Ultrasound dose fractionation in sonodynamic therapy.

Sonodynamic therapy (SDT) is a new modality in cancer therapy and it is based on preferential uptake and/or retention of a sonosensitizing drug in tumor tissues and subsequent activation of the drug by ultrasound. The dose fractionation effect in radiation therapy has been known for more than a century, but it is not reported in SDT so far. In this study, the in vivo antitumor effect of the simultaneous dual-frequency ultrasound (1 MHz and 150 kHz) at low-level intensity (cumulative I(SATA) = 2.2W/cm(2); total energy density 3960J/cm(2); for 30 min sonication) in combination with the sonosensitizer of photofrin (PF) (sodium porfimer) was investigated in dose fractionation regime in a spontaneous murine model of breast adenocarcinoma in Balb/c mice. The tumor-bearing mice were divided into six groups (n = 8 to 10): Untreated groups included control and sham; experimental groups were treated with 5 mg/kg intravenous injection of PF alone, with combined PF and ultrasound for 30-min sonication in one fraction at 24 h after PF administration; with combined PF and ultrasound for 30 min sonicatin in three fraction at 18, 24 and 30 h after PF administration; and finally with combined PF and ultrasound for 30 min sonication in five fraction at 12, 18, 24, 30 and 36 h after PF administration. The tumor growth delay (TGD) parameters and the percent of apoptotic index AI (%) were measured in treated and untreated groups. The results show that the TGD parameters in treatment groups with combined drug and ultrasound fractionation mode were significantly different compared with other groups (p < 0.05). Also the sonodynamic ultrasound dose fractionation in five fractions is more effective than of the three-fraction regime. The AI of the tumor tissues treated by ultrasound dose fractionation was also significantly higher in the other groups (p < 0.05), in which the AI (%) in the group treated with five fractions was higher with respect to group treated with 3 fractions (11.56 +/- 1.2; 8.7 +/- 0.87), respectively. In conclusion, the ultrasound dose fractionation can be useful in therapeutic effect in SDT and may have future clinical applications.

Treatment of murine tumors using dual-frequency ultrasound in an experimental in vivo model.

Acoustic inertia cavitation is the primary mechanism underlying sonochemical reactions and has potential for use in tumor treatment. In in vitro experiments that were performed previously and are thus not included in this paper, we found that the ultrasonically-induced chemical reactions are greatly accelerated when ultrasound is simultaneously applied at frequencies of 1 MHz and 150 kHz.. In this study, the in vivo anti-tumor effect of the simultaneous dual-frequency ultrasound at low level intensity (I(SPTA) <6 W/cm(2)) was investigated in a murine model of breast adenocarcinoma in Balb/c mice. The tumor-bearing mice were divided into five groups: those treated with combined dual-frequency ultrasound in continuous mode (1 MHz(con)+150 kH(zcon)) for 30 and 15 min (C and D), those treated with dual-frequency ultrasound in which the source of 1 MHz was in pulse mode (duty cycle of 80%) and that of 150 kHz was in continuous mode for 30 min (E), and untreated control and sham groups (A and B). The tumor growth parameters evaluated to assess delay include tumor volume, relative tumor volume, and T(5) and T(2), which are the time needed for each tumor to reach 5 and 2 times its initial volume, respectively. The survival period and percent of tumor growth inhibition ratio and were measured at various times after treatment. The results show that treatment with a combined continuous mode of 1 MHz(con)+150 kHz(con) and a pulse mode of 1 MHz(pl,80%)+150 kHz(con) effectively delayed tumor growth and increased the tumor growth inhibitory ratio compared to the sham group. When the tumor volume growth and relative volume of tumors in treated groups C, D and E were examined, an anti-tumor effect was observed in groups E and C. There is a significant difference between groups E and C and the sham group 12 d after treatment for tumor volume growth and 18 d after treatment for relative tumor volume (p < 0.05). The mean survival periods for animals in groups C and E were 16% and 17% more than the control group. T(5) and T(2) (in days) of groups E, C and B are 19.1 +/- 0.4 and 7.6 +/- 1.5, 17.2 +/- 0.6 and 6.3 +/- 2.1, 14.3 +/- 1.1 and 5.1 +/- 2.5 d, respectively. There was a significant difference between groups C and E and the sham group (B) for T(5) (p < 0.05), but for T(2), there was no significant difference between groups (p > 0.05). The tumor growth inhibition ratio in groups C, D and E was 23, 20 and 37% of that in group B, and those differences are statistically significant (p <0.05). It is concluded that sonodynamic therapy with combined dual-frequency ultrasound in a progressive wave mode can be useful for cancer therapy.

Effect of exposure parameters on cavitation induced by low-level dual-frequency ultrasound.

In order to quantify the effects of exposure parameters under therapeutic conditions such as sonodynamic therapy, it is necessary initially to evaluate the inertial cavitation activity in vitro. In this study, the dependence of cavitation activity induced by the low-level dual-frequency ultrasound irradiation on exposure parameters has been studied. Experiments were performed in the near 150 kHz and 1 MHz fields in the progressive wave mode. It has been shown that at constant ultrasound energy the fluorescence intensity for continuous sonication is higher than for pulsed mode. With increasing the duty cycle of pulsed field, the inertial cavitation activity is increased. The activity of cavitation produced by simultaneous combined sonication by two ultrasound fields is remarkably higher than the algebraic sum of effects produced by fields separately (p-value<0.05). This study shows that simultaneous combined dual-frequency ultrasound sonication in continuous mode is more effective in producing inertial cavitation activity at low-level intensity. Therefore, it is concluded that investigations in this combined ultrasound sonication can be useful in sonodynamic therapy for superficial tumors.