A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

Abstract

Radiotherapy has become a critical component for the treatment of all stages and types of lung cancer, often times being the primary gateway to a cure. However, given that radiation can cause harmful side effects depending on how much surrounding healthy tissue is exposed, treatment of the lung can be particularly challenging due to the presence of moving targets. Careful implementation of every step in the radiotherapy process is absolutely integral for attaining optimal clinical outcomes. With the advent and now widespread use of stereotactic body radiation therapy (SBRT), where extremely large doses are delivered, accurate, and precise dose targeting is especially vital to achieve an optimal risk to benefit ratio. This has largely become possible due to the rapid development of image-guided technology. Although imaging is critical to the success of radiotherapy, it can often be plagued with uncertainties due to respiratory-induced target motion. There has and continues to be an immense research effort aimed at acknowledging and addressing these uncertainties to further our abilities to more precisely target radiation treatment. Thus, the goal of this article is to provide a detailed review of the prevailing uncertainties that remain to be investigated across the different imaging modalities, as well as to highlight the more modern solutions to imaging motion and their role in addressing the current challenges.

Intrafraction target shift comparison using two breath-hold systems in lung stereotactic body radiotherapy

“…Hence, steep dose gradients must be achieved to spare as much normal tissue as possible. Respiratory motion is one of the major uncertainty sources in lung treatments [2] . The current practice to account for respiratory motion uncertainties is to increase Planning Target Volume (PTV) margins, thus ensuring the prescribed dose delivery [3] .…”

Evaluation of lung tumor motion in a large sample: Target‐related and clinical factors influencing tumor motion based on four‐dimensional CT

“…For a single patient, whether a 4DCT scanning could provide a reliable tumor motion for treatment has been controversial. 15 , 16 The tumor motion magnitude could be influenced by target‐related (e.g., size and location) and clinical factors (tumor origin and history of pulmonary surgery). 17 Understanding the tumor motion magnitude for different patient subgroups and using this information in constructing ITVs is crucial.…”

Technical Note: A 3D‐printed phantom for radiochromic film evaluation of moving lung tumor SBRT without dose convolution

“…However, this technology, whose efficacy depends acutely on the precision with which the tumor is targeted, can be hampered by respiration‐related lung tumor movement. This issue has long attracted considerable interest in the radiotherapy field 2–5 …”

“…This issue has long attracted considerable interest in the radiotherapy field. [2][3][4][5] To take tumor movement into account, the general workflow involves first acquiring four-dimensional computed tomography (4DCT) time-resolved volumetric images and then using the maximum intensity projection (MIP) and average intensity projection (AIP) image set to contour the target volume and plan the treatment. 3,6,7 Finally, before treating the patient, a patient-specific quality assurance (QA) procedure is conducted to ensure that the radiation is delivered precisely to the tumor while sparing the surrounding healthy tissue.…”