Application of Statistical Process Control for Setting Action Thresholds as Quality Assurance of Dose Verifications in External Beam Radiotherapy

Purpose: To test the concept of Statistical Process Control (SPC) as a Quality Assurance (QA) procedure for dose verifications in external beam radiation therapy in conventional and 3D Conformal Radiotherapy (3D-CRT) treatment of cervical cancer. Materials and Methods: A study of QA verification of target doses of 198 cervical cancer patients undergoing External Beam Radiotherapy (EBRT) treatments at two different cancer treatment centers in Kenya was conducted. The target doses were determined from measured entrance doses by the diode in vivo dosimetry. Process Behavior Charts (PBC) developed by SPC were applied for setting Action Thresholds (AT) on the target doses. The AT set was then proposed as QA limits for acceptance or rejection of verified target doses overtime of the EBRT process. Result and Discussion: Target doses for the 198 patients were calculated and SPC applied to test whether the action limits set by the Process Behavior Charts could be applied as QA for verified doses in EBRT. Results for the two sub-groups of n = 3 and n = 4 that were tested produced action thresholds which are within clinical dose specifications for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. Conclusion: Action thresholds set by SPC were within the clinical dose specification of ±5% uncertainty for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. So the concept of SPC could be applied in setting QA action limits for dose verifications in EBRT.

Delivered Dose Verification for Lung Cancer Stereotactic Body Radiotherapy Using Cone-Beam CT

Purpose: Verified the delivered dose distribution of lung cancer Stereotactic Body Radiotherapy (SBRT) using the cone-beam CT images. Methods: Twenty lung cancer patients who underwent SBRT with 100 CBCT images were enrolled in this study. Delivered dose distributions were recalculated on CBCT images with the deformed and non-deformed methods, respectively. The planned and delivered dose distributions were compared using the dose-volume histograms. Results: The delivered target coverage (V100) per patient inside target volume deviated on average were 0.83% ± 0.86% and 1.38% ± 1.40% for Pct vs. Pcbct and Pct vs. Pdcbct, respectively. The Conformity Index (CI) and Gradient Index (GI) showed a good agreement among the plans. For the critical organs, only minor differences were observed between the planned dose and the delivered dose. Conclusions: CBCT images were a useful tool for setup and dose delivery verification for lung cancer patients who underwent SBRT.

Research Progress of Two-d imensional Matrix Detectors in IMRT Dose Verification

With the continuous development of science and technolog ies in China,radiotherapy technology in medical field has been very significant ly developing,and intensity modulated radiation therapy(IMRT)technology has been the most widely used.This paper first introduces the components and types of two-dimensional matrix detector,two-dimensional ionization chamber matrix detector and two-dimensional semiconductor matrix detector,then analyzes the dosimetric characteristics of the two-dimensional matrix detector.In the end,the various applications of the two-dimensional matrix detector are analyzed and discussed in detail.The paper aims to promote the two-dimensional matrix detector’s development in the field of radiotherapy in China.

A preliminary study of a new high-resolution detector matrix applied to three-dimensional dose verification in intensity-modulated radiotherapy

Objective:To test the basic dosimetry characteristics of a new high-resolution matrix and to perform a preliminary study on the three-dimensional(3D)dose verification of intensity-modulated treatment(IMRT).Methods:The dosimetry characteristics of the new matrix were investigated,including repeatability,dose-rate response,and dose linearity.Twenty cases of nasopharyngeal carcinoma(NPC)and 20 cases with lung cancer were randomly selected for IMRT plans,and the novel matrix was employed for 3D dose verification.The measured results were evaluated using the gamma passing rate(GPR)and dose volume histogram(DVH).The action limit(AL)and tolerance limit(TL)of the target volume and each organ at risk(OAR)were calculated with reference to the American Association of Physicists in Medicine(AAPM)TG218 report.Results:The matrix performed well for all dosimetry characteristic tests,with a deviation of<1%.The average GPRs of the body were(99.32±0.32)%,(98.36±0.59)%,and(96.27±1.20)%for NPC,and(99.17±0.74)%,(98.09±1.33)%,and(95.83±2.22)%for lung cancer at the gamma standards of 3%/3 mm,3%/2 mm,and 2%/2 mm.The average GPRs difference between the head-neck and thorax-abdomen plans were<1%for the same gamma standard.For both the target volumes and OARs,the average GPRs were>90%under the relatively strict standard of 2%/2 mm.The DVH showed that the measurement results of D_(98) and D_(95) for the target volumes were slightly lower and D_(2) were higher than those of treatment planning system(TPS)(P<0.01).In addition,with the same standard,there may be significant differences in the values of AL and TL between different structures for target volumes and OARs,especially small-volume OARs such as the chiasma and optic nerve-L.Conclusions:The new matrix showed good dosimetry characteristics and can be effectively applied to the treatment planning dose verification of the head-neck and lung cancer.Further research is needed to establish how to analyze the GPR and DVH of the target volume and OARs,and to determine more precise dose verification standards combined with the parameters of AL and TL to better guide 3D dose verification in clinic.