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.