Dosimetric comparison of high-dose rate cervix brachytherapy with and without interstitial needles and the impact on target volume coverage, and organ at risk constraints.

INTRODUCTION

The aim of this audit was to compare the data from the Wellington Blood and Cancer Centre (WBCC) with international reported experience by quantifying the dosimetric impact of interstitial needles on target coverage and organ at risk (OAR) doses.

METHODS

All patients identified as having had interstitial needles as part of their treatment out of a cohort of 120 radically treated cervical cancer patients between 2013 and 2019 were included. Each patient acted as their own control with two treatment plans optimised for each fraction; the clinically treated plan and a re-optimisation without the use of interstitial needles. Plan optimisation was completed according to the departmental protocol and cumulative equivalent doses for 2 Gy fractions (EQD2) were calculated.

RESULTS

Eighteen patients were suitable for evaluation. A total of 52 insertions with interstitial needles were performed, of the 148 needles inserted, 119 (80.4%) were loaded. HRCTV D90% coverage mean was EQD2 5.4 Gy (0.5-10.6 Gy) higher for the course containing loaded interstitial needles, while no significant change was observed with regards to OAR doses. This improved coverage is in line with international standards which report 4.4-9.0 Gy.

CONCLUSION

WBCC's early experience of interstitial cervix brachytherapy has shown our target coverage improvements meet previously published international standards and confirms the value of this technique. This audit supports ongoing use of interstitial needles at the WBCC.