• Takuya Nishimura, Hideya Yamazaki, Kazuki Iwama, Tomoya Kotani, Yoshitaka Oota, Hironori Aibe, Satoaki Nakamura, Hiroyasu Ikeno, Ken Yoshida, Fumiaki Isohashi, and Haruumi Okabe.
• Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
• Anticancer Res. 2013 Jun 1; 33 (6): 2453-6.

AimTo evaluate an appropriate planning target volume (PTV) margin in for one to three vertebral metastases using megavolt computed tomography (MVCT) images during the course of image-guided and stereotactic intensity-modulated radiotherapy (IGRT-IMRT) by use of helical tomotherapy.Patients And MethodsA total of 25 lesions in 24 patients with vertebral metastases who received IGRT-IMRT were analyzed. MVCT images were acquired before and after radiation therapy. Intra-fractional movement and PTV margin were calculated by comparing treatment planning images and these 310 MVCT images for right-left (RL), superior-inferior (SI), and anteroposterior (AP) dimensions. Five patients were treated by 35 Gy/5 fractions, 17 by 30 Gy/5 fractions, one by 25 Gy/5 fractions, and one by 60 Gy/30 fractions. A margin to compensate for these variations was calculated with the formula of vanHerk's equation.ResultsThe intra-fractional motion was 0.02 (-1.3 to 1.4) ± 0.34 mm in the RL direction, -0.09 (-1.8 to 0.28) ± 0.44 mm in the SI direction, and 0.20 (-1.8 to 1.8) ± 0.36 mm in the AP direction. The required PTV margin was 0.98 mm in the RL direction, 0.69 mm in the SI direction, and 1.26 mm in the AP direction. No patient showed a deviation greater than 2 mm.ConclusionThe PTV margin in hypofractionated IGRT-IMRT, using helical tomotherapy for a few vertebral metastases, was 2 mm or less and our tentative PTV margin of 5 mm was sufficient and reducible.

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