Outcomes of 30 Gy/5 Fr Hypofractionated Stereotactic Radiation Therapy for Small Brain Metastases (≤2 cm).

BACKGROUND/AIM: Stereotactic radiosurgery (SRS)-used for brain metastases (BMs) with a tumor diameter of ≤2 cm-has a high local control rate, however, it can cause symptomatic radiation-induced brain necrosis. Hypofractionated stereotactic radiation therapy (HFSRT) is not commonly used for such lesions and its effectiveness remains unknown. Herein, the efficacy of 30 Gy 5-fraction HFSRT for treating BMs of <2 cm was retrospectively evaluated. PATIENTS AND METHODS: Patients who received HFSRT and had a gross tumor volume (GTV) of ≤2 cm in maximum diameter were included in the study (49 patients; 179 BMs; median follow-up period, 11.9 months). RESULTS: The mean GTV Peripheral Dose (D95) was 36.2 Gy. The local control (LC) rates at 1 and 2 years were 93.0% and 81.5%, respectively, for all lesions. The 1-year LC rates were 93.6% and 92.0% for ≤1.0-cm and 1.0-2.0-cm lesions, respectively. Multivariate analysis revealed that the only significant difference was in GTV maximal tumor diameter (HR=1.961, p=0.0002). Notably, only one patient had asymptomatic radiation necrosis. CONCLUSION: Owing to the high toxicity of SRS, 5-fraction HFSRT can be an effective treatment strategy for BMs of <2 cm.

First Clinical Experience of Tungsten Rubber Electron Adaptive Therapy With Real-time Variable-shape Tungsten Rubber.

BACKGROUND/AIM: We investigated the dosimetric characteristics of electron radiotherapy for auricular keloid using real-time variable-shape tungsten rubber (STR). PATIENTS AND METHODS: For the first evaluation, STR was shaped into a rectangular irradiation field (3.0×5.0 cm2). In the next step, the STR was reshaped to fit the target (3.5×6.5 cm2) for the second evaluation. Percentage depth doses (PDDs) and lateral dose profiles were obtained with 6-MeV electron beams and compared with those of low-melting-point lead (LML). RESULTS: Compared to the LML on electron applicator, PDD differences were within 0.4 mm, while the penumbras as width of 20-80% dose levels were smaller (maximum reductions: 75.8% and 82.9% at first and second evaluations, respectively). The treatment process of shaping the STR, decision on output, and irradiation was completed within 45 min. CONCLUSION: Electron radiotherapy using STR for keloid can be performed with excellent dose distribution in a short time. First clinical experience found the STR is suitable for use in individualized and immediate electron radiotherapy.

Dosimetric Characterization of a Novel Surface Collimator With Tungsten Functional Paper for Electron Therapy.

BACKGROUND/AIM: The aim of the study was to investigate the dosimetric characteristics of electron beams with a tungsten functional paper (TFP) surface collimator. MATERIALS AND METHODS: The circular field of 6.0 cm diameter was created with the TFP collimator put on the phantom. Depth and lateral dose profiles for 4 and 6 MeV electron beams were obtained. The characteristics of lateral dose profile, treatment diameter as width over 90% of the dose, and penumbra as width of the off-axis positions from 80% to 20% dose levels were evaluated. RESULTS: Compared to the lead collimator, the TFP collimator generated higher surface doses, the treatment diameters were increased from 42.8 to 48.6 mm and from 40.0 to 41.4 mm, and the penumbras were reduced from 15.0 to 9.6 mm and from 16.4 to 13.0 mm for 4 and 6 MeV electron beams, respectively. CONCLUSION: The TFP surface collimator can provide an excellent dose distribution compared to the conventional lead collimator.