Abstract
Interplay effects in highly modulated stereotactic body radiation therapy lung cases treated with volumetric modulated arc therapy.PurposeTo evaluate the influence of tumor motion on dose delivery in highly modulated stereotactic body radiotherapy (SBRT) of lung cancer using volumetric modulated arc therapy (VMAT).Methods4D‐CT imaging data of the quasar respiratory phantom were acquired, using a GE Lightspeed 16‐slice CT scanner, while the phantom reproduced patient specific respiratory traces. Flattening filter‐free (FFF) dual‐arc VMAT treatment plans were created on the acquired images in Pinnacle3 treatment planning system. Each plan was generated with varying levels of complexity characterized by the modulation complexity score. Static and dynamic measurements were delivered to GafChromic EBT3 film inside the respiratory phantom using an Elekta Versa HD linear accelerator. The treatment prescription was 10 Gy per fraction for 5 fractions. Comparisons of the planned and delivered dose distribution were performed using Radiological Imaging Technology (RIT) software.ResultsFor the motion amplitudes and periods studied, the interplay effect is insignificant to the GTV coverage. The mean dose deviations between the planned and delivered dose distribution never went below −2.00% and a minimum dose difference of −5.05% was observed for a single fraction. However for amplitude of 2 cm, the dose error could be as large as 20.00% near the edges of the PTV at increased levels of complexity. Additionally, the modulation complexity score showed an ability to provide information related to dose delivery. A correlation value (R) of 0.65 was observed between the complexity score and the gamma passing rate for GTV coverage.ConclusionsAs expected, respiratory motion effects are most evident for large amplitude respirations, complex fields, and small field margins. However, under all tested conditions target coverage was maintained.
Highlights
1.1 Background and Significance 1.1.1 Lung CancerLung cancer is the second most diagnosed cancer in men and women, but the leading cause of cancer death in both (American Lung Association, 2015)
The phantom is composed of an acrylic body and an electric drive unit designed to simulate one-dimensional internal lung motion with various cylindrical “lung” inserts that move in the longitudinal direction while simultaneously simulating one-dimensional external chest motion with a platform that moves in the anterior-posterior direction
The calculated complexity score for these plans resulted in a complexity score of 0.70 and 0.75 for the 1 cm and 2 cm target amplitude, respectively
Summary
1.1 Background and Significance 1.1.1 Lung CancerLung cancer is the second most diagnosed cancer in men and women, but the leading cause of cancer death in both (American Lung Association, 2015). 1.1 Background and Significance 1.1.1 Lung Cancer. When an individual is diagnosed after the cancer has metastasized, the expected 5-year survival is approximately 4%. When an individual is diagnosed in the localized stage of the disease the expected 5-year survival is approximately 54%. The number of individuals with a localized diagnosis represents a small percentage of the total number of diagnosed lung cancers, this number is expected to increase with the use of computed tomography (CT) scans as a lung cancer screening tool for high-risk individuals
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