Effect of stereotactic dosimetric end points on overall survival for Stage I non-small cell lung cancer: a critical review

Feasibility of a TPS-integrated method to incorporate tumor motion in the margin recipe

BACKGROUND AND PURPOSE

There are several alternatives to the widespread ITV strategy in order to account for breathing-induced motion in PTV margins. The most sophisticated one includes the generation of a motion-compensated CT scan with the CTV placed in its average position - the mid-position approach (MidP). In such configuration, PTV margins integrate breathing as another random error. Despite overall irradiated volume reduction, such approach is barely used in clinical practice because of its dependence to deformable registration and its unavailability in commercial treatment planning systems. As an alternative, the mid-ventilation approach (MidV) selects the phase in the 4D-CT scan that is the closest to the MidP, with a residual error accounted for in the PTV margin. We propose a treatment planning system-integrated strategy, aiming at better approximating the MidP approach without its drawbacks: Hybrid MidV-MidP approach, i.e., the delineation on the MidV-CT and translation at the mid-position coordinates using treatment planning system built-in capabilities.

MATERIAL AND METHODS

Forty-five lung lesions treated with stereotactic radiotherapy were selected. PTV was defined using MidP, MidV, Hybrid MidV-MidP and ITV strategies. Margin definitions were adapted and resulting PTVs were compared.

RESULTS

Hybrid MidV-MidP showed similar target volume and location than the MidP and confirmed that margin-incorporated tumor motion strategies lead to significantly smaller PTVs than the ITV with mean reduction of 26 ± 7%.

CONCLUSION

We report on the successful implementation of a pseudo-MidP solution without its inherent drawbacks. It answers the need for TPS-embedded tumor motion range identification and related margin's component calculation.

microRNA-181b suppresses the metastasis of lung cancer cells by targeting sex determining region Y-related high mobility group-box 6 (Sox6)

BACKGROUND

The aim of the study was to measure the expression of microRNA (miR)-181b in patients with lung cancer, investigate its biological function and elucidate the underlying mechanisms associated with the development of lung cancer.

METHODS

miR-181b expression in tissues was measured via RT-qPCR. After A549 cells were transfected with miR-181b mimic or si-Sox6, the proliferation, migration and cell cycle distribution of A549 were evaluated using cell counting kit-8 assay, transwell assay and flow cytometry. The levels of cell cycle-related proteins and Sox6 were analyzed by western blotting. Gene targets of miR-181b were predicted via bioinformatics analysis and verified using a dual-luciferase reporter gene assay.

RESULTS

Expression of miR-181b was significantly downregulated in lung cancer tissues (P < 0.05), and was inversely correlated with the degree of cell differentiation and clinical stages of lung cancer (both P < 0.05). Additionally, the expression of miR-181b was significantly lower in adenocarcinoma compared with squamous cell carcinoma in the lungs (P < 0.05). Overexpression of miR-181b significantly decreased the protein level of Sox6 and significantly suppressed the cell proliferation and metastasis (both P < 0.05); this effect was also observed in A549 cells transfected with si-Sox6. The luciferase activity of a Sox6 3'-untranslated region-based reporter construct was significantly lower when transfected with miR-181b (P < 0.05), which suggests that Sox6 is a direct target of miR-181b.

CONCLUSION

The results of the present study suggest that miR-181b may function as a tumor inhibitor in the development of lung cancer via targeting Sox6 to decrease the proliferation and metastasis of lung cancer cells.

Fine-tuning the normal tissue objective in eclipse for lung stereotactic body radiation therapy

The purpose of this study was to characterize the effects of the normal tissue objective (NTO) on lung stereotactic body radiation therapy (SBRT) dose distributions. The NTO is a spatially varying constraint used in Eclipse to limit dose to normal tissues by steepening the dose gradient. However, the multitude of potential NTO setting combinations challenges optimal NTO tuning. In the present study, a broad range of NTO settings are investigated for lung SBRT treatment planning with volumetric modulated arc therapy(VMAT). Ten prior lung SBRT cases were replanned using NTO priorities of 1, 50, 100, 200, 500, and 999 in combination with fall-off values of 0.01, 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 1.00, and 5.00 mm^-1 and the automatic NTO. NTO distances to planning target volume (PTV), start dose, and end dose were 1 mm, 100%, and 10%, respectively, for all 600 plans. Prescription dose covered 95% of the PTV. The following metrics were recorded: conformity index (CI), ratio of the 50% prescription isodose volume to PTV (R_50%), maximum dose 2 cm away from PTV (D_2cm), lung volume of ≥20 Gy (V_20Gy), maximum PTV dose (PTV_max), and monitor units (MUs). Differences between prior plans and NTO plans were evaluated using the Wilcoxon signed-rank test. Different combinations of NTO settings resulted in wide-ranging plan quality metrics: CI (1.00 to 1.54), R_50% (3.95 to 7.57), D_2cm (33.4% to 67.9%), V_20Gy (1.66% to 2.75%), MU (1.81 cGy^-1 to 4.69 cGy^-1), and PTV_max (118% to 175%). Although no settings were optimal for all metrics, a fall-off of 0.15 mm^-1 and a priority of 500 best satisfied institutional criteria. Compared with prior plans, NTO plans resulted in significantly lower R_50% (4.00 vs 4.35, p = 0.002), lower V_20Gy (1.22% vs 1.32%, p = 0.006), and higher PTV_max (138% vs 122%, p = 0.002). All of the prior and well-tuned NTO plans met Radiation Therapy Oncology Group (RTOG) 0813 guidelines. Lung SBRT dose distributions were characterized across a range of NTO settings. NTO plans with well-tuned settings compared favorably with prior plans.

Adherence to ICRU-83 reporting recommendations is inadequate in prostate dosimetry studies

PURPOSE

This study aimed to investigate if the International Commission on Radiation Units and Measurements (ICRU) 83 recommendations for reporting dosimetric endpoints are followed in published prostate studies using modulated techniques.

METHODS AND MATERIALS

Prostate dosimetry studies using inverse planning techniques were identified through a search of PubMed and EMBASE databases. These studies were analyzed to determine if the endpoints reported followed the recommendations outlined in ICRU-83. A data collection form was completed and any alternative methods of reporting were recorded. Results were analyzed using frequencies, percentages, and Fisher exact tests.

RESULTS

The ICRU-83 recommendations were not followed in the majority of studies. For the planning target volume, the dose received by 2% of the volume, the dose received by 98% of the volume, and the dose received by 50% of the volume were reported in 22.9%, 18.8%, and 8.3% of studies, respectively. The adherence to reporting for the clinical target volume was below 5% for all specifications. The mean dose, the dose received by a specified volume, and dose received by 2% of the volume for organs at risk were reported in 47.1%, 83.3%, and 16.7%, respectively. The homogeneity index was used in 14.6% of studies. Conformity was discussed in 45.8% of studies. Confidence intervals were included in 37.5% of studies.

CONCLUSIONS

The reporting recommendations of ICRU-83 were not adhered to in the majority of the dosimetry studies reviewed, highlighting the need for greater diligence for authors and reviewers when publishing planning outcomes for modulated techniques.