Room: ePoster Forums
Purpose: To explore the effect of pitch on helical tomography radiotherapy for cervical cancer.
Methods: Six patients previously treated for cervical cancer with tomotherapy were randomly selected. Three pitches (0.43, 0.287 and 0.215) were used with the same field width (FW) and modulation factor (MF) for each patientï¼Œthe plans were named Plan1ï¼ˆ0.43ï¼‰ï¼ŒPlan2ï¼ˆ0.287ï¼‰ï¼ŒPlan3ï¼ˆ0.215ï¼‰. 18 treatment plans were generated using an identical optimization procedure (e.g., number of iterations, objective weights, and penalties, etc.). Dosimetric comparison was assessed for doses to targets (homogeneity indexes(HI), conformity indexes(CI))and organs at risk (bladder, rectum and femoral heads). Delivery time, monitor units and gantry period were also compared.
Results: For GTV and PTV ,there were no significant differences in CI and HI among Plan1,Plan2 and Plan3(p=0.79). Changes in dosimetric differences in the bladder, rectum, and femoral head were also small. When the pitch were 0.287, the gantry period reached the limit of 11.8s. Delivery time and monitor units increased slightly. When the pitch continued to decrease to 0.215, the gantry period is the limit value (11.8s), delivery time and monitor units increase significantly, and there is a statistical difference(p=0.001, p<0.05).
Conclusion: We have shown that the choice of pitch is crucial for cervical cancer of helical tomography radiotherapy. With appropriate pitch, the treatment time can be reduced without reducing the quality of the plan, and the treatment gain ratio can be improved.