ESTRO 2024 - Abstract Book

S249

Brachytherapy - Gynaecology

ESTRO 2024

Amani A Chowdhury 1 , Gerry Lowe 1 , Mohammed Abdul-Latif 1 , Hannah Tharmalingam 1 , Roberto Alonzi 1 , Peter J Hoskin 1,2 1 Mount Vernon Cancer Centre, Oncology, Northwood, United Kingdom. 2 University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom

Purpose/Objective:

Image-guided brachytherapy (IGBT) represents an integral component of treatment for cervical cancer. Intracavitary brachytherapy (IC) comprises placement of an intrauterine applicator paired with a ring or ovoid. This configuration allows for a ‘pear-shaped’ dose distribution to encompass the high risk clinical target volume (CTV HR ). However, variation in pelvic anatomy and tumour response to external beam therapy means that residual tumour at the time of brachytherapy often does not conform to the dosimetric distribution provided by IC alone. This can result in the need to compromise between tumour control probability at the expense of reduced normal tissue damage or vice versa. Interstitial catheters can be employed in combination with intracavitary brachytherapy (IC/IS) using hybrid applicators, perineal templates or freehand insertion to improve tumour control probability by enabling better dose distributions without further compromising dose to organs at risk (OARs). It therefore seems intuitive that increasing the number of catheters inserted (albeit to a point) will result in improved dosimetry. However, there are challenges with IC/IS, which include variation in technical skill amongst centres, the increased risk of damage to nearby structures and a lack of international guidelines defining the steps for optimal interstitial catheter placement.

The purpose of this study was to evaluate the use of IC/IS brachytherapy in cervical cancer and investigate the association between number of catheters and dosimetric targets.

Material/Methods:

A retrospective analysis of 153 patients treated with high dose rate (HDR) brachytherapy following (chemo)radiotherapy for cervical cancer between 2014-2020 was performed. Patients underwent a single implant and received 4 x 7Gy over 3 days. The type of implant and number of interstitial needles were recorded for each case. Dosimetry including D 90 CTV HR , total dose delivered (external beam and brachytherapy) and D 2cc to the bladder, rectum and sigmoid were reported.

Results:

128 patients had combination IC/IS and 25 patients had IC alone.

80% of patients received a total dose >85Gy EQD2 10 . With regards to OARs, assuming an EQD2 3 , in 51% of cases the D 2cc rectum <65Gy, 52% demonstrated a D 2cc bladder <80Gy and 37.2% achieved a D 2cc sigmoid <70Gy.

Table 1. Table showing the number of patients, mean CTV HR volume and mean number of interstitial catheters according to FIGO 2018 stage groups.

FIGO 2018 Stage

Number Patients *

of

Mean CTV HR volume (cc)

Mean

number

of

interstitial needles

IA

0

-

-