Clinical Implementation of Lung Stereotactic Body Radiation Therapy (SBRT)

Abstract

The stereotactic Body Radiation Therapy (SBRT) technique was developed to treat lung cancers at the Komfo Anokye Teaching Hospital without a four-dimensional computed tomography (4-D CT) scanner to account for motion in treatment planning and delivery. A tank-type water lung phantom was designed and developed from locally available materials, including wood, perspex and acrylic filled roll-on ball implanted in the wood to simulate the lung field, body, and tumour. A motion platform was developed to mimic breathing. The lung phantom underwent a standard and a slow CT scan to account for motion (0.5 cm and 1 cm). Radiation treatment plans were generated according to the Radiation Therapy Oncology Group (RTOG) 0915 protocol for lung SBRT and delivered with a Varian Clinac iX linear accelerator to the phantom for dosimetric verification with a dose prescription of 50 Gy in five fractions. Clinical tumour sizes of 1 cm and 3 cm were used as case studies to demonstrate the dose to organs at risk (OARs). Average measured doses were compared to treatment planning calculated doses for the phantom with and without motion. Dose deviation for treating static mimicked tumour was 8.43%, -4.31% for phantom in 0.5 cm motion, and -25.96% for phantom in 1 cm motion. Phantom dosimetric analysis for PTV V100%, V99%, V90% at 50 Gy/5 without motion were 86.77%, 91.19% and 99.96%; with 0.5 cm motion were 98.60%, 99.61% and 100%; and with 1 cm motion were 72.72%, 90.47% and 99.65%, respectively. Clinical analysis for PTV V100%, V99%, V90% at 48 Gy/5 were 101.10%, 102.62% and 100.49%, respectively. For a tumour size of 3 cm at 50 Gy/5 were 98.10%, 99.68% and 100%, respectively; and for 1 cm tumour size were 97.36%, 99.19% and 100 %, respectively. SBRT treatment planning and delivery were feasible without 4-D CT from phantom studies at the study site. The statistics propose that the target was sufficiently covered with the dose for all scenarios, thereby achieving the primary radiotherapy goal without excessively dosing OARs to minimise toxicity.