Interinstitutional Plan Quality Assessment of 2 Linac-Based, Single-Isocenter, Multiple Metastasis Radiosurgery Techniques

Abstract

Purpose: Interest and application of stereotactic radiosurgery for multiple brain metastases continue to increase. Various planning systems are available for linear accelerator (linac)ebased single-isocenter multiple metastasis radiosurgery. Two of the most advanced systems are BrainLAB Multiple Metastases Elements (MME), a dynamic conformal arc (DCA) approach, and Varian RapidArc (RA), a volumetric modulated arc therapy (VMAT) approach. In this work, we systematically compared plan quality between the 2 techniques. Methods and Materials: Thirty patients with 4 to 10 metastases (217 total; median 7.5; V min Z 0.014 cm 3 ; V max Z 17.73 cm 3 ) were planned with both Varian RA and MME at 2 different institutions with extensive experience in each respective technique. All plans had a single isocenter and used Varian linac equipped with high-definition multileaf collimator. RA plans used 2 to 4 noncoplanar VMAT arcs with 10 MV flattening filter-free beam. MME plans used 4 to 9 noncoplanar DCAs and 6 MV flattening filter-free beam, (minimum planning target volume [PTV min] Z 0.49 cm 3 ; PTV max Z 27.32 cm 3 ; PTV median Z 7.05 cm 3 ). Prescriptions were 14 to 24 Gy in a single fraction. Target coverage goal was 99% of volume receiving prescription dose (D99% ! 100%). Plans were evaluated by Radiation Therapy Oncology Group/Paddick conformity index (CI) score, 12 Gy volume (V 12Gy ), V 8Gy , V 5Gy , mean brain dose (D mean ), and beam-on time.Results: Conformity was favorable among RA plans (median: MME CI RTOG Z 1.38; RA CI RTOG Z 1.21; P < .0001). V 12Gy and V 8Gy were lower for RA plans (median: MME V12 Z 23.7 cm 3 ; RA V12 Z 19.2 cm 3 ; P Z .0001; median: MME V 8Gy Z 53.6 cm 3 ; RA V 8Gy Z 44.1 cm 3 ; P Z .024). V 5Gy was lower for MME plans (median: MME V 5Gy Z 141.4 cm 3 ; RA V 5Gy Z 142.8 cm 3 ; P Z .009). Mean brain was lower for MME plans (median: MME D mean Z 2.57 Gy; RA D mean Z 2.76 Gy; P < .0001). Conclusions: For linac-based multiple metastasis stereotactic radiosurgery, RapidArc VMAT facilitates favorable conformity and V 12Gy /V 8Gy volume compared with the MME DCA plan. MME planning facilitates reduced dose spill at levels V 5Gy .

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.…”

“… 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. 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.…”

The development and testing of a novel spherical radiotherapy phantom system for the commissioning and patient‐specific quality assurance of mono‐isocentric multiple mets SRS plans

“…The phantom setups, prescribed doses, plane override distances, and gamma pass-rates are listed in Table II. The software successfully computed all geometric phantom setups and was able to accurately extract the relevant dose plane for each measurement geometry at the chosen planar resolution of 0.5 9 0.5 mm 2 .…”

“…This approach can significantly spare the dose to normal brain tissue while simultaneously delivering a therapeutic dose to a multitude of target volumes. 2 This delivery technique is in contrast to the more classical practice of treating a limited number of targets (<3-4) by placing each target sequentially to the machine isocenter. Indeed, in most cases treatment plans utilizing a mono-isocentric approach will have no target present at the isocenter of the machine during treatment delivery.…”

“…In the mLSRS treatment approach, many targets are assigned to be treated using a single isocenter. This approach can significantly spare the dose to normal brain tissue while simultaneously delivering a therapeutic dose to a multitude of target volumes 2 . This delivery technique is in contrast to the more classical practice of treating a limited number of targets (<3–4) by placing each target sequentially to the machine isocenter.…”