Image Guidance in Non–Small Cell Lung Cancer

Advances in the use of motion management and image guidance in radiation therapy treatment for lung cancer

The development of advanced radiation technologies, including intensity-modulated radiation therapy (IMRT), stereotactic body radiation therapy (SBRT) and proton therapy, has resulted in increasingly conformal radiation treatments. Recent evidence for the importance of minimizing dose to normal critical structures including the heart and lungs has led to incorporation of these advanced treatment modalities into radiation therapy (RT) for non-small cell lung cancer (NSCLC). While such technologies have allowed for improved dose delivery, implementation requires improved target accuracy with treatments, placing increasing importance on evaluating tumor motion at the time of planning and verifying tumor position at the time of treatment. In this review article, we describe issues and updates related both to motion management and image guidance in the treatment of NSCLC.

CALIPER: A deformable image registration algorithm for large geometric changes during radiotherapy for locally advanced non-small cell lung cancer

PURPOSE

Locally advanced non-small cell lung cancer (NSCLC) patients may experience dramatic changes in anatomy during radiotherapy and could benefit from adaptive radiotherapy (ART). Deformable image registration (DIR) is necessary to accurately accumulate dose during plan adaptation, but current algorithms perform poorly in the presence of large geometric changes, namely atelectasis resolution. The goal of this work was to develop a DIR framework, named Consistent Anatomy in Lung Parametric imagE Registration (CALIPER), to handle large geometric changes in the thorax.

METHODS

Registrations were performed on pairs of baseline and mid-treatment CT datasets of NSCLC patients presenting with atelectasis at the start of treatment. Pairs were classified based on atelectasis volume change as either full, partial, or no resolution. The evaluated registration algorithms consisted of several combinations of a hybrid intensity- and feature-based similarity cost function to investigate the ability to simultaneously match healthy lung parenchyma and adjacent atelectasis. These components of the cost function included a mass-preserving intensity cost in the lung parenchyma, use of filters to enhance vascular structures in the lung parenchyma, manually delineated lung lobes as labels, and several intensity cost functions to model atelectasis change. Registration error was quantified with landmark-based target registration error and post-registration alignment of atelectatic lobes.

RESULTS

The registrations using both lobe labels and vasculature enhancement in addition to intensity of the CT images were found to have the highest accuracy. Of these registrations, the mean (SD) of mean landmark error across patients was 2.50 (1.16) mm, 2.80 (0.70) mm, and 2.04 (0.13) mm for no change, partial resolution, and full atelectasis resolution, respectively. The mean (SD) atelectatic lobe Dice similarity coefficient was 0.91 (0.08), 0.90 (0.08), and 0.89 (0.04), respectively, for the same groups. Registration accuracy was comparable to healthy lung registrations of current state-of-the-art algorithms reported in literature.

CONCLUSIONS

The CALIPER algorithm developed in this work achieves accurate image registration for challenging cases involving large geometric and topological changes in NSCLC patients, a requirement for enabling ART in this patient group.

Faculty of Radiation Oncology Position Paper on the use of Image-Guided Radiation Therapy

The development of technology such as intensity-modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and stereotactic ablative body radiotherapy (SABR) has resulted in highly conformal radiotherapy treatments. While such technology has allowed for improved dose delivery, it has also meant that improved accuracy in the treatment room is required. Image-guided radiotherapy (IGRT), the use of imaging prior to or during treatment delivery, has been shown to improve the accuracy of treatment delivery and in some circumstances, clinical outcomes. Allied with the adoption of highly conformal treatments, there is a need for stringent quality assurance processes in a multidisciplinary environment. In 2015, the Royal Australian and New Zealand College of Radiologist (RANZCR) updated its position paper on IGRT. The draft document was distributed through the membership of the Faculty of Radiation Oncology (FRO) for review and the final version was endorsed by the board of FRO. This article describes issues that radiotherapy departments throughout Australia and New Zealand should consider. It outlines the role of IGRT and reviews current clinical evidence supporting the benefit of IGRT in genitourinary, head and neck, and lung cancers. It also highlights important international publications which provide guidance on implementation and quality assurances for IGRT. A set of key recommendations are provided to guide safe and effective IGRT implementation and practice in the Australian and New Zealander context.