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SU‐E‐T‐527: Is CTV‐Based Robust Optimized IMPT in Non‐Small‐Cell Lung Cancer Robust Against Respiratory Motion?
Author(s) -
Anetai Y,
Takegawa H,
Inoue T,
Mizuno H,
Sumida I,
Koizumi M,
Ogawa K,
van't Veld A,
Korevaar E
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4924889
Subject(s) - mathematics , nuclear medicine , lung cancer , medicine
Purpose: To determine which proton planning technique on average‐CT is more vulnerable to respiratory motion induced density changes and interplay effect among (a) IMPT of CTV‐based minimax robust optimization with 5mm set‐up error considered, (b, c) IMPT/SFUD of 5mm‐expanded PTV optimization. Methods: Three planning techniques were optimized in Raystation with a prescription of 60/25 (Gy/fractions) and almost the same OAR constraints/objectives for each of 10 NSCLC patients. 4D dose without/with interplay effect was recalculated on eight 4D‐CT phases and accumulated after deforming the dose of each phase to a reference (exhalation phase). The change of D98% of each CTV caused by density changes and interplay was determined. In addition, evaluation of the DVH information vector (D99%, D98%, D95%, Dave, D50%, D2%, D1%) which compares the whole DVH by η score = (cosine similarity × Pearson correlation coefficient − 0.9) × 1000 quantified the degree of DVH change: score below 100 indicates changed DVH. Results: Three 3D plans of each technique satisfied our clinical goals. D98% shift mean±SD (Gy) due to density changes was largest in (c): −0.78±1.1 while (a): −0.11±0.65 and (b): − 0.59±0.93. Also the shift due to interplay effect most was (c): −.54±0.70 whereas (a): −0.25±0.93 and (b): −0.12±0.13. Moreover lowest η score caused by density change was also (c): 69, while (a) and (b) kept around 90. η score also indicated less effect of interplay than density changes. Note that generally the changed DVH were still acceptable clinically. Paired T‐tests showed a significantly smaller density change effect in (a) (p<0.05) than in (b) or (c) and no significant difference in interplay effect. Conclusion: CTV‐based robust optimized IMPT was more robust against respiratory motion induced density changes than PTV‐based IMPT and SFUD. The interplay effect was smaller than the effect of density changes and similar among the three techniques. The JSPS Core‐to‐Core Program (No. 23003), Japan Society for the Promotion of Science Grant‐in‐Aid for Scientific Research (No. 23390300), Grant‐in‐Aid for Young Scientists (B) (No. 21791194) and Grant‐in‐Aid for Cancer Research (H22‐3rd Term Cancer Control‐General‐043)