ABSTRACT
Objective:To explore the application value of skin lead marker combined with iSCOUT image-guided positioning system in monitoring and correcting the setup error of intensity-modulated radiotherapy (IMRT) for breast cancer and calculate the PTV margin, aiming to provide reference for clinical practice.Methods:25 breast cancer patients treated with IMRT after modified radical mastectomy in Fujian Medical University Union Hospital from April to August 2019 were enrolled in this study. The skin lead marker combined with iSCOUT image-guided positioning system was employed for image-guided positioning based on the gold standard registration algorithm. Initial setup errors on the x (lateral), y (craniocaudal) and z (anteroposterior) axis and residual errors after the position correction were recorded and analyzed. The effect of the errors before and after image-guided correction upon the plan dose was compared and the reasonable PTV margin was calculated.Results:25 patients received 150 times of positioning verification using skin lead marker combined with iSCOUT image-guided positioning system. The absolute residual errors on the x-, y-and z-axis were (1.53±0.96), (1.30±0.99) and (1.34±0.92) mm, significantly smaller than the initial setup errors of (2.63±2.12), (2.41±2.45) and (3.07±2.77) mm (all P<0.001). The percentage of dose deviation due to residual errors was also smaller than that of the initial errors. Significant differences were observed in D 98%, D 2%, D max of PTV, D max of the heart, D max of the healthy breast, and D mean of the affected lung and both lungs. The percentage deviation from the original plan was decreased from 2.18%, 3.19%, 10.66%, 8.75%, 48.21%, 10.50%, and 3.66% to 0.38%, 0.23%, 2.31%, 0.04%, 13.78%, 6.35% and 0.41%, respectively (all P<0.05). PTV margins on the x-, y-and z-axis after correction were calculated as 1.87, 1.75 and 1.69 mm, respectively. Conclusion:It is feasible and valuable to apply the skin lead marker combined with iSCOUT image-guided positioning system in the positioning verification and correction of breast cancer radiotherapy position, providing novel reference for clinical PTV margin.
ABSTRACT
Objective To analyze the relationship between planning factors of intensity-modulated radiation therapy (IMRT) and gamma index and investigate the effect of each parameter upon the γ passing rate of IMRT.Methods Gamma analysis was performed using 3％/3 mm acceptance criteria for 457 IMRT beams with different planning factors.During multi-factor ANOVA analysis of planning factors and gamma passing rate,the control variables primarily included the minimum segment area,minimum number of monitor unit (MU),number of segment,segment conversation,and the spatial resolution in the measured dose distribution.Results The percentage of pixels with passingγsignificantly differed under different minimum segment area,segment conversation and the spatial resolution in the measured dose distribution (all P＜ 0.05).No significant correlation was observed between the passing rate and the minimum number of MU and the number of segment (P＞ 0.05).Conclusions According to the actual situation of the equipment,the minimum segment area should be determined during IMRT planning.Direct machine parameter optimization should be performed.Appropriate resolution of the plane dose images can be chosen according to the minimum detector interval of dose matrix device,
ABSTRACT
Background and purpose: The literature on dose-volume parameters and pneumonitis is extensive. The results are inconsistent, both for the best predictive metrics and significant comorbid factors. This study aimed to investigate a prospective functional equivalent uniform dose (fEUD) with perfusion single photon emission computed tomography (SPECT) images as predictors of radiation pneumonitis (RP) in patients undergoing curative radiotherapy (RT). Methods: Functional lung imaging was performed using SPECT for perfusion imaging. Perfusion factors were defined as the mean percentile perfusion levels of the 4 areas, top to 75%, 75% to 50%, 50% to 25%, 25% to 0%, re-spectively. fEUD was calculated from perfusion factors and standard dose-volume parameters extracted from treatment planning computed tomography (CT) scans. Total lung (TL), ipsilateral (IL) and contralateral lung (CL) volumes minus gross tumor volume (GTV), whole-lung V5, V20, whole lung fEUD, IL and CL fEUD, and general equivalent uniform dose (gEUD) were analyzed to evaluate correlations between RP using Common Terminology Criteria for Adverse Events (CTCAE) version 4.03. Statistical significance was defined as P<0.05. Results: A total of 15 patients treated with intensity modulated RT or 3D conformal RT were analyzed, grades≥3 RP were observed in 6 patients. There was only a trend toward significance for unilateral (UL) fEUD of higher dose side (P=0.007). Whole-lung V5, V20 were almost identical between patients who developed pneumonitis and patients who did not, as the values were below the recommended thresholds from published papers. Unilateral fEUDs were linear with unilateral gEUDs (t=0.815, P=0.000). Conclusion: SPECT-based equivalent uniform dose appears to be a better predictor of RP compared to stan-dard dose-volume parameters. Planning constraints should aim to keep unilateral fEUD below 21 Gy.