Abstract
Background and purposeTotal body irradiation (TBI) is a treatment used in the conditioning of patients prior to hematopoietic stem cell transplantation. We developed an extended-distance TBI technique using a conventional linac with multi-leaf collimator to deliver a homogeneous dose, and spare critical organs.Materials and methodsPatients were treated either in lateral recumbent or in supine position depending on the dose level. A conventional linac was used with the patient midline at 350 cm from the beam source. A series of beams was prepared manually using a 3D treatment planning system (TPS) aiming to improve dose homogeneity, spare the organs at risk and facilitate accurate patient positioning. An optimized dose calculation model for extended-distance treatments was developed using phantom measurements. During treatment, in-vivo dosimetry was performed using electronic dosimeters, and accurate positioning was verified using a mobile megavoltage imager. We analyzed dose volume histogram parameters for 19 patients, and in-vivo measurements for 46 delivered treatment fractions.ResultsOptimization of the dose calculation model for TBI improved dose calculation by 2.1% at the beam axis, and 17% at the field edge. Treatment planning dose objectives and constraints were met for 16 of 19 patients. Results of in-vivo dosimetry were within the set limitations (±10%) with mean deviations of 3.7% posterior of the lungs and 0.6% for the abdomen.ConclusionsWe developed a TBI treatment technique using a conventional linac and TPS that can reliably be used in the conditioning regimen of patients prior to stem cell transplantation.
Highlights
In the treatment of hematological malignancies, a hematopoietic stem cell transplantation (HSCT), either autologous or allogenic, can be part of the treatment, depending on the risk profile of the disease, and age and comorbidities of the patient
Three extra radio-opaque markers were placed on the skin to mark points for in-vivo dosimetry in the following areas, for patients treated in lateral recumbent position: posterior of the left lung (“Lung P”), lower back (“Abdomen”), and on the chest anterior of point Lung P (“Lung A”)
Using the optimized total body irradiation (TBI) beam model, a treatment plan was prepared in the treatment planning system (TPS) that consisted of several different beams from both the anterior (A) and posterior (P) direction or left (L) and right (R) direction
Summary
In the treatment of hematological malignancies, a hematopoietic stem cell transplantation (HSCT), either autologous or allogenic, can be part of the treatment, depending on the risk profile of the disease, and age and comorbidities of the patient. A higher total dose of up to 14.4 Gy is given in up to eleven fractions [3]. A large survey from 2013 showed that for myeloablative schemes, a total dose of 12 Gy, given in six fractions (12 Gy/6fr), is used most often [4]. Instead of using cast lead blocks, the multi-leaf collimator (MLC) in the linac can be used to improve homogeneity, and to reduce dose to risk organs. Patient position was verified using a commercially available mobile megavoltage imager, and accurate dose delivery was assessed by in-vivo dosimetry with electronic dosimeters. To our knowledge, this is the first reported TBI technique combining all these aspects. We aim to demonstrate our technique, and show that accurate delivery of a homogeneous dose distribution is possible using a standard linac and commercially available technology
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