Author: Kazi Towmim Afrin, Imad M. Ali, Jordan West 👨🔬
Affiliation: University of Oklahoma Health Sciences Center, University of Oklahoma 🌍
Purpose: To simulate total-body-irradiation (TBI) with field-in-field treatment planning techniques and test portal dosimetry for dose verification and quality assurance.
Methods: CT images of full body scans of TBI-patients were acquired during simulation which then were used for treatment planning. Right and left lateral field-in-field with extended-SSD of 540cm were used for treatment planning. The simulation study was performed with the regular millennium-MLC on a TrueBeam and high-definition-MLC on Edge machine. The AAA-dose calculation algorithm in the Eclipse treatment planning system was used for dose calculation.
Results: 3D-treatment planning with field-in-field provided superior uniform dose distribution instead of using conventional large open fields with lead shielding. The mean dose for the total body decreased by about 10% using the field-in-field technique. The maximum dose decreased by about 5% for the same prescription dose. Setup fields with MLC shaping that are defined with patient body contour can be used for fast and accurate patient setup. The portal dosimetry can be used for dose measurement for second dose verification instead of lengthy and single point measurements with in-vivo dosimeters. The limitations of this technique include the dosimetric uncertainties associated with the dose calculation algorithm with large fields and lengthy extended-SSD where the beam will scatter in a longer air column before being transferred in the patient. Furthermore, the ability of the machines to deliver field-in-field with large extended-SSD will be the subject of future research.
Conclusion: This field-in-field 3D-treatment planning technique provided superior uniform dose coverage compared to conventional open field with lead shielding. It also generates comparable uniform dose distributions and lung sparing with VMAT with much shorter time and treatment planning requirements for contouring, optimization, and dose calculation. The dose delivery with this field-in-field 3D-technique uses a single isocenter with more accurate patient setup and shorter time for dose delivery.