ABSTRACT
Objective:To evaluate the effect of radical image-guided radiotherapy (IGRT) on the target dose in cervical cancer and investigate the appropriate application mode.Methods:Twenty patients with cervical cancer treated with helical tomotherapy (HT) in Seventh Medical Center of PLA General Hospital from 2012 to 2016 were selected. A megavoltage CT (MVCT) scan was performed before each treatment. The obtained MVCT images were used for dose parameter in the adaptive module of HT to obtain the actual dose (Plan 1) and the non-image-guided dose parameter was simulated (Plan 2). Each single dose distribution and the corresponding fused CT images were transferred to the software Mimvista 6.5 to obtain the total radiation dose parameter by dose superposition.Results:The motion of CTV, uterus and GTV in Plan 2 was significantly larger than that of Plan 1(all P<0.05), and the largest changes were seen in the ventrodorsal and uterine direction. The V 45Gy, V 50Gy, D 98% and D mean of CTV and uterus and V 50Gy of GTV in Plan 2 were significantly decreased compared with those in Plan 1(all P<0.05). The left-right motion of Plan 1 was negatively correlated with D 2% and D 98% of CTV and uterus (both P<0.05). The head-foot motion was negatively associated with V 45Gy and V 50Gy of GTV (both P<0.05). The ventrodorsal motion was negatively correlated with D 98% of uterus ( P<0.05). The left-right motion of Plan 2 was negatively correlated with D 2% of CTV and V 50Gy of uterus (both P<0.05). The head-foot motion was negatively associated with D 98% of CTV, and D 98%, D mean, V 45Gy and V 50Gy of uterus (all P<0.05). The ventrodorsal motion was negatively correlated with D 98% of CTV, D 98%, D mean, V 45Gy and V 50Gy of uterus, and D mean and V 45Gy of GTV (all P<0.05). Conclusions:In intensity-modulated radiotherapy for cervical cancer, the uterine body displacement is large and the low CTV area is mainly located in the uterine body. IGRT can significantly reduce the dosimetric deviation induced by organ movement.
ABSTRACT
Objective To analyze the changes in volume and the planning volume of the bladder and rectum during helical tomotherapy (HT) treatment for cervical cancer,and to evaluate the impacts of bladder and rectum filling on their dosimetric parameters.Methods Twenty patients with cervical cancer who received HT in our hospital from 2012 to 2016 were enrolled as subjects.Before treatment,megavolt computed tomography (MVCT) and registration of planning CT images were preformed to recalculate the dose distribution,delineate the target volume,and measure the volume and position of the bladder and the rectum.Each MVCT image and the corresponding single dose were obtained by dose reconstruction using the Planned Adaptive module in HT planning workstation.The fused MVCT images and the corresponding single dose for each MVCT were loaded to MIM Maestro software 6.0 for dose stacking.The obtained total radiation dose was compared with that obtained by kilovolt CT.Between-group comparison was made by paired t-test or analysis of variance.Results If the volume change in the bladder was more than 400 ml or the rate of volume change was higher than 60％,the displacements of the bladder centroid toward the foot and dorsal sides were significantly increased;the Dmean and V50 were significantly increased (P＜0.05).If the volume change in the rectum was more than 30 ml or the rate of volume change was higher than 30％,the displacements of the rectum centroid toward the head and ventral sides were significantly increased;the V45 and V50 for the rectum were significantly increased (P＜0.05).Conclusions Although the bladder filling status has little effect on the radiation dose to the bladder,the volume change or the rate of volume change should be no more than 400 ml or 60％,respectively.Moderately filled bladder is recommended for positioning and treatment,which achieves satisfactory repeatability of the treatment.A volume change of more than 30 ml or a rate of volume change of higher than 30％ can result in an increase in the dose to the rectum.Empty rectum can effectively reduce the dose to the rectum.
ABSTRACT
Objective To analyze the effect of image guidance on the doses to the rectum and bladder in radical external beam radiotherapy for cervical cancer, and to investigate the reasonable application mode of image-guided radiotherapy (IGRT) in the treatment of cervical cancer. Methods A total of 20 patients with cervical cancer who underwent helical tomotherapy(HT) in PLA Army General Hospital from 2012 to 2016 were enrolled in this study. A megavoltage computed tomography(MVCT) scan was performed before each treatment. The obtained MVCT images were used for dose reconstruction in the adaptive module of HT to obtain the actual dose (Plan-1) and the non-image-guided dose was simulated (Plan-2). Each single dose distribution and the corresponding fused CT image were sent to the software MIM 6.0 to obtain the total radiation dose by dose superposition. The radiation doses and volumes of the rectum and bladder were compared between the two therapeutic plans. Results The radiation doses to the rectum and bladder in Plan-2 were significantly higher than those in Plan-1. There were significant differences in Dmaxand V50of the rectum and V50of the bladder between Plan-1 and Plan-2(P=0.040;P=0.000;P=0.047). Compared with Plan-1, there were statistical differences in inter-fractional Dmaxand V50during the initial treatment (P=0.047,0.037), and V50of the rectum within the 13thto 21stradiotherapy, respectively (P=0.009, 0.017, 0.028). Besides, differences regarding Vmaxand V50in the initial treatment and the 21stto 23rdradiotherapy were close to the statistical significance when compared to those in Plan-1, respectively (P= 0.061,0.053; P= 0.072,0.058). Conclusions IGRT can reduce the radiation doses and volumes of the rectum and bladder, especially the rectum. The therapeutic plan should be rescheduled when tumor retraction is evident at half of the total radiation dose (around 13thfraction) in external beam radiotherapy. If it is difficult to achieve image guidance in each treatment,selective image guidance could be performed to effectively reduce the injuries of the rectum and bladder.