Proton therapy for thoracic malignancies: a review of oncologic outcomes

ABSTRACT

Introduction: Radiotherapy is an integral component in the treatment of the majority of thoracic malignancies. By taking advantage of the steep dose fall-off characteristic of protons combined with modern optimization and delivery techniques, proton beam therapy (PBT) has emerged as a potential tool to improve oncologic outcomes while reducing toxicities from treatment.

Areas covered: We review the physical properties and treatment techniques that form the basis of PBT as applicable for thoracic malignancies, including a brief discussion on the recent advances that show promise to enhance treatment planning and delivery. The dosimetric advantages and clinical outcomes of PBT are critically reviewed for each of the major thoracic malignancies, including lung cancer, esophageal cancer, mesothelioma, thymic cancer, and primary mediastinal lymphoma.

Expert opinion: Despite clear dosimetric benefits with PBT in thoracic radiotherapy, the improvement in clinical outcomes remains to be seen. Nevertheless, with the incorporation of newer techniques, PBT remains a promising modality and ongoing randomized studies will clarify its role to determine which patients with thoracic malignancies receive the most benefit. Re-irradiation, advanced disease requiring high cardio-pulmonary irradiation volume and younger patients will likely derive maximum benefit with modern PBT.

KEYWORDS:

• Esophageal cancer
• lung cancer
• mediastinal lymphoma
• mesothelioma
• proton therapy
• radiotherapy
• thoracic
• thymic cancer

Article highlights

• While intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT) have been successful in reducing toxicity and improving clinical outcomes, proton beam therapy (PBT) provides a promising tool to advance treatment delivery in the thorax

• By taking advantage of the sharp dose gradient at the distal range of the beam, PBT allows for better sparing of critical structures in the thorax, including the heart, lungs, esophagus, and spinal cord.

• Despite the uncertainties in the dosimetry of PBT, particularly in relation to motion management, recent advances in treatment planning and delivery are promising

• A clear dosimetric benefit has been demonstrated with PBT in multiple thoracic malignancies, including lung cancer, esophageal cancer, mesothelioma, thymic cancer, and primary mediastinal lymphoma.

• Current clinical data for thoracic PBT are mostly limited to single-arm prospective trials or retrospective series, but randomized trials are ongoing.

Declaration of interest

A Sawant has received research funding from NIH (R01 CA169102 and R01 CA202761), Varian Medical Systems, and Vision RT. TT Sio provides strategic and scientific recommendations as a member of the Advisory Board and speaker for Novocure Inc. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper received no funding.