Tolerance of organs at risk in small-volume, hypofractionated, image-guided radiotherapy for primary and metastatic lung cancers.
OBJECTIVE
To determine the organ at risk and the maximum tolerated dose (MTD) of radiation that could be delivered to lung cancer using small-volume, image-guided radiotherapy (IGRT) using hypofractionated, coplanar, and noncoplanar multiple fields.


METHODS
Patients with measurable lung cancer (except small-cell lung cancer) 6 cm or less in diameter for whom surgery was not indicated were eligible for this study. Internal target volume was determined using averaged CT under normal breathing, and for patients with large respiratory motion, using two additional CT scans with breath-holding at the expiratory and inspiratory phases in the same table position. Patients were localized at the isocenter after three-dimensional treatment planning. Their setup was corrected by comparing two linacographies that were orthogonal at the isocenter with corresponding digitally reconstructed images. Megavoltage X-rays using noncoplanar multiple static ports or arcs were used to cover the parenchymal tumor mass. Prophylactic nodal irradiation was not performed. The radiation dose was started at 60 Gy in 8 fractions over 2 weeks (60 Gy/8 Fr/2 weeks) for peripheral lesions 3.0 cm or less, and at 48 Gy/8 Fr/2 weeks at the isocenter for central lesions or tumors more than 3.0 cm at their greatest dimension.


RESULTS
Fifty-seven lesions in 45 patients were treated. Tumor size ranged from 0.6 to 6.0 cm, with a median of 2.6 cm. Using the starting dose, 1 patient with a central lesion died of a radiation-induced ulcer in the esophagus after receiving 48 Gy/8 Fr at isocenter. Although the contour of esophagus received 80% or less of the prescribed dose in the planning, recontouring of esophagus in retrospective review revealed that 1 cc of esophagus might have received 42.5 Gy, with the maximum dose of 50.5 Gy. One patient with a peripheral lesion experienced Grade 2 pain at the internal chest wall or visceral pleura after receiving 54 Gy/8 Fr. No adverse respiratory reaction was noted in the symptoms or respiratory function tests. The 3-year local control rate was 80.4% +/- 7.1% (a standard error) with a median follow-up period of 17 months for survivors. Because of the Grade 5 toxicity, we have halted this Phase I/II study and are planning to rearrange the protocol setting accordingly. The 3-year local control rate was 69.6 +/- 10.6% for patients who received 48 Gy and 100% for patients who received 60 Gy (p = 0.0442).


CONCLUSIONS
Small-volume IGRT using 60 Gy in eight fractions is highly effective for the local control of lung tumors, but MTD has not been determined in this study. The organs at risk are extrapleural organs such as the esophagus and internal chest wall/visceral pleura rather than the pulmonary parenchyma in the present protocol setting. Consideration of the uncertainty in the contouring of normal structures is critically important, as is uncertainty in setup of patients and internal organ in the high-dose hypofractionated IGRT.
Onimaru
Rikiya
R
Department of Radiology, Hokkaido University School of Medicine, Sapporo, Japan. oni@radi.med.hokudai.ac.jp
Shirato
Hiroki
H
Shimizu
Shinichi
S
Kitamura
Kei
K
Xu
Bo
B
Fukumoto
Shin-ichi
S
Chang
Ta-Chen
TC
Fujita
Katsuhisa
K
Oita
Masataka
M
Miyasaka
Kazuo
K
Nishimura
Masaharu
M
Dosaka-Akita
Hirotoshi
H
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000401:mortality / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D004935:Esophageal Diseases / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015993:Life Tables; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000401:mortality / Q000532:radiotherapy* / Q000556:secondary; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D009038:Motion; D009928:Organ Specificity; D011653:Pulmonary Diffusing Capacity; D011832:Radiation Injuries / Q000209:etiology* / Q000401:mortality / Q000517:prevention & control; D011836:Radiation Tolerance; D011881:Radiotherapy, Computer-Assisted / Q000009:adverse effects* / Q000379:methods; D011882:Radiotherapy, High-Energy / Q000009:adverse effects / Q000379:methods*; D012119:Respiration; D016019:Survival Analysis; D014057:Tomography, X-Ray Computed; D014456:Ulcer / Q000209:etiology; D014797:Vital Capacity