Evaluation of tumor motion effects on dose distribution for hypofractionated intensity-modulated radiotherapy of non-small-cell lung cancer

Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Journal of Applied Clinical Medical Physics (Impact Factor: 1.17). 01/2010; 11(3):3182.
Source: PubMed

ABSTRACT Respiration-induced tumor motion during intensity-modulated radiotherapy (IMRT) of non-small-cell lung cancer (NSCLC) could cause substantial differences between planned and delivered doses. While it has been shown that, for conventionally fractionated IMRT, motion effects average out over the course of many treatments, this might not be true for hypofractionated IMRT (IMHFRT). Numerical simulations were performed for nine NSCLC patients (11 tumors) to evaluate this problem. Dose distributions to the Clinical Target Volume (CTV) and Internal Target Volume (ITV) were retrospectively calculated using the previously-calculated leaf motion files but with the addition of typical periodic motion (i.e. amplitude 0.36-1.26cm, 3-8sec period). A typical IMHFRT prescription of 20Gy x 3 fractions was assumed. For the largest amplitude (1.26 cm), the average +/- standard deviation of the ratio of simulated to planned mean dose, minimum dose, D95 and V95 were 0.98+/-0.01, 0.88 +/- 0.09, 0.94 +/- 0.05 and 0.94 +/- 0.07 for the CTV, and 0.99 +/-0.01, 0.99 +/- 0.03, 0.98 +/- 0.02 and 1.00 +/- 0.01 for the ITV, respectively. There was minimal dependence on period or initial phase. For typical tumor geometries and respiratory amplitudes, changes in target coverage are minimal but can be significant for larger amplitudes, faster beam delivery, more highly-modulated fields, and smaller field margins.

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    Medical Physics 08/2011; 38(8):4689-99. DOI:10.1118/1.3613153 · 2.64 Impact Factor
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    ABSTRACT: IntroductionIntrafraction tumour motion in helical tomotherapy was investigated by comparing pre- and mid-fraction CT scans in patients with early non-small cell lung carcinoma (NSCLC) to assess the efficacy of a 7-mm margin around gross tumour volumes (GTVs) in stereotactic body radiation therapy (SBRT).Methods Thirty patients with early-stage NSCLC received SBRT in four or five fractions for a total of 141 treatments. A slow positron emission tomography/CT scan was fused with the simulation CT to determine the GTV. A planning target volume was created by placing an isotropic margin of 7 mm around the GTV. Data were retrospectively analyzed to assess translational tumour positional changes along the x, y and z axes and vector changes in millimeters from the pretreatment megavoltage (MV)-CT to the mid-fraction MV-CT.ResultsAverage movements for all 141 treatment days along the x, y and z axes were 0.5 ± 2.3, −0.3 ± 3.0 and 0.9 ± 3.0 mm, respectively. Average movements for each patient along the x, y and z axes were 0.5 ± 1.5, −0.2 ± 2.0 and 0.9 ± 1.9 mm, respectively. Average vector displacement was 4.3 ± 2.4 mm for all treatment days and 4.2 ± 1.7 mm for each patient. Of 141 treatments, 137 (97.2%) fell within 7.0 mm in all axes.Conclusion The addition of a 7-mm margin to the GTV for patients receiving SBRT for NSCLC using tomotherapy is adequate to account for tumour movement. Mid-fraction CT scans proved to be valuable in assessing intrafraction tumour motion.
    Journal of Medical Imaging and Radiation Oncology 05/2014; 58(6). DOI:10.1111/1754-9485.12179 · 1.11 Impact Factor


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