Volumetric reduction of brain metastases after stereotactic radiotherapy: Prognostic factors and effect on local control

Kanayama, Naoyuki; Ikawa, Toshiki

doi:10.1002/cam4.4809

Cited by 12 publications

(7 citation statements)

References 26 publications

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“…Although generally unregarded dose attenuation margin outside the prescription IDS can cover these uncertainties to some degree, an approximately 1-mm setup error likely leads to marginal tumor residues, given the generally steep dose gradient for LGK [5]. Meanwhile, recent studies also suggest that the higher proportion of GTV receiving ≥30-32 Gy in the single fraction, i.e., internal dose escalation, is likely associated with superior tumor shrinkage and LC [8,9,19]. In LGK, 50% IDS is generally used for target coverage and dose prescription in multi-shot planning, i.e., a combination of multi-isocenter, which can lead to superior tumor response, particularly if concentrically laminated steep dose increase inside the GTV boundary is achieved [5,11].…”

Section: Discussionmentioning

confidence: 99%

“…The dose fall-off outside the small GTV tends to be excessively precipitous, especially with an MLC of 2.5-mm leaf width [12]. Meanwhile, insufficient dose increase inside the GTV boundary, i.e., less inhomogeneous GTV dose, likely leads to inferior and less sustainable tumor response [15,19]. The more inhomogeneous GTV dose is prone to the steeper dose gradient outside the GTV and vice versa [7].…”

Section: Discussionmentioning

confidence: 99%

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Modified Dynamic Conformal Arcs With Forward Planning for Radiosurgery of Small Brain Metastasis: Each Double Arc and Different To-and-Fro Leaf Margins to Optimize Dose Gradient Inside and Outside the Gross Tumor Boundary

Ohtakara¹,

Suzuki²

2023

Cureus

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Dynamic conformal arcs (DCA) are a widely used technique for stereotactic radiosurgery (SRS) of brain metastases (BM) using a micro-multileaf collimator (mMLC), while the planning design and method considerably vary among institutions. In the usual forward planning of DCA, the steepness of the dose gradient outside and inside the gross tumor volume (GTV) boundary is simply defined by the leaf margin (LM) setting to the target volume edge. The dose fall-off outside the small GTV tends to be excessively precipitous, especially with an MLC of 2.5-mm leaf width, which is predisposed to the insufficient coverage of microscopic brain invasion and other inherent inaccuracies. Meanwhile, insufficient dose increase inside the GTV boundary, i.e., less inhomogeneous GTV dose, likely leads to inferior and less sustainable tumor response. The more inhomogeneous GTV dose is prone to the steeper dose gradient outside the GTV and vice versa. Herein, we describe an alternative simply modified DCA (mDCA) planning that was uniquely devised to optimize the dose gradient outside and inside the GTV boundary for further enhancing and consolidating local control of small BM.For a succinct exemplification, a 10-mm spherical target was assumed as a GTV for DCA planning using a 2.5-mm mMLC. The benchmark plan was generated by adding a 0-mm LM to the GTV edge by assigning a single fraction of 30 Gy to the isocenter, in which the GTV coverage by 24 Gy with 80% isodose surface (IDS) was 96%, i.e., D 96% , while the coverage of GTV + isotropic 2 mm volume by 18 Gy with 60% IDS was 70%, with the D 98% being 12 Gy with 40% IDS, viz., too steep dose fall-off outside the GTV boundary.Alternatively, the increase of LM with or without decreasing the isocenter dose enables the increase of the GTV + 2 mm coverage by 18 Gy while resulting in an inadequate GTV dose with either a less inhomogeneous dose or an excessive marginal dose. Meanwhile, in the newly devised mDCA planning, every single arc was converted to a double to-and-fro arc with different LM settings under the same spatial arrangement, which enabled GTV + 2 mm volume coverage with 18 Gy while preserving the GTV marginal dose and inhomogeneity similar to those for the benchmark plan. Additionally, the different collimator angle (CA) setting for the to-and-fro arcs led to further trimming of the dose conformity.The limitations of general forward planning with only adjusting the LM for every single arc were demonstrated, which can be a contributing factor for local tumor progression of small BM. Alternatively, the mDCA with each double to-and-fro arc and different LM and CA settings enables optimization of the dose gradient both outside and inside the GTV boundary according to the planners' intent, e.g., moderate dose spillage margin outside the GTV and steep dose increase inside the GTV boundary.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Modified Dynamic Conformal Arcs With Forward Planning for Radiosurgery of Small Brain Metastasis: Each Double Arc and Different To-and-Fro Leaf Margins to Optimize Dose Gradient Inside and Outside the Gross Tumor Boundary

Ohtakara¹,

Suzuki²

2023

Cureus

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“…The clinical characteristics and planning parameters of the four cases are summarized in Table 1. Differences in BED to estimate the anti-tumor effect and the corresponding physical doses in 10 fr equivalent to a single dose of 24 Gy are tabulated in Table 2 as a function of the BED model formulas and the values of the alpha/beta ratio [9]. Notably, the corresponding absolute doses in 10 fr range from 36.9 to 53.2 Gy, and the BED ranges from 48.4 to 81.6 Gy.…”

Section: Case Presentationmentioning

confidence: 99%

“…Differences in BED to estimate the anti-tumor effect and the corresponding physical doses in 10 fr equivalent to a single dose of 24 Gy are tabulated in Table 2 as a function of the BED model formulas and the values of the alpha/beta ratio [ 9 ].…”

Section: Case Presentationmentioning

confidence: 99%

“…The 10 fr SRS dose that provides an anti-tumor effect clinically equivalent to that of 24 Gy in 1 fr or yields a 1-year local TCP of ≥95% for BM of >10 cm 3 remains uncertain [6][7][8]. The most appropriate biological effective dose (BED) formula, along with an alpha/beta ratio that estimates similar anti-BM efficacy for SRS doses in 10 fr and 1 fr, has continued to be controversial [8,9].…”

Section: Introductionmentioning

confidence: 99%

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Ten-Fraction Stereotactic Radiosurgery With Different Gross Tumor Doses and Inhomogeneities for Brain Metastasis of >10 cc: Treatment Responses Suggesting Suitable Biological Effective Dose Formula for Single and 10 Fractions

Ohtakara¹,

Nakabayashi²,

Suzuki³

2023

Cureus

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Stereotactic radiosurgery (SRS) with >5 fractions (fr) has been increasingly adopted to improve local control and safety for brain metastases (BM) of >10 cm 3 , given the limited brain tolerance of SRS with ≤5 fr. However, the optimal indication and treatment design, including the prescribed dose and distribution for 10 fr SRS, remains uncertain. A single fr of 24 Gy provides approximately 95% of the one-year local tumor control probability. The potential SRS doses in 10 fr that is clinically equivalent to a single fr of 24 Gy regarding anti-tumor effect range from 48.4 to 81.6 Gy as biological effective doses (BED) as a function of the BED model formulas along with the alpha/beta ratios. The most appropriate BED formula in conjunction with an alpha/beta ratio to estimate similar anti-BM effects for single and 10 fr remains controversial.Herein, we describe four cases of symptomatic radiation-naïve BM >10 cm 3 (range, 11 to 26 cm 3 ), treated with 10 fr SRS with a standard prescribed dose of 42 Gy, for which modified dynamic conformal arcs were used with forward planning to improve dose conformity. In the first two cases with gross tumor volumes (GTV) of 15.3 and 10.9 cm 3 , 42 Gy was prescribed to 70%-80% isodose, normalized to 100% at the isocenter, which encompasses the boundary of the planning target volume: GTV + isotropic 1 mm margin. The tumor responses were initially marked regression followed by regrowth within three months in case 1 and no shrinkage with subsequent progression within three months in case 2. In the remaining two cases with larger GTVs of 19.1 and 26.2 cm 3 , the GTV boundary and 2-3 mm margin-added object volume was covered by 80% and 56% isodoses with 53 Gy and 37 Gy, respectively, to further increase the marginal and internal doses of GTV and to ensure moderate dose spillage outside the GTV, while >1-1.5 mm outside the GTV was covered by 42 Gy with 63% isodose. According to the BED based on the linear-quadratic (LQ) model with an alpha/beta ratio of 10 (BED 10 ), 53 Gy corresponds to approximately 81 Gy in BED 10 and 24 Gy in a single fr.Excellent initial maximum tumor response and subsequently sustained tumor regression (STR) were achieved in both cases. Subsequently, enlarging nodules that could not exclude the possibility of tumor regrowth were disclosed within two years, while late adverse radiation effects remained moderate.These dose-effect relationships suggest that a GTV marginal dose of ≥53 Gy with ≤80% isodose would be preferred to effect ≥1-year STR and that further dose escalation of both marginal and internal GTV may be necessary to achieve ≥2-year STR, while GTV of >25 cm 3 may be unsuitable for 10 fr SRS in terms of longterm brain tolerance. Among LQ, LQ-cubic, and LQ-linear model formulas and alpha/beta ratios of 10-20, BED 10 may be clinically most suitable to estimate a 10 fr SRS dose that provides anti-BM efficacy similar to that for a single fr.

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What is the optimal isodose line for stereotactic radiotherapy for single brain metastases using HyperArc?

Sagawa,

Ikawa,

Ohira

et al. 2024

J Applied Clin Med Phys

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PurposeThe study aimed to investigate the optimal isodose line (IDL) in linear accelerator‐based stereotactic radiotherapy for single brain metastasis, using HyperArc. We compared the dosimetric parameters for target and normal brain tissue among six plans with different IDLs.MethodsThis study included 30 patients with single brain metastasis. We retrospectively generated six plans for each tumor with different IDLs (80%, 70%, 60%, 50%, 40%, and 33%) using HyperArc. All treatment plans were normalized to the prescription dose of 35 Gy in five fractions which was covered by 95% of the planning target volume (PTV), defined by adding a 1.0 mm margin to the gross tumor volume (GTV). The dosimetric parameters were compared among the six plans.ResultsFor GTV > 0.1 cm3, the ratio of brain–GTV volumes receiving 25 Gy to PTV (V25Gy/PTV) was significantly lower at IDL 40%–70% than at IDL 80% and 33% (p < 0.01, retrospectively). For GTV < 0.1 cm3, V25Gy/PTV decreased continuously as IDL decreased. The values of D99% and D80% for GTV increased with decreasing IDL. An IDL of 50% or less was required to achieve D99% of greater than 43 Gy and D80% of greater than 50 Gy. The mean values of D99% and D80% for IDL 50% were 44.3 and 51.9 Gy.ConclusionThe optimal IDL is 40%–50% for GTV > 0.1 cm3. These lower IDLs could increase D99% and D80% of GTV while lowering V25Gy of normal brain tissue, which may help reduce the risk of radiation necrosis and improve local control.

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Volumetric reduction of brain metastases after stereotactic radiotherapy: Prognostic factors and effect on local control

Cited by 12 publications

References 26 publications

Modified Dynamic Conformal Arcs With Forward Planning for Radiosurgery of Small Brain Metastasis: Each Double Arc and Different To-and-Fro Leaf Margins to Optimize Dose Gradient Inside and Outside the Gross Tumor Boundary

Modified Dynamic Conformal Arcs With Forward Planning for Radiosurgery of Small Brain Metastasis: Each Double Arc and Different To-and-Fro Leaf Margins to Optimize Dose Gradient Inside and Outside the Gross Tumor Boundary

Ten-Fraction Stereotactic Radiosurgery With Different Gross Tumor Doses and Inhomogeneities for Brain Metastasis of >10 cc: Treatment Responses Suggesting Suitable Biological Effective Dose Formula for Single and 10 Fractions

What is the optimal isodose line for stereotactic radiotherapy for single brain metastases using HyperArc?

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