ABSTRACT
Objective To analyze the dosimetric effect of the optimization tool, normal tissue objective (NTO), in Eclipse on the intensity modulated radiation therapy (IMRT) for postoperative patients with rectal cancer. Methods Twenty postoperative patients with rectal cancer were randomly selected. Based on the Eclipse treatment planning system, three IMRT plans were formulated for each patient, with manual NTO as the control group, and automatic NTO and no NTO as the other two groups. The dosimetric parameters of the target volume and organs at risk (OAR) and the monitor units (MU) were compared between the automatic NTO and no NTO groups and the control group under the same optimization conditions. Results Compared with the control group, the automatic NTO group showed a worse conformity index (CI) (t = 3.248, P < 0.05), a 0.6% higher Dmean of normal tissues (t = -3.678, P < 0.05), and no significant difference in the dose to OAR and the MU (P > 0.05); the no NTO group showed a worse CI (t = 16.716, P < 0.05), a better homogeneity index (t = 6.594, P < 0.05), a 3.19% higher Dmean of normal tissues (t = -8.560, P < 0.05), no significant difference in the dose to OAR except the small intestine with higher Dmax (P > 0.05), and a 3.95% increase in the MU. Conclusion From the dosimetry results of the target volume and OAR, the plans with manual NTO and automatic NTO, and without NTO can meet clinical needs, but the plan without NTO increases the hot spots outside the target volume and the MU as well as the Dmean of normal tissues. Manual NTO has no obvious advantages over automatic NTO which is recommended for the fixed-field IMRT of rectal cancer.
ABSTRACT
Objective To compare the dosimetric differences of fixed field intensity-modulated radiation therapy(IMRT),volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) for nasopharyngeal carcinoma (NPC) patients.Methods Eighteen NPC patients previously treated with VMAT were retrospectively included and re-planned using HT and IMRT (7 fields) techniques utilizing the same dose prescription and optimization objectives.The following parameters were compared across the three types of plans:homogeneity index (HI),conformity index (CI),maximum dose (Dmax) and mean dose (Dmean) of targets ; the Dmax and Dmean of organs at risk (OARs) ; the doses and volumes of volume of interest; the treatment delivery time and monitor units (MU).Results Clinically acceptable target coverage could be achieved by IMRT,VMAT and HT plans.The HT plans were the best yet IMRT plans were the worst in HI and CI of targets.IMRT imposed highest doses to OARs while HT deposited least doses to the spinal cord,brainstem and parotid.However,the VMAT plans displayed the lowest doses on optic nerves,chiasma and lens while highest doses were found in IMRT plans.The average delivery time per fraction of IMRT (8.0±0.5) min were more than that of HT (7.4 ±0.9) min and VMAT (3.9 ±0.1) min plans.The MUs of IMRT plans (711.4 ±78.7) were larger than that of VMAT plans (596.4 ±33.7).Conclusions Three types of plans can all achieve the clinical dosimetric demands,but HT has the best performance on CI and HI.VMAT is most efficient regarding the delivery time and total MUs.