Adaptive Stereotactic Body Radiation Therapy Planning for Lung Cancer

Abstract

Purpose: Tumor size reduction has been observed for patients underwent lung stereotactic body radiation therapy (SBRT). Adaptive planning has the potential to reduce normal tissue toxicity and/or escalate dose to target in these patients. In this study, we evaluated the dosimetric effectiveness of adaptive planning in lung SBRT for patients who presented large target volume changes during the treatment.Methods and Materials: 20 out of 66 consecutive lung SBRT patients who showed largest percentage internal target volume (ITV) change throughout the treatment were included in the study. All patients went through 3D and 4DCT before treatment, and treatment on a Linear Accelerator machine equipped with kV imager, kV CBCT, and MV electronic portal imaging device (EPID). CBCT images were acquired at each fraction for patient positioning purpose. CBCT images for all fractions were used for contour and treatment planning. Adaptive plans were created on the CBCT images using the same planning parameters as the original CT-based plan, with the goal to achieve comparable conformality index (CI). For each patient, two cumulative plans, non-adaptive plan (PNON) and adaptive plan (PADP), were generated and compared for the following organs-at-risks (OARs): cord, esophagus, chest wall, and the lungs.Correlations were evaluated between changes in dosimetric metrics induced by adaptive planning and potential impacting factors, including tumor-to-OAR distances (dT-OAR), initial ITV (ITV1), ITV change (∆ITV), and effective ITV diameter change (∆dITV).Results: For the 20 selected patients, percentage ITV change ranged from 16.4% to 59.6%, with a mean (±SD) of 38.8% (±12.5%). CI of all plans ranged from 1.03 to 1.46, with small intra-subject variations (0.01-0.1). Compared to PNON, PADP resulted in significantly (p=0-0.02) lower values for all dosimetric metrics. ∆dITV/dT-OAR was found to correlate with changes in dose to 5cc (∆D5cc) of esophagus (r=0.77) and dose to 30cc (∆D30cc) of chest v wall (r=0.72). Stronger correlations between ∆dITV/dT-OAR and ∆D30cc of chest wall were discovered for peripheral (r=0.82) and central (r=0.94) tumors, respectively. Conclusions:Adaptive lung SBRT planning can potentially reduce dose to adjacentOARs if patients present significant tumor volume shrinkage during the treatment.

A comprehensive evaluation of the accuracy of CBCT and deformable registration based dose calculation in lung proton therapy

“…The dosimetric advantage of protons over photons has been used to improve the poor outcome of lung cancer patients (DeSantis et al 2014, Wink et al 2014). Passive scattering proton therapy (PSPT) has predominantly been used as a robust strategy to deal with the intra-fractional motion of lung tumors; however, other inter-fractional changes during the course of radiotherapy may also affect the dose delivered to target and healthy tissues (Guckenberger et al 2011, Qin et al 2013. These factors include changes in tumor size and position, alterations in tissue anatomy, variations in respiratory patterns, and fluctuations in patient weight (Gomez and Chang 2011).…”

What if a tumor is significantly enlarged just before stereotactic body radiation therapy? A case report and review of the literature

“…Optimal management in this scenario requires further investigation. A recent textbook considered the concept of re‐examination using CBCT and re‐simulation for adaptive SBRT to tailor technical aspects of treatment, as up to 32% of patients experienced significant changes in their tumor during SBRT . Significant dosimetric improvement could be achieved by tailoring SBRT to each patient after reassessing tumor growth before proceeding with SBRT.…”

A clinical 3D/4D CBCT‐based treatment dose monitoring system

“…Treatment delivered dose in patient could vary from the planned one due to patient setup, target motion, and anatomic variation . For lung cancer treatment, the percentage of ITV volume changes of a cohort of 40 Stereotactic Body Radiation Therapy (SBRT) lung patients were reported to range from −59.6% to 13.0% (−21.0 ± 21.4%) at the end of treatment . The anatomic change caused by atelectasis, pleural effusion, and pneumonia could also significantly affect the dose distribution .…”