Optimized Conformal Total Body Irradiation with VMAT Using a Linear-Accelerator-Based Radiosurgery Treatment System in Comparison to the Golden Standard Helical TomoTherapy

SIMPLE SUMMARY: Total body irradiation (TBI) as a component of conditioning regimens prior to hematopoietic stem cell transplantation is performed differently by various radiotherapy centers. In general, conventional methods are predominantly applied. With the introduction of advanced irradiation techniques such as Helical TomoTherapy (HT) and Volumetric Modulated Arc Therapy (VMAT), dose-optimized total body irradiation could be realized with good target volume coverage and adequate dose reduction in organs at risk (OAR). This requires a well-coordinated team and suitable equipment capabilities. Centers similar to ours can offer HT treatment as a gold standard for highly conformal TBI. Based on the limited replacement equipment availability in case of HT device failure, we developed a method carrying out highly conformal VMAT irradiation with a linear accelerator originally suitable for radiosurgery or stereotactic radiotherapy. Using a dosimetric comparison between both modalities, we examined whether VMAT—even with linear accelerator radiosurgery technology—is capable of performing optimized conformal TBI. ABSTRACT: Modern irradiation techniques for optimized conformal TBI can be realized by Helical Tomotherapy (HT) or Volumetric Modulated Arc Therapy (VMAT), depending on the availability of suitable specialized equipment. In this dosimetric planning study, we compared both modalities and addressed the question of whether VMAT with small field sizes is also suitable as a backup in case of HT equipment malfunctions. For this purpose, we retrospectively used planning computed tomography (CT) data from 10 patients treated with HT with a total dose of 8 Gy (n = 5) or 12 Gy (n = 5) for treatment planning for VMAT with a small field size (36 × 22 cm). The target volume coverage, dose homogeneity at target volume, and dose reduction in organs at risk (OAR) (lungs, kidneys, lenses) were analyzed and compared. One patient was irradiated with both modalities due to a device failure of the HT equipment during the study, which facilitated a comparison in a real clinical setting. The findings indicate that in addition to a higher mean dose to the lenses in the 12 Gy group for VMAT and a better dose homogeneity in the target volume for HT, comparably good and adequate target dose coverage and dose reduction in the other OAR could be achieved for both modalities, with significantly longer treatment times for VMAT. In conclusion, after appropriate optimization of the treatment times, VMAT using linear accelerator radiosurgery technology can be used both as a backup in addition to HT and in clinical routines to perform optimized conformal TBI.