PURPOSETo validate that DMPO model for "one step" algorithm can reduce the total MLC segments number, we compare the dosage distribution of "one-step" algorithm with "two-step" algorithm for generating IMRT MLC segments.

METHODSOn the platform of "Pinnacle 8.0h" version radiation treatment planning system developed by Philips, we respectively select one head and neck tumor case, one thorax tumor case and one abdomen tumor case, by means of designing seven fields IMRT planning, then utilized "one-step" algorithm and "two-step" algorithm to optimize and generate IMRT MLC segments, and then calculated dosage distribution, evaluated dosage distribution lines and DVH diagram, in order to compare the two MLC segment groups generated by the two different algorithm.

RESULTFor the three IMRT plans selected by us, the number of MLC segments generated by "two-step" algorithm appear to be larger than "one-step" algorithm but dosage distribution seems to be worse than the latter.

DISCUSSIONFor utilizing the "Pinnacle" plan system to design IMRT plan, "one-step" algorithm with "DMPO" definitely can effectively reduce the number of MLC segments, what's more, the result of dosage distribution seems to be better.

Algorithms ; Humans ; Radiotherapy, Intensity-Modulated ; methods

OBJECTIVETo research the method of dosimetric verification of the intensity modulated radiation therapy (IMRT).

METHODSThe IMRT treatment plans were designed by Eclipse TPS and were implemented in Varian ClinacIX LA with 6MV X-ray. The absolute point doses were measured using a PTW 0.6 cc ion chamber with UNIDOS E dosimeter and the planes dose distributions were measured using PTW 2D-Array ion chamber in the phantom.

RESULTSThe error between the measured dose and calculated dose in the interesting points was less than 3%. The points passed ratio was more than 90% in gamma analysis method (3 mm 13%) about the plane dose distribution verification.

CONCLUSIONThe method of dosimetric verification of IMRT is reliable and efficient in the implementation.

To investigate the dose effect of isocenter difference during IMRT dose verification with the 2D chamber array. The samples collected from 10 patients were respectively designed for IMRT plans, the isocenter of which was independently defined as P(o), P(x) and P(y). P(o) was fixed on the target center and the other points shifted 8cm from the target center in the orientation of x/y. The PTW729 was used for 2D dose verification in the 3 groups which beams of plans were set to 0 degrees. The γ-analysis passing rates for the whole plan and each beam were gotten using the different standards in the 3 groups, The results showed the mean passing rate of γ-analysis was highest in the P(o) group, and the mean passing rate of the whole plan was better than that of each beam. In addition, it became worse with the increase of dose leakage between the leaves in P(y) group. Therefore, the determination of isocenter has a visible effect for IMRT dose verification of the 2D chamber array, The isocenter of the planning design should be close to the geometric center of target.
Gamma Rays ; Humans ; Radiotherapy Dosage ; Radiotherapy, Intensity-Modulated ; instrumentation ; methods

UNLABELLEDThe aim of this study is to investigate the characteristics of Elekta delivery system for volumetric modulated arc therapy (VMAT). Five VMAT plans were delivered in service mode and dose rates, and speed of gantry and MLC leaves were analyzed by log files. Results showed that dose rates varied between 6 dose rates. Gantry and MLC leaf speed dynamically varied during delivery.

CONCLUSIONThe technique of VMAT requires linac to dynamically control more parameters, and these key dynamic variables during VMAT delivery can be checked by log files. Quality assurance procedure should be carried out for VMAT related parameter.

OBJECTIVETo implement dose reconstruction and dose-guided intensity modulated radiotherapy for helical tomotherapy.

METHODSDose reconstruction was implemented on adaptive helical tomotherapy with the online megavoltage CT (MVCT) imaging from a patient with nasopharyngeal cancer. The differences of isodose line between actual and planned deposition were analysis in 3D distribution, on which the hot spot and cold spot were lined. The dose delivered to these areas was modulated in later fractions to keep the planned requirement.

RESULTSThe differences between actual and planned isodose line were shown on the image visually. The modulation to the hot spot and cold spot in later fraction corrected the incorrectly delivered dose to achieve the requirement of primary plan.

CONCLUSIONSThe dose reconstruction and dose-guided intensity modulated radiotherapy can be implemented in adaptive helical tomotherapy.

The purpose of this study is to establish and apply a correction method for titanium alloy implant in spinal IMRT plan, a corrected CT-density table was revised from normal CT-density table to include the density of titanium alloy implant. Dose distribution after and before correction were calculated and compared to evaluate the dose deviation. Plans were also copied to a spinal cancer simulation phantom. A titanium alloy fixation system for spine was implanted in this phantom. Plans were recalculated and compared with the measurement result. The result of this study shows that the max dose of spinal cord showed significant difference after correction, and the deviation between calculation results and measurement results was reduced after correction. The method for expanding the range CT-density table, which means that the density of titanium alloy was included, can reduce the error in calculation.
Radiotherapy, Intensity-Modulated/methods* ; Titanium ; Radiotherapy Dosage ; Alloys ; Radiometry/methods* ; Radiotherapy Planning, Computer-Assisted/methods*

To study the feasibility of ArcCheck verification system in dosimetric verification for stereotactic radiotherapy (SRT) the stereotactic radiotherapy (SRT) with flattening filter free (FFF) model.
 Methods: A total of 76 cases under SRT treatment plans were introduced into ArcCheck phantom and recalculated. Threshold criteria was set as (3%, 3 mm, 10%) or (2%, 2 mm, 10%). The calculated dose distribution and the measured dose distribution of ArcCheck phantom were compared by means of distance to agree (DTA) and Gamma analysis method respectively.
 Results: Based on the threshold criteria (3%, 3 mm, 10%), the relative and absolute mean pass rates of SRT treatment plans by DTA and Gamma analysis were greater than 95%. Based on the threshold criteria (2%, 2 mm, 10%), the relative and absolute mean pass rates of SRT treatment plan by DTA and Gamma analysis were about 90%. The dose pass rate of Gamma analysis method was slightly higher than that of DTA analysis method (P<0.001).
 Conclusion: The ArcCheck verification system is a rapid and accurate method for SRT dose verification, and discrepancies are found in different analysis methods.
Feasibility Studies ; Humans ; Phantoms, Imaging ; Radiosurgery ; methods ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted ; Radiotherapy, Intensity-Modulated

With increasing clinical use, radiotherapy (RT) has been considered reliable and effective method for hepatocellular carcinoma (HCC) treatment, depending on extent of disease and patient characteristics. RT for HCC can improve therapeutic outcomes through excellent local control, downstaging, conversion from unresectable to resectable status, and treatments of unresectable HCCs with vessel invasion or multiple intrahepatic metastases. In addition, further development of modern RT technologies, including image-guided radiotherapy (IGRT), intensity-modulated radiotherapy (IMRT), and stereotactic body radiotherapy, has expanded the indication of RT. An essential feature of IGRT is that it allows image guidance therapy through in-room images obtained during radiation delivery. Compared with 3D-conformal RT, distinctions of IMRT are inverse treatment planning process and use of a large number of treatment fields or subfields, which provide high precision and exquisitely conformal dose distribution. These modern RT techniques allow more precise treatment by reducing inter- and intra-fractional errors resulting from daily changes and irradiated dose at surrounding normal tissues. More recently, particle therapy has been actively investigated to improve effectiveness of RT. This review discusses modern RT strategies for HCC, as well as optimal selection of RT in multimodal approach for HCC.
Carcinoma, Hepatocellular* ; Humans ; Methods ; Neoplasm Metastasis ; Radiosurgery ; Radiotherapy* ; Radiotherapy, Image-Guided ; Radiotherapy, Intensity-Modulated

In Vivo Dosimetry ; Radiotherapy Dosage ; Radiometry/methods* ; Electronics ; Radiotherapy, Intensity-Modulated/methods* ; Phantoms, Imaging ; Algorithms