# Application of the Deep Inspiration Breath-Hold Technique in Proton Therapy for Mediastinal Lymphomas: Initial Experience

## TL;DR

This paper describes using a deep breath-hold technique during proton therapy to reduce radiation to the heart and lungs in lymphoma patients.

## Contribution

The study introduces a new imaging protocol and positioning system to improve proton therapy accuracy for mediastinal lymphomas.

## Key findings

- The deep inspiration breath-hold technique reduced heart and lung radiation doses significantly.
- A new CT protocol lowered radiation exposure by over six times compared to standard methods.
- The positioning system showed high reproducibility, with minor differences between male and female patients.

## Abstract

The aim of this work is to present the use of the deep inspiration breath-hold technique for mediastinal lymphoma patients treated with proton therapy. This study also explores the use of a patient positioning system to improve treatment accuracy. Six patients participated in this study. Special imaging protocols and treatment workflows were developed, and data from the treatment planning system and other tools helped assess the differences between the deep inspiration breath-hold technique and traditional treatment. The new imaging protocol reduced radiation doses compared with the standard protocol, and the deep inspiration breath-hold technique lowered the dose delivered to the heart and lungs. Additionally, the patient positioning system showed high reproducibility, with differences observed between men and women.

Background: This work presents the procedures and application of the deep inspiration breath-hold (DIBH) technique for mediastinal lymphoma patients at a proton therapy (PT) center. It also discusses the implementation and validation of the surface-guided radiotherapy (SGRT) protocol in terms of positioning accuracy. Methods: This study included six lymphoma patients. Dedicated computed tomography (CT) protocols and a treatment workflow based on international guidelines were developed. Clinical data from the treatment planning system (TPS) were used to assess the difference between DIBH and free-breathing irradiation. Additionally, data from an optical patient positioning system and kilovoltage (kV) imaging system were used to estimate positioning shifts. The new CT protocol reduced the volume CT dose index by over six times compared with the standard protocol. Results: The DIBH method decreased the mean dose to the heart and lungs by up to 7.02 Gy(RBE) and 0.83 Gy(RBE), respectively. The median magnitude of patient setup errors and repeatability in DIBH positioning was 0.4 cm and 0.18 cm (mean for males and females) for the SGRT protocol. The kV imaging showed a setup error of over 0.3 cm for both groups. Conclusions: Despite the small size of the patient cohort, the relatively large number of individual positioning sessions enabled the detection of statistically significant differences (p < 0.05) in certain areas between male and female patients; however, no significant difference in the displacement vector magnitude was observed. DIBH treatment with SGRT offers high reproducibility for patient positioning.