Dosimetric and Patient Preference Analysis between 4-Dimension CT (4D CT) Scan and Deep Inspiration Breath Holding (DIBH) for SBRT in Lung Tumors

Purpose/Objective(s)

Stereotactic body radiation therapy (SBRT) for early lung tumors and oligometastasis in the lung is a proven treatment technique. Motion management plays an essential role in very accurate treatment delivery. Among the various techniques available, the most widely implemented are Deep Inspiration Breath holding (DIBH) and 4 Dimensional CT (4DCT) scan. This study aims to compare the techniques mentioned above dosimetrically and according to patient preferences. This analysis would let us know the better motion management technique for each patient

Materials/Methods

All eligible patients for SBRT of lung treatment undergo both DIBH and 4D CT scans planning images. Contouring and planning are done on both these sets of images, and based on the dosimetric profile and patient preference, select the appropriate treatment. We retrospectively analyzed the initial five patients who were treated with SBRT for lung. All these patients underwent CT simulation using 4D CT and DIBH techniques. For the 4D CT, Maximum intensity projection (MIP) images were created, and contouring was done on these images. Planning Target Volume (PTV) was created, and planning was done on treatment planning system planning software. 6MV FFF beam (Dose rate of 1400MU/min) using Volumetric Modulated Arc Therapy (VMAT) technique was used for planning. The dose to the target volume was kept uniform and doses to normal tissue were noted for both the plans

Results

The dose to the PTV was 54 Gy in 3 fractions, and all were able to adapt to the deep breath-hold technique. With the DIBH increased lung volume, the mean right lung and left lung volumes were 1848.4 cc and 1636.2 cc, respectively, 1.49 times and 1.64 times more than the mean right lung (1237.5 cc) and left lung (993.46 cc) on 4D CT respectively. The mean GTV on DIBH was 30.62 cc, and that on 4D CT was 37.21 cc. This 4D CT GTV, in effect, was nearly 1.2 times more in volume than DIBH. The mean dose of the ipsilateral lung on DIBH was 5.35 Gy, and on 4D CT, it was 6.16 Gy, which is 1.15 times more than DIBH, both well within the tolerance limits of the lung. The Conformity index (CI) and homogeneity index (HI) for both the plans were similar. The dose to other normal tissue was the same for both plans. Peripheral lesions that are adherent to pleura GTV/ ITVs are almost the same in both DIBH and 4D CT

Conclusion

The volume of GTV was slightly lesser in DIBH because of the breath-holding. But for peripheral tumors (metastasis), which are adherent to pleura, given decreased movements of GTV/ ITV, are almost the same in both DIBH and 4D CT. The mean dose to the ipsilateral lung is less in DIBH than 4D CT. The analysis shows that SBRT in DIBH and 4D CT is an equally good technique with a dose to the normal tissues well within normal limits and can be individualized according to the patient's comfort and location of the tumor, with an overall preference for the DIBH technique