Dosimetric feasibility of iterative kV CBCT for radiation therapy planning for pelvis / 中华放射医学与防护杂志

Objective:To study the feasibility of using pelvic iterative cone beam CT images for dose calculation of radiation therapy planning, so as to provide support for adaptive radiotherapy.Methods:The CIRS 062 M phantom was scanned by Varian Halcyon v2.0 o-ring accelerator, and the average CT number under different scattering conditions was calculated, and then the ICBCT-ED conversion curve was established. CT images of CIRS 002PRA pelvic IMRT phantom and ICBCT images at different positions were collected. Treatment plan using VMAT technique based on CT image was designed and transplanted into ICBCT image with dose recalculated. The differences of gamma passing rate among target volume, organs at risk and 3-dimensional dose were compared. Based on the actual treatment plan of patients, the differences of 3-dimensional dose gamma passing rate in 10 pelvic patients were analyzed retrospectively.Results:There was a large CT value deviation at central position between the isolated no-scattering condition and the full-scattering condition, and the maximum deviation was 144 HU. The CT values of other positions in full-scattering condition were similar to those of the central position, and the maximum deviation was less than 50 HU. Based on the calculated result of ICBCT images at different positions of the pelvic phantom, the dose deviation of the target volume or organs at risk was less than 1 Gy. Compared with the plan based on CT images, the average 3-dimensional dose gamma passing rate under the criteria of 1% dose difference (DD)/1 mm distance-to-agreement (DTA) and 2% DD/2 mm DTA in plan based on ICBCT images were (88.86 ±1.18)% and (98.38±0.89)%, respectively. The ranges of average 3-dimensional dose gamma passing rate under the criteria of 2% DD/2 mm DTA and 3% DD/3 mm DTA in 10 patients with pelvic tumors were 90.03%-95.43% and 93.58%-97.78%, respectively, and the worst result was only 85.90% and 92.90%, respectively. The main reason of the worst result was the dose difference caused by large variation of bladder contour due to over-filling.Conclusions:Under comprehensive scattering conditions, the ICBCT-ED conversion curve is reconstructed and the treatment plan can be designed by using the ICBCT image of Halcyon v2.0 linear accelerator. The accuracy meets the standards of clinical application, which provides assurance for adaptive radiotherapy in the future.

The differences among the pass rate of intensity modulated radiation therapy planning in different tumors / 中华放射肿瘤学杂志

Objective To investigate the difference in the pass rate of intensity?modulated radiation therapy ( IMRT) planning in patients with different tumors and its value in determining pass rate thresholds. Methods A total of 35 verified IMRT plans for each of esophageal cancer, nasopharyngeal carcinoma, breast cancer, cervical cancer, and lung cancer were selected consecutively, and a one?way analysis of variance was used to investigate the difference in pass rate. A single pass rate threshold was used to test all IMRT plans, and the pass rate thresholds of IMRT plans for different tumors were calculated based on normal distribution law. Results There was a significant difference in the means between the 5 groups of data ( F=35. 83, P<0. 01) , and there was also a significant difference between any two groups ( P=0. 000) . There were statistically significant differences between nasopharyngeal carcinoma group and other four groups ( P=0. 000) . The difference was not only significant between the breast cancer group and the esophageal cancer group ( P=0. 001) , but also between the breast cancer group and the lung cancer group ( P=0. 033) . The calculated results of each threshold were 93. 37%, 89. 34%, 97. 68%, 95. 99%, and 95. 42%, respectively. Conclusions Different thresholds should be used for IMRT plans for different tumors, and the normal distribution law can be used to calculate the threshold.

Partial Block Technique for Radiation Therapy of Lung Cancer with Dynamic Multi-leaf Collimator

PURPOSE: A spinal cord partial block technique (PBT) with dynamic multileaf collimator (dMLC) for the reduction of the spinal cord dose while keeping the tumor dose unchanged has been developed and its effectiveness has been examined. MATERIALS AND METHODS: Conventional 3-D conformal therapy treatment plan is deigned prior to the PBT application. Beam parameters such as, number of beams, beam directions were determined during 3-D conformal therapy planning process. The shape and the weight of the partial block for optimizing the dose distribution are designed with the forward intensity modulated radiation therapy (fIMRT). Eight cases of lung cancer, in which it was found to be impossible to deliver enough doses to targets with the conventional technique because the doses of the normal lungs or the spinal cords were over the tolerance limit, are used to verify the usefulness of this technique. Comparison of the dose volume histogram (DVH) is performed to compare the treatment plan. RESULTS: PBT plan cauld reduce the maximum dose to the spinal cord up to 29.7% and the mean dose to the lungs up to 11.1%. CONCLUSION: All of the cases showed that the PBT plans are better than the conventional 3-D plans and the spinal cord doses or the normal lung doses can be reduced to tolerance limit

Magnification Device of Computed Tomography in Radiation Therapy Planning / 대한치료방사선과학회지

Computed tomography(CT) adds a new dimension in the study of body contour, organs and tissues as well as various pathologic conditions. This modality provides a great degree of accuracy in radiation therapy planning(RTP). However, CT images are usually taken on a small reduced format so that possible errors can be made during inputting the CT data into an automatic planner. Authors have designed a simple inexpensive magnifying device of CT images to obviate errors created by reduced image.