Biomedical subjects

Lijun Ma

Publications and source records attributed to Lijun Ma.

21 records · Page 2Linked to original sources

PubMed2002

Influence of gamma knife radiosurgery on the quality of life in patients with brain metastases.

Quality of life (QOL) is an important issue in the treatment of patients with brain metastases. With median survival times often less than 4 months, less invasive treatment options that maximize QOL parameters are essential. In recent years, stereotactic radiosurgery (SRS) has been commonly used as a noninvasive alternative to surgical resection for such patients. This prospective study was undertaken to evaluate QOL in patients undergoing SRS for brain metastases. Between 1999 and 2000, 20 patients with metastatic disease to the brain were evaluated and treated in our Gamma Knife unit. All patients performed the Spitzer QOL survey (10-point scale) both before stereotactic radiosurgery and at each follow-up visit. Primary sites of disease included lung (n = 10), breast (n = 5), melanoma (n = 2), thyroid (n = 1), uterine (n = 1), and kidney (n = 1). Fifteen (75%) had prior whole brain radiotherapy (median dose: 35 Gy). The median age and Karnofsky Performance Status were 58 years and 80, respectively. The median Spitzer score before SRS was 9 (range: 7-10), and the median follow-up time of the patients in this series was 7 months. The median posttreatment Spitzer score at 1 and 3 months after SRS was 9 (range: 5-10) and 8 (range: 4-10), respectively. Crude intracranial tumor control in this cohort of patients was 90%. Extracranial tumor progression was noted in 8 patients (40%), and in these patients, Spitzer scores tended to decrease in value. In those patients who had no evidence of intracranial or extracranial tumor progression, Spitzer scores remained either unchanged or improved. Gamma knife SRS is an appropriate treatment modality for maintaining QOL parameters in patients with brain metastases. Tumor progression both intracranially and extracranially influences QOL parameters. Confirmation of this finding will require further investigation.

Aged↗

PubMed2002

An empirical model for independent dose verification of the Gamma Knife treatment planning.

A formalism for an independent dose verification of the Gamma Knife treatment planning is developed. It is based on the approximation that isodose distribution for a single shot is in the shape of an ellipsoid in three-dimensional space. The dose profiles for a phantom along each of the three major axes are fitted to a function which contains the terms that represent the contributions from a point source, an extrafocal scattering, and a flat background. The fitting parameters are extracted for all four helmet collimators, at various shot locations, and with different skull shapes. The 33 parameters of a patient's skull shape obtained from the Skull Scaling Instrument measurements are modeled for individual patients. The relative doses for a treatment volume in the form of 31 x 31 x 31 matrix of points are extracted from the treatment planning system, the Leksell Gamma-Plan (LGP). Our model evaluates the relative doses using the same input parameters as in the LGP, which are skull measurement data, shot location, weight, gamma-angle of the head frame, and helmet collimator size. For 29 single-shot cases, the discrepancy of dose at the focus point between the calculation and the LGP is found to be within -1% to 2%. For multi-shot cases, the value and the coordinate of the maximum dose point from the calculation agree within +/-7% and +/-3 mm with the LGP results. In general, the calculated doses agree with the LGP calculations within +/-10% for the off-center locations. Results of calculation with this method for the dimension and location of the 50% isodose line are in good agreement with results from Leksell GammaPlan. Therefore, this method can be served as a useful tool for secondary quality assurance of Gamma Knife treatment plans.

Computer Simulation↗

PubMed2002

Smoothing intensity-modulated treatment delivery under hardware constraints.

A method is developed to smooth intensity-modulated beam delivery while considering hardware constraints. The method uses matrix algebra to model MLC leaf motion and hardware constraints such as interleaf digitization, synchronization requirements, and intersegment field abutment to deliver intensity modulated beam sequences. It was implemented and demonstrated for simulated and clinical intensity modulated cases. The simulated cases included intensity distributions from 3 x 3 to 30 x 30 in dimension with 1,000 intensity levels. The clinical examples included four treatments sites: prostate, head and neck, lung, and esophagus cancers. In particular, we studied the relationships between the intensity levels, segment numbers and their influence on the dose-volume histograms of the inversely optimized IMRT treatment plans. It was found that a significant reduction in the leaf segment numbers was achieved by applying the smoothing approach. The effects were found to be more significant for the unconstrained delivery than for the constrained delivery. The effects were also found to be more sensitive for the complex intensity distributions such as the head-and-neck cases than for the less complex ones such as the prostate cases. These results demonstrated the feasibility of maintaining inversely optimized treatment plans under acceptable tolerance levels while smoothing IMRT treatments with hardware constraints.

Algorithms↗