Dosimetric Factors Used for Thoracic X-Ray Radiotherapy are not Predictive of the Occurrence of Radiation Pneumonitis after Carbon-Ion Radiotherapy

Dosimetric Factors Used for Thoracic X-Ray Radiotherapy are not Predictive of the Occurrence of Radiation Pneumonitis after Carbon-Ion Radiotherapy

MASASHI KOTO,^1,2 HIROHIKO TSUJII,¹ NAOYOSHI YAMAMOTO,¹ HIDEKI NISHIMURA,¹ SHOGO YAMADA² and TADAAKI MIYAMOTO¹

¹Research Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan
²Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan

Radiation pneumonitis (RP) is one of the most common dose-limiting toxicities in thoracic X-ray radiotherapy (XRT). Dosimetric factors are used for prediction of the occurrence of RP after XRT. Carbon-ion radiotherapy (CRT) is a promising modality because of its excellent dose localization and high biological effect on tumors. This study aims to analyze the relationship between dosimetric factors developed for XRT and the incidence of RP in patients with stage I non-small cell lung cancer (NSCLC) after CRT. We examined 80 inoperable patients with NSCLC. The ranges of the daily fraction sizes and the total doses were from 3.3 to 8.8 GyE and from 59.4 to 95.4 GyE, respectively. These doses were successfully delivered with acceptable toxicity; ≥grade 2 RP was observed in 8 patients (10%). The severity of RP was graded within 6 months of the initiation of CRT using the Radiation Therapy Oncology Group criteria. These results indicate the excellent dose distribution of CRT. We then compared the dosimetric data of the 8 patients developed ≥grade 2 RP with those of 72 patients developed ≤grade 1 RP. Dosimetric factors useful for predicting RP in XRT, such as the percentage of the computed tomography-defined total lung volume receiving > 5, > 20, and > 30 GyE, and mean lung dose, were not predictive factors for RP after CRT. The dosimetric factors used for XRT are not applicable for CRT in patients with NSCLC. The dosimetric factors for CRT remain to be developed.

keywords —— non-small cell lung cancer; carbon-ion radiotherapy; radiation pneumonitis; dosimetric factor; normal tissue

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Tohoku J. Exp. Med., 2007, 213, 149-156

Correspondence: Masashi Koto, Department of Radiation Oncology, Tohoku University School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.

e-mail: koto@rad.med.tohoku.ac.jp