Fig 1.
(Color online) example of acoustic angiography maximum intensity projections around tumors (tumor size denoted with dashed yellow lines) in a rat fibrosarcoma allograft, with tortuous angiogenesis extending beyond the tumor margins (red arrows).
The small tumor (a) is also shown to be more enhanced, denoting its higher perfusion compared to the larger tumor (b).
Fig 2.
a) Schematic of the experimental set-up used for in-vivo hypoxia modulation measurements using the Zenascope system. b) Schematic of tumor volume assessment via B-mode ultrasound imaging. Two cross-sectional images were acquired and lengths a, b and c were used to calculate tumor volume. c) Radiotherapy pre and post-imaging experimental protocol.
Table 1.
Experimental rounds for the radiotherapy experiments.
Fig 3.
In vitro oxygen microbubble characterization.
a) Measured oxygen microbubble size distribution, displayed with a diameter bin size of 0.032 μm, as mean ± standard deviation (gray area) from 3 independent samples; b) Measured change in oxygen % saturation in vitro after 300 μL OMB (n = 3) or NMB (n = 3) injection into 70 mL partially degassed water (p<0.05).
Fig 4.
Change in tumoral oxygenation with intra-tumoral injection of OMB or NMB.
The time to peak was found to be 97 s after injection on average, and the OMB-induced increase in tumoral oxygenation lasted for over 18 min on average (our protocol’s maximum 1 h experiment time meant that we could not wait for a complete return to baseline in some cases). A) Average peak change in tumoral hemoglobin saturation after OMB or NMB administration (n = 4/group). B) Individual data points showing pre- and post-injection values. This demonstrates baseline hypoxia in all tumors (0–83% hemoglobin saturation across all 8 tumors).
Table 2.
Individual datapoints for radiotherapy tumor control times (in days) stratified by matched initial tumor size for each treatment group, showing RT effect size depends on initial tumor volume.
Fig 5.
A single oxygen microbubble administration alone does not influence tumor control.
No significant difference was found between the no treatment and oxygen microbubble group in the absence of any radiotherapy (n = 4 per group). Box-and-whisker plots represent all data from the No treatment and OMB alone controls.
Fig 6.
Tumor control time comparison between RT groups.
OMB significantly improve RT outcome, whereas NMB as controls do not (n = 6 per group). Box-and-whisker plots show all data from the three radiotherapy treatment groups.
Fig 7.
Plot of gain in tumor control time against initial tumor volume, the confounding variable.
An on/off effect (threshold) is observed around 0.5 cm3 initial tumor volume. Below this size, tumors are controlled for 31 days with RT alone. Above this size, tumors are large enough that RT alone cannot control them for 31 days, and therefore, OMB administration can provide a substantial improvement in tumor control time. Additionally, the benefit offered by OMB administration diminishes as initial tumor volume exceeds ~2 cm3. Given our study design, the slope describing the inverse relationship between improvement in tumor control and initial tumor volume (above the threshold value of 0.5 cm3) could in theory guide optimal OMB dosing with respect to tumor volume (confounder) in order to maximize tumor control benefit for a given RT dose.