Dosimetric influence of dwell weight standard deviation and applicator displacement in patients with cervical cancer

Objective To investigate the dosimetric influence of dwell weight standard deviation (DWSD) and applicator displacement in cervical cancer patients treated with three-dimensional brachytherapy. Methods A total of 20 cervical cancer patients who had completed radical treatment were selected in this study. The Fletcher applicator (Nucletron#189.730) was used for these patients. A new plan, based on the former CT images and structures, was designed for each patient. In former and new plans, dwell weight was recorded, and DWSD was calculated. Two groups, low-DWSD (LDWSD, 0.141-0.299) and high-DWSD (HDWSD, 0.211-0.337), were set according to the DWSD size for the two plans. Dosimetric effects from ±1 mm displacement of tandem applicator or ovoid applicator were simulated with Oncentra®Brachy V4.3 treatment planning system. D100, D90, and V150 for clinical target volume (CTV) and D0.1cc, D1cc, and D2cc for the bladder, rectum, and sigmoid were evaluated. Dosimetric comparisons were made between the LDWSD group and HDWSD group to study the dosimetric effects of DWSD and applicator displacement in cervical cancer patients. Results The dosimetric effects from applicator displacement increased with increasing DWSD. If there was a 1 mm displacement of tandem applicator or ovoid applicator, D100, D90, and V150 of CTV were 3.0%, 23.8%, and 4.8% higher or 0.5%, 1.2%, and 5.2% higher in the HDWSD group than in the LDWSD group; D0.1cc, D1cc, and D2cc of the bladder and rectum were significantly higher in the HDWSD group than in the LDWSD group, particularly for the sigmoid (up 44.0%, 22.8%, and 16.8%) and (up 10.3%, 14.4%, and 12.4%). Conclusions DWSD should be considered in plan evaluation for cervical cancer patients treated with three-dimensional brachytherapy. The dosimetric influence from applicator displacement can be decreased by reducing DWSD properly. Key words: Dwell weight; Cervical cancer/brachytherapy; Dose