Biomedical subjects

Weihua Fu

Publications and source records attributed to Weihua Fu.

4 recordsLinked to original sources

PubMed2006

Dosimetric effects of patient rotational setup errors on prostate IMRT treatments.

The purpose of this work is to determine dose delivery errors that could result from systematic rotational setup errors (DeltaPhi) for prostate cancer patients treated with three-phase sequential boost IMRT. In order to implement this, different rotational setup errors around three Cartesian axes were simulated for five prostate patients and dosimetric indices, such as dose-volume histogram (DVH), tumour control probability (TCP), normal tissue complication probability (NTCP) and equivalent uniform dose (EUD), were employed to evaluate the corresponding dosimetric influences. Rotational setup errors were simulated by adjusting the gantry, collimator and horizontal couch angles of treatment beams and the dosimetric effects were evaluated by recomputing the dose distributions in the treatment planning system. Our results indicated that, for prostate cancer treatment with the three-phase sequential boost IMRT technique, the rotational setup errors do not have significant dosimetric impacts on the cumulative plan. Even in the worst-case scenario with DeltaPhi=3 degrees, the prostate EUD varied within 1.5% and TCP decreased about 1%. For seminal vesicle, slightly larger influences were observed. However, EUD and TCP changes were still within 2%. The influence on sensitive structures, such as rectum and bladder, is also negligible. This study demonstrates that the rotational setup error degrades the dosimetric coverage of target volume in prostate cancer treatment to a certain degree. However, the degradation was not significant for the three-phase sequential boost prostate IMRT technique and for the margin sizes used in our institution.

Body Burden↗

PubMed2004

Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter: a planning study.

The treatment delivery time of intensity-modulated radiation therapy (IMRT) with a multileaf collimator (MLC) is generally longer than that of conventional radiotherapy. In theory, removing the flattening filter from the treatment head may reduce the beam-on time by enhancing the output dose rate, and then reduce the treatment delivery time. And in practice, there is a possibility of delivering the required fluence distribution by modulating the unflattened non-uniform fluence distribution. However, the reduction of beam-on time may be discounted by the increase of leaf-travel time and (or) verification-and-recording (V&R) time. Here we investigate the overall effect of flattening filter on the treatment delivery time of IMRT with MLCs implemented in the step and shoot method, as well as with compensators on six hybrid machines. We compared the treatment delivery time with/without flattening filter for ten nasopharynx cases and ten prostate cases by observing the variations of the ratio of the beam-on time, segment number, leaf-travel time and the treatment delivery time with dose rate, leaf speed and V&R time. The results show that, without the flattening filter, the beam-on time reduces for both static MLC and compensator-based techniques: the number of segments and the leaf-travel time increase slightly for the static MLC technique; the relative IMRT treatment delivery time decreases more with lower dose rate, higher leaf speed and shorter V&R overhead time. The absolute treatment delivery time reduction depends on the fraction dose. It is not clinically significant at a fraction dose of 2 Gy for the technique of removing the flattening filter, but becomes significant when the fraction dose is as high as that for radiosurgery.

Algorithms↗

PubMed2004

The influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer irradiation.

Using higher energy photons can obtain better target dose uniformity and skin sparing for treating deep lesions, but the effect of lacking lateral scattering in the low-density lung may degrade the target coverage. To analyze the influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer, three dimension conformal treatment (3D-CRT) plans of using 6 MV and 18 MV X-ray respectively for a lung cancer case have been worked out by using pencil beam algorithm and collapsed cone algorithm provided by Helax-TMS treatment planning system for the same radiation field arrangement for both energies. Dose volume histogram (DVH) in target and organs at risk (OARs) are used for comparison of different plans. The study shows that using pencil beam algorithm, the target DVH are similar for 6 MV and 18 MV plan. However, using collapsed cone algorithm that can make account of lateral electron scattering, the target is underdosed. The change is even more pronounced for 18 MV plan. The doses for lung and spinal cord are similar for these two energies and two algorithms. Therefore, for lung cancer, dose calculation algorithm should have the ability of handling accurately the effect of the tissue density heterogeneity. It is better to use the lower-energy photons (6 MV) than to use the higher-energy photons (18 MV).

Humans↗

PubMed2002

[PIV: a computer-aided portal image verification system].

Portal image verification (PIV) is one of the key actions in QA procedure for sophisticated accurate radiotherapy. The purpose of this study was to develop a PIV software as a tool for improving the accuracy and visualization of portal field verification and computing field placement errors. PIV was developed in the visual C++ integrated environment under Windows 95 operating system. It can improve visualization by providing tools for image processing and multimode images display. Semi-automatic register methods make verification more accurate than view-box method. It can provide useful quantitative errors for regular fields. PIV is flexible and accurate. It is an effective tool for portal field verification.

Algorithms↗