INTRODUCTION

Total body irradiation (TBI) is a well-established conditioning regimen used in bone marrow or stem cell transplantation during which the whole body is irradiated with the intention of eliminating malignant cells and preventing the rejection of donor cells through immunosuppression. Even though this regimen is effective1, it is associated with significant side effects including pulmonary toxicity (approximately 25% of patients),2,3 cataracts (30-40% of patients)4, gonadal failure5, thyroid and kidney dysfunction6,7 and decreased bone mineral density8. Based on the most recent Children Oncology Group (COG) survey on TBI techniques9, most conventional AP/PA TBI techniques use partial transmission lung blocks of non-patient-specific thickness to limit the lung toxicity. However, lateral TBI techniques rarely incorporate lung blocks, resulting in lung dose that is equal to or higher than the prescription dose. In addition, inconsistent lung dose reporting, and manual monitor unit calculation in a homogenous medium based on patient thickness measurements limit accuracy in lung dose determination. The importance of reduction of lung dose in decreasing the risks of pneumonitis and potentially lethal pulmonary toxicity has been demonstrated, with recent studies have demonstrated that mean lung doses below 8 Gy are needed to decrease lung toxicity risks and improve overall survival10.
The Children’s Oncology Group survey of 152 COG institutions on the practice patterns in pediatric TBI in 2020-21 found that 100% of physician respondents were interested in refining the conventional TBI techniques to lower lung dose and 75% of physicians were interested in implementing VMAT or Tomotherapy TBI9. But, as shown by the survey, the supply does not meet the demand: only 14% of institutions adapted VMAT-TBI and Tomotherapy TBI.
Several studies showed the benefit of modern treatment planning and treatment delivery approaches to TBI, including helical tomotherapy11-12 or volumetric modulated radiation therapy (VMAT)13-15 allowing for superior organ sparing and more comfortable patient positioning during treatment. However, these treatment techniques require expertise and special equipment, which has limited their accessibility, and relatively little data regarding dosimetric comparisons has been reported. We have developed the Stanford auto-planned VMAT-TBI technique13,16-17 and shared the auto-planning scripts with the public to make VMAT-TBI more wide-spread (https://github.com/esimiele/VMAT-TBI). Our technique was also included as a basis for VMAT-TBI methodology among 2D and Tomotherapy TBI techniques on the Children Oncology Group (COG) ASCT2031 trial. In this work, we report the comparison between our auto-planned VMAT-TBI for myeloablative and nonmyeloablative regimens and our 2D-conventional TBI technique. These results are relevant for institutions intending to switch from 2D to VMAT-TBI technique and can be beneficial for creation of future analysis and dosimetric correlatives for Children Oncology Group (COG) ASCT2031 trial.