Technical Note: Comparison of the internal target volume (ITV) contours and dose calculations on 4DCT, average CBCT, and 4DCBCT imaging for lung stereotactic body radiation therapy (SBRT)

Abstract

Purpose: To investigate the differences between internal target volumes (ITVs) contoured on the simulation 4DCT and daily 4DCBCT images for lung cancer patients treated with stereotactic body radiotherapy (SBRT) and determine the dose delivered on 4D planning technique. Methods: For nine patients, 4DCBCTs were acquired before each fraction to assess tumor motion. An ITV was contoured on each phase of the 4DCBCT and a union of the 10 ITVs was used to create a composite ITV. Another ITV was drawn on the average 3DCBCT (avgCBCT) to compare with current clinical practice. The Dice coefficient, Hausdorff distance, and center of mass (COM) were averaged over four fractions to compare the ITVs contoured on the 4DCT, avgCBCT, and 4DCBCT for each patient. Planning was done on the average CT, and using the online registration, plans were calculated on each phase of the 4DCBCT and on the avgCBCT. Plan dose calculations were tested by measuring ion chamber dose in the CIRS lung phantom. Results: The Dice coefficients were similar for all three comparisons: avgCBCT-to-4DCBCT (0.7 ± 0.1), 4DCT-to-avgCBCT (0.7 ± 0.1), and 4DCT-to-4DCBCT (0.7 ± 0.1); while the mean COM differences were also comparable (2.6 ± 2.2mm, 2.3 ± 1.4mm, and 3.1 ± 1.1mm, respectively). The Hausdorff distances for the comparisons with 4DCBCT (8.2 ± 2.9mm and 8.1 ± 3.2mm) were larger than the comparison without (6.5 ± 2.5mm). The differences in ITV D95% between the treatment plan and avgCBCT calculations were 4.3 ± 3.0% and −0.5 ± 4.6%, between treatment plan and 4DCBCT plans, respectively, while the ITV V100% coverages were 99.0 ± 1.9% and 93.1 ± 8.0% for avgCBCT and 4DCBCT, respectively. Conclusion: There is great potential for 4DCBCT to evaluate the extent of tumor motion before treatment, but image quality challenges the clinician to consistently delineate lung target volumes.

Intrafraction target shift comparison using two breath-hold systems in lung stereotactic body radiotherapy

“…However, the volume of normal tissue is increased, which might increase the risk of radiation-related toxicity [4] , [5] . Dose delivery accuracy can be augmented by the use of respiratory management techniques such as abdominal compression [6] , 4-dimensional Computed Tomography (4DCT) [7] , Deep Inspiration Breath-Hold (DIBH) [8] and real-time tumor tracking [9] , [10] .…”

A four‐dimensional dynamic conformal arc approach for real‐time tumor tracking: A retrospective treatment planning study

“…After obtaining institutional ethics approval (Lawson Approval Number: R-23-086), ten (10) patients with early-stage NSCLC treated with a hypofractionated treatment scheme using a free-breathing VMAT technique were retrospectively analyzed in the treatment planning system Eclipse v15.6 (Varian Medical Systems, Palo Alto, USA). Seven patients were treated with an ablative dose defined by a BED 10 > 100 Gy, while three were retreatment scenarios with a reduced dose per fraction.…”

“…An internal target volume (ITV) is defined as a combination of the visible tumor while considering the potential motion and deformation of the volume during treatment. Typically, an ITV is created either by taking the union of the gross tumor volume (GTV) at every respiratory phase of the patient's 4D‐CT or by directly contouring on the patient's free‐breathing CT 10 . However, widening the field size inevitably increases the amount of dose delivered to the surrounding healthy tissue.…”

Deep Learning-Based Internal Target Volume (ITV) Prediction Using Cone-Beam CT Images in Lung Stereotactic Body Radiotherapy

“…Dumas (2019) studied 9 patients and found that the Dice similarity coefficient (DSC) and mean center of mass (COM) is similar for avgCBCT and 4DCT. 13 Thus, we want to use a deep learning-based method to predict the ITV in CBCT and evaluate the accuracy against 4DCT delineation in this study. 4D-CBCT was not used in the current study because 4D-CBCT images also suffer from reduced image quality because of deficient projections in each phase bin after phase-sorting.…”

“…Moreover, the disagreement between the external surface and actual tumor motion, especially tumors close to the diaphragm, would also result in inappropriate binning, inaccurate tumor location, and noticeable imaging artifacts. 8 , 13 …”