Gross tumor volume dependency on phase sorting methods of four-dimensional computed tomography images for lung cancer

Quantification of Lung Tumor Motion and Optimization of Treatment

Background

Mobility of lung tumors is induced by respiration and causes inadequate dose coverage.

Objective

This study quantified lung tumor motion, velocity, and stability for small (≤5 cm) and large (>5 cm) tumors to adapt radiation therapy techniques for lung cancer patients.

Material and Methods

In this retrospective study, 70 patients with lung cancer were included that 50 and 20 patients had a small and large gross tumor volume (GTV). To quantify the tumor motion and velocity in the upper lobe (UL) and lower lobe (LL) for the central region (CR) and a peripheral region (PR), the GTV was contoured in all ten respiratory phases, using 4D-CT.

Results

The amplitude of tumor motion was greater in the LL, with motion in the superior-inferior (SI) direction compared to the UL, with an elliptical motion for small and large tumors. Tumor motion was greater in the CR, rather than in the PR, by 63% and 49% in the UL compared to 50% and 38% in the LL, for the left and right lung. The maximum tumor velocity for a small GTV was 44.1 mm/s in the LL (CR), decreased to 4 mm/s for both ULs (PR), and a large GTV ranged from 0.4 to 9.4 mm/s.

Conclusion

The tumor motion and velocity depend on the tumor localization and the greater motion was in the CR for both lobes due to heart contribution. The tumor velocity and stability can help select the best technique for motion management during radiation therapy.

Dosimetric comparison between three- and four-dimensional computerised tomography radiotherapy for breast cancer

At present, methods of radiotherapy simulation for breast cancer based on four-dimensional computerised tomography (4D-CT) or three-dimensional CT (3D-CT) simulation remain controversial. In the present study, 7 patients with residual breast tissue received whole breast radiotherapy based on 3D-CT and 4D-CT simulation. For the 4D-CT plan, four types of CT images were produced, including images of the end of inspiration and the end of expiration, and images acquired by the maximal intensity projection (MIP) and average intensity projection (AIP). In the 3D-CT plan, the clinical target volume (CTV) and plan target volume (PTV) were marginally higher compared with the 4D-CT plan. In addition, the minimum point dose of the target volume (D_min), the maximum point dose of the target volume (D_max) and the mean point dose of the target volume (D_mean) of the CTV and PTV in the MIP and AIP plans were marginally higher compared with the 3D-CT plan. For the contralateral breast (C-B), volumes of the 4D-CT plan were markedly lower compared with the 3D-CT plan. Furthermore, D_min, D_max and D_mean of the 3D-CT plan were higher compared with the AIP and MIP plans. For the ipsilateral lungs (I-L), volumes of the 3D-CT and AIP plans were higher compared with the MIP plan. Furthermore, when breast lesions were on the left side, for the heart, the volume receiving no less than 40% of the prescription dose (V₄₀) and the volume receiving no less than 30% of the prescription dose (V₃₀) of the MIP and AIP plans were slightly lower compared with those of the 3D plan. In conclusion, 4D-CT radiotherapy based on the MIP and AIP plans provides a slightly smaller radiation area and slightly higher radiotherapy dosage of the CTV and PTV compared with 3D-CT radiotherapy for breast radiotherapy. Therefore, the MIP and AIP plans prevent C-B radiation exposure and improve sparing of the heart and I-L.

Effect of low magnetic field on single-diode dosimetry for clinical use

PURPOSE

To evaluate the effect of a low magnetic field (B-field, 0.35 T) on QED™ for clinical use.

METHODS

Black and Blue QED were irradiated using tri-Co-60 magnetic resonance image-guided radiation therapy systems with and without the B-field. For both detectors, angular dependence of the beam orientation was evaluated by rotating the gantry and detector in parallel and perpendicular directions to the B-field. Angular dependence betweenthe directions of both QED and B-field was also measured. Response on the depth and output factor of both detectors was investigated for parallel and perpendicular setups, respectively.

RESULTS

When Black QED was placed on a surface, detector response decreased by 1.8% and 4.5% for parallel and perpendicular setups, respectively, owing to the B-field. The angular dependence of the beam orientation was not affected by B-field for both detectors. There was a significant angular dependence between Black QED and B-field direction and for the Black QED when the gantry was rotated. Owing to the B-field, the detector response at 90° decreased by 2.4%, response of Black QED on the depth was changed only on the surface, and output factor of Black QED was changed only on the surface. The response of Blue QED was not affected by the B-field for all examined situations.

CONCLUSIONS

Using Black QED on a surface in the same position as that in the calibration requires some correction to the B-field. Blue QED does not require correction as it is not affected by the B-field.

Effects of respiratory motion on volumetric and positional difference of GTV in lung cancer based on 3DCT and 4DCT scanning

Differences in gross target volume (GTV) and central point positions among moving lung cancer models constructed by CT scanning at different frequencies were compared, in order to explore the effect of different respiratory frequencies on the GTV constructions in moving lung tumors. Eight models in different shapes and sizes were established to stimulate lung tumors. The three-dimensional computed tomography (3DCT) and four-dimensional computed tomography (4DCT) scanning were performed at 10, 15 and 20 times/min in different models. Differences in GTV volumes and central point positions at different motion frequencies were compared by means of GTV3Ds (GTV_3D-10, GTV_3D-15, GTV_3D-20) and IGTV4Ds (IGTV_4D-10, IGTV_4D-15, IGTV_4D-20). Volumes of GTV_3D-10, GTV_3D-15, GTV_3D-20 were 12.41±14.26, 10.38±11.18 and 12.50±15.23 cm³ respectively (P=0.687). Central point coordinates in the x-axis direction were −8.16±96.21, −8.57±96.08 and −8.56±95.73 respectively (P=0.968). Central point coordinates in the y-axis direction were 108.22±25.03, 110.41±22.47 and 109.04±24.24 (P=0.028). Central point coordinates in the z-axis direction were 65.19±13.68, 65.43±13.40 and 65.38±13.17 (P=0.902). The difference was significant in the y-axis direction (P=0.028). Volumes of IGTV_4D-10, IGTV_4D-15, IGTV_4D-20 were 17.78±19.42, 17.43±19.56 and 17.44±18.80 cm³ (P=0.417). Central point coordinates in the x-axis direction were −7.73±95.93, −7.86±95.56 and −7.92±95.14 (P=0.325). Central point coordinates in the y-axis direction were 109.41±24.54, 109.60±24.13 and 109.16±24.28 (P=0.525). Central point coordinates in the z-axis direction were 65.52±13.31, 65.59±13.39 and 65.51±13.34 (P=0.093). However, the central point position of GTV in the head and foot direction by 3DCT scanning was severely affected by the respiratory frequency.