Fractionated FLASH radiation in xenografted lung tumors induced FLASH effect at a split dose of 2 Gy.

PURPOSE: To explore the minimum split dose of FLASH radiotherapy (FLASH). MATERIAL AND METHODS: Lungs of nude mice were used to verify the capacity of normal tissue sparing of FLASH, while tumor-bearing nude mice were used to evaluate the curative power. Xenografted tumor models were established in Balb/c-nu mice using A549 cells at a concentration of 5×106/100 µL. With the same total dose (20 Gy), the dose rate of FLASH was 200 Gy/s when conventional radiotherapy(CONV) was 0.033 Gy/s. Two schemes of FLASH irradiations were applied: single pulse (FLASH1) and ten pulses (FLASH10). Then, according to the different tissue types and irradiation schemes, mice were divided into eight groups: Control-T, CONV-T, FLASH1-T, FLASH10-T (T for tumor) and Control-L, CONV-L, FLASH1-L, FLASH10-L (L for lung). Evaluation of FLASH effect was based on the changes in tumor volume and pathological analysis of tumor and lung tissues before and after irradiation. RESULTS: Compared to control group, the mean volume of tumors in nude mice increased slowly or decreased after irradiation with both FLASH and CONV (Control-T: 233.6±55.19 mm3, CONV-T: 146.1±50.62 mm3, FLASH1-T: 148±18.83 mm3, FLASH10-T: 119.1±50.62 mm3, p ≤ .05) . Tumor cells of irradiated groups had similar degrees of dissolution damage and inflammation, while the acute radiation pneumonia induced by FLASH was less severe. The pulmonary pathology of FLASH1-L and FLASH10-L were similar, and only a few neutrophils were observed. In addition to inflammatory cells, slight thickening of alveolar septum and obvious interstitial hemorrhage were also observed in the CONV-L group. CONCLUSION: The FLASH effect was successfully reproduced in both single and fractionated irradiation, with 2 Gy being the minimum split dose to achieve the FLASH effect in existing experiments. It is suggested that the transient oxygen depletion might not be the only mechanism behind the FLASH effect.

[Treatment of nasal malignant tumor with electron beam irradiation after repair of nasolabial flap].

OBJECTIVE: To explore the appropriate reconstructive methods and curative effect after nasal skin malignant tumor excision. METHOD: Nasolabial flap was selected to cover the nasal defects in 15 cases which nasal tumors were removed. The secondary defect of donor site was directly sutured. Electron beam conventional radiotherapy (DT40-50 Gy/20-25 times/4-5 weeks) was delivered to the involved field after incision sutured out 2-5 days. RESULT: A total of 15 patients with nasal tumor were available for follow-up of 6 to 24 months, no tumor recurrence occurred, and the repaired tissue were good match with surrounding tissue, good nasal contour was obtained with an inconspicuous scar. CONCLUSION: These data indicate that the nasolabial flap can be used to repair defects of the nose tumors in 15 cases and is surgically convenient. Combination of nasolabial flap repairing and postoperative local electron beam irradiation, inhibited the recurrence of nose tumor effectively, is an ideal method.