared with the conventional template-guided brachytherapy, respectively.

CONCLUSIONS

Through analysis of the selected patients with thoracoabdominal tumors, the robot-assisted 3D personalized template in 125I seed brachytherapy was a more effective and safer method. It can achieve a more favorable OS and LC.

Performance of a palladium-103 line source for prostate brachytherapy implants: A Phase I trial

PURPOSE

To evaluate the use of a polymer-encapsulated palladium-103 (¹⁰³ Pd) source with a unique linear radioactive distribution in prostate brachytherapy. This feasibility study assessed dosimetry, ease and efficiency of use, and side effects. The number of needles required for adequate coverage was the primary end point.

METHODS AND MATERIALS

CivaString ¹⁰³ Pd Model CS10 implants were preplanned for 25 patients. CivaStrings were custom manufactured according to plan. CivaStrings were implanted with 18 gauge needles. Post-implant dosimetry was performed at 3-6 weeks.

RESULTS

Monotherapy (125 Gy) was prescribed for 11 implants. External beam radiation with CivaString boost (100 Gy) was prescribed for 14 implants. The mean time to implant the sources was 23.5 min. The number of planned needles and prostate sizes ranged from 14 to 25 and 21-101 cm₃, respectively. 70% of implants in prostates less than 50 cm₃ required ≤17 needles. Planned source strength ranged from 2.8 U/cm to 3.9 U/cm. Total source strength averaged 216 U (130-323 U) for monotherapy and 154 U (92.4-245 U) for boost. Nomograms were generated at both prescription dose levels.

CONCLUSIONS

The linear ¹⁰³Pd source provides good dose coverage to the prostate. Prostate volume changes were minimal suggesting minimal swelling using the CivaString device.

Review of advanced catheter technologies in radiation oncology brachytherapy procedures

The development of new catheter and applicator technologies in recent years has significantly improved treatment accuracy, efficiency, and outcomes in brachytherapy. In this paper, we review these advances, focusing on the performance of catheter imaging and reconstruction techniques in brachytherapy procedures using magnetic resonance images and electromagnetic tracking. The accuracy of catheter reconstruction, imaging artifacts, and other notable properties of plastic and titanium applicators in gynecologic treatments are reviewed. The accuracy, noise performance, and limitations of electromagnetic tracking for catheter reconstruction are discussed. Several newly developed applicators for accelerated partial breast irradiation and gynecologic treatments are also reviewed. New hypofractionated high dose rate treatment schemes in prostate cancer and accelerated partial breast irradiation are presented.

Urethral toxicity after LDR brachytherapy: experience in Japan

Urinary toxicity is common after low-dose-rate (LDR) brachytherapy, and the resolution of urinary toxicity is a concern. In particular, urinary frequency is the most common adverse event among the urinary toxicities. We have previously reported that approximately 70% of patients experience urinary frequency during the first 6 months after seed implantation. Most urinary adverse events were classified as Grade 1, and Grade 2 or higher adverse events were rare. The incidence of urinary retention was approximately 2-4%. A high International Prostate Symptom Score before seed implantation was an independent predictor of acute urinary toxicity of Grade 2 or higher. Several previous reports from the United States also supported this trend. In Japan, LDR brachytherapy was legally approved in 2003. A nationwide prospective cohort study entitled Japanese Prostate Cancer Outcome Study of Permanent Iodine-125 Seed Implantation was initiated in July 2005. It is an important issue to limit urinary toxicities in patients who undergo LDR brachytherapy.

103Pd strings: Monte Carlo assessment of a new approach to brachytherapy source design

PURPOSE

A new type of (103)Pd source (CivaString and CivaThin by CivaTech Oncology, Inc.) is examined. The source contains (103)Pd and Au radio-opaque marker(s), all contained within low-Zeff organic polymers that permit source flexibility. The CivaString source is available in lengths L of 10, 20, 30, 40, 50, and 60 mm, and referred to in the current study as CS10-CS60, respectively. A thinner design, CivaThin, has sources designated as CT10-CT60, respectively. The CivaString and CivaThin sources are 0.85 and 0.60 mm in diameter, respectively. The source design is novel and offers an opportunity to examine its interesting dosimetric properties in comparison to conventional (103)Pd seeds.

METHODS

The MCNP5 radiation transport code was used to estimate air-kerma rate and dose rate distributions with polar and cylindrical coordinate systems. Doses in water and prostate tissue phantoms were compared to determine differences between the TG-43 formalism and realistic clinical circumstances. The influence of Ti encapsulation and 2.7 keV photons was examined. The accuracy of superposition of dose distributions from shorter sources to create longer source dose distributions was also assessed.

RESULTS

The normalized air-kerma rate was not highly dependent on L or the polar angle θ, with results being nearly identical between the CivaString and CivaThin sources for common L. The air-kerma strength was also weakly dependent on L. The uncertainty analysis established a standard uncertainty of 1.3% for the dose-rate constant Λ, where the largest contributors were μen/ρ and μ/ρ. The Λ values decreased with increasing L, which was largely explained by differences in solid angle. The radial dose function did not substantially vary among the CivaString and CivaThin sources for r ≥ 1 cm. However, behavior for r < 1 cm indicated that the Au marker(s) shielded radiation for the sources having L = 10, 30, and 50 mm. The 2D anisotropy function exhibited peaks and valleys that corresponded to positions adjacent to (103)Pd wells and Au markers, respectively. Dose distributions of both source types had minimal anisotropy in comparison to conventional (103)Pd seeds. Contributions by 2.7 keV photons comprised ≤ 0.1% of the dose from all photons at positions farther than 0.13 mm from the polymer source surface. Differences between absorbed dose to water and prostate became more substantial as distance from the sources increased, with prostate dose being about 13% lower for r = 5 cm. Using a cylindrical coordinate system, dose superposition of small length sources to replicate the dose distribution for a long length source proved to be a robust technique; a 2.0% tolerance compared with the reference dose distribution did not exceed 0.1 cm(3) for any of the examined source combinations.

CONCLUSIONS

By design, the CivaString and CivaThin sources have novel dosimetric characteristics in comparison to Ti-encapsulated (103)Pd seeds. The dosimetric characterization has determined the reasons for these differences through analysis using Monte Carlo-based radiation transport simulations.