HyperArc VMAT planning for single and multiple brain metastases stereotactic radiosurgery: a new treatment planning approach

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PurposeIn stereotactic radiosurgery (SRS) with single‐isocentric treatments for brain metastases, rotational setup errors may cause considerable dosimetric effects. We assessed the dosimetric effects on HyperArc plans for single and multiple metastases.MethodsFor 29 patients (1–8 brain metastases), HyperArc plans with a prescription dose of 20–24 Gy for a dose that covers 95% (D95%) of the planning target volume (PTV) were retrospectively generated (Ref‐plan). Subsequently, the computed tomography (CT) used for the Ref‐plan and cone‐beam CT acquired during treatments (Rot‐CT) were registered. The HyperArc plans involving rotational setup errors (Rot‐plan) were generated by re‐calculating doses based on the Rot‐CT. The dosimetric parameters between the two plans were compared.ResultsThe dosimetric parameters [D99%, D95%, D1%, homogeneity index, and conformity index (CI)] for the single‐metastasis cases were comparable (P > 0.05), whereas the D95% for each PTV of the Rot‐plan decreased 10.8% on average, and the CI of the Rot‐plan was also significantly lower than that of the Ref‐plan (Ref‐plan vs Rot‐plan, 0.93 ± 0.02 vs 0.75 ± 0.14, P < 0.01) for the multiple‐metastases cases. In addition, for the multiple‐metastases cases, the Rot‐plan resulted in significantly higher V10Gy (P = 0.01), V12Gy (P = 0.02), V14Gy (P = 0.02), and V16Gy (P < 0.01) than those in the Ref‐plan.ConclusionThe rotational setup errors for multiple brain metastases cases caused non‐negligible underdosage for PTV and significant increases of V10Gy to V16Gy in SRS with HyperArc.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dosimetric effect of rotational setup errors in stereotactic radiosurgery with HyperArc for single and multiple brain metastases

Sagawa

Ohira

Ueda

et al. 2019

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“…With the recent introduction of commercial single‐isocenter planning algorithms for simultaneously treating multiple brain metastases, either using automated dynamic conformal arcs or automated VMAT, more dosimetric comparison to GK is required. These studies have already demonstrated a reduction in monitor units compared with conventional VMAT.…”

Section: Discussionmentioning

confidence: 99%

GammaKnife versus VMAT radiosurgery plan quality for many brain metastases

Potrebko

Keller

All

et al. 2018

The purpose of this work was to compare dose distributions between two radiosurgery modalities, single‐isocenter volumetric modulated arc therapy (VMAT), and GammaKnife Perfexion (GK), in the treatment of a large number (≥7) of brain metastases. Twelve patients with 103 brain metastases were analyzed. The median number of targets per patient was 8 (range: 7–14). GK plans were compared to noncoplanar VMAT plans using both 6‐MV flattening filter‐free (FFF) and 10‐MV FFF modes. Parameters analyzed included radiation therapy oncology group conformity index (CI), 12, 6, and 3 Gy isodose volumes (V12 Gy, V6 Gy, V3 Gy), mean and maximum hippocampal dose, and maximum skin dose. There were statistically significant differences in CI (2.5 ± 1.6 vs 1.6 ± 0.8 and 1.7 ± 0.9, P < 0.001, P < 0.001), V12 Gy (2.8 ± 6.1 cc vs 3.0 ± 5.2 cc and 3.1 ± 5.4 cc, P = 0.003, P < 0.001), and V3 Gy (323.0 ± 294.8 cc vs, 880.1 ± 369.1 cc and 937.9 ± vs 361.9 cc, P = 0.005, P = 0.001) between GK versus both 6‐MV FFF and 10‐MV FFF. No significant differences existed for maximum hippocampal or skin doses. In conclusion, highly optimized VMAT produced improved conformity at the expense of a higher V12 Gy and V3 Gy volume when compared with highly optimized GK.

“…The TrueBeam (Varian Medical Systems) is one of the latest generations of linacs. This machine and recent technologies have enabled reduction of the treatment time by use of flattening filter‐free (FFF) beams, volumetric‐modulated arc therapy, and linac‐based single‐isocenter noncoplanar techniques . Although a few studies have investigated the inter‐unit variability of the TrueBeam, none has yet explored very small‐field (≤10 mm) dosimetry of the TrueBeam.…”

Section: Introductionmentioning

confidence: 99%

Small‐field dosimetry of TrueBeam^TM flattened and flattening filter‐free beams: A multi‐institutional analysis

Akino

Mizuno

Isono

et al. 2019

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Purpose: Detector-dependent interinstitutional variations of the beam data may lead to uncertainties of the delivered dose to patients. Here we evaluated the interunit variability of the flattened and flattening filter-free (FFF) beam data of multiple TrueBeam (Varian Medical Systems) linear accelerators focusing on the small-field dosimetry.Methods: The beam data of 6-and 10-MV photon beams with and without flattening filter measured for modeling of an iPLAN treatment planning system (BrainLAB) were collected from 12 institutionsten HD120 Multileaf Collimator (MLC) and two Millennium120 MLC. Percent-depth dose (PDD), off-center ratio (OCR), and detector output factors (OF det ) measured with different detectors were evaluated.To investigate the detector-associated effects, we evaluated the inter-unit variations of the OF det before and after having applied the output correction factors provided by the International Atomic Energy Agency (IAEA) Technical Reports Series no. 483.Results: PDD measured with a field size of 5 × 5 mm 2 showed that the data measured using an ionization chamber had variations exceeding 1% from the median values. The maximum difference from median value was 2.87% for 10 MV photon beam. The maximum variations of the penumbra width for OCR with 10 × 10 mm 2 field size were 0.97 mm. The OF det showed large variations exceeding 15% for a field size of 5 × 5 mm 2 . When the output correction factors were applied to the OF det , the variations were greatly reduced. The relative difference of almost all field output factors were within ± 5% from the median field output factors. Conclusion:In this study, the inter-unit variability of small-field dosimetry was evaluated for TrueBeam linear accelerators. The variations were large at a field size of 5 × 5 mm 2 , and most occurred in a detector-dependent manner.