ESTRO 2024 - Abstract Book

S4056

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Figure 1: Boxplots showing median, interquartile range and 10-90% of accumulated dose parameters ten patients comparing the described dose-adaptive to the conventional approach. Significant differences (paired t-test; p<0.05) are indicated with *.

Conclusion:

We have shown that a significant reduction in accumulated dose to organs at risk is possible while maintaining target coverage by adjusting the treatment plan of the last fraction to the accumulated physical dose of previous fractions.

Keywords: Dose accumulation, margins, online adaptive RT

1820

Poster Discussion

Balancing coverage and OAR dose in hypofractionated salvage radiation therapy after prostatectomy

Floor H.E. Staal, Jorinde Janssen, Sajee Krishnapillai, Johannes A. Langendijk, Stefan Both, Charlotte L. Brouwer, Shafak Aluwini

University of Groningen, University Medical Centre Groningen, Department of Radiation Oncology, Groningen, Netherlands

Purpose/Objective:

This study aimed to assess target coverage and the dose received by organs at risk (OARs) in moderately hypofractionated salvage external beam radiotherapy (sEBRT) after prostatectomy. Additionally, we evaluated the currently used PTV margin of 8 mm to investigate opportunities for PTV margin reduction.

Material/Methods:

Cone-beam computed tomography (CBCT) images from the first 20 patients included in the PERYTON-trial, a phase III randomised controlled trial investigating the role of moderately hypofractionated sEBRT (NCT04642027), were analysed. Ten patients received conventional sEBRT (35 x 2 Gy), and 10 received hypofractionated sEBRT (20 x 3 Gy). Patients received instructions to void one hour prior to the planning-CT and before each treatment fraction, and were asked to drink 500 mL of water during the waiting hour. No rectal preparations were used. CBCTs were matched with the corresponding planning-CT using a registration mask including pelvic bone structures. Bladder and rectum were delineated on all CBCTs. The percentual changes (compared to the planning-CT) in interfractional OAR volumes were compared between the conventional schedule and the hypofractionated schedule. Furthermore, the correlation between the number of fractions and interfractional volume change was analysed.