Whole-ventricular irradiation for intracranial germ cell tumors: Dosimetric comparison of pencil beam scanned protons, intensity-modulated radiotherapy and volumetric-modulated arc therapy

Abstract

Background: Whole-ventricular radiotherapy (WV-RT) followed by a boost to the tumor bed (WV-RT/TB) is recommended for intracranial germ cell tumors (IGCT). As the critical brain areas are mainly in the target volume vicinity, it is unclear if protons indeed substantially spare neurofunctional organs at risk (NOAR). Therefore, a dosimetric comparison study of WV-RT/TB was conducted to assess whether proton or photon radiotherapy achieves better NOAR sparing. Methods: Eleven children with GCT received 24 Gy(RBE) WV-RT and a boost up to 40 Gy(RBE) in 25 fractions of 1.6 Gy(RBE) with pencil beam scanning proton therapy (PBS-PT). Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans were generated for these patients. NOAR were delineated and treatment plans were compared for target volume coverage (TVC), homogeneity index (HI), inhomogeneity coefficient (IC) and (N)OAR sparing. Results: TVC was comparable for all three modalities. Compared to IMRT and VMAT, PBS-PT showed statistically significant optimized IC, as well as dose reduction, among others, in mean and integral dose to the: normal brain (-35.2%,-32.7%; À35.2%,-33.0%, respectively), cerebellum (-53.7%,-33.1%;-53.6%,-32.7%) and right temporal lobe (-14.5%, À31.9%; À14.7%, À29.9%). The Willis' circle was better protected with PBS-PT than IMRT (À7.1%; À7.8%). The left hippocampus sparing was higher with IMRT. Compared to VMAT, the dose to the hippocampi, amygdalae and temporal lobes was significantly decreased in the IMRT plans. Conclusions: Dosimetric comparison of WV-RT/TB in IGCT suggests PBS-PT's advantage over photons in conformality and NOAR sparing, whereas IMRT's superiority over VMAT, thus potentially minimizing long-term sequelae.

Proton versus Photon Radiotherapy for Pediatric Central Nervous System Malignancies: A Systematic Review and Meta-Analysis of Dosimetric Comparison Studies

“…Boehling compared mean and maximum doses to vascular structures of the circle of Willis between PBT (with both 3D-PBT and IMPT) and IMRT, confirming the dosimetric advantages of protons [10]. In the study by Correia, only the mean dose to the circle of Willis was reduced by PBT as compared to IMRT and VMAT [11].…”

“…Globally, three studies [11, 14, 17] provided useful dosimetric data for extracranial OARs of the cephalic district: mean left lens dose, maximum left lens doses, and mean doses to lacrimal glands were significantly improved in PBT plans (Figure 5). Three supplementary studies [15, 18, 19] assessed dosimetry of cervical, thoracic, and abdominal OARs: mean doses to the esophagus, thyroid, lungs, and liver were significantly improved with PBT, while no significant overall advantage for the kidneys was observed ( P =0.11) (Figure 5).…”

“…Single studies reporting dosimetric comparisons for the heart mean dose [19], right lens mean dose [14], and optic chiasm and pituitary and lacrimal gland maximum doses [11] substantially confirmed the advantages of PBT over photon RT (see Supplementary Materials) (), with the exception of pituitary gland Dmax in Correia's study [11]. Boehling compared mean and maximum doses to vascular structures of the circle of Willis between PBT (with both 3D-PBT and IMPT) and IMRT, confirming the dosimetric advantages of protons [10].…”

“…In our meta-analyses for intracranial and extracranial OARs, we specifically evaluated dosimetric data of OARs involved in neurogenesis (hippocampus [10, 11, 27]), sensory functions (optic chiasm, lens, retina, lacrimal gland, and cochlea), endocrine functions (pituitary gland and thyroid), neurocognition (hippocampus, normal brain, and brainstem), and tissues exposed to SMNs risk (normal brain tissue and brainstem [10, 11]) or late toxicity (circle of Willis for cerebrovascular disease [10, 11] and esophagus, thyroid, heart, lungs, liver, and kidneys).…”

Proton therapy for brain tumours in the area of evidence-based medicine

“…Even for very complex target volumes ( Figure 2) involving large parts of the brain, such in whole-ventricular RT for intracranial germ cell tumours, a dosimetric comparison study showed an approximately one-third reduction in integral dose to the brain, and also a better sparing of the circle of Willis with PT. 11 This may be clinically significant, as radiation dose delivered to the circle of Willis was recently proposed as the best predictor of stroke in childhood brain cancer survivors. 12 Moreover the dosimetric advantage is particularly striking for large target volumes, such in the case of craniospinal irradiation (CSI), where PT is able to completely spare OARs anterior to the vertebrae, as it is demonstrated in Figure 1b.…”