ESTRO meets Asia 2024 - Abstract Book

S54

Interdisciplinary – Brachytherapy

ESTRO meets Asia 2024

79

Proffered Paper

Impact of Endocavity Balloon Use during MRI-Based Endorectal Brachytherapy For Rectal Cancer

Rahul Krishnatry 1,2 , Aditi Jain 1 , Jeevanshu Jain 1 , Priyanka Halsana 1 , Abhishek Laxman Wagh 1 , Shivakumar Gudi 1 , Reena Engineer 1

1 RADIATION ONCOLOGY, TATA MEMORIAL CENTRE, MUMBAI, India. 2 RO, HBNI University, mumbai, India

Purpose/Objective:

Brachytherapy (BT) boost is one of the methods for dose escalation, improving rates of successful watch and wait in suitable rectal cancer patients. We review the dosimetric impact of additional endocavity balloons (CIVCO; Lowa, US) during the MRI-based brachytherapy using the indigenously developed rectal applicator to develop recommendations for its use.

Material/Methods:

16 consecutive patients of locally advanced carcinoma rectum with a suitable response post neoadjuvant chemoradiation were planned for brachytherapy boost as per departmental protocol. All patients underwent local application with an indigenously developed and in-house 3D printed MRI compatible applicator and two endocavity balloons on top of each other such that the inner balloon faced the tumour side and the outer balloon faced the opposite side. T-2 axial planning sequences 2 – 3 mm slice thickness with no to minimum gap) were done thrice on 1.5 Tesla (A: both balloons deflated representing no balloon: NB; B: outer single balloon inflated towards normal rectal mucosa: SB; both outer and inner balloon inflated: DB); Figure 1. The balloons were inflated in a ratio of 2:1 (outer: inner) with normal saline. The scans were imported to Oncentra v 4.6 treatment planning system (TPS) (Elekta, Sweden), and the target volume was defined as a residual tumour or fibrosis in concurrence with clinical findings (TV) and organs at risk (OARs) as their walls (rest of rectum, bladder, urethra, penile bulb/vagina) upto 2cm cranial and caudal from TV. Best optimal plans were generated with standard loading and prescription of 7 Gy to TV, followed by graphical optimisation. On the day of treatment, the most optimal plan based on TV and OAR doses was selected to treat the patients. For this study, each plan was reviewed afresh to see if further improvement could be achieved, and various doses (TV: D90%, D100%, D0.1cc, D1cc, D2cc, D5cc, V50%, V95%, V98%, V100%, V150%, V200%, V250%, V300%; OARs: D0.1cc, D1cc, D2cc, D5cc, V50%, V95%, V98%, V100%, V150%, V200%) and volume parameters were recorded. Paired t-tests and repeated measures ANOVA are used to identify best plan state recommendations.