Motion mitigation for lung cancer patients treated with active scanning proton therapy. Issue 5 (21st April 2015)

• Record Type: Journal Article
• Authors: Grassberger, Clemens; Dowdell, Stephen; Sharp, Greg; Paganetti, Harald
• Is Part Of: Medical physics. Volume 42:Issue 5(2015)
• Page Start: 2462
• Page End: 2469
• Publication Date: 2015-04-21
• Subjects: biological effects of ionising particles -- cancer -- dosimetry -- lung -- Monte Carlo methods -- motion compensation -- motion control -- pneumodynamics -- radiation therapy -- tumours; Monte Carlo methods -- Dosimetry/exposure assessment -- Therapeutic applications, including brachytherapy -- Conformal radiation treatment -- Pneumodyamics, respiration; Radiation therapy -- Analysis of motion -- Scintigraphy; lung cancer -- motion mitigation -- active scanning proton therapy -- interplay effect; Lungs -- Cancer -- Dosimetry -- Protons -- Proton therapy -- Statistical analysis -- Monte Carlo methods -- Tissues -- Drug delivery; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4916662
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: Motion interplay can affect the tumor dose in scanned proton beam therapy. This study assesses the ability of rescanning and gating to mitigate interplay effects during lung treatments. Methods: The treatments of five lung cancer patients [48 Gy(RBE)/4 fx ] with varying tumor size (21.1–82.3 cm 3 ) and motion amplitude (2.9–30.6 mm) were simulated employing 4D Monte Carlo. The authors investigated two spot sizes ( σ ∼ 12 and ∼3 mm), three rescanning techniques (layered, volumetric, breath‐sampled volumetric) and respiratory gating with a 30% duty cycle. Results: For 4/5 patients, layered rescanning 6/2 times (for the small/large spot size) maintains equivalent uniform dose within the target >98% for a single fraction. Breath sampling the timing of rescanning is ∼2 times more effective than the same number of continuous rescans. Volumetric rescanning is sensitive to synchronization effects, which was observed in 3/5 patients, though not for layered rescanning. For the large spot size, rescanning compared favorably with gating in terms of time requirements, i.e., 2 x ‐rescanning is on average a factor ∼2.6 faster than gating for this scenario. For the small spot size however, 6 x ‐rescanning takes on average 65% longer compared to gating. Rescanning has no effect on normal lung V 20 and mean lung dose (MLD), though it reduces the maximum lung dose by on average 6.9 ± 2.4/16.7 ± 12.2 Gy(RBE) for the large and small spot sizes, respectively. Gating leads to a similar reduction in maximum dose and additionally reduces V 20 and MLD. Breath‐sampled rescanning is most successful in reducing the maximum dose to the normal lung. Conclusions: Both rescanning (2–6 times, depending on the beam size) as well as gating was able to mitigate interplay effects in the target for 4/5 patients studied. Layered rescanning is superior to volumetric rescanning, as the latter suffers from synchronization effects in 3/5 patients studied. Gating minimizes the irradiated volume of normal lung more efficiently, while breath‐sampled rescanning is superior in reducing maximum doses to organs at risk.