Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_11_3226 - Effect of the Number of Arcs and Target Dose Homogeneity on the Normal Tissue Sparing for SBRT Plan in Liver Cancer Patients

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Effect of the Number of Arcs and Target Dose Homogeneity on the Normal Tissue Sparing for SBRT Plan in Liver Cancer Patients
J. Xiao, H. Shi, J. He, K. Yang, X. Wang, and N. Chen; Department of Radiation Oncology, Cancer Center and State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China

Purpose/Objective(s): To evaluate the effect of the number of arcs and target dose homogeneity on the dose sparing of normal tissue for stereotactic radiotherapy (SBRT) plans in liver cancer patients.

Materials/Methods: Ten patients (4 males and 6 females) with primary or metastatic liver cancer were analyzed. Two groups of volumetric modulated arc therapy (VMAT) plans (Group A and B) with 1 to 4 arcs (239-359°) were generated by RayStation treatment planning system and customized to the Versa HD accelerator. In Group A, the PTV dose was controlled in 90% - 120% of the prescription dose (based on RTOG 0438), and the dose homogeneity of target was not restricted in Group B. A total dose of 48 Gy in 4 fractions was prescribed to the PTV. Ten rings (5 mm width for each ring) outside the PTV were created to limit the dose of normal tissue and evaluate the dose fall-off. All the plans were optimized by using an automatic optimizer developed by our team to avoid the effects of man-made factors. The dose-volume parameters, delivery time among ≥3 plans were analyzed by Friedman test and those between two values were compared by Wilcoxon signed ranks test; p < 0.05 (2-tailed, Friedman) and p < 0.05/N (2-tailed, Wilcoxon, N = n(n-1)/2, where n is the number of groups) was considered statistically significant.

Results: All the VMAT plans achieved acceptable target coverage with 43.2 Gy delivered to more than 99% of the PTV and 95% of the target receiving 48 Gy. As the number of arc increased, the doses of organs at risk (OARs, such as the mean liver dose, the maximum dose of stomach, etc.) were reduced by up to 21.5% (2 arcs vs. 1 arc), 17.8% (3 arcs vs. 2 arcs) in Group A (p < 0.008) and 23.4% (2 arcs vs. 1 arc), 32.2% (3 arcs vs. 2 arcs) in Group B (p < 0.008), while the value was only 1.38% (4 arcs vs. 3 arcs) in Group A and there was no statistic difference between 4 arcs and 3 arcs in Group B. The dose of ring 1-10 was improved when using more arcs, in which the mean dose was reduced by 9.1-13.3% (2 arcs vs. 1 arc), 1.5-5.1% (3 arcs vs. 2 arcs) for Group A and 12.3-17.2% (2 arcs vs. 1 arc), 0.9-3.2% (3 arcs vs. 2 arcs) for Group B. The gradient index (GI) was improved by approximately 14% (2 arcs vs. 1 arc) for both Group A and B (p < 0.008). The doses of OARs in Group B were improved by up to 7.5% compared to those in Group A (p < 0.05). Similarly, the value was 5.2% and 5.0% for the mean rings dose and GI (p < 0.05). The monitor units (MUs) and delivery time increased with the number of arc (p < 0.008). For 1-4 arcs VMAT plans, the median delivery time increased from approximately 3 min to 5min.

Conclusion: The VMAT SBRT plans with inhomogeneous target dose yielded better dose fall-off and OARs sparing for liver cancer patients. Increasing the number of arcs reduced the dose of normal tissue but at the expense of more delivery time. The three arc VMAT plans without constraint of target dose homogeneity seemed to provide a good trade-off between delivery efficiency and plan quality for liver cancer SBRT.

Author Disclosure: J. Xiao: None. H. Shi: None. J. He: None.

Jianghong Xiao

Biography:
Jianghong Xiao
Ph.D, Radiation Oncology Physicist.
Department of Radiation Oncology, Cancer Center,
West China Hospital, Sichuan University
37 Guoxue Lane, Chengdu, Sichuan, PR. China
Office Phone: +86 28 85423529
Mobile Phone: +86 28 13688031116
Postal code: 610041
Email: xiaojh86@foxmail.com
Research Interests
 Medical Imaging for Radiation Therapy
 Automatic Radiotherapy Planning
Education
 Sep., 2016 - 2018 Sichuan University, West China Clinical Medical College, Doctor
 Sep., 2006 - Jun., 2010, Sichuan University, West China Clinical Medical College, Master
 Sep., 1998 – Jun., 2003, Sichuan University, West China Clinical Medical College, Bachelor
Certifications
 Radiation Oncology Physicist (2008).
Representative Publications
Jianghong Xiao#, Yan Li#, Huashan Shi#, Tangel Chang, Yong Luo, Xuetao Wang, Yang He, Nianyong Chen*, Multi-criteria optimization achieves superior normal tissue sparing in intensity-modulated radiation therapy for oropharyngeal cancer patients, Oral oncology, 2018 May;vol 80: 74-81. doi: 10.1016/j. oraloncology.2018.03.020
Jinlan He#, Jianghong Xiao#, Xingchen Peng#, Baofeng Duan, Yan Li, Ping Ai, Min Yao and Nianyong Chen*, Dose escalation by image-guided intensity-modulated radiotherapy leads to an increase in pain relief for spinal metastases: a comparison study with a regimen of 30 Gy in 10 fractions, Oncotarget, 2017 Jul 4;8(68):112330-112340. doi: 10.18632/oncotarget.18979
Jianghong Xiao#, Yan Li#, Qingfeng Jiang#, Lan Sun#, Fraser Henderson Jr, Yongsheng Wang, Xiaoqin Jiang, Guangjun Li and Nianyong Chen*, Hepatic arterial phase and portal venous phase computed tomography for dose calculation of stereotactic body radiation therapy plans in liver cancer: a dosimetric comparison study, Radiat Oncol, 2013 Nov 9;8:264. doi: 10.1186/1748-717X-8-264
Jianghong Xiao#, Hong Zhang#, Youling Gong#, Yuchuan Fu*, Bin Tang, Shichao Wang, Qingfeng Jiang, Ping Li, Feasibility of using intravenous contrast-enhanced computed tomography (CT) scans in lung cancer treatment planning, Radiother Oncol, 2010, 96(1): 73-77

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