ABSTRACT
Objective:To investigate the dosimetry differences in the treatment of locally advanced cervical cancer with intracavitary/interstitial brachytherapy (IC/IS BT), intracavity brachytherapy combined with intensity modulated radiotherapy (ICBT+ IMRT) and simple IMRT.Methods:Totally 16 patients with local advanced cervical cancer were retrospectively selected, which were treated by three-dimensional brachytherapy. On the basis of the original three-dimensional intracavitary/interstitial brachytherapy plan, ICBT+ IMRT and IMRT plans were designed respectively to study the dosimetry differences of target and different organs at risk for the three kinds of plans.Results:A total of 75 brachytherapy treatment plans were designed, including 25 IC/IS BT, 25 ICBT+ IMRT and 25 IMRT. There was not statistically significant difference of target dose parameters between ICBT+ IMRT and IC/IS BT plan ( P>0.05). ICBT+ IMRT plans had better OAR sparing than IC/IS BT. The doses of OARs in the IMRT plans were relatively large and the volume irradiated to more than 60 Gy ( V60) was significantly higher( t=6.77, 10.37, 4.61, 2.83, P<0.05). Conclusions:The ICBT+ IMRT technique not only provides better target coverage, but also maintains low doses to the OARS, which can be used as an alternative treatment to IC/IS BT. Although the target coverage of IMRT is better, the protection of OARs is not satisfied, so it is not suitable for local boost therapy of advanced cervical cancer.
ABSTRACT
Objective To compare the sensitivity of Deha4 and ArcCHECK 3D detectors to detect the multi-leaf collimator (MLC) positioning errors in the dose verification of volumetric modulated arc therapy (VMAT) plans for nasopharyngeal carcinoma (NPC).Methods Ten NPC patients receiving VMAT plans were selected.The positioning error of 0.5-4.0 mm was introduced into the leaves of each MLC segment in the original file to expand,contract or shift the whole segments.The possible positioning errors of MLC in the treatment of VMAT were simulated.The Delta4 and ArcCHECK were utilized to verify the measurements.The absolute gamma passing rate was compared between the calculated dose and the measured dose of the VMAT plan by using the paired t-test.Results When the evaluation criterion was taken as 3 mm/3％,the absolute passing rate verified by the original plans of two detectors was greater than 95％.The positioning errors of MLC expansion,contraction and shifting detected by Delta4 and ArcCHECK were 1.5 mm,1.0 mm,2.0 mm and 3.0 mm,1.0 mm,and 3.0 mm,respectively.When taking 2 mm/2％ as the evaluation criterion,the absolute passing rate verified by the original plan was decreased significantly.Delta4 and ArcCHECK detected that the positioning errors of MLC expansion,contraction and shifting were 1.0 mm,1.0 mm,2.0 mm and 1.5 mm,0.5 mm,and 2.0 mm,respectively.Conclusions The dose verification of the VMAT plan for NPC by Delta4 and ArcCHECK can detect different types and sizes of MLC positioning errors,whereas the detection sensitivity slightly differs between Delta4 and ArcCHECK.Both of them are not sensitive to detect the MLC positioning errors less than 1.0 mm.It is fairly necessary to strengthen the quality assurance of MLC in the daily work.