Similar survival for patients undergoing reduced-intensity total body irradiation (TBI) versus myeloablative TBI as conditioning for allogeneic transplant in acute leukemia

A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques

Objective

The aim of this study is to implement a new treatment technique in total body irradiation (TBI) using the manual field-in-field-TBI (MFIF-TBI) technique and dosimetrically verifying its results with respect to compensator-based TBI (CB-TBI) and open field TBI technique.

Materials and Methods

A rice flour phantom (RFP) was placed on TBI couch with knee bent position at 385 cm source to surface distance. Midplane depth (MPD) was calculated for skull, umbilicus, and calf regions by measuring separations. Three subfields were opened manually for different regions using the multi-leaf collimator and jaws. The treatment Monitor unit (MU) was calculated based on each subfield size. In the CB-TBI technique, Perspex was used as a compensator. Treatment MU was calculated using MPD of umbilicus region and the required compensator thickness was calculated. For open field TBI, treatment MU was calculated using MPD of umbilicus region, and the treatment was executed without placing compensator. The diodes were placed on the surface of RFP to measure the delivered dose and the results were compared.

Results

The MFIF-TBI results showed that the deviation was within ± 3.0% for the different regions, except for the neck for which the deviation was 8.72%. In the CB-TBI delivery, the dose deviation was ± 3.0% for different regions in the RFP. The open field TBI results showed that the dose deviation was not within the limit ± 10.0%.

Conclusion

The MFIF-TBI technique can be implemented for TBI treatment as no TPS is required, and laborious process of making a compensator can be avoided while ensuring that the dose uniformity in all the regions within the tolerance limit.

Commissioning of total body irradiation using plastic bead bags

The goal of total body irradiation (TBI) is to deliver a dose to the whole body with uniformity within ±10%. The purpose of this study was to establish the technique of TBI using plastic bead bags. A lifting TBI bed, Model ORP-TBI-MN, was used. The space between the patient's body and the acrylic walls of the bed was filled with polyacetal bead bags. Patients were irradiated by a 10 MV photon beam with a source to mid-plane distance of 400 cm. The monitor unit (MU) was calculated by dose-per-MU, tissue-phantom-ratio and a spoiler factor measured in solid water using an ionization chamber. The phantom-scatter correction factor, off-center ratio and the effective density of the beads were also measured. Diode detectors were used for in vivo dosimetry (IVD). The effective density of the beads was 0.90 ± 0.09. The point doses calculated in an I'mRT phantom with and without heterogeneity material showed good agreement, with measurements within 3%. An end-to-end test was performed using a RANDO phantom. The mean ± SD (range) of the differences between the calculated and IVD-measured mid-plane doses was 1.1 ± 4.8% (-5.9 to 5.0%). The differences between the IVD-measured doses and the doses calculated with Acuros XB of the Eclipse treatment planning system (TPS) were within 5%. For two patients treated with this method, the differences between the calculated and IVD-measured doses were within ±6% when excluding the chest region. We have established the technique of TBI using plastic bead bags. The TPS may be useful to roughly estimate patient dose.

Genetic network profiles associated with established resistance to ionizing radiation in acute promyelocytic leukemia cells and their extracellular vesicles

Radiation-resistant acute promyelocytic leukemia (APL) cells present challenges to treatment, and the acquisition of resistance to ionizing radiation (IR) is a matter of clinical concern. However, little information is available on the behavior of radio-resistant APL in terms of gene expression profiles and intercellular communication. In this study, cDNA microarray and RT-PCR were used to analyze the intracellular genetic network and extracellular vesicles (EVs), respectively, in the established radio-resistant HL60 (Res-HL60) cell line. Significant changes in the expression of 7,309 known mRNAs were observed in Res-HL60 relative to control. In addition, 7 mRNAs were determined as targets because significant changes in the expression were observed using Ingenuity analysis software, confirming the quantitative RT-PCR. However, EVs from Res-HL60 cells did not include these target molecules. These results suggest that radio-resistant APL is regulated by the expression and suppression of specific molecules, and these molecules are not transferred between cells by EVs.

Marrow damage and hematopoietic recovery following allogeneic bone marrow transplantation for acute leukemias: Effect of radiation dose and conditioning regimen

BACKGROUND AND PURPOSE

Total body irradiation (TBI) is a common component of hematopoietic cell transplantation (HCT) conditioning regimens. Preclinical studies suggest prolonged bone marrow (BM) injury after TBI could contribute to impaired engraftment and poor hematopoietic function.

MATERIALS AND METHODS

We studied the longitudinal changes in the marrow environment in patients receiving allogeneic HCT with myeloablative (MA, n=42) and reduced intensity (RIC, n=56) doses of TBI from 2003-2013, including BM cellularity, histologic features of injury and repair, hematologic and immunologic recovery.

RESULTS

Following MA conditioning, a 30% decrease in the marrow cellularity persisted at 1 year post-transplant (p=0.03). RIC HCT marrow cellularity transiently decreased but returned to baseline by 6 months even though the RIC group received mostly umbilical cord blood (UCB) grafts (82%, vs. 17% in the MA cohort, p<0.01). There was no evidence of persistent marrow vascular damage or inflammation. Recipients of more intensive conditioning did not show more persistent cytopenias with the exception of a tendency for minimal thrombocytopenia. Immune recovery was similar between MA and RIC.

CONCLUSIONS

These findings suggest that TBI associated with MA conditioning leads to prolonged reductions in marrow cellularity, but does not show additional histological evidence of long-term injury, which is further supported by similar peripheral counts and immunologic recovery.