Brachytherapy-on-Chip: A Microfluidic Setup for In Vitro Interrogation of Hypoxic Spheroids

PURPOSE/OBJECTIVE(S)

Despite evidence of its advantages in many cancers, brachytherapy (BT) remains clinically underused and understudied in the pre-clinical setting due to a lack of versatile RT-compatible in vitro tools that can emulate the tumor microenvironment and radiobiology of various cancers. Microfluidic devices use conventional cell culture methods in 3D-tumor models, are radiocompatible and can integrate radiobioassays. However, they are seldom used in pre-clinical BT research. This project engineered the first microfluidic tool for in vitro testing of BT, with applications in translational radiobiology.

MATERIALS/METHODS

PDMS microfluidic chips were engineered to grow and culture concentric rows of hypoxic spheroids, and to allow the insertion of a clinical iodine-125 BT seed at the center of the device. FaDu (hypopharyngeal squamous cell carcinoma), SK-LMS-1 (leiomyosarcoma) and HCT116 (colorectal carcinoma) cell lines were selected for their clinical relevance and ability to form spheroids. Presence of hypoxia in spheroids was assessed by immunofluorescence (IF) staining for hypoxic protein CAIX. On-chip dose distribution was calculated using clinical TG-43 parameters and compared to EBT-XD radiographic film. Target dose criteria was fixed at 8 Gy in the center of the first row of spheroids. Treatment response was quantified by DNA damages (γH2AX IF, comet assay) and cell survival (clonogenic assay). Response of hypoxic and normoxic regions of spheroids will be compared in IF.

RESULTS

A total of 15 spheroids that are 750µm or larger can be cultured in our device, arranged as 5 rows of 3 spread from 1.5mm to 7.5mm away from a central iodine-125 seed. 48h after cell seeding, hypoxic cores were observed in spheroids derived from FaDu (50 ± 4% of cross-section, N = 3) and SK-LMS-1 (46 ± 4% of cross-section, N = 3) cells, results are pending for HCT116. TG-43 formula predicts that the center of each row receives 8 Gy, 2.6 Gy, 1.2 Gy, 0.7 Gy and 0.4 Gy respectively. Radiographic film analysis confirms on-chip TG-43 calculated doses (N = 5, R2 = 0.999). Similarly, tail moment from comet assays follows predicted dose trends (n>60, N = 3). There was no statistical difference between 8 Gy BT and 8 Gy GammaCell (8 Gy BT vs 8 Gy GammaCell, p = 0.8758), with a statistical difference between 8 Gy BT (8 Gy BT vs 2.6 Gy BT,1.2 Gy BT,0.7 Gy BT,0.4 Gy BT,0 Gy, p < 0.0001), 2.6 Gy BT (2.6 Gy BT vs 1.2 Gy BT,0.7 Gy BT,0.4 Gy BT,0 Gy, p < 0.05) or 8 Gy GammaCell (8 Gy GammaCell vs 2.6 Gy BT,1.2 Gy BT,0.7 Gy BT,0.4 Gy BT,0 Gy, p < 0.0001) and other lower BT doses.

CONCLUSION

For the first time, brachytherapy can be easily integrated on-chip and its effects evaluated on relevant 3D-tumor models. Our system allows simultaneous quantification of BT efficacy on normoxic and hypoxic cells treated at various doses. On-chip combination of BT with antitumor drug will be explored in future work. We hope this device will serve as further proof of the potential of BT/RT-on-chip systems for better drug development, treatment planification and theranostics.

Focal HDR brachytherapy boost to stereotactic radiotherapy (fBTsRT) for prostate cancer: a phase II randomized controlled trial

BACKGROUND

For patients with a higher burden of localized prostate cancer, radiation dose escalation with brachytherapy boosts have improved cancer control outcomes at the cost of urinary toxicity. We hypothesize that a focal approach to brachytherapy boosts targeting only grossly visualized tumor volumes (GTV) combined with stereotactic radiotherapy will improve quality of life (QoL) outcomes without compromising cancer control.

METHODS

150 patients with intermediate or high-risk prostate cancer will be enrolled and randomized 1:1 in a cohort multiple randomized clinical trial phase 2 design. Patients are eligible if planned for standard-of-care (SOC) high dose rate (HDR) brachytherapy boost to radiotherapy (RT) with GTVs encompassing < 50% of the prostate gland. Those randomly selected will be offered the experimental treatment, consisting of focal HDR brachytherapy boost (fBT) of 13-15 Gy in 1 fraction followed by stereotactic radiotherapy (sRT) 36.25-40 Gy in 5 fractions to the prostate (+/- 25 Gy to the elective pelvis) delivered every other day. The primary endpoint is to determine if fBTsRT is superior to SOC by having fewer patients experience a minimally important decline (MID) in urinary function as measured by EPIC-26 at 1 and 2 years. Secondary endpoints include rates of toxicity measured by Common Terminology Criteria for Adverse Events (CTCAE), and failure-free survival outcomes.

DISCUSSION

This study will determine whether a novel approach for the treatment of localized prostate cancer, fBTsRT, improves QoL and merits further evaluation. Trial registration This trial was prospectively registered in ClinicalTrials.gov as NCT04100174 as a companion to registry NCT03378856 on September 24, 2019.

Validation ofGEANT4, an object-oriented Monte Carlo toolkit, for simulations in medical physics

GEANT4 (GEometry ANd Tracking 4) is an object-oriented Monte Carlo simulation toolkit that has been developed by a worldwide collaboration of scientists. It simulates the passage of particles through matter. In order to validate GEANT4 for medical physics applications, different simulations are conducted. The results are compared to published results based on three Monte Carlo codes widely used in medical physics: MCNP, EGS4, and EGSnrc. When possible, the simulation results are also compared to experimental data. Different geometries are tested (multilayer and homogeneous phantoms), different sources considered (point-source and broad parallel beam), and different primary particles simulated (photons and electrons) at different energies. For the heterogeneous media, there are notable differences between the Monte Carlo codes reaching up to over 5% in relative difference. For the monoenergetic electrons in a homogeneous medium, the difference between GEANT4 and the experimental measurements is similar to the difference between EGSnrc and the experimental measurements; for the depth-dose curves, the difference expressed as a fraction of the peak dose is always smaller than 4%. We conclude that GEANT4 is a promising Monte Carlo simulation toolkit for low-energy medical applications.