case_images: PMC11821596_01
case_images: (A, B) Axial magnetic resonance contrast-enhanced T2/FLAIR image sequence prior to the first tumor resection showed a nonenhancing cystic lesion in the left temporal lobe, suspicious for diffuse low-grade glioma. The tumor measured 5 x 4 x 5 centimeters in its largest dimension. (C, D) Axial magnetic resonance contrast-enhanced T2/FLAIR image sequence three months after completion of proton beam therapy. A new 15 x 13 x 11 millimeters nonenhancing lesion, highly suspicious of distant neoplastic recurrence in the left subcortical, parasagittal left limbic area was found. The appearance of the lesion was relatively well-defined and expansive, and it was located 46 millimeters from the resection cavity.
case_images: fonc-15-1397912-g001.jpg
case_images: PMC11821596_03_fonc-15-1397912-g001.jpg
case_images: f1
case_images: The first postradiation MRI undertaken three months after completion of radiotherapy showed stable disease in the primary tumor area; however, surprisingly, with a new nonenhancing lesion in the left anterior cingulate gyrus measuring 15 x 13 x 11 millimeters (mm;  Figures 1C, D ).
case_images: PMC11821596_02
case_images: PMC11821596_03
case_images: (A, B) Axial magnetic resonance contrast-enhanced T2/FLAIR image sequence prior to the first tumor resection showed a nonenhancing cystic lesion in the left temporal lobe, suspicious for diffuse low-grade glioma. The tumor measured 5 x 4 x 5 centimeters in its largest dimension. (C, D) Axial magnetic resonance contrast-enhanced T2/FLAIR image sequence three months after completion of proton beam therapy. A new 15 x 13 x 11 millimeters nonenhancing lesion, highly suspicious of distant neoplastic recurrence in the left subcortical, parasagittal left limbic area was found. The appearance of the lesion was relatively well-defined and expansive, and it was located 46 millimeters from the resection cavity.
case_images: fonc-15-1397912-g001.jpg
case_images: PMC11821596_03_fonc-15-1397912-g001.jpg
case_images: f1
case_images: The first postradiation MRI undertaken three months after completion of radiotherapy showed stable disease in the primary tumor area; however, surprisingly, with a new nonenhancing lesion in the left anterior cingulate gyrus measuring 15 x 13 x 11 millimeters (mm;  Figures 1C, D ).
case_images: Beam angles for the patient's proton plan in relation to the original gross target volume (GTV, orange), clinical target volume (CTV, red), and the location of the new lesion suspicious of a recurrence (brown). (A) displays the field with 320 gantry degree and a 90 couch degree, (B) the second field with a 70 gantry degree and a couch degree of 10, and (C) the third beam with a gantry degree of 100 and a couch degree of 0.
case_images: fonc-15-1397912-g002.jpg
case_images: PMC11821596_03_fonc-15-1397912-g002.jpg
case_images: f2
case_images: Apart from this, the new lesion appeared highly suspicious for a distant recurrence of the IDH-mutant astrocytoma.  Figure 2  illustrates the radiotherapy beam angles in relation to the original GTV and CTV, as well as the location of the new lesion which was radiologically deemed suspicious of a recurrence.
case_images: PMC11821596_04
case_images: The patient's proton plan showing isodose levels and radiotherapy target volumes. The resection cavity after primary surgery and the suspected residual tumor were delineated as gross target volume (GTV, orange). A margin of 15 mm was added to GTV to define the clinical target volume (CTV, red), which was also modified against natural anatomical barriers. The new lesion found by MRI three months after proton therapy was retrospectively delineated (brown, arrows) to calculate dose levels in the region of the lesion. The 51.4 Gray (Gy) (95%) isodose line is shown in yellow, 43.3 Gy (80%) in purple, 27.1 Gy (50%) in green, and 13.5 Gy (25%) in turquoise.
case_images: fonc-15-1397912-g003.jpg
case_images: PMC11821596_04_fonc-15-1397912-g003.jpg
case_images: f3
case_images: Retrospectively, D98% (radiotherapy dose received by 98%) of the new lesion was estimated to be 15 Gy RBE ( Figure 3 ); however, parts of the new lesion had received up to 50 Gy RBE.
case_images: PMC11821596_05
case_images: The patient's timeline. CNS, central nervous system; GTR, gross total resection, Gy, Gray; IDH, isocitrate dehydrogenase; mo, month; mos, months; MRI, magnetic resonance imaging; RBE, relative biological effectiveness; TMZ, temozolomide; WHO, World Health Organization.
case_images: fonc-15-1397912-g004.jpg
case_images: PMC11821596_05_fonc-15-1397912-g004.jpg
case_images: f4
case_images: Figure 4 . Fortunately, the patient has no sequelae following surgery.