ESTRO 2024 - Abstract Book

S3723

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

On analysis of the subtraction dose map generated by VelocityTM Accumulation: ACTIVE Dosimetry, which subtracted the planned dose from the delivered dose, 4 out of 7 of the patient treatments had cold spots along and inside the inferior medial edge of CTVp_5400. However, due to the proximity of CTVp_6500, the planned dose to the CTVp_5400 had a mean dose of 64.93Gy, and was typically on a steep dose gradient from 65Gy to 54Gy, which suggests these cold spots as shown in figure 1 were indicative of a high dose gradient and didn't significantly affect the clinical dose to CTVp_5400.

Conclusion:

There was no significant reduction in dose for dose delivered during treatment, meaning variation in daily patient set up did not affect clinical dose delivery to CTVp_6500 and CTVp_5400 for all patients.

Future studies will build on this research to utilise outcome data for OSCC patients to identify ways to improve the clinical service.

Keywords: deformable, recurrence, OSCC

2953

Digital Poster

Reduction of organ-at-risk doses by omission of selected elective targets in head and neck cancer

Kristoffer Moos 1,2 , Anne I.S. Holm 3 , Jesper G. Eriksen 2,3 , Stine S. Korreman 1,2

1 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark. 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark. 3 Aarhus University Hospital, Department of Oncoloy, Aarhus, Denmark

Purpose/Objective:

In current curatively intended radiotherapy the clinical target volumes (CTVs) often consist of sub-volumes that account for varying degree of risk. Particularly, a low-dose elective CTV (CTVe) is often defined to encompass elective lymph nodes that may involve malignant formations. Although the prescribed dose to the CTVe is relatively low, it still results in considerable irradiated volumes with associated risk of acute and late side-effects.

This study aimed to explore the potential for reducing irradiation to OAR in head-and-neck cancer patients by omitting lymph node levels associated with the lowest risk of sub-clinical disease.

Material/Methods:

In this study, 20 patients with oropharyngeal cancer were retrospectively included. Three independent treatment plans (TPs) were created. Initially, a baseline plan (BaseP) was generated following the current consensus guidelines for delineation and dose planning from DAHANCA [1]. Subsequently, a second plan was created in which lymph node levels with expected risk of sub-clinical disease of <10% were omitted. The expected risk was estimated by mimicking the patient population in the LyProX database [2]. These are referred to as selected omission plans (SelectP). SelectPs were only created for patients in which there was a comparable population in