Comparison of normal tissue doses in deep inspiration breath-hold and free breathing methods for radiotherapy of left-sided breast cancer using 4D-XCAT digital phantom.

Purpose: To evaluate normal lung and heart tissue doses for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB) as a function of breast size and diaphragm displacement using 4D-XCAT digital phantom in a simulation study. Materials and Methods: 4D-XCAT digital phantom was used to create 36 left-sided breast cancer digital phantom datasets with different breast height (BH) of 40, 50, and 60 mm, breast length (BL) of 16, 17, and 18 mm, and diaphragm excursion of 20, 25, 30, and 35 mm. For each dataset, DIBH and FB treatment plans were prepared using planning computerized radiotherapy-three dimensional (PCRT-3D) treatment planning system (TPS) with superposition computational algorithm. Dose differences in DIBH and FB plans were assessed in terms of mean lung dose (MLD), the lung volume receiving ≤20 Gy (V20), normal tissue complication probability (NTCP) of the lung, mean heart dose (MHD), and the heart volume receiving ≤30 (V30). Results: DIBH reduced mean dose and V20 and NTCP of the lung in all cases, by up to 4.37 Gy, 7.62%, and 18.95%. Mean dose and V30 of the heart were also significantly reduced by 5.02 Gy and 8.23%. Conclusions: The use of DIBH for left-sided breast cancer radiotherapy offers excellent possibilities for sparing critical normal tissue without compromising radiation dose to the target.

Normal lung tissue complication probability in MR-Linac and conventional radiotherapy.

PURPOSE: To study normal lung tissue (NLT) complications in magnetic resonance (MR) image based linac and conventional radiotherapy (RT) techniques. MATERIALS AND METHODS: The Geant4 toolkit was used to simulate a 6 MV photon beam. A homogenous magnetic field of 1.5 Tesla (T) was applied in both perpendicular and parallel directions relative to the radiation beam.Analysis of the NLT complications was assessed according to the normal lung tissue complication probability (NTCP), the mean lung dose (MLD), and percentage of the lung volume receiving doses greater than 20 Gy (V20), using a sample set of CT images generated from a commercially available 4D-XCAT digital phantom. RESULTS: The results show that the MLD and V20 were lower for MR-linac RT. The largest reduction of MLD and V20 for MR-linac RT configurations were 5 Gy and 29.3%, respectively. CONCLUSION: MR-linac RT may result in lower NLT complications when compared to conventional RT.

Evaluation of the organs at risk doses for lung tumors in gated and conventional radiotherapy.

PURPOSE: The purpose of this study was to evaluate the organs at risk (OARs) doses for lung tumors in gated radiotherapy (RT) compared to conventional RT using the four-dimensional extended cardiac-torso (4D-XCAT) digital phantom in a simulation study. MATERIALS AND METHODS: 4D-XCAT digital phantom was used to create 32 digital phantom datasets of different tumor diameters of 3 and 4 cm, and motion ranges (MRs) of 2, 2.5, 3, and 3.5 cm and each tumor was placed in four different lung locations (right lower lobe, right upper lobe, left lower lobe, and left upper lobe). XCAT raw binary images were converted to the digital imaging and communication in medicine format using an in-house MATLAB-based program and were imported to treatment planning system (TPS). For each dataset, gated and conventional treatment plans were prepared using Planning Computerized RadioTherapy-three dimensional (PCRT-3D) TPS with superposition computational algorithm. Dose differences between gated and conventional plans were evaluated and compared (as a function of 3D motion and tumor volume and its location) with respect to the dose-volume histograms of different organs-at-risk. RESULTS: There are statistically significant differences in dosimetric parameters among gated and conventional RT, especially for the tumors near the diaphragm (P < 0.05). The maximum reduction in the mean dose of the lung, heart, and liver were 6.11 Gy, 1.51 Gy, and 10.49 Gy, respectively, using gated RT. CONCLUSIONS: Dosimetric comparison between gated and conventional RT showed that gated RT provides relevant dosimetric improvements to lung normal tissue and the other OARs, especially for the tumors near the diaphragm. In addition, dosimetric differences between gated and conventional RT did generally increase with increasing tumor motion and decreasing tumor volume.

Evaluation of normal lung tissue complication probability in gated and conventional radiotherapy using the 4D XCAT digital phantom.

PURPOSE: The present study was conducted to investigate normal lung tissue complication probability in gated and conventional radiotherapy (RT) as a function of diaphragm motion, lesion size, and its location using 4D-XCAT digital phantom in a simulation study. MATERIALS AND METHODS: Different time series of 3D-CT images were generated using the 4D-XCAT digital phantom. The binary data obtained from this phantom were then converted to the digital imaging and communication in medicine (DICOM) format using an in-house MATLAB-based program to be compatible with our treatment planning system (TPS). The 3D-TPS with superposition computational algorithm was used to generate conventional and gated plans. Treatment plans were generated for 36 different XCAT phantom configurations. These included four diaphragm motions of 20, 25, 30 and 35 mm, three lesion sizes of 3, 4, and 5 cm in diameter and each tumor was placed in four different lung locations (right lower lobe, right upper lobe, left lower lobe and left upper lobe). The complication of normal lung tissue was assessed in terms of mean lung dose (MLD), the lung volume receiving ≥20 Gy (V20), and normal tissue complication probability (NTCP). RESULTS: The results showed that the gated RT yields superior outcomes in terms of normal tissue complication compared to the conventional RT. For all cases, the gated radiation therapy technique reduced the mean dose, V20, and NTCP of lung tissue by up to 5.53 Gy, 13.38%, and 23.89%, respectively. CONCLUSIONS: The results of this study showed that the gated RT provides significant advantages in terms of the normal lung tissue complication, compared to the conventional RT, especially for the lesions near the diaphragm.