Single isocenter stereotactic radiosurgery for patients with multiple brain metastases: dosimetric comparison of VMAT and a dedicated DCAT planning tool

Abstract

Background In this dosimetric study, a dedicated planning tool for single isocenter stereotactic radiosurgery for multiple brain metastases using dynamic conformal arc therapy (DCAT) was compared to standard volumetric modulated arc therapy (VMAT). Methods Twenty patients with a total of 66 lesions who were treated with the DCAT tool were included in this study. Single fraction doses of 15–20 Gy were prescribed to each lesion. Patients were re-planned using non-coplanar VMAT. Number of monitor units as well as V 4Gy , V 5Gy and V 8Gy were extracted for every plan. Using a density-based clustering algorithm, V 10Gy and V 12Gy and the volume receiving half of the prescribed dose were extracted for every lesion. Gradient indices and conformity indices were calculated. The correlation of the target sphericity, a measure of how closely the shape of the target PTV resembles a sphere, to the difference in V 10Gy and V 12Gy between the two techniques was assessed using Spearman’s correlation coefficient. Results The automated DCAT planning tool performed significantly better in terms of all investigated metrics ( p < 0.05), in particular healthy brain sparing (V 10Gy : median 3.2 cm 3 vs. 4.9 cm 3 ), gradient indices (median 5.99 vs. 7.17) and number of monitor units (median 4569 vs. 5840 MU). Differences in conformity indices were minimal (median 0.75 vs. 0.73) but still significant ( p < 0.05). A moderate correlation between PTV sphericity and the difference of V 10Gy and V 12Gy between the two techniques was found (Spearman’s rho = 0.27 and 0.30 for V 10Gy and V 12Gy , respectively, p < 0.05). Conclusions The dedicated DCAT planning tool performed better than VMAT in terms of healthy brain sparing and treatment efficiency, in particular for nearly spherical lesions. In contrast, VMAT can be superior in cases with irregularly shaped lesions.

Recent advances in Surface Guided Radiation Therapy

“…Therefore, it is essential to treat the BM with smaller treatment margins, which requires a 6DOF correction under the guidance of on-board CBCT and a thermoplastic mask [ 46 ]. This improved patient setup makes it possible to treat multiple lesions with a single isocenter, which in combination with flattening filter free (FFF) beams can further decrease the beam-on time [ 47 , 48 ].…”

Stereotactic radiosurgery combined with targeted/ immunotherapy in patients with melanoma brain metastasis

“…Besides, the risk of RN also increases with the increasing tumor volume and with the consequently rising PTV, V10 and V12 volume [28,29]. The latest study reported that multiple brain metastases (up to 10 metastases and maximum diameter of 2.5 cm) could be treated in single fraction SRS, which offered an option not just to defer WBRT but also to start TT/IT expeditiously in patients with metastatic melanoma [35,36]. The limitation of our study is its retrospective characters with small numbers of patients including a heterogeneous patient population.…”

Initial Experience With Single-Isocenter Radiosurgery to Target Multiple Brain Metastases Using an Automated Treatment Planning Software: Clinical Outcomes and Optimal Target Volume Margins Strategy

“…Median conformity index and gradient index, which are commonly used to describe SRS quality planning, were 1.32 and 3.94, respectively, consistent with those reported in other published studies using either DCA or VMAT techniques. 8 , 9 , 10 , 11 , 12 , 13 , 28 , 29 , 30 In a comparative study of SIMT DCA and VMAT SRS plans generated by the commercially available automated planning software Multiple Brain Metastases (Brainlab) and HyperArc (Varian), respectively, Ruggeri et al 29 observed comparable high plan quality in 20 patients with 2 to 10 BM, although the conformity index was slightly better for VMAT plans. In another study comparing SIMT DCA to VMAT SRS plans in 30 patients with 4 to 10 BM, Liu et al 30 showed that the VMAT technique resulted in better conformity and V12Gy-8Gy volumes; in contrast, other studies suggest that DCA plans perform better than VMAT in terms of healthy brain sparing and treatment efficiency.…”

“…In another study comparing SIMT DCA to VMAT SRS plans in 30 patients with 4 to 10 BM, Liu et al 30 showed that the VMAT technique resulted in better conformity and V12Gy-8Gy volumes; in contrast, other studies suggest that DCA plans perform better than VMAT in terms of healthy brain sparing and treatment efficiency. 13 , 28 Although such indexes remain of interest to assess the dosimetric quality of treatment plans, the correlation between planning quality and clinical outcomes remains to be clarified, 31 and the superiority of one technique over another in terms of plan quality metrics is unsustained.…”