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

Abstract

Background and purpose:

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.

Materials and methods:

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 $D_{\text{98\%}}$ tumour coverage on 17 patients, was conducted.

Results:

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%.

Conclusions:

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.