Preliminary exploration of the influence of beam orientation and beam number on the optimization of IMRT plan with cervical cancer / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the influence of the number and orientation of the beams on the optimization of IMRT plan.Methods Four IMRT plans were designed for 9 patients with cervical cancer,and 7 and 15 fields were applied.The 15-field plans had 30 segments and the 7-field plans had 55 segments.The initial beam angle degrees were 0° and 180°,respectively.Dose delivery time,MUs of plans,the dose distributions of the targets,organs at risk and normal tissues were analyzed and compared in the plans.Results Compared the plans with different beam directions under the same amount,no difference of the irradiation dosimetry in the target and organs at risk was found,except for irradiation dosimetry received by the 7-field 180° small intestine was about 4％ higher than the other three plans(F=6.164,P＜0.05).The terms of the volume of organs at risk got high dose irradiation(V40 and V30 of the rectum and bladder,V40 of the small intestine),which was similar in the 7-and 15-field plans.V20 and Dmean of organs at risk were significantly smaller(F=3.665-10.503,P＜0.05)in the 15-field plans.The 15-field plans needed a little longer treatment time(F=0.312,P＜0.05)and HI was slightly worse (F=12.933,P＜0.05),but the number of MUs was significantly reduced(F=4.650,P＜0.05).Conclusions Increasing the beam number will offset the negative impact of sub field reduction and get the similar dose distribution result.