ABSTRACT
BACKGROUND: To evaluate the role of RapidArc (RA) for stereotactic radiosurgery (SRS) of benign brain lesions in comparison to GammaKnife (GK) based technique. METHODS: Twelve patients with vestibular schwannoma (VS, n = 6) or cavernous sinus meningioma (CSM, n = 6) were planned for both SRS using volumetric modulated arc therapy (VMAT) by RA. 104 MV flattening filter free photon beams with a maximum dose rate of 2400 MU/min were selected. Data were compared against plans optimised for GK. A single dose of 12.5 Gy was prescribed. The primary objective was to assess treatment plan quality. Secondary aim was to appraise treatment efficiency. RESULTS: For VS, comparing best GK vs. RA plans, homogeneity was 51.7 ± 3.5 vs. 6.4 ± 1.5%; Paddick conformity Index (PCI) resulted 0.81 ± 0.03 vs. 0.84 ± 0.04. Gradient index (PGI) was 2.7 ± 0.2 vs. 3.8 ± 0.6. Mean target dose was 17.1 ± 0.9 vs. 12.9 ± 0.1 Gy. For the brain stem, D(1cm3) was 5.1 ± 2.0 Gy vs 4.8 ± 1.6 Gy. For the ipsilateral cochlea, D(0.1cm3) was 1.7 ± 1.0 Gy vs. 1.8 ± 0.5 Gy. For CSM, homogeneity was 52.3 ± 2.4 vs. 12.4 ± 0.6; PCI: 0.86 ± 0.05 vs. 0.88 ± 0.05; PGI: 2.6 ± 0.1 vs. 3.8 ± 0.5; D(1cm3) to brain stem was 5.4 ± 2.8 Gy vs. 5.2 ± 2.8 Gy; D(0.1cm3) to ipsi-lateral optic nerve was 4.2 ± 2.1 vs. 2.1 ± 1.5 Gy; D(0.1cm3) to optic chiasm was 5.9 ± 3.1 vs. 4.5 ± 2.1 Gy. Treatment time was 53.7 ± 5.8 (64.9 ± 24.3) minutes for GK and 4.8 ± 1.3 (5.0 ± 0.7) minutes for RA for schwannomas (meningiomas). CONCLUSIONS: SRS with RA and FFF beams revealed to be adequate and comparable to GK in terms of target coverage, homogeneity, organs at risk sparing with some gain in terms of treatment efficiency.
Subject(s)
Brain Neoplasms/surgery , Cavernous Sinus/surgery , Meningioma/surgery , Photons , Radiosurgery , Radiotherapy Planning, Computer-Assisted , Radiotherapy, Intensity-Modulated , Adolescent , Adult , Aged , Brain Neoplasms/pathology , Cavernous Sinus/pathology , Female , Follow-Up Studies , Humans , Male , Meningeal Neoplasms/pathology , Meningeal Neoplasms/surgery , Meningioma/pathology , Middle Aged , Neoplasm Staging , Neuroma, Acoustic/pathology , Neuroma, Acoustic/surgery , Organs at Risk , Prognosis , Radiotherapy Dosage , Young AdultABSTRACT
The purpec: of this study is to investigate the behaviour of the percent depth dose curves (%DD) and surface doses of electronbeams at extended Source-to Surface Distances (SSDS). A (GE) Saturne 42 linear accelerator was used in this study, which produces dual photon energies of 6 and 15 MV as well as eight electron energies ranging between 4.5 and 21 MeV. The % Depth Dose curves were geneated with water scanning equipment at 6, 9, and 15 MeV for 4x4 cm(2) and 20x20 cm(2) field sizes at SSDS of 100 cm, 108 cm, and 115 cm. According to the measurements from surface to the depth of dose maximum the surface dose increased for all of the electron energies studied at extended SSDS for small field sizes. On the other hand for larger field sizes the surface doses decreased at extended SSDS. It was also observed that the increase in the surface dose diminished as the field size approached to 10x10cm(2) then the surface dose started decreasing at extended SSDS as the field sizes increased. Extended SSDS have no observable effect on the tail portion of the depth dose curves.
ABSTRACT
When treating tumors from surface to a certain depth (<5 cm), electron beams are preferred in radiotherapy. To increase the surface doses of lower electron beams, tissue-equivalent bolus materials are often used. We observed that the surface doses increased with increasing field sizes and electron energies. At the same time, we also observed that all electron parameters were shifted toward the skin as much as the thickness of the bolus used. The effect of bolus to the surface doses was more significant at low electron energies than at higher electron energies. Rando phantom measurements at 6-, 7.5-, and 9-MeV were slightly lower than the solid phantom measurements, which could only be explained by the inverse square law effect and the Rando phantom contour irregularity.
