Journal article
Motion Interplay as a Function of Patient Parameters and Spot Size in Spot Scanning Proton Therapy for Lung Cancer
International journal of radiation oncology, biology, physics, v 86(2), pp 380-386
01 Jun 2013
PMID: 23462423
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
To quantify the impact of respiratory motion on the treatment of lung tumors with spot scanning proton therapy.
Four-dimensional Monte Carlo simulations were used to assess the interplay effect, which results from relative motion of the tumor and the proton beam, on the dose distribution in the patient. Ten patients with varying tumor sizes (2.6-82.3 cc) and motion amplitudes (3-30 mm) were included in the study. We investigated the impact of the spot size, which varies between proton facilities, and studied single fractions and conventionally fractionated treatments. The following metrics were used in the analysis: minimum/maximum/mean dose, target dose homogeneity, and 2-year local control rate (2y-LC).
Respiratory motion reduces the target dose homogeneity, with the largest effects observed for the highest motion amplitudes. Smaller spot sizes (σ ≈ 3 mm) are inherently more sensitive to motion, decreasing target dose homogeneity on average by a factor 2.8 compared with a larger spot size (σ ≈ 13 mm). Using a smaller spot size to treat a tumor with 30-mm motion amplitude reduces the minimum dose to 44.7% of the prescribed dose, decreasing modeled 2y-LC from 87.0% to 2.7%, assuming a single fraction. Conventional fractionation partly mitigates this reduction, yielding a 2y-LC of 71.6%. For the large spot size, conventional fractionation increases target dose homogeneity and prevents a deterioration of 2y-LC for all patients. No correlation with tumor volume is observed. The effect on the normal lung dose distribution is minimal: observed changes in mean lung dose and lung V20 are <0.6 Gy(RBE) and <1.7%, respectively.
For the patients in this study, 2y-LC could be preserved in the presence of interplay using a large spot size and conventional fractionation. For treatments using smaller spot sizes and/or in the delivery of single fractions, interplay effects can lead to significant deterioration of the dose distribution and lower 2y-LC.
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Details
- Title
- Motion Interplay as a Function of Patient Parameters and Spot Size in Spot Scanning Proton Therapy for Lung Cancer
- Creators
- Clemens Grassberger - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsStephen Dowdell - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsAntony Lomax - Center for Proton Radiotherapy, Paul Scherrer Institute, Villigen, SwitzerlandGreg Sharp - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsJames Shackleford - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsNoah Choi - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsHenning Willers - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MassachusettsHarald Paganetti - Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
- Publication Details
- International journal of radiation oncology, biology, physics, v 86(2), pp 380-386
- Publisher
- Elsevier
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Electrical and Computer Engineering
- Web of Science ID
- WOS:000319500200033
- Scopus ID
- 2-s2.0-84877579543
- Other Identifier
- 991014878363504721
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- Collaboration types
- Domestic collaboration
- International collaboration
- Web of Science research areas
- Oncology
- Radiology, Nuclear Medicine & Medical Imaging