Influence of sub-field area on dose distribution in intensity-modulated radiotherapy for cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate the optimization of therapeutic regimen through the adjustment of the minimum sub-field area in intensity-modulated radiotherapy (IMRT) for cervical cancer,under the premise of no influence on the dose to target volume or organs at risk.Methods A total of 12 patients with pathologically confirmed cervical cancer were enrolled,and the prescribed dose to the planning target volume (PTV) was 50 Gy in 25 fractions.The Pinnacle 8.0m treatment planning system was used for all patients,and 16 IMRT plans were developed for each patient,with the application of 9 evenly distributed fixed incidence directions (0°,40°,80°,120°,160°,200°,240°,280°,and 320°),a minimum sub-field number of 80,and a minimum sub-field hop count (MU) of 5 MU.The range of sub-field area was 2-81 cm2.Direct machine parameter optimization was used for inverse-planned optimization calculation,and all the plans met the requirements of the clinical prescribed dose.The dose-volume histogram was used to evaluate the dose distribution in target volume and organs at risk.Results With the sub-field area increasing from 2 cm2 to 81cm2,the total hop count of IMRT plan was reduced from (1405±170) MU to (490±47) MU (P=0.000),and when the sub-field area increased above 6 cm×6 cm,the total hop count was reduced significantly (P=0.000).In the IMRT plan with a minimum sub-field area of 2-49 cm2,there was no significant difference in dose between the target volume and the organs at risk (P＞0.05).The dose to the rectum,the bladder,and both femoral heads showed no significant differences across the IMRT plans with different minimum sub-field areas (P＞0.05).Conclusions When the Pinnacle 8.0m treatment planning system is used to develop IMRT plans for cervical cancer,the requirements for clinical dose can still be met with a minimum sub-field area reaching 7 cm×7 cm,and there are significant reductions in sub-field hop count and total hop count.