Purpose: A comprehensive quality assurance program has been established in Beijing hospital to ensure that "radiosurgery" be carried out precisely and safetely.Materials and Methods: A film checking technique was used to verify the localization accuracy and the setting-up accuracy.Results: The figures taken from 80 cases treated show that the setting-up accuracy of the target positions be within ?1mm .Conclusion: The positional accura cies during target localization and setting-up are guaranteed by using our QA procedures.

Objective To evaluate the clinical feasibility of quality assurance of intensity modulated radiation therapy(IMRT) through a series of clinical case studies. Methods Helios inverse planning system was used to provide optimized IMRT treatment plans for brain tumor, nasopharyngeal carcinoma, pancreatic cancer, spinal metastatic tumor and prostatic cancer. To verify the conformation between the fluence map of each beam predicted by the planning system and that actually delivered, a piece of film under a homogeneous polystyrene phantom was irradiated vertically with each of the beams to record the deposited dose. This measured fluence map was compared with that predicted by the planning. The dose distribution was recorded by irradiating the film in an anthropomorphic phantom using patients' treatment plan, then compared with that predicted by the planning. An ionization chamber in a water phantom was used to measure the central point dose and another eccentric point dose. Results The fluence map measured by the film was well consistent with that predicted by the planning. The error between the measured dose and predicted dose in the central point was less than 3%, whereas the error of the dose in another eccentric point varied greatly. The isodose distribution (on axial plane) measured by the film was consisent with the predicted one. Conclusions The procedures for quality assurance of IMRT are feasible in our experience.

Objective To compare the dose to the contralateral breast, ipsilateral lung, and the whole lung in the tangential field radiotherapy for primary breast cancer using the dynamic wedge or physical wedge. Methods With thirteen breast cancer patients chosen, the dose distribution was computed for the plan used in practical treatment with the dynamic wedge and physical wedge. Plans were compared using dose volume histograms for the contralateral breast, ipsilateral lung and the whole lung. As for the contralateral breast, the dose distributions were not computed for the whole breast but computed for the two regions similar to a rectangular area in the axial slice and parts of the whole breast. The mean dose was used to evaluate CB1, CB2 and ipsilateral lung, and V_ 20 was used to evaluate the whole lung. The treatment planning system used was Varian CadPlan. An ionization chamber in a water phantom was used to measure some point doses to simulate the dose to the contralateral breast. Results When using the 30? dynamic wedge, the mean dose to CB1 and CB2 was 1.5%-3.9% and 1.1%- 2.6% , and the mean dose to the ipsilateral lung was 4.1%-14.7%. When using the 30? physical wedge, the mean dose to CB1 and CB2 were 1.5%-4.4% and 1.2%-3.0%, respectively, and the mean dose to the ipsilateral lung was 4.4%-15.2%. The values of V_ 20 were equal. When using the 15? dynamic wedge, the mean dose to CB1 and CB2 decreased compared to 15? physical wedge, but the value reduced was smaller than when using 30? wedge. Also, the measured results verified that the dose to the normal tissue is reduced using the dynamic wedge. Conclusions The mean dose to the contralateral breast was reduced by using the dynamic wedge instead of the physical wedge, and the mean dose to the ipsilateral lung or V_ 20 is reduced or equal to each other. So the probability of normal tissue complication such as a second breast malignancy or pneumonitis associated with radiotherapy are likely to be reduced.