Improving radiation conformality in the treatment of non-small cell lung cancer

Abstract

One of the many challenges of lung cancer radiotherapy is conforming the radiation dose to the target due to tumor/organ motion and the need to spare surrounding critical structures. Evolving radiotherapy technologies, such as four-dimensional (4-D) image-based motion management, daily on-board imaging and adaptive radiotherapy, have enabled us to improve the therapeutic index of radiation therapy for lung cancer by permitting the design of personalized treatments that deliver adequate doses conforming to the target while sparing the surrounding critical normal tissues. Four-dimensional computed tomography (CT) image-based motion management provides an opportunity to individualize target motion margins and reduce the risk of a geographical target miss. Daily on-board imaging and adaptive radiotherapy reduce set-up and motion/anatomy uncertainties over the course of radiotherapy. These achievements in image guidance have permitted the implementation in lung cancer patients of highly conformal treatment delivery techniques that are exquisitely sensitive to organ motion and anatomic change such as intensity-modulated radiation therapy, stereotactic body radiation therapy, and proton therapy. More clinical studies are needed to further optimize conformal radiotherapy using individualized treatment adaptations based on changes in anatomy and tumor motion during the course of radiotherapy and using functional and biological imaging to selectively escalate doses to radioresistant subregions within the tumor.

Figure 1

PET image-guided dose-painting to 74 Gy in region with SUV>13.8 using IMRT to improve biological conformality while keeping rest of target volume in 60 Gy to keep normal lung within dose volume constraint in stage IIIB NSCLC with contra-lateral mediastinal/hilar lymph node involvement.

Figure 2

Conformal ablative SBRT (50 Gy in 4 fractions) sparing surrounding critical structures in a tumor near the spinal cord (SC), bronchial tree (BT), esophagus (E), heart (H) and aorta (A). Color wash dose distributions are shown with corresponding scales.

Figure 3

Improving conformality from 3-DCRT to IMRT, PSPT and IMPT in a stage III B NSCLC with a complicated anatomy. IMPT provided optimal target coverage while sparing critical structures including spinal cord, esophagus, heart and lung.