Fictive Field-based Feathering for Extended-SSD Total Body Irradiation: A Single-institution Planning and Dosimetric Analysis
Vijay Kumar Mogulagani, Mohan Raj Uthiran, Ben Johnson Varghese, Siva Kumar Radhakrishnan, Lakshmana Perumal, Madhuri DumpalaAbstract
Purpose:
The purpose of this study was to describe the planning, dosimetric evaluation, quality assurance (QA), and clinical implementation of a feathered junction technique for low-dose total body irradiation (TBI) using a common coordinate system and fictive field approach with an extended source-to-skin distance (SSD) anteroposterior/posteroanterior (AP/PA) couch-based linear accelerator technique.
Materials and Methods:
Six patients treated with low-dose TBI for hematopoietic stem cell transplant conditioning were included. Two patients had aplastic anemia (2 Gy/1 fraction), two had myelodysplastic syndrome (4 Gy/2 fractions), and two had leukemia (2 Gy/1 fraction). Computed tomography (CT) simulation was performed in head-first supine and feet-first supine positions using a full-body Vac-Lok system, with a pelvic fiducial marker defining a common coordinate origin. Treatment planning was performed in the Monaco treatment planning system for an Elekta Synergy linear accelerator (6 MV, MLCi2). An extended-SSD AP/PA technique with jaw-based feathered junctions was used. Dosimetric evaluation included target coverage, junction dose characteristics, and organ-at-risk doses. QA included ionization chamber measurements and cone-beam CT verification.
Results:
Adequate target coverage was achieved. The mean planning target volume D95% and V95% were 92.9% ±2.05% and 94.03% ±1.47%, respectively. The mean maximum dose was 115.51% ±0.32%, mainly in peripheral regions. The mean lung doses were 103% ±1.2% and 104% ±0.8%, and kidney doses were 102% ±0.96% and 101.5% ±1.35%. Junction doses ranged from 102.5% ±0.5% to 105.5% ±0.6%.
Conclusion:
The technique achieved acceptable dose homogeneity and controlled junction doses. It provides a reproducible and feasible approach for low-dose TBI using standard linear accelerator infrastructure without organ shielding.