ABSTRACT
Objective To investigate the precision of full six-degree target shift corrections using the ArcCHECK system.Metbods Fourteen patients receiving intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) in Fujian Medical University Cancer Hospital from May to September,2015 were selected.The first treatment setup errors were obtained using cone-beam computed tomography.The setup errors were simulated in ArcCHECK,and the full six-degree target shift corrections was used to correct the errors.The plans without and with setup errors and the plan with corrected setup errors were taken.The paired t-test was used to compare dose to agreement (DTA) and Gamma passing rates between the plan without setup errors and the plan with setup errors and plan with corrected setup errors.Results The DTA and Gamma passing rates were (96.76± 1.57)％ and (98.35±0.92)％ for the plan without setup errors,(59± 21.42) ％ and (62.86± 21.63) ％ for the plan with setup errors,and (91.41± 4.82) ％ and (94.11±4.33)％ for the plan with corrected setup errors.There were significant differences between the plan without setup errors and the plan with setup errors and plan with corrected setup errors in DTA passing rate (t=6.64 and 5.13,both P＜0.05) and Gamma passing rate (t=6.15 and 4.19,both P＜0.05).Conclusions The full six-degree target shift corrections can be used in IMRT for NPC,with good results in correcting setup errors and improving the precision for IMRT dose distribution.
ABSTRACT
Objective To compare the dosimetric difference among plans designed by 4-field,6-field TomoDirect and TomoHelical techniques in Tomotherapy system for left-breast cancer patients with radiotherapy after breast-conserving surgery.Method A total of 16 patients with left-breast cancer following breast-conserving surgery and intensity-modulated radiation therapy were enrolled in this retrospective study.The 4-field TomoDirect (TD4),6-field TomoDirect (TD6),and TomoHelical (TH) techniques were applied to design simulation plans in tomotherapy system for each patient,respectively.The differences of dose distribution and treatment parameters were analyzed in this study.Results Three plans all met the clinical requirement.Thereinto,TD4 was superior to TH in the dose limitation of organs at risk (OARs),especially the max dose of cord and right-breast,thc 5 Gy radiation volume of lung,and the mean dose of heart(F =595.60,129.24,60.44,65.37,P ＜ 0.05),but inferior to TH in dose homogeneity (HI) and conformity (CI) (F =2.78,60.93,P ＜ 0.05).However,TD6 improved TD4's HI and CI when delivered the lower OARs dose compared to TH.Meanwhile,the number of monitor units was less in TD technique and reduced the treatment times (F =24.89,3.75,P ＜ O.05).Conclusions For the radiotherapy of left-breast cancer patients after breast-conserving surgery,TD6 technique appeared to be superior,with the lower radiation dose of OARs compared to TH technique,and the better target's HI and CI in comparison with TD4 technique,especially in patients with early stage breast cancer.
ABSTRACT
Objective To simulate the possible systematic delivery errors introduced by monitor units ( MU) and multi-leaf collimator ( MLC) in radiotherapy plans for nasopharyngeal carcinoma ( NPC) , and to analyze the dosimetric sensitivity of static intensity-modulated radiotherapy ( IMRT ) and volumetric modulated arc therapy ( VMAT) with these errors. Methods Five IMRT plans were replanned using VMAT modality with the same physical parameters, and then MU errors of 125%, 250%, and 5. 00% were introduced into IMRT and VMAT plans. Meanwhile, to simulate leaf position errors during delivery, MLC position errors (025 mm, 050 mm, 100 mm, 150 mm, and 200 mm) were introduced by modifying the original plan documents. The types of MLC errors were as follows:( 1) the MLC banks moved in the same direction;( 2) the MLC banks moved in opposing directions ( expand or contract the MLC gaps ) . The differences in dosimetric sensitivity introduced by MU and MLC errors between IMRT and VMAT plans for NPC were calculated by linear regression analysis. Results With the increase in MU errors, the doses to target and organs at risk ( OARs) of IMRT and VMAT plans increased in a linear way, and met R2=0992-1000( P<005) . For MLC errors, the average dosimetric sensitivity for target and OARs of IMRT and VMAT were-026%/mm and-065%/mm in case of offset errors, 487%/mm and 868%/mm in case of expansion errors, and -604%/mm and -988%/mm in case of indentation errors. In addition, the dosimetric sensitivity with the three types of MLC errors was greater for VMAT plan than for IMRT plan. ConclusionsMU and MLC errors have a significant effect on the dose distribution of IMRT, and particularly VMAT, for NPC. It is important to execute routine quality assurance of MLC to ensure accurate radiotherapy.
ABSTRACT
Objective To simulate the possible systematic delivery errors introduced by monitor units ( MU) and multi-leaf collimator ( MLC) in radiotherapy plans for nasopharyngeal carcinoma ( NPC) , and to analyze the dosimetric sensitivity of static intensity-modulated radiotherapy ( IMRT ) and volumetric modulated arc therapy ( VMAT) with these errors. Methods Five IMRT plans were replanned using VMAT modality with the same physical parameters, and then MU errors of 125%, 250%, and 5. 00% were introduced into IMRT and VMAT plans. Meanwhile, to simulate leaf position errors during delivery, MLC position errors (025 mm, 050 mm, 100 mm, 150 mm, and 200 mm) were introduced by modifying the original plan documents. The types of MLC errors were as follows:( 1) the MLC banks moved in the same direction;( 2) the MLC banks moved in opposing directions ( expand or contract the MLC gaps ) . The differences in dosimetric sensitivity introduced by MU and MLC errors between IMRT and VMAT plans for NPC were calculated by linear regression analysis. Results With the increase in MU errors, the doses to target and organs at risk ( OARs) of IMRT and VMAT plans increased in a linear way, and met R2=0992-1000( P<005) . For MLC errors, the average dosimetric sensitivity for target and OARs of IMRT and VMAT were-026%/mm and-065%/mm in case of offset errors, 487%/mm and 868%/mm in case of expansion errors, and -604%/mm and -988%/mm in case of indentation errors. In addition, the dosimetric sensitivity with the three types of MLC errors was greater for VMAT plan than for IMRT plan. ConclusionsMU and MLC errors have a significant effect on the dose distribution of IMRT, and particularly VMAT, for NPC. It is important to execute routine quality assurance of MLC to ensure accurate radiotherapy.