Commissioning of 6 and 10 MV beams for Total Body Irradiation (TBI)

The objective of the TBI treatment is the ablation of the bone marrow and the destruction of the circulating leukemia cells, once they are widely distributed throughout the body.Using beam parameters acquired under conventional SSD in TBI treatments may add non-negligible uncertainties in the monitor units calculation or in the beam profiles.The study,aims to commission the 6 and 10 MV photon beams,of the Varian accelerator CX model. A slab phantom and dosimetric assembly were used under TBI conditions. The accuracy of the TPS was evaluated against the experimental data. A set of data were acquired, highlighting the TPR table and methodology for calculating MU has been implemented. The TPS has presented a statistical uncertainty of ± 2.7 % compared to the experimental data for monitor unit calculation. The use of an acrylic spoiler has been shown to be clinically advantageous where, for a 6 MV beam, the entrance PDD was 75 % without a spoiler and 99.5 % with a spoiler. For a 10 MV beam, it was verified that without a spoiler, the entrance PDD was about 55 %, but with a spoiler, it was about 93 %. For medium Heterogeneous the TPS underestimated dose values by up to -3.5 % with a mean deviation of –2.9 %, for 6 MV and for 10 MV, the TPS overestimated the dose values by up to 1.1 %,with an average deviation of 1.0 % using the acrylic thorax phantom. The data obtained can be used clinically. (author)