ESTRO 2022 - Abstract Book

S1601

Abstract book

ESTRO 2022

1 IRCCS ISTITUTO NAZIONALE DEI TUMORI DI MILANO, Radiotherapy, Milano, Italy; 2 Ospedale di Circolo e Fondazione Macchi di Varese, Radiotherapy, Varese, Italy; 3 Ospedale di Busto Arsizio, Radiotherapy, Busto Arsizio, Italy; 4 IRCCS-ISTITUTO NAZIONALE DEI TUMORI DI MILANO, Unit of Medical Physics, Milano, Italy; 5 IRCCS-ISTITUTO NAZIONALE DEI TUMORI DI MILANO , Unit of Medical Physics, Milano, Italy; 6 Università degli Studi di Milano, Unit of Medical Physics , Milano, Italy; 7 IRCCS-ISTITUTO NAZIONALE DEI TUMORI DI MILANO, Radiotherapy, Milano, Italy Purpose or Objective To improve target volume coverage with the implementation of combined intracavitary and interstitial brachytherapy (ICIS- BT) in locally advanced cervical cancer treatment. Materials and Methods Intracavitary brachytherapy (BT) in addition to external-beam radiotherapy (EBRT) is a standard treatment for locally advanced cervical cancer. Interstitial BT was applied In patients with large residual tumor volumes and minor parametrial response to improve target coverage. In our department, from October 2017 to November 2019, 22 patients (pts) were treated using combined ICIS-BT for primary cervical cancer. The morphological and/or dimensional features of the target volume (i.e. ≥ 30 cc) drove our choice. All pts received EBRT (VMAT) with concomitant chemotherapy (CT) and sequential BT boost. The prescribed dose was 45Gy in 25 fractions over 5 weeks. CT regimen was weekly Cisplatin (40 mg/m2). Image- guided adaptive BT based on magnetic resonance imaging (MRI) was performed for all pts. According to Gynecological GEC ESTRO recommendations, GTV, High Risk CTV (HR-CTV), Intermediate Risk CTV (IR-CTV), bladder, rectum and sigmoid were delineated for each BT fraction on para-axial MR images with the applicator in place. Dose-volume histograms were calculated to evaluate doses target and organs at risk doses (OAR). The total dose prescribed was 28Gy in 4 fractions. EBRT and BT cumulative doses were evaluated by calculation of a biologically equieffective dose in 2Gy per fraction (EQD2) using the linear-quadratic model with α / β = 10Gy for tumor effects and α / β = 3Gy for late normal tissue damage. Acute genitourinary, gastro-enteric and vaginal toxicity was monitored at each fraction and recorded according to the CTCAE criteria version 4.03. The planning aims, according to the EMBRACE II protocol, were achieved for all pts (i.e. HR-CTV D90 between 90 and 95Gy and GTV D98>95Gy). OAR hard constraints were never exceeded (bladder D2cm ³ <80 Gy, rectum D2cm ³ <65Gy, sigmoid/bowel D2cm ³ <70 Gy). All pts were re optimized without interstitial needles dose contribution to demonstrate the improvement in target dose coverage due to the interstitial component. The HR-CTV D90 obtained with and without ICIS-BT were compared using matched pair two-tailed t-test statistics. All analyses were performed with significance level of 5%. Results BT was well tolerated by all pts. Figure 1 shows the variation of CTV-HR D90 for each patient at the first treatment fraction, with and without the contribution of the interstitial needles. The average gain in terms of target coverage was of 21% in favor of the ICIS-BT treatments(p value:0,0007).

Conclusion In pts with large tumor volumes at the time of BT, with minor parametrial response, the concomitant implementation of the interstitial and the intracavitary techniques allows to guarantee an adequate target coverage, with a consequent better local control of the disease.

PO-1796 Dosimetric comparison of rectal dose reduction methods in brachytherapy for cervical cancer

M. Sawada 1 , Y. Shiraishi 1 , T. Nemoto 1 , T. Tanaka 1 , R. Kota 1 , N. Koike 1 , N. Shigematsu 1

1 Keio university, Radiation oncology, Shinjuku, Japan

Purpose or Objective Rectal complications are common in radiotherapy for cervical cancer and correlates with rectal dose. Vaginal gauze packing (VP) and rectal retractor (RR) are widely used for rectal dose reduction in high dose rate brachytherapy. The purpose of this study is dosimetric comparison of these two methods in 3D image-guided adaptive brachytherapy.