# Potential of automated online adaptive proton therapy to reduce margins for oesophageal cancer

## TL;DR

This study shows that automated adaptive proton therapy can reduce the need for manual replanning and allow smaller treatment margins for oesophageal cancer.

## Contribution

The study introduces and evaluates two automated online adaptive proton therapy strategies for margin reduction in oesophageal cancer treatment.

## Key findings

- Non-adapted plans with 7 mm margins required manual replanning for 18% of patients.
- Automated Full Adaptation (AFA) eliminated the need for manual replanning in all cases.
- AFA reduced manual replanning to 11% when using 2 mm margins.

## Abstract

Proton therapy for oesophageal cancer is administered over multiple fractions, based on a single pre-treatment image. However, anatomical changes can lead to the deterioration of the treatment plan, necessitating manual replanning. To keep this within limits, increased residual margins are employed. This study aimed to evaluate the proposed automated Online Adaptive Proton Therapy (OAPT) strategies on their capability to reduce the need for manual replanning, while also exploring the possibility of margin reduction.

Two automated OAPT methods were examined: Automated Dose Restoration (ADR) and Automated Full Adaptation (AFA). ADR makes use of dose restoration, restoring the original dose map based on the patient’s altered anatomy. AFA adapts the contours used for plan optimization by applying a deformation field, not only correcting for density changes, but also for the relative location of organs. A comparative analysis of OAPT strategies, evaluating D98% tumour coverage on 17 patients, was conducted.

The nominal results of non-adapted plans with 7 mm residual margins required manual replanning for 18% of the patients. ADR reduced this to 6%, while AFA eliminated the need for manual replanning. With 2 mm margins, 47% of cases required manual replanning. ADR reduced this to 18%, and AFA further reduced it to 11%.

The proposed OAPT strategies offered a marked improvement compared to a non-adaptive approach. ADR and AFA significantly reduced the necessity for manual replanning and facilitated the reduction of residual margins, enhancing dose conformity and reducing treatment toxicity.

•Inadequate target coverage in 18% of non-adapted proton plans for oesophageal cancer.•Online adaptive strategies improve target coverage, reducing manual replanning need.•Online adaptive strategies allow reduced margins with manageable replanning levels.

Inadequate target coverage in 18% of non-adapted proton plans for oesophageal cancer.

Online adaptive strategies improve target coverage, reducing manual replanning need.

Online adaptive strategies allow reduced margins with manageable replanning levels.