Session Item

Brachytherapy to bulky and asymmetrical cervical tumours is challenging even with combined intracavitary/interstitial (IC/IS) brachytherapy. Therefore, new brachytherapy applicator (Venezia) has been developed which allows the insertion of both parallel and oblique interstitial needles to improve dose coverage. Meanwhile, simpler method intracavitary brachytherapy with top-up IMRT boost was introduced by previous studies to treat advanced staged cervical cancer. Hence, the purpose of this study is to compare the dosimetric outcome between combined IC/IS brachytherapy and intracavitary brachytherapy with top-up IMRT in treating bulky and asymmetrical cervical tumours.

Five patients with cervical cancer of FIGO staged III or above treated by Venezia applicator were retrospectively recruited. The 4 brachytherapy fractions of each patients were re-planned by 2 treatment methods: combined IC/IS brachytherapy with parallel and oblique needles (IC/IS method) and intracavitary brachytherapy with top-up IMRT (IC/IM method). Analysis was made according to the summation of dose from external beam radiotherapy and brachytherapy, and the fractional dose of each brachytherapy session. Dosimetric comparison was carried out between the 2 planning methods in terms of dose delivered to the target volumes and dose sparing to OARs. The relationship between the tumour volume, weighting of IMRT used in IC/IM method and planning parameters was also analyzed by correlation test.

The median dose that IC/IM method can further escalate from IC/IS method was 7.53 Gy to GTV D98, 6.86 Gy to HRCTV D98 and 6.54 Gy to IRCTV D98. The fractional dose from IC/IM method could delivered a significant higher dose to GTV D98, HRCTV D98 and IRCTV D98 than IC/IS method. However, the D2cc of sigmoid colon and small bowel were significantly higher for IC/IM method. The volume irradiated by low dose (V3.3) was also significantly higher for all OARs including bladder, rectum, sigmoid colon and small bowel for IC/IM method. The HRCTV volume was found to be significantly correlated with D98 of HRCTV and IRCTV, and V3.3 of all OARs. Meanwhile, the IMRT proportion in IC/IM method was only significantly correlated with the V3.3 of sigmoid colon.

The IC/IM method may allow further dose escalation to target volumes compared with IC/IS method. However, the dose sparing to OARs of IC/IM method was inferior to IC/IS method. Moreover, the top-up IMRT boost in IC/IM technique may suffer from uncertainties including intra-fractional deviation and setup error. Therefore, IC/IM technique should only be an alternative treatment approach when IC/IS technique was not able to deliver sufficient dose to target volumes.