Dosimetric comparison of high dose rate (HDR) cervix brachytherapy with and without interstitial needles and the impact on target volume coverage and organ at risk (OAR) doses

The use of interstitial brachytherapy for cervical cancer in New Zealand practice has not been reviewed nor data published. The aim of this audit is to review the dosimetric impact of interstitial needles on target coverage and OAR doses and to compare the data from the Wellington Blood and Cancer Centre with international reported experience. Review of our practice should aid patient selection for future use of interstitial needles and indicate areas requiring technique development.
Patient demographics were collated for 19 patients who received interstitial cervix brachytherapy from a cohort of 120 radical cervical cancer patients between 2013 and 2019. The patients included in this audit had a diagnosis of cervical cancer and received standard chemotherapy, external beam radiation treatment and high-dose rate brachytherapy. Patient computed tomography datasets were retrospectively anonymised and transferred to the clinical development testing treatment planning system, Brachytherapy Planning v13.7 (Varian Medical Systems, CA and USA). Each patient was used as their own control with two treatment plans optimised for each fraction; the clinically treated plan and one without interstitial needles. Plan optimisation was completed according to the departmental protocol and cumulative equivalent doses for 2 Gy fractions (EQD2) were calculated using an in-house developed spreadsheet. All plans and EQD2 spreadsheets were independently reviewed by the Radiation Oncologist, Radiation Therapists and Medical Physics and amended if required.
Eighteen patients were suitable for evaluation. Patient demographics, staging, histology, tumour volumes, HRCTV D90% and IRCTV D90% were reported and organ at risk doses were explored. A total of 52 insertions with interstitial needles were performed. Of the 148 needles inserted, 119 needles (80.4%) were loaded. HRCTV D90% coverage was on average 5.4 Gy (from 0.5 Gy to 10.6 Gy) higher for the course when interstitial needles were used, while no significant change was observed with regards to organ at risk doses.
WBCC’s early experience of interstitial cervix brachytherapy has demonstrated the value of this technique in improving target coverage. This audit will support ongoing use of interstitial needles with the incorporation of the next generation of interstitial guided applicators

Khadiga Mohammed

Wellington hospital
Radiation Oncologist

Dr Khadiga Mohammed Is a Radiation Oncologist who currently working at Wellington Blood and Caner Centre in New Zealand. She has completed her under graduate study in Medicine in 2004 and completed her specialist training in Cape Town South Africa Khadiga holds a Fellowship of radiation oncology from South Africa and Masters in medicine in Radiation Oncology from university of Cape Town. She has actively participated in clinical trials and research, with membership of ESTRO, and ANZCGO. Khadiga has special interest in Gynaecological cancer, Breast cancer, Lymphoma and Paediatric malignancies.