Room: AAPM ePoster Library
Purpose: Approximately 85% of acute lymphoid and acute myeloid leukemia patients receive total body irradiation(TBI) to suppress the immune system in preparation for a bone marrow transplant(BMT). Additionally, TBI treats “chemotherapy sanctuary sites” including the central nervous system, testes and chemotherapy refractory clonogens of malignant disease. However, TBI has potential severe complications, including pneumonitis, renal dysfunction, gastrointestinal complications and secondary malignancies. Total marrow irradiation(TMI) has been proposed to reduce toxicities, but studies have shown that sanctuary sites are not adequately treated. In anticipation of a clinical trial to investigate a novel conditioning regimen that uses a simultaneous integrated marrow and body approach(SIMBA), this study demonstrates the dosimetric feasibility of balancing the clinical benefit of TBI with the toxicity decrease of TMI using two prescription volumes simultaneous integrated and delivered with 6MV-VMAT.
Methods: patients, previously treated with VMAT-TBI, were re-planned with SIMBA and compared using standard OAR dosimetric indices. PTV_Marrow was contoured using the bone auto segmentation, and PTV_TotalBody was defined as the body-OAR-PTV_marrow. 12Gy and 8Gy in six fractions were prescribed to the PTV_Marrow and PTV_TotalBody, respectively. The plans were normalized so that 100% of the PTV_Marrow received at least 90% of the dose with the PTV_TotalBody optimized to stay as close to 100% at 90% as possible.
Results: ten patient plans achieved 12Gy/8Gy to at least 90% of the PTV_Marrow and PTV_TotalBody, respectively, with max dose of <16Gy(130%). As compared with the delivered TBI, the following reductions in mean dose were notable: small bowel 21.5±3.9%, lung 16.9±7.5%, heart 18.3±5.6% and kidney 14.8±4.4%. Coverage of the sanctuary sites was maintained despite significant reduction to sensitive OARs.
Conclusion: study demonstrates that SIMBA can dosimetrically provide the same PTV/sanctuary site doses as TBI while reducing the doses to OARs. The future clinical trial will interrogate the clinical benefit of these dosimetric balances.