Abstract
BackgroundHigh-precision radiation therapy techniques such as IMRT or sterotactic radiosurgery, delivers more complex treatment fields than conventional techniques. The increased complexity causes longer dose delivery times for each fraction. The purpose of this work is to explore the radiobiologic effect of prolonged fraction delivery time on tumor response and survival in vivo.Methods1-cm-diameter Lewis lung cancer tumors growing in the legs of C57BL mice were used. To evaluate effect of dose delivery prolongation, 18 Gy was divided into different subfractions. 48 mice were randomized into 6 groups: the normal control group, the single fraction with 18 Gy group, the two subfractions with 30 min interval group, the seven subfractions with 5 min interval group, the two subfractions with 60 min interval group and the seven subfractions with 10 min interval group. The tumor growth tendency, the tumor growth delay and the mice survival time were analyzed.ResultsThe tumor growth delay of groups with prolonged delivery time was shorter than the group with single fraction of 18 Gy (P < 0.05). The tumor grow delay of groups with prolonged delivery time 30 min was longer than that of groups with prolonged delivery time 60 min P < 0.05). There was no significant difference between groups with same delivery time (P > 0.05). Compared to the group with single fraction of 18 Gy, the groups with prolonged delivery time shorten the mice survival time while there was no significant difference between the groups with prolonged delivery time 30 min and the groups with prolonged delivery time 60 min.ConclusionsThe prolonged delivery time with same radiation dose shorten the tumor growth delay and survival time in the mice implanted with Lewis lung cancer. The anti-tumor effect decreased with elongation of the total interfractional time.
Highlights
New radiation therapy techniques such as sterotactic radiosurgery and IMRT are featured with improving target dose conformity while minimizing radiation exposure to surrounding normal tissues [1,2,3,4,5]
A number of studies have been published to investigate the impact of prolonged delivery time on biological effects at the cellular level and demonstrated that the total time to deliver a single fraction may have a significant impact on treatment outcome [8,9,10,11,12,13,14,15]
We attempt to evaluate the impact of prolonged fraction delivery time on tumor control and survival in C57BL mice implanted with Lewis lung cancer using growth delay assay and survival analysis
Summary
New radiation therapy techniques such as sterotactic radiosurgery and IMRT are featured with improving target dose conformity while minimizing radiation exposure to surrounding normal tissues [1,2,3,4,5] These technologies require complex planning and delivery procedure a substantially prolongerd delivery time for each fraction. There were only two studies to evaluate the effect of proloned delivery time in SCCVII tumors using an in vivo-in vitro assay and they found that cell survival from clamped tumors tended to increase with elongation of the intervals, but not significantly [16,17]. The purpose of this work is to explore the radiobiologic effect of prolonged fraction delivery time on tumor response and survival in vivo
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