This study was to evaluate the reduction of dose undulation at the field edge, gap leakage and interleaf transmission by utilizing a dual-level four-bank micro multileaf collimator (mMLC) and compare with standard MLC. Method and Materials: A 6MV Varian 600C linear accelerator has been collimated with a dual-level fourbank mMLC. The dual mMLC consists of four banks of leaves with upper and lowe...

PURPOSE To investigate the sensitivity of traditional gamma-index-based analysis using diode arrays to detect significant dosimetric errors in patientspecific measurements for VMAT brain SRT plans. METHODS Quality assurance measurements were performed using an ion chamber and two different diode array devices for four brain SRT treatment plans. All cases were planned with Eclipse AAA RapidArc...

Most of the treatment units, both new and old models, are equipped with a megavoltage portal imager but its use for volumetric imaging is limited. This is mainly due to the poor image quality produced by the high-energy treatment beam (> 6MV). A linac at our center is equipped with a prototype 2.5 MV imaging beam. This study evaluates the feasibility of low-dose megavoltage cone-beam imaging wi...

PURPOSE Cyberknife system is used for providing stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) hypofractionation scheme. The whole treatment delivery is based on live imaging of the patient. The minor error made at any stage may bring severe radiation injury to the patient or damage to the system itself. Several safety measures were taken to make the system safer...

PURPOSE To design an efficient method for utilizing phase-space source models in the GPU-based Monte Carlo (MC) dose calculation engine gDPM. METHODS In GPU-based MC algorithms, particles are transported in parallel on different threads. Particles of different types and energies can require significantly different execution times. This can cause "thread divergence" and lower efficiency when s...

Magnetic resonance (MR) imaging of Gafchromic film causes perturbation to absolute dosimetry measurements; the purpose of this work was to characterize the perturbation and develop a correction method for it. Three sets of Gafchromic EBT2 film were compared: radiation (control), radiation followed by MR imaging (RAD + B), and MR imaging followed by radiation (B + RAD). The T1-weighted and T2-we...

PURPOSE There is great recent interest in the potential value of using pentoxifylline (3,7-dimethyl-1(5-oxyhexyl)-xanthine, PTX) as an inhibitor of radiation-induced late normal tissue damage. The effects of PTX on the radiobiological parameters (alpha/beta ratio, repair half time T(1/2)) of radiation myelopathy were studied in a rat model. MATERIALS AND METHODS Anesthetized Sprague-Dawley ra...

PURPOSE To investigate the critical structure sparing achievable by biological optimization for modulated volumetric arc (VMAT) of head and neck (H&N) cancer. METHODS Ten H&N VMAT patients who were originally planned and treated with simultaneous integrated boost technique using dose-volume based optimization, were selected. For each patient, a new VMAT plan was generated using the generalize...

The plasticity of a synapse in the molluscan peripheral nervous system was examined under a variety of experimental, physiological, and pharmacological conditions. These studies employed the isolated salivary glands and attached buccal ganglia of the freshwater snail Helisoma. Action potentials evoked in buccal neuron 4 normally evoke a large excitatory postsynaptic potential (EPSP) which drive...

Objectives Radiotherapy is one of the most effective modalities of cancer therapy, but clinical responses of individual patients varies considerably. To enhance treatment efficiency it is essential to implement an individual-based treatment. The aim of present study was to identify the mechanism of intrinsic apoptosis pathway on radiosensitivity and normal tissue complications caused by the rad...