title: IMRT or 3D-CRT in glioblastoma? A dosimetric criterion for patient selection.
abstract: Intensity modulated radiation therapy (IMRT) is increasingly employed in glioblastoma (GBM) treatment. The present work aimed to assess which clinical-dosimetric scenario could benefit the most from IMRT application, with respect to three-dimensional conformal radiation therapy (3D-CRT). The number of organs at risk (OARs) overlapping the planning target volume (PTV) was the parameter describing the clinical-dosimetric pattern. Based on the results, a dosimetric decision criterion to select the most appropriate treatment technique is provided. Seventeen previously irradiated patients were retrieved and re-planned with both 3D-CRT and IMRT. The prescribed dose was 60 Gy/30fx. The cases were divided into 4 groups (4 patients in each group). Each group represents the scenario where 0, 1, 2 or 3 OARs overlapped the target volume, respectively. Furthermore, in one case, 4 OARs overlapped the PTV. The techniques were compared also in terms of irradiated healthy brain tissue. The results were evaluated by paired t-test. IMRT always provided better target coverage (V95%) than 3D-CRT, regardless the clinical-dosimetric scenario: difference ranged from 0.82% (p = 0.4) for scenario 0 to 7.8% (p = 0.02) for scenario 3, passing through 2.54% (p = 0.18) and 5.93% (p = 0.08) for scenario 1 and 2, respectively. IMRT and 3D-CRT achieved comparable results in terms of dose homogeneity and conformity. Concerning the irradiation of serial-kind OARs, both techniques provided nearly identical results. A statistically significant dose reduction to the healthy brain in favor of IMRT was scored. IMRT seems a superior technique compared to 3D-CRT when there are multiple overlaps between OAR and PTV. In this scenario, IMRT allows for a better target coverage while maintaining equivalent OARs sparing and reducing healthy brain irradiation. The results from our patients dataset suggests that the overlap of three OARs can be used as a dosimetric criterion to select which patients should receive IMRT treatment.
authors.affiliation: Agenzia Provinciale per la Protonterapia, Trento, Italy. lorentini@atrep.it.
authors.forename: S
authors.initials: S
authors.lastname: Lorentini
authors.forename: D
authors.initials: D
authors.lastname: Amelio
authors.forename: M G
authors.initials: MG
authors.lastname: Giri
authors.forename: F
authors.initials: F
authors.lastname: Fellin
authors.forename: G
authors.initials: G
authors.lastname: Meliado
authors.forename: A
authors.initials: A
authors.lastname: Rizzotti
authors.forename: M
authors.initials: M
authors.lastname: Amichetti
authors.forename: M
authors.initials: M
authors.lastname: Schwarz
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D001933:Brain Stem / Q000528:radiation effects; D003661:Decision Support Techniques; D019583:Dose Fractionation, Radiation; D005909:Glioblastoma / Q000532:radiotherapy* / Q000601:surgery; D006801:Humans; D009897:Optic Chiasm / Q000528:radiation effects; D058958:Organs at Risk / Q000528:radiation effects*; D018579:Patient Selection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D018714:Radiotherapy, Adjuvant; D050397:Radiotherapy, Intensity-Modulated