子野面积对宫颈癌IMRT剂量分布的影响

摘要

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.%目的 在不影响治疗靶区剂量和OAR受量前提下,调整宫颈癌IMRT计划的最小子野面积,优化治疗方案.方法 选择经病理证实的12例宫颈癌资料,PTV处方剂量为50Gy分25次.使用Pinnacle 8.0mTPS,每例设计16个IMRT计划,均采用9个均匀分布的固定入射方向(200°、240°、280°、320°、0°、40°、80°、120°、160°),最小子野数设定为80个,最小子野跳数设定为5 MU.最小子野面积分别选择2～81cm2,采用DMPO逆向优化计算,所有计划均达到临床处方剂量要求,通过DVH评价靶区及OAR剂量分布.结果 随着最小子野面积从2cm2增大至81cm2,IMRT计划的总跳数从(1405±170) MU降至(490±47) MU (P=0.000),子野面积＞6cm×6cm后、总子野数明显减少(P=0.000).最小子野面积为2～49cm2的IMRT计划,靶区及OAR剂量学均相近(P＞0.05);不同最小子野面积的IMRT计划间,直肠、膀胱和双侧股骨头受照剂量均相近(P＞0.05).结论 使用Pinnacle 8.0mTPS设计宫颈癌IMRT计划时,最小子野面积放大至7cm×7cm仍可满足临床剂量要求,且子野数和总跳数均明显减少.