AIM: To analyze an intrafractional organ motion for patients with prostate cancer using soft tissue matching by megavolt computed tomography (MVCT) images during the course of image-guided intensity-modulated radiotherapy (IGRT-IMRT) using helical tomotherapy.
PATIENTS AND METHODS: Data from a total of 10 patients with prostate cancer who received IGRT-IMRT were analyzed, and MVCT images were acquired before and after radiation therapy. Intra-fractional movement and PTV margins for soft tissue matching were calculated by comparing treatment planning images with 740 MVCT images for right-left (RL), superior-inferior (SI), and anteroposterior (AP) dimensions. A total of 74 Gy/37 fractions were administered. A margin to compensate for these variations was calculated using the van Herk's equation.
RESULTS: The intrafractional motion was 0.03 (-1.3 to 1.4) ±0.39 mm in the RL dimension, 0.08 (-1.8 to 0.28) ±0.73 mm in the SI dimension, and 0.52 (-1.8 to 1.8) ±0.63 mm in the AP dimension. The required PTV margin was 0.60 mm, 1.10 mm, and 0.78 mm in the RL, SI, and AP dimensions, respectively. Only one patient exhibited a deviation greater than 5 mm only once in 37 fractions (1/370=0.2%) caused by anal contraction.
CONCLUSION: The PTV margin in soft tissue matching IGRT-IMRT by helical tomotherapy for a patient with prostate cancer was 3 mm or less, and our tentative PTV margin of 3-5 mm is sufficient for most patients, if adequate instruction for avoiding anal contraction is given.
Written by:
Iwama K, Yamazaki H, Nishimura T, Oota Y, Aibe H, Nakamura S, Ikeno H, Yoshida K, Okabe H. Are you the author?
Department of Radiology, Kyoto Prefectural University of Medicine, 465 Kajiicho Kawaramachi Hirokoji, Kamigyo-ku, Kyoto, Kyoto 602-8566 Japan.
Reference: Anticancer Res. 2013 Dec;33(12):5675-9.
PubMed Abstract
PMID: 24324116
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