Simplified low dose rate infant total body irradiation

Publication date: Available online 24 October 2016
Source:Practical Radiation Oncology
Author(s): Nels Knutson, Y. James Rao, Sridhar Yaddanapudi, Stephanie M. Perkins, H. Harold Li
PurposeLow dose rate total body irradiation (LDR-TBI) in infants possesses unique challenges due to the setup limitations imposed by anesthesia. We present a LDR-TBI method with an AP/PA arrangement and dose rate<10cGy/min for infant patients (thickness<14cm) without the use of a beam attenuator.Materials and methodsThe delivery utilized a 6 MV TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA) with adjustable meterset rates below 100 MU/min. A platform was constructed to support the patient 6cm above the floor (~2 meters from the source). A 40x40 cm² field at isocenter along with a 45 degree collimator rotation was used to achieve a maximum field width of approximately 113cm at 2 meters. The patient was positioned supine with head turned towards the patient's right side for the AP beam and prone with the head continuing to turn towards the patient's right side for the PA beam. A scattering plate with custom organ blocks was placed approximately 20cm from the patient's surface. Output, depth-dose, surface-dose, block transmission, and off-axis measurements were taken using solid water slabs, ion chambers, and film.ResultsThe TrueBeam provides several options for this treatment geometry to deliver LDR-TBI at less than 10cGy/min by lowering the linear accelerator meterset rate below 100 MU/min. This allowed for a compromise between dose rate and treatment time to be selected by the radiation oncology team without the use of a beam attenuator, thus improving patient safety. Depth-dose and off-axis measurements confirmed a dose distribution within ±5% of the central-axis dose. A scattering plate distance of ~20cm from the patient's increases surface dose while allowing easy access to the patient during anesthesia.ConclusionsThe method described is useful to pediatric radiation oncologists seeking to deliver LDR-TBI to an infant patient.



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