Strategies for Motion Robust Proton Therapy With Pencil Beam Scanning for Esophageal Cancer

Ditte Sloth Møller; Per Rugaard Poulsen; Andreas Hagner; Mathieu Dufour; Marianne Nordsmark; Tine Bisballe Nyeng; Hanna Rahbek Mortensen; Christina Maria Lutz; Lone Hoffmann

doi:10.1016/j.ijrobp.2021.04.040

Strategies for Motion Robust Proton Therapy With Pencil Beam Scanning for Esophageal Cancer

Int J Radiat Oncol Biol Phys. 2021 Oct 1;111(2):539-548. doi: 10.1016/j.ijrobp.2021.04.040. Epub 2021 May 8.

Authors

Ditte Sloth Møller¹, Per Rugaard Poulsen², Andreas Hagner³, Mathieu Dufour⁴, Marianne Nordsmark⁵, Tine Bisballe Nyeng⁵, Hanna Rahbek Mortensen⁶, Christina Maria Lutz³, Lone Hoffmann³

Affiliations

¹ Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark. Electronic address: dittmoel@rm.dk.
² Department of Oncology, Aarhus University Hospital, Aarhus, Denmark; Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark.
³ Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark.
⁴ Department of Physics, University of Turin, Turin, Italy.
⁵ Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
⁶ Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark.

PMID: 33974885
DOI: 10.1016/j.ijrobp.2021.04.040

Abstract

Purpose: Proton therapy of esophageal cancer is superior to photon radiation therapy in terms of normal tissue sparing. However, respiratory motion and anatomical changes may compromise target dose coverage owing to density changes, geometric misses, and interplay effects. Here we investigate the combined effect on clinical target volume (CTV) coverage and compare proton therapy with intensity modulated radiation therapy (IMRT).

Methods and materials: This study includes 26 patients with esophageal cancer previously treated with IMRT planned on 4-dimensional computed tomography (4D-CT). For each patient, 7 proton pencil beam scanning (PBS) plans were created with different field configurations and optimization strategies. The effect of respiration was investigated by calculating the phase doses, 4D dose, and 4D dynamic dose (including interplay effects). The effect of anatomical changes was investigated by recalculating all plans on all phases of a 4D-CT surveillance scan.

Results: The most robust PBS plans were achieved using 2 posterior beams requiring coverage of planning target volume (PTV) and simultaneously using robust optimization (RO) of CTV (2PA_PTVRO), resulting in only 1 patient showing V95%_CTV <97% in 1 or more phases of the planning CT. For the least robust PBS plans obtained using lateral + posterior beams and CTV-RO, but not requiring PTV coverage (2LP_RO), 10 patients showed underdosage. For IMRT, 2 patients showed underdosage. Interplay effects reduced V95%_CTV significantly when delivering only 1 fraction, but the effects generally averaged out after 10 fractions. The effect of interplay was significantly larger for RO-only plans compared with plans optimized with RO combined with PTV coverage. Combining the effect of anatomical changes and respiration on the 4D-CT surveillance scan resulted in V95%_CTV <97% for 3 2PA_PTVRO, 16 2LP_RO, and 8 IMRT patients.

Conclusions: PBS using posterior beam angles was more robust to anatomical changes and respiration than IMRT. The effect of respiration was enhanced when anatomical changes were present. Single fraction interplay effects deteriorated the dose distribution but were averaged out after 10 fractions.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aged
Aged, 80 and over
Esophageal Neoplasms / diagnostic imaging
Esophageal Neoplasms / pathology
Esophageal Neoplasms / radiotherapy*
Female
Four-Dimensional Computed Tomography
Humans
Male
Middle Aged
Motion
Proton Therapy / methods*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods*
Radiotherapy, Intensity-Modulated
Respiration