Importance of four-dimensional computed tomography simulation in locally advanced lung cancer radiotherapy: Impact on reducing planning target volume

Background/Aim. Four dimensional (4DCT) simulation is a useful tool for motion assessment in lung cancer radiotherapy. Conventional Three dimensional (3D) - Free Breathing simulation is static, with limited motion information. The aim of this study was to compare clinically significant differences between the target volumes defined on 3D CT vs. 4D CT simulation and potential impact on the planning target volume (PTV). In addition, to quantify movements of primary tumour (GTV) during 4D CT simulation on three axis -Z-supero inferior (SI), X-mediolateral (ML), and Y-anteroposterior (AP). Methods. This retrospective study evaluated 20 lung cancer patients who underwent CT simulation for radical radiotherapy treatment. Free Breathing 3D CT and 4D CT simulation were acquired for each patient in accordance with our institutional protocol. Volumetric comparison radiation volumes defined on 3D CT vs. 4D CT simulation was done-Gross tumour volume GTV 3D vs. internal GTV- (iGTV 4D) and PTV 3D vs. iPTV 4D. Volumetric values expressed in cm3 and equivalent spherical diameter (ESD) expressed in cm were assessed. Comparison of GTV movement in the phase FB-GTV FB, phase 0-GTV0, phase 50-GTV 50, and phase Maximum intensity projection (MIP) -GTV MIP was made with GTV FB as the basic value. The evaluation was made in three axis. Results. Comparison volumetric values between GTV 3D vs. iGTV 4D was 63.15 vs.85.51 (p<0.001) respectively. iGTV 4D was significantly larger than GTV 3D (p<0.001). The mean value (ESD) PTV 3D vs.iPTV 4D was 8.44 vs. 7.82 (p<0.001) respectively, and mean value volume PTV 3D vs. iPTV 4D was 352.70 vs. 272.78 (p<0.001) respectively. PTV 3D was significantly larger than iPTV 4D (p<0.001). Statistically significant difference (p<0.05) was identified in the deviation related to Z axis between the upper and lower lobe. Conclusion. 4D CT simulation based delineation can reduce planning target volume compared to 3D simulation based radiation therapy and therefore, it is a prerequisite for high-quality and precise radiation therapy treatment.

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The impact of four dimensions CT simulation on planning target volume in radiotherapy for primary lung cancer.

Journal of Clinical Oncology ◽

10.1200/jco.2017.35.15_suppl.e20091 ◽

2017 ◽

Vol 35 (15_suppl) ◽

pp. e20091-e20091

Author(s):

Fawzi Jamil Abuhijla ◽

Lubna Abdelrahman Hammoudeh ◽

Ramiz Ahmad Abu-Hijlih ◽

Jamal Khader

Keyword(s):

Lung Cancer ◽

Planning Target Volume ◽

Tumor Volume ◽

Multivariable Analysis ◽

Primary Lung Cancer ◽

Free Breathing ◽

Target Volume ◽

4D Ct ◽

Ct Simulation ◽

The Impact

e20091 Background: 4D CT simulation has been evolved to estimate the internal body motion and considered as a useful tool for intra-thoracic tumor definition. This study aimed to evaluate the impact of using 4D simulation on the planning target volume (PTV) for primary lung tumor. Methods: Patients who underwent CT simulation for primary lung cancer radiotherapy between 2012-2016 using 3D- (free breathing) and 4D- (respiratory gated) institutional protocol were included in this retrospective review. For each patient, gross tumor volume (GTV) was contoured in free breathing scan (3D-GTV), exhale scan (e-GTV) and inhale scan (i-GTV). The corresponding CTVs (3D-CTV, e-CTV and i-CTV) were created by adding 1 cm in all directions. 3D-internal target volume (3D-ITV) was generated by 0.5 cm cranio-caudal expansion of 3D-CTV, while 4D-ITV was created by combination of e-CTV and i-CTV. Subsequently, a 0.5 cm margin was added to generate the 3D-PTV and 4D-PTV respectively. The volumes of 3D-PTV and 4D-PTV were compared to examine the impact of 4D CT simulation on changes in the volume of PTV. Univariable and multivariable analysis were performed to test the impact of volume and location of GTV on the changes of PTV volume by more than 10 % between free breathing and respiratory gated scans. Results: A total of 10 patients were identified. The median [range] GTV, i-GTV, e-GTV volumes were 13.55 [1.44-628.66], 13.17 [1.77-627.36], 12.85 [1.34-630.25] cc respectively. The 3D-CTV, i-CTV, e-CTV volumes were 86.37 [23.76-1209], 84.97 [25.5- 1220.4], 83.40 [23.36-1224.12] cc respectively. 3D-ITV and 4D-ITV median volume was 106.06 [3.99-1422.8], 88.02 [20.51-1338.18] cc respectively. 3D-PTV was significantly larger than the 4D-PTV; median [range] volumes were 182.79 [58.65- 1861.05] vs. 158.21 [52.76-1771.02] cc, p = 0.0068). On multivariable analysis, neither the volume of GTV (p = 0.4917), nor the location of the tumor (peripheral, p = 0.4914 or lower location, p = 0.9594) had an in impact on PTV differences between free breathing and respiratory gated scans. Conclusions: The use of 4D simulation reduces the PTV for primary lung cancer, and it should be routinely implemented in clinical practice regardless the tumor volume or location.

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