PMC9899121_01
Magnetic resonance images for 10-fraction stereotactic radiosurgery planning.. The images show contrast-enhanced (CE) T1-weighted images (T1-WI) (A-C, G-I); T2-weighted images (T2-WI) (D-F, J-L); axial images (A, D, G, J); coronal images (B, E, H, K); and sagittal images (C, F, I, L).. (A-F) A cystic lesion (arrow in A) in the left parietal lobe is associated with massive surrounding edema and fluid sedimentation within the cyst (dashed arrow in D). The ventral side of the lesion is near the lateral ventricular wall (arrow in F). (G-I, J-L) A cystic lesion (arrow in G) in the pons with mild perilesional edema.
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FIG1
Imaging studies showed two cystic-enhancing lesions located in the left parietal lobe and pons, with a maximum diameter of 41 mm and 16 mm, respectively (Figures 1A-1L). Each gross tumor volume (GTV), 19.93 cm3 and 1.09 cm3, was defined as encompassing the contrast-enhancing lesion that was almost consistent with the visible mass on T2-weighted images (T2-WI) (Figures 1A-1L, 3A-3F). T2-WI, the GTV is defined as an enhancing lesion, as mentioned above (Figures 1A-1L, 3A-3F).
Principles of dose prescription and distribution design for 10-fraction stereotactic radiosurgery of brain metastases.. The most prioritized foundation for dose distribution design is the gross tumor volume (GTV) boundary, not the margin-added planning target volume (PTV). The dose prescription is based on the biologically effective dose (BED) derived from the linear-quadratic formula with an alpha/beta ratio of 10 (BED10) and three-tiered dose gradient optimization both just outside and inside the GTV boundary. The GTV margin was covered by 53 Gy, with a BED10 of >=80 Gy, which was highly prioritized. To ensure a moderate, not too steep or gradual, dose spillage (attenuation) margin outside the GTV boundary, 2-3 mm outside the GTV margin was covered by 37 Gy, with a BED10 of  50 Gy. To attain a concentrically laminated steep dose increase inside the GTV boundary, 2 mm inside the GTV margin was covered by >=62 Gy, with a BED10 of >=100 Gy, by intentionally increasing the centrum dose by >=71 Gy, a BED10 of >=120 Gy. The BED10 values of 37, 53, 62, and 71 Gy correspond to 50.7, 81.1, 100.4, and 121.4 Gy, respectively. The constancy of the maximum dose or % isodose of 53 Gy, that is, the degree of GTV dose inhomogeneity, is considered insignificant, with the variations being allowed up to approximately 106 Gy at the maximum dose.
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FIG2
Through multi-disciplinary deliberation, these BMs were initially treated with 10 fr of SRS (Figures 2, 3A-3F, and Table 1). Each gross tumor volume (GTV), 19.93 cm3 and 1.09 cm3, was defined as encompassing the contrast-enhancing lesion that was almost consistent with the visible mass on T2-weighted images (T2-WI) (Figures 1A-1L, 3A-3F). T2-WI, the GTV is defined as an enhancing lesion, as mentioned above (Figures 1A-1L, 3A-3F). The dose gradient optimization strategies just outside and inside the GTV boundary are described in Figure 2. (3) To minimize the risk of radiation injury, various flexible dose fr (3-15 fr, mainly 3, 5, 8, and 10 fr) were subtilized according to the GTV size, location, and the distances between multiple targets to reduce the susceptibility to dose interference.
Target definitions, planned dose distributions, and dose-volume histograms.. The images show the parietal lesion (A-C); the pons lesion (D-F); target definitions including gross tumor volume (GTV) and two other objects for dose evaluation (A, D); planned dose distributions (B, E); and dose-volume histograms (C, F).
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FIG3
Through multi-disciplinary deliberation, these BMs were initially treated with 10 fr of SRS (Figures 2, 3A-3F, and Table 1). Each gross tumor volume (GTV), 19.93 cm3 and 1.09 cm3, was defined as encompassing the contrast-enhancing lesion that was almost consistent with the visible mass on T2-weighted images (T2-WI) (Figures 1A-1L, 3A-3F). T2-WI, the GTV is defined as an enhancing lesion, as mentioned above (Figures 1A-1L, 3A-3F).
Irradiated isodose volumes compared to each gross tumor volumes before stereotactic radiosurgery and at 10 fractions.. The images show (A) the parietal lesion and (B) the pons lesion. The irradiated isodose volumes (IIV) are the total volumes, including the gross tumor volume (GTV) and surrounding brain, receiving at least the corresponding doses. The dashed lines show the IIV and dose corresponding to each GTV.
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FIG4
T2-weighted images obtained two days before stereotactic radiosurgery, at 5 and 10 fractions.. The images show (A) the actual schedule for fractionated SRS (fSRS) and MRI acquisition; (B-J) the parietal lesion; (K-S) the pons lesion; (B-G, K-P) axial images; (H-J, Q-S) sagittal images; (B, E, H, K, N, Q) before fSRS (pre); (C, F, I, L, O, R) at 5 fraction (fr); and (D, G, J, M, P, S) at 10 fr.. These T2-weighted image datasets were co-registered to the dedicated workstation, MIM MaestroTM (Cleveland, OH: MIM Software) and then fused to coincide with each other through the cranium. The pre-fSRS GTVs were contoured in red and green for the axial and sagittal images, respectively. In the parietal lesion, slight dorsomedial displacement of the lesion along with disappearance of the preexisting fluid sedimentation (arrows in E, H) was observed at 5 fr (dashed arrows in F, I). At 10 fr, a 39% (7.71 cm3) reduction in the GTV (19.93 to 12.22 cm3) and dorsomedial shifting of the tumor center were noted along with an improvement in the mass effect. Slight evisceration of the GTV dorsomedially from the initial dimensions was found ad eundem at 5 and 10 fr. In the pons lesion, no significant change was observed, apart from regression of the mild surrounding edema.
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FIG5
In contrast, the pons lesion showed no notable change during fSRS (Figures 5A-5S), gradual tumor shrinkage over several months, and nearly complete remission at 7.5 months with its sustainment at 30.5 months (Figures 8A-8J).
Serial magnetic resonance images for brain metastasis in the left parietal lobe.. The images show (A-E, K-O) axial CE-T1-WI; (F-J, P-T) axial T2-WI; (A, F) before fSRS (pre); (B, G) at 1.7 months (mo); (C, H) at 4.3 months; (D, I) at 10.5 months; (E, J) at 13.5 months; (K, P) at 14.5 months; (L, Q) at 16.7 months; (M, R) at 17.3 months; (N, S) at 19 months; (O, T) at 30.5 months. These serial image datasets were co-registered and fused on MIM MaestroTM (Cleveland, OH: MIM Software). The volumes of the visible mass on CE-T1-WI and/or T2-WI at 4.3 and 17.3 months are 0.94 and 3.19 cm3, respectively. At 13.5 months, increased enhancement (arrow in E) and a cystic change (arrow in J) are noted at the ventral and dorsal part of the remnant lesion, respectively.. CE: contrast-enhanced; T1-WI: T1-weighted image; T2-WI: T2-weighted image
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FIG6
At 23.2 months, MRI revealed slight enlargement of the ventral enhancement near the cavity, without subsequent aggravation at 30.5 months (Figures 6A-6T).
Discrepancy between planned and actually absorbed doses at the completion of stereotactic radiosurgery and its comparison with magnetic resonance images before lesionectomy.. Axial images (A-D, G, H); sagittal images (E, F); T2-WI (A, B, E-H); CE-T1-WI (C, D); before fSRS (pre) (A, E); at 10 fr (B, F); at 17.3 months after fSRS, just before craniotomy (C, D, G, H). Planned representative isodose lines are superimposed onto T2-WI (A, B, E, F). Of note, the maximum dose to the adjacent brain parenchyma finally increased up to 7.5 Gy per fraction at the ventral side of the GTV (B, F). On T2-WI, the dorsal low-intensity stable remnant (highlighted in light blue, arrow in D) and the ventral iso-intensity blurry-demarcated enlarging component (orange, dashed arrow in D) are contrasting.. CE: contrast-enhanced; T1-WI: T1-weighted image; T2-WI: T2-weighted image
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FIG7
T2-WI. These findings were significantly correlated with the dynamic dosimetric changes in the surrounding brain, as well as the GTV during fSRS (Figures 7A-7H).
Serial magnetic resonance images for brain metastasis in the pons.. The images show (A-E) axial CE-T1-WI; axial T2-WI (F-J); before fSRS (pre) (A, F); at 1.7 months (mo) after fSRS (B, G); at 4.3 months (C, H); at 7.5 months (D, I); and at 30.5 months (E, J). These serial image datasets were co-registered and fused on MIM MaestroTM (Cleveland, OH: MIM Software).. CE: contrast-enhanced; T1-WI: T1-weighted image; T2-WI: T2-weighted image
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FIG8
In contrast, the pons lesion showed no notable change during fSRS (Figures 5A-5S), gradual tumor shrinkage over several months, and nearly complete remission at 7.5 months with its sustainment at 30.5 months (Figures 8A-8J).