Abstract
Image guidance allows delivery of very high doses of radiation over a few fractions, known as stereotactic ablative radiotherapy (SABR). This treatment is associated with excellent outcome for early stage non-small cell lung cancer and metastases to the lungs. In the delivery of SABR, central location constantly poses a challenge due to the difficulty of adequately sparing critical thoracic structures that are immediately adjacent to the tumor if an ablative dose of radiation is to be delivered to the tumor target. As of current, various respiratory motion management and image guidance strategies can be used to ensure accurate tumor target localization prior and/or during daily treatment, which allows for maximal and safe reduction of set up margins. The incorporation of both may lead to the most optimal normal tissue sparing and the most accurate SABR delivery. Here, the clinical outcome, treatment related toxicities, and the pertinent respiratory motion management/image guidance strategies reported in the current literature on SABR for central lung tumors are reviewed.
Highlights
In the past, thoracic radiotherapy has constantly been limited by toxicity to the normal tissue, such as the lungs and the esophagus, which hinders dose escalation to the gross disease to a desired therapeutic level [1,2,3]
A planning target volume (PTV) margin reduction is possible through accurate delineation of the internal target volume (ITV), which allows for dose escalation to the gross tumor
The mean lung dose and the V20 were reduced by 47–77.3%; while the spinal cord dose was reduced by 55.2– 58.5% for central lung lesions when cone beam CT (CBCT) image guidance was used with active breathing control in the delivery of lung stereotactic ablative radiotherapy (SABR) as a result of reduction in treatment set up margins enabled by combining image guidance and respiratory motion management [49]
Summary
Thoracic radiotherapy has constantly been limited by toxicity to the normal tissue, such as the lungs and the esophagus, which hinders dose escalation to the gross disease to a desired therapeutic level [1,2,3]. Severe toxicities and deaths following SABR for centrally located lung lesions have been reported in many studies, which brought great concern regarding the feasibility of SABR for centrally located lung tumors [13, 14, 17,18,19,20,21, 30, 32,33,34,35] In these studies, large fractional dose, and/or failure to exclude OARs immediately adjacent to the tumor target from the high dose volume were frequently observed. SABR may not be the best treatment option for endobronchial lesions as it was Frontiers in Oncology | Radiation Oncology www.frontiersin.org
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