Pre-treatment 2D and 3D dosimetric verification of volumetric arc therapy. A correlation study between gamma index passing rate and clinical dose volume histogram

Abstract

Objectives To evaluate methods for the pre-treatment verification of volumetric modulated arc therapy (VMAT) based on the percentage gamma passing rate (%GP) and its correlation and sensitivity with percentage dosimetric errors (%DE). Methods A total of 25 patients with prostate cancer and 15 with endometrial cancer were analysed. The %GP values of 2D and 3D verifications with different acceptance criteria (1%/1 mm, 2%/2 mm, and 3%/3 mm) were obtained using OmniPro and Compass. The %DE was calculated using a planned dose volume histogram (DVH) created in Monaco’s treatment planning system (TPS), which relates radiation dose to tissue and the patient’s predicted dose volume histogram in Compass. Statistical correlation between %GP and %DE was verified using Pearson’s correlation coefficient. Sensitivity was calculated based on the receiver operating characteristics (ROC) curve. Plans were calculated using Collapsed Cone Convolution and the Monte Carlo algorithm. Results The t -test results of the planned and estimated DVH showed that the mean values were comparable ( P > 0.05). For the 3%/3 mm criterion, the average %GP was acceptable for the prostate and endometrial cancer groups, with average rates of 99.68 ± 0.49% and 99.03 ± 0.59% for 2D and 99.86 ± 0.39% and 99.53 ± 0.44% for 3D, respectively. The number of correlations was poor for all analysed data. The mean Pearson’s R-values for prostate and endometrial cancer were < 0.45 and < 0.43, respectively. The area under the ROC curve for the prostate and endometrial cancer groups, was lower than 0.667. Conclusions Analysis of the %GP versus %DE values revealed only weak correlations between 2D and 3D verifications. DVH results obtained using the Compass system will be helpful in confirming that the analysed plans respect dosimetric constraints.

Implementation of TG‐218 for patient‐specific quality assurance tolerance and action limits determination: Gamma passing rate evaluation using 3DVH software

“…Generally, there was an underestimation of the dose to all structures by 3DVH. Similar results have been noted in previous studies 15,16,19 . Higher DDs were observed for the OARs of both tumor sites, while for the PTVs, only one plan of each anatomical region had a %DE higher than 3%.…”

“…Similar results have been noted in previous studies. 15,16,19 Higher DDs were observed for the OARs of both tumor sites, while for the PTVs, only one plan of each anatomical region had a %DE higher than 3%. Specifically, the OARs for which the %DE was the highest (bladder and rectum for prostate plans, parotids for H&N plans) were the ones that usually have the F I G U R E 5 Comparative receiver operating characteristic (ROC) curves of 2D and 3D dosimetric verification methods with two acceptance criteria for head and neck (H&N) plans, along with their respective area under the curve (AUC) values steepest dose gradients, since they are anatomically closer to the target volume.…”

“…Further analysis of the sensitivity of the two methods was performed through comparative ROC curves for the two acceptance criteria. As previous studies have shown, 18,19,28 the sensitivity of %GP is expected to be better for the 3D verification method, since it provides individual results for each structure. In our study, for the H&N plans, the 3D verification method proved to be a better classifier than the 2D one; however, it was still not sensitive enough to be clinically acceptable, with AUC values <0.66.…”

“…Furthermore, even if the %GP are within the AL, the PSQA process cannot be deemed sensitive enough. Several studies [12][13][14][15][16][17][18][19] have proven that %GP are not correlated with clinically relevant parameters, such as the estimated dose variations in the dose-volume histograms (DVH) from the measurement-reconstructed 3D dose distributions.…”

Comparison of pre-treatment and in-vivo dosimetry for advanced radiotherapy of prostate cancer

“…There is a wide interest in developing accurate dosimetry tools, such as diverse detectors capable of reconstructing dose distribution in dynamic treatment plans [ 16 – 18 ]. For example, Delta4 phantom applies a 3D phantom with an array of diode detectors on two orthogonal planes.…”