Impact of setup errors on multi‐isocenter volumetric modulated arc therapy for craniospinal irradiation

Abstract

Multi-isocenter volumetric modulated arc therapy (VMAT) is recommended for craniospinal irradiation (CSI) to smooth the dose distribution in the junction regions relying solely on inverse optimization. However, few studies have measured the dosimetric impact of setup errors on this multi-isocenter VMAT in the junction areas. The purpose of this study is to evaluate the impact of positional errors during VMAT CSI with twodimension (2D) and three-dimension (3D) dosimetric measurements. A total of 20 patients treated by three-isocenter VMAT CSI were retrospectively reviewed and analyzed. A 3D diode array ArcCHECK and radiochromic film EBT3 were applied to measure the percentage gamma passing rates (%GPs) and dose distributions in the junction areas between the cranial/upper-spinal and the upper/lower-spinal fields with intentionally introduced setup errors of ± 1 mm, ±2 mm, ±3 mm, ±5 mm, and ± 8 mm, respectively. The length and volume of planning target volume (PTV) for these CSI patients ranged from 50.14 to 80.8 cm, and 1572.3 to 2114.5 cm 3 , respectively. The %GPs for ±3 mm, ±5 mm, and ±8 mm positional errors were around 95%, 90%, and 85%, respectively, in the junction areas. The dosimetric verification results with EBT3 films indicated that cold and hot areas were observed with the increase of introduced setup errors. In conclusion, the dosimetric verification with intentionally introduced setup errors demonstrated that positional errors within 3 mm have a little impact for VMAT CSI, although setup errors should be minimized. Relying on the inverse optimization of VMAT to smooth the dose distribution in the junction areas is feasible for CSI.

Modified volumetric modulated arc therapy technique with reduced planning and treatment time for craniospinal irradiation utilising two isocentres

“…also concluded that accuracy will not be deteriorated when larger errors of >5 mm were simulated 7 . The findings of these publications 4,7,17 along with acceptable dose variation of up to 5 ‐mm positional errors supports our clinical decisions.…”

“…Zhou et al. also reports that positional errors within 3 mm have little impact on dosimetry for VMAT CSI 17 and Meyer et al. also concluded that accuracy will not be deteriorated when larger errors of >5 mm were simulated 7 .…”

“…4 Zhou et al also reports that positional errors within 3 mm have little impact on dosimetry for VMAT CSI 17 and Meyer et al also concluded that accuracy will not be deteriorated when larger errors of >5 mm were simulated. 7 The findings of these publications 4,7,17 along with acceptable dose variation of up to 5 -mm positional errors supports our clinical decisions.…”

Three-Dimensional Dosimetry by Optical-CT and Radiochromic Gel Dosimeter of a Multiple Isocenter Craniospinal Radiation Therapy Procedure

“…Zhou et al used the ArcCHECK and EBT3 film dosimeters to perform CSI plan QA, analyzing the impact of setup errors. They presented the pass rate ranging from 85% to 95% on the gamma analysis with 3% dose deviation and multiples distance to agreement (1 mm to 8 mm) criteria [ 30 ]. Nguyen et al used an electronic portal-imaging device panel as the detector and EPIDQA software with gamma analysis 3%/3 mm and accuracy above 90% as the pass criteria.…”

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

“…Modern TPSs allow the combined optimization of multiple isocentres and, thus, homogeneity constraints will automatically include junction areas. This issue has been extensively addressed in the context of CSI, which has even more challenging homogeneity requirements (296)(297)(298). Special complexity in TBI results from isocentre extension over two separate datasets with different patient orientations.…”