Dosimetric effect of Varian high-definition multi-leaf collimator leaf position error on stereotactic body radiation therapy for lung tumors / 中华放射肿瘤学杂志

Objective:To evaluate the effect of leaf position error of Varian high-definition multi-leaf collimator (HD120) on the dosimetry of stereotactic body radiation therapy (SBRT) for lung tumors.Methods:Nine SBRT plans based on HD120 for lung tumors were selected as the reference plans. The parameters of the plans were modified by the in-house program based on the Varian Eclipse 15.6 scripting application program interface to generate the simulation plans with three types of leaf position errors including the isotropic systematic error, the anisotropic systematic error and the random error, respectively. Then, the dosimetric metric deviation between each simulation plan and the corresponding reference plan was calculated and regression analysis was performed to evaluate the dosimetric effect of three types of leaf position errors of HD120 on SBRT.Results:The planning target volume (PTV) D 99%, D 2cm and V 5Gy of double lungs were decreased quadraticly with the increase of the absolute value of the isotropic systematic error. The first-order sensitivity was -0.06%/mm to -0.26%/mm, and the second-order sensitivity was -0.55%/mm 2 to -1.17%/mm 2 ( R2=0.96-0.99, P<0.01). The maximum change of PTV D 99% was -3.13%. The linear regression analysis of the effects of the anisotropic systematic error and random error showed that the sensitivity of CI was 25.16%/mm ( R2=0.98, P<0.01) and -4.84%/mm( R2=0.99, P<0.01), and the sensitivity of other dosimetric deviations with the anisotropic systematic error was 4.80%/mm to 5.12%/mm ( R2=0.96-0.98, P<0.01), whereas the sensitivity with the random error was -0.47%/mm to -1.01%/mm ( R2=0.96-0.99, P=0-0.02). Conclusions:The dosimetric deviation of SBRT plan based on HD120 for lung cancer is highly sensitive to the anisotropic systematic error of leaf position, but less sensitive to the random error. In addition, the isotropic systematic error of leaf position will lead to the decrease of target coverage to a certain extent. Consequently, it is necessary to strictly control the systematic error of HD120 leaf position in the implementation of SBRT plan in clinical work.

Optimization of Strategy for Image Guided Radiotherapy in Tomotherapy / 中山大学学报(医学科学版)

[Objective]To explore the different scanning frequency for the MVCT scanning in the tomotherapy , and seek the best strategy of the scanning.[Methods]Patients were treated by tomotherapy in SYSUCC from January 1, 2015 to May 15, 2016, includ?ing 88 head&neck patients, 63 chest&abdomen patients and 19 pelvis patients. All patients have had a daily MVCT scanning for po?sition verification before the treatment. The data retrieved from"the first five times of the very first week"and"the every first time of each week", were compared with"the whole course"data, respectively.[Results]There are no significant difference between"the whole course"and"the first five times of the very first week"or"the every first time of each week"for pelvis patients and chest and abdomen patients. There are significant differences between Z axis of"the whole course"and"the first five times of the very first week"only for head&neck patients.[Conclusion]It is a good scanning choice of"the first five times of the very first week"and"the every first time of each week"for the those patients with thoracic&abdominal or pelvic tumors to reduce the extra radiation dose from the MVCT. There are significant differences between Z axis of"the whole course"and"the first five times of the very first week"in the head&neck patients. Therefore,"the first five times of the very first week"cannot be used as a solid position information for daily verification. And"the every first time of each week"may be a good compromise solution.

The impact of electronic portal imaging device position error on 3D dose verification of volumetric modulated arc therapy / 中华放射医学与防护杂志

Objective To analyze the impact of electronic portal imagingdevice (EPID) position error on three-dimensional dose verification of volumetric modulated arc therapy (VMAT).Metbods Five Suremark SL-20 lead points were fixed on Elekta tray,and EPID images were collected in 0-360° rotation,one image per 5°.The position error relative to the accelerator was analyzed via Matlab.Then the images position error was corrected according to the analysis,and the 3D dose was reconstructed with the corrected images.The dose distributions of double arcs,clockwise arc(arc 1),and counterclockwise arc (arc 2) of 16 nasopharyngeal carcinoma patients' VMAT plan were evaluated by γ analysis,and the results of before and after position error correction were compared.Results Compared to 0° gantry angle,the error of source to the image distance (SID) was maximum (1.20 cm) when the gantry angle was 180°.On account of the SID change,the maximum error along the up-down (y) direction in the iso-center planar was 2.28 mm and the left-right (x) direction error was within ± O.5 mm.The 3D γ analyses of 16 nasopharyngeal carcinoma in VMAT plans were obviously increased after the position error along y was corrected.The double arcs,arc1 and arc 2 were increased by (4.12 ±1.67) ％ (t =-9.86,P＜ 0.05),(3.47±1.64) ％ (t=-8.46,P＜ 0.05) and (5.08±1.30) ％ (t=-15.63,P＜ 0.05) in 5％/3 mm standard,respectively.However,in 3％/3 mm standard,γ value of the double arcs,arc 1 and arc2 were increased by (7.63 ±2.24) ％ (t =-13.63,P＜ 0.05),(6.03 ±2.07) ％ (t =-11.66,P＜ 0.05),(9.17 ±2.23) ％ (t =-16.41,P＜ 0.05),respectively.Since the EPID position error along x was corrected after y,the 3D γ analysis of reconstruction dose indicated that the average of the 5％/3 mm and 3％/3 mm γ value were increased by 0.23％ and 0.24％,respectively.Conclusions EPID motion error along the gantry to table direction of the accelerator can't be ignored.When reconstruct dose based on EPID,a modification should be made for rebuilding more accurate patients' 3D dose distribution.

Effect of leaf movement speed on setup error of multileaf collimator in volumetric modulated arc therapy mode / 中华放射肿瘤学杂志

Objective To study the effect of leaf movement speed on the setup error of multileaf collimator (MLC) in RapidArc mode,and to improve quality assurance and verify the reliability of RapidArc.Methods Referring to the PicketFenceStatic_M120.dcm and PicketFenceRA_Ml20.dcm files,the Tilt tests with different adjacent leaf speed were designed and setup errors of MLC were obtained by analyzing electronic portal imaging device images.Results In the Tilt tests,the setup errors gradually increased from gapl 1 to gapS0 in both static gantry mode and RapidArc mode.With a gantry angle of 270°,gap41 had the maximum setup error of-0.55 mm.In the RapidArc mode,gap46 had the maximum setup error of-0.67 mm.The deviation of gap width was no greater than 15％ in any mode.There was no significant difference in deviation pattern of gap width between four modes with different gantry angles.The same gaps in different stripes showed a consistent trend in gap width.The RapidArc mode had a larger variation in percentage deviation of gap width than the static gantry mode.Conclusions The setup error increases with the increase in the speed of MLC leaf.The variation in the leaf speed has no significant impact on the gap width.There is no correlation between the leaf speed and the deviation of gap width.Four different gantry angles give similar deviation patterns of gap width,suggesting that the deviation of gap width is related to the leaf rather than the gantry angle.The RapidArc mode has a greater impact on the gap width than the fixed gantry mode.

Analysis of multi-leaf collimator leaf position deviation in volumetric modulated arc therapy / 中华放射医学与防护杂志

Objective To evaluate the position deviation of multi-leaf collimator (MLC) in volumetric modulated arc therapy for nasopharyngeal carcinoma and to verify a method of detecting the leaf position accuracy.Methods Thirty-two volumetric modulated arc plans of nasopharyngeal carcinoma were randomly selected.A clockwise arc with a gantry range of 181° to 179° and a counterclockwise arc with a gantry range of 179° to 181° were uscd for each plan.Each arc contained two leaf groups,groups A and B.By using the Argus software,the actual MLC leaf positions were extracted from the Dynalog files in the Varian Trilogy accelerator.The planed MLC leaf positions were compared with the actual positions,and the differences were calculated between them.Results The proportions of the leaf position errors within ± 2,± 1.5,± 1 and ± 0.5 mm were 99.99％,99.90％,99.07％ and 93.98％,respectively.The proportions of the leaf position errors within ± 1 mm were 98.08％,100％,98.97％ and 99.01％ for the first therapeutic arc (ARC1),second therapeutic arc (ARC2),A and B groups,respectively.The leaf position errors range of ARC1 and ARC2 were-2.95 to 2.99 and-0.22 to 0.23 mm (t =2.35,P ＜ 0.01).The leaf position errors range of leaf bank A and leaf bank B were-2.95 to 2.68 and-2.92 to 2.99 mm(P ＞ 0.05).Conclusions During the volumetric modulated arc radiotherapy,the leaf positions deviation are in control.The Dynalog files can be used as an effective way to analysis the leafposition errors.

A comparison of the dosimetric effects of systematic MLC leaf position errors on flattening filter and flattening filter-free IMRT for nasopharyngeal carcinoma / 中华放射医学与防护杂志

Objective To compare the dosimetric effects of systematic MLC leaf position errors on flattening filter (FF) and flattening filter-free (FFF) IMRT for nasopharyngeal carcinoma (NPC).Methods In totaly of ten patients with NPC were enrolled in the current study.FF IMRT and FFF IMRT plans were designed for each patient, and in-house software was developed to modify the corresponding MLC files.Briefly, three kinds of systematic MLC error presented with 0.5 and 1 mm magnitudes error were simulated.The modified MLC files were re-imported into IMRT plans for dose recalculation, and differences in the dosimetry trends between FF-IMRT and FFF-IMRT plans were analyzed using a dosevolume histogram.Results Upon closed MLC, the average changes in D95％ of PTV and D of parotid glands in FFF-IMRT plans were more sensitive than in FF-IMRT plans (t =3.298-4.793, P ＜ 0.05).Otherwise, when MLC are shifted in the same direction, changes in D95％of PTV, D of PGTV, PTV as well as D of left parotid gland in FFF-IMRT plans were also more sensitive (t =2.372-6.844, P ＜ 0.05), whereas average changes in D of right parotid gland presented with less sensitivity (t =-4.049,-3.378, P ＜ 0.05).Conclusions For out-of-field or large organs, FFF-IMRT plans are more sensitive to leaf position error than FF-IMRT plans.

Estimativas da qualidade de linhas poligonais topográficas / Quality estimations of topographical traverses

O objetivo deste artigo é descrever um procedimento que contribui com estimativas de qualidade de levantamento topográficos mediante a pré-análise e estimativas obtidas a partir de análise pós-ajustamento. As estimativas são dadas pelo teste qui-quadrado da forma quadrática do erro de fechamento, pelo teste qui-quadrado da forma quadrática dos resíduos obtidos no ajustamento pelo método dos mínimos quadrados, pelo teste data snooping de Baarda, pela elipse dos erros, pela elipse de confiança, pelo círculo do erro de posição e pelo círculo do erro médio. Estes conceitos são examinados por meio de valores numéricos no caso de uma linha poligonal simples implantada no campus da Universidade Federal de Santa Maria e medida com um taquímetro eletrônico.

The objective through this article is to describe a procedure that contributes with quality survey estimations by means pre-analysis survey and estimations by means post-adjustment. The estimations are given by the chi-square test of the quadratic form of misclosures, the chi-square of the quadratic form of residuals from the least-squares adjustment method, the Baarda's data snooping test, the standard ellipse, the confidence ellipse, position error circle and mean error circle. These concepts are examined through the numerical values provided in the case of a simple topographical traverse which was implanted at the Universidade Federal de Santa Maria Campus with electronic tachymeter.