ESTRO 2024 - Abstract Book

S4071

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

A daily CBCT with bone (translation) correction is sufficient to ensure adequate CTV doses. With the drinking and bowel preparation protocol, margins of 5 mm anteriorly and 7 mm on other sides are effectively accommodating the anatomical variability of the target structures.

Keywords: Rectum, IGRT, short course RT

References:

1. Fields EC, Kaplan BJ, Karlin J, et al. Phase 1 Study of Neoadjuvant Short-Course Radiation Therapy Concurrent With Infusional 5-Fluorouracil for the Treatment of Locally Advanced Rectal Cancer. Adv Radiat Oncol.2019;4:605-612.

2. Appelt AL, Kerkhof EM, Nyvang L, et al. Robust dose planning objectives for mesorectal radiotherapy of early stage rectal cancer - A multicentre dose planning study. Tech Innov Patient Support Radiat Oncol.2019;11:14-21.

3. Park J, Venkatesulu BP, Kujundzic K, et al. Consensus Quality Measures and Dose Constraints for Rectal Cancer From the Veterans Affairs Radiation Oncology Quality Surveillance Program and American Society for Radiation Oncology (ASTRO) Expert Panel. Pract Radiat Oncol. 2022;12:424-436.

2098

Digital Poster

A geometric parameter to predict the risk of exceeding tolerance doses during pancreas SBRT.

Mauro Loi 1 , Laura Masi 2 , Raffaella Doro 2 , Margherita Zani 1 , Gabriele Simontacchi 1 , Lorenzo Livi 1

1 Azienda Ospedaliero-Universitaria Careggi, Università di Firenze, Radiation Oncology Unit, Florence, Italy. 2 Istituto fiorentino di cura e assistenza- IFCA, Department of Medical Physics and Radiation Oncology, Florence, Italy

Purpose/Objective:

Inter-fraction organ deformations during SBRT for pancreatic patients can lead to excessive doses to OARs. A simple geometric parameter (EIV) is proposed as a tool to predict the risk of exceeding dose tolerances as well as to select patients needing adaptive re-planning.

Material/Methods:

20 patients were treated for pancreatic cancer delivering 40/50Gy in 5 fractions at a CyberKnife (CK) system and requiring V35Gy < 0.5 cc for duodenum, stomach and bowel. A parameter (EIV) was defined to quantify target to OAR proximity. For each patient the expansion-intersection volume (EIV), was computed on the planning CT (pCT) as the intersection volume between the PTV expanded by 5 mm and duodenum, stomach and bowel separately. Pre-fraction CT scans were acquired with a maximum of 2 repeated scans per patient, for a total of 25 scans. OARs were first