Changes of rectal volume and location and their influence on rectal dose during the course of intensity-modulated radiotherapy of cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

ObjectiveTo investigate the anatomical changes and dose variation of rectum during radiotherapy in patients with cervical cancer.Methods Ten patients with cervical cancer underwent intensity-modulated radiotherapy using online cone beam computed tomography (CBCT) before each fraction.Rectum was contoured on each CBCT and projected onto the planning CT to analyze the changes of the rectal volume and position.The rectal volume receiving ≥ 45 Gy ( V45 ) was evaluated accordingly.Results227 CBCT images in 10 patients were collected.The rectal volume changed from ( 35.0 ± 7.3)cm3 to (97.7±14.7) cm3.The shift of rectal center was (0.14 ±0.06) cm in left and right direction,(0.24±0.10) cm in anterior and posterior direction,and (0.55±0.28) cm in superior and inferior direction.The V45 of rectum varied from (9.19±2.46)％ to (60.54 ±11.67)％.In7 of the 10 patients,rectal volume and V45 of the rectum had significant positive correlation (r =0.582 - 0.743,all P ＜ 0.01 ).Among the 227 images,the V45 of rectum was ≤50％ in 68 images (30.0％ ).ConclusionsSignificant changes in rectal volume and position occurred during fractionated radiotherapy in patients with cervical cancer,which resuhs in variations in the dose rectum received.For most patients,rectal volume and the V45of rectum had significant positive correlation.