Effects of tumor motion in GRID therapy

Medientyp: E-Artikel
Titel: Effects of tumor motion in GRID therapy
Beteiligte: Naqvi, Shahid A.; Mohiuddin, Majid M.; Ha, Jonathan K.; Regine, William F.
Erschienen: Wiley, 2008
Erschienen in: Medical Physics, 35 (2008) 10, Seite 4435-4442
Sprache: Englisch
DOI: 10.1118/1.2977538
ISSN: 0094-2405; 2473-4209
Entstehung:
Anmerkungen:
Beschreibung: <jats:p>Clinical and biological evidence suggest that the success of GRID therapy in debulking large tumors depends on the high peak‐to‐valley contrast in the dose distribution. In this study, we show that the peaks and valleys can be significantly blurred out by respiration‐induced tumor motion, possibly affecting the clinical outcome. Using a kernel‐based Monte Carlo dose engine that incorporates phantom motion, we calculate the dose distributions for a GRID with hexagonally arranged holes. The holes have a diameter of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0001.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0001" /> and a minimum center‐to‐center separation of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0002.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0002" /> (projected at the isocenter). The phantom moves either in the <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0003.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0003" /> direction, which is parallel to a line joining any two nearest neighbors, or in the perpendicular <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0004.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0004" /> direction. The displacement‐time waveform is modeled with a <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0005.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0005" /> function, with <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0006.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0006" /> assigned 1 for symmetric motion, or 6 to simulate a large inhale‐exhale asymmetry. Dose calculations are performed on a water phantom for a <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0007.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0007" /> x‐ray beam. Near <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0008.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0008" />, the static valley dose is <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0009.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0009" />, where <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0010.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0010" /> is the peak static dose. For motion in the <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0011.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0011" /> direction, the peak and valley doses vary periodically with the amplitude of motion <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0012.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0012" /> and the transverse dose profiles are maximally flat near <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0013.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0013" /> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0014.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0014" />. For the cos waveform, the minimum peak dose <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0015.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0015" /> is <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0016.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0016" /> and the maximum valley dose <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0017.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0017" /> is <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0018.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0018" />. Less dose blurring is seen with the <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0019.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0019" /> waveform, with <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0020.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0020" /> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0021.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0021" />. For motion in the <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0022.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0022" /> direction, the maximum flattening of dose profiles occurs at <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7538-math-0023.png" xlink:title="urn:x-wiley:00942405:media:mp7538:mp7538-math-0023" />. GRIDs with smaller hole separations produce similar blurring at proportionally smaller amplitudes. The reported clinical response data from GRID therapy seem to indicate that mobile tumors, such as those in the thorax and abdomen, respond worse to GRID treatments than stationary tumors, such as those in the head and neck. To establish a stronger correlation between clinical response and tumor motion, and possibly improve the clinical response rates, it is recommended that prospective GRID therapy trials be conducted with motion compensation strategies, such as respiratory gating.</jats:p>

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