real-time tumor tracking radiation therapy (RTRT) system in which the linear ...
motion, SBRT using the RTRT system achieved LC and OS comparable to other.
Stereotactic Body Radiotherapy using Gated Radiotherapy with Real-time Tumor-tracking for Stage I Non-Small Cell Lung Cancer Tetsuya Inoue1, M.D., Norio Katoh1, M.D., Rikiya Onimaru1, M.D., Ryusuke Suzuki2, Ph.D., 3 3 3 1 Jun Sakakibara-Konishi , M.D., Naofumi Shinagawa , M.D., Satoshi Oizumi , M.D., Hiroki Shirato M.D. 1
Department of Radiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan 2 Department of Medical Physics, Hokkaido University Graduate School of Medicine, Sapporo, Japan 3 First Department of Medicine, Hokkaido University School of Medicine, Sapporo, Japan
Summary The clinical outcomes of stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer using a real-time tumor-tracking radiation therapy system was investigated. We found that there was no correlation between larger maximum amplitude of marker movement and larger planning target volume, mean lung dose (MLD), or the volume of lung receiving 20 Gy (V20). We achieved local control and overall survival rates comparable to other SBRT with very low incidence of radiation pneumonitis, which was consistent with small MLD and V20 irrespective of respiratory amplitude of the tumor motion.
■ Results With a median follow-up period of 25 months (range, 4 to 72 months), the 5year local control rate (LC) was 78% and the 5-year overall survival rate (OS) was 64%. The 5-year LC was 83% and the 5-year OS was 75% in patients with T1a (tumor diameter ≤ 20 mm), compared with 72% and 56% for those with T1b or T2 (tumor diameter > 20 mm). The OS in patients with T1a was significantly better than those with T1b or T2 (p = 0.01). LC
T1a
OS Probability
Probability
T1b/T2
■ Purpose/Objective The aim of the present study was to clarify the clinical outcomes of stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC) using a real-time tumor tracking radiation therapy (RTRT) system in which the linear accelerator is gated to irradiate the tumor only when the implanted fiducial marker is within 2 mm from its planned position.
■ Materials/Methods Characteristics Age (years) Median Range Gender (n) Male Female Histology (n) Adenocarcinoma Squamous cell carcinoma Large cell carcinoma Unclassified NSCLC Histological unproved T stage (n) T1a T1b T2 Tumor site (n) Upper lobe Middle lobe Lower lobe Dose prescription (n) 48Gy/4fr at isocenter 40Gy/4fr to the 95% volume of PTV
Value 78 47-90 74 35 65 29 1 8 6 47 32 30 50 13 46 30 79
Gross tumor volume (GTV) was defined using multi-slice computed tomography (CT) taken at the end of expiration during breath holding. The clinical target volume (CTV) was the GTV plus 6 mm for squamous cell carcinoma and 8 mm for adenocarcinoma. The planning target volume (PTV) was the CTV plus a 5-mm margin irrespective of the amplitude of the tumor. Target volume margins were fixed irrespective of the tumor amplitude. Therefore, the target volume did not increase when the tumor movement was large, especially in the lower lobe. In our RTRT system, the irradiated volume depended only on tumor size. Using a superposition algorithm, we administered 48 Gy in 4 fractions at the isocenter in 2005‒2006 and 40 Gy in 4 fractions to the 95% volume of PTV in 2007‒2010 with a treatment period of 4 to 7 days.
Acknowledgments This work was supported in part by a grant from “the Matching Program for Innovations in Future Drug Discovery and Medical Care”.
OS Months
Months
Grade 2, 3, 4, and 5 radiation pneumonitis (RP) was experienced by 15 (13.8%), 3 (2.8%), 0, and 0 patients, respectively. The mean lung dose (MLD) and the volume of lung receiving 20 Gy (V20) were significantly higher in patients with RP Grade 2/3 than in those with RP Grade 0/1 (MLD p = 0.002, V20 p = 0.003).There was a strong correlation between larger PTV and larger MLD (r = 0.535, p < 0.001) and V20 (r = 0.627, p < 0.001).
PTV (ml)
PTV (ml)
The mean of maximum amplitude of the marker movement of the lower lobe was 27.2 ± 13.8 mm, which was significantly greater than that of the upper lobe (11.3 ± 9.9 mm, p < 0.001). There was no correlation between larger maximum amplitude of marker movement and larger PTV (r = 0.137), MLD (r = 0.046), or V20 (r = 0.158).
■ Conclusion Using only a 5-mm PTV margin to CTV without additional margin for organ motion, SBRT using the RTRT system achieved LC and OS comparable to other SBRT series with very low incidence of RP, which was consistent with the small MLD and V20 irrespective of respiratory amplitude of the tumor motion. For stage-I NSCLC, SBRT using RTRT was suggested to be reliable and effective, especially for patients with large amplitude of tumor movement.
