Dosimetric evaluation of image based brachytherapy using tandem ovoid and tandem ring applicators

Abstract

Aim

The aim of the study is to evaluate the differences in dosimetry between tandem-ovoid and tandem-ring gynaecologic brachytherapy applicators in image based brachytherapy.

Background

Traditionally, tandem ovoid applicators were used to deliver dose to tumor in intracavitary brachytherapy. Tandem-ring, tandem-cylinder and hybrid intracavitary, interstitial applicators are also used nowadays in cervical cancer brachytherapy.

Methods and materials

100 CT datasets of cervical cancer patients (stage IB2 – IIIB) receiving HDR application (50 tandem-ovoid and 50 tandem-ring) were studied. Brachytherapy was delivered using a CT-MRI compatible tandem-ovoid (50 patients) and a tandem-ring applicator (50 patients). DVHs were calculated and D2cc was recorded for the bladder and rectum and compared with the corresponding ICRU point doses. The point B dose, the treated volume, high dose volume and the treatment time were recorded and compared for the two applicators.

Results

The mean D2cc of the bladder with TR applicator was 6.746[[ce:hsp sp="0.25"/]]Gy. TO applicator delivered a mean D2cc of 7.160[[ce:hsp sp="0.25"/]]Gy to the bladder. The mean ICRU bladder points were 5.60 and 5.63[[ce:hsp sp="0.25"/]]Gy for TR and TO applicator, respectively. The mean D2cc of the rectum was 4.04[[ce:hsp sp="0.25"/]]Gy and 4.79[[ce:hsp sp="0.25"/]]Gy for TR and TO applicators, respectively. The corresponding ICRU point doses were 5.10[[ce:hsp sp="0.25"/]]Gy and 5.66[[ce:hsp sp="0.25"/]]Gy, respectively.

Conclusions

The results indicate that the OAR doses assessed by DVH criteria were higher than ICRU point doses for the bladder with both tandem-ovoid and tandem-ring applicators whereas DVH based dose was lower than ICRU dose for the rectum. The point B dose, the treated volume and high dose volume was found to be slightly higher with the tandem-ovoid applicator. The mean D2cc dose for the bladder and rectum was lower with tandem-ring applicators. The clinical implication of the above dosimetric differences needs to be evaluated further.