ABSTRACT
Objective To analyze the effect of the fixed-jaw technique on dosimetric parameters during dynamic intensity-modulated radiotherapy (DIMRT) planning. Methods Ten patients each with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery were selected for this study; all patients underwent DIMRT in our hospital in 2020. After administration at the prescribed dose, two methods were used to design the radiotherapy plan for each patient: split-field technique (SFT) and fixed-jaw technique (FJT). The two plans were compared for the differences in the dosimetric parameters and plan verification pass rate. Results Compared with SFT, FJT showed significant decreases (P <0.05) in the following parameters for patients with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery: number of radiation fields (down by 41.5%, 47.3%, and 34.9%, respectively, t = 7.954, 24.2, and 4.949, respectively), total number of monitor units (MUs) (down by 5.6%, 5.3%, and 13.5%, respectively, t = 3.211, 2.423, and 5.481, respectively), and actual beam-on time (down by 25.3%, 23.8%, and 13.6%, respectively, t = 5.814, 9.208, and 5.655, respectively). There were significant differences in some of the dosimetric parameters for all three types of cancer patients between the two plans (P <0.05). There were no significant differences in the plan verification pass rate (P >0.05). Conclusion FJT can reduce the total number of MUs and actual beam-on time while meeting the requirements for clinically prescribed doses in DIMRT planning.
ABSTRACT
Objective To analyze the dosimetric effect of inconsistent bladder filling states between the CT simulation and treatment for prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT).Methods A total of 42 prostate cancer patients treated with IMRT were selected.After vacuum pad immobilization and simulation CT scan,the delineation of targets and organs-at-risk (OARs),treatment planning and dose calculation were performed on treatment planning system (TPS).The cone-beam-CT (CBCT) acquired before the first treatment was registered to planning CT,on which the target contours were duplicated and OARs were delineated.After dose recalculation on the CBCT using the same plan,the dosimetric differences on the CT and CBCT were compared,including mean dose of the planning target volume (PTV),homogeneity index (HI),conformity index (CI);the mean dose,V30,V40,V50,V60,and V65 of bladder and rectum respectively.Results Relative to the bladder volumes at simulation,the patients were divided into two groups with larger (15 cases) or smaller (27 cases) bladders at the first treatment.Comparing the parameters obtained from simulation CT with that from CBCT,the differences of the following parameters were of statistical significance:the bladder volume,PTV HI,PTV CI in both groups (t =6.838,-4.372,-3.553,-3.462,6.380,5.037,P＜ 0.05),the bladder V30,V40,V50,V60,V65(t=-5.004,-4.092,-3.124,-2.707,-2.489,P ＜0.05) and rectal V40,V50,V60,V65,mean dose in the group with smaller bladders (t=-2.946,-2.643,-2.426,-3.127,-2.530,P ＜ 0.05),and the bladder V30,V40,V50 and mean dose in group with larger bladders (t =5.107,4.204,3.777,4.155,P＜0.05).Conclusions For prostate cancer patients undergoing IMRT,the inconsistent bladder filling states between the planning and treatment will cause disimetric differences of targets and OARs.
ABSTRACT
Objective To study the impacts of bladder filling status on the dosimetric parameters of the target volume and organs at risk (OAR) in intensity-modulated radiotherapy (IMRT) for prostate cancer.Methods Ten localized prostate cancer patients without serious complications treated with IMRT were selected for this study.These patients underwent CT scans of the whole pelvic cavity three times in different bladder filling status (empty and injected with 150 ml and 300 ml of normal saline) to obtain three series of pelvic CT images.The three sets of CT images were transferred to the treatment planning system.The target volume and OAR such as the rectum,bladder,and femoral heads were contoured by the same doctor.The treatment planning was performed and optimized by the physicist.The dosimetric parameters of the target volume and OAR in three bladder filling status were subjected to analysis by paired t-test.Results If the bladder filling status was consistent in orientation and radiation,the bladder filling status was not associated with the dosimetric parameters of the target volume and femoral heads (P =0.077-0.998 ; P =0.219-0.969) ;it had significant impacts on the dosimetric parameters of the bladder (P =0.000-0.562) and some dosimetric parameters of the rectum (P =0.000-0.645),and bladder filling was favorable for the protection of the bladder and rectum.If the bladder filling status was not consistent in orientation and actual radiation,the calculated planning target volume,the dosimetric parameters of the bladder,and some dosimetric parameters of the rectum were different from those in actual treatment (P =0.000-0.913).Conclusions For the prostate cancer patients treated with IMRT,it is recommended to keep the bladder well and consistently filled.