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SU‐GG‐T‐482: Effects of Normal Lung Delineation Using PTV Vs. GTV On NTCP and Vx for Lung Cancer Cases Planned with and Without Tissue Inhomogeneity Correction
Author(s) -
Podder T,
Harrison A,
WernerWasik M,
Xia Y,
Galvin J,
Yu Y
Publication year - 2008
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 - 10.1118/1.2962231
Subject(s) - medicine , nuclear medicine , lung , lung cancer , radiation therapy , pneumonitis , lung volumes , radiation pneumonitis , respiratory system , radiology
Purpose: There is no clear consensus as to how to define normal lung volume; clinicians subtract either PTV or GTV from total lung volume. This study quantifies the dosimetric and biological differences between these definitions for radiotherapy planning with and without inhomogeneity corrections. Method and Materials: In this study, ten lung cancer patient cases with prescription doses (PD) 50–70Gy (average 62Gy) were evaluated. Dosimetric plans were generated using XIO‐CMS software. Complex (4–6 fields) 3D conformal radiation therapy plans with and without tissue heterogeneity corrections were compared. NTCPs were computed for three scenarios; respiratory pneumonitis (RP) endpoint of SWOG grade ⩾2RP (TD 50 =30.8Gy, n=0.99, m=0.37; NTCP 1 ), SWOG ⩾1RP (TD 50 =28Gy, n=0.87, m=0.18; NTCP 2 ), and radiographic & symptomatic pneumonitis (TD 50 =21.9Gy, n=0.8, m=0.37; NTCP 3 ). Normal lung for NTCP was defined in two ways: [(left lung + right lung) − PTV], and [(left lung + right lung) − GTV]. Volume (V x ) of normal lung receiving 5Gy (V 5 ), 13Gy (V 13 ), 20Gy (V 20 ) and 30Gy (V 30 ) were also investigated. Results: For inhomogeneity non‐corrected plans: average PTV dose coverage was 97% (92.1–101.7%) of PD; with −PTV definition, average V 5 =41.3% (24.3–70.2%), V 13 =26.4% (15.9–36.8%), V 20 =22.2% (13.1–32.4%), V 30 =18.3% (10.9–27.8%), NTCP 1 =6.5% (2–16.5%), NTCP 2 =1.3% (0.01–8.6%), NTCP 3 =23.3% (6.7–51.2%); and with −GTV definition, average V 5 =43.2% (25.6–71.3%), V 13 =28.7% (17.9–39.2%), V 20 =24.7% (15.1–34.9%), V 30 =21% (13–30.5%), NTCP 1 =8.8% (2.6–20.7%), NTCP 2 =3.5% (0.02–16.3%), NTCP 3 =31% (9.7–60.8%). For inhomogeneity corrected plans: average PTV dose coverage was 99.6% (93.1–107.6%); with −PTV definition, average V 5 =43.7% (25.3–74%), V 13 =27.9% (17–42.7%), V 20 =23.2% (14.7–33.7%) and V 30 =19% (11.2–28.5%), NTCP 1 =7.8% (2.2–19.9%), NTCP 2 =2.5% (0.01–14.1%), NTCP 3 =27.9% (7.4–58.2%); and with −GTV definition, average V 5 =45.5% (26.5–75%), V 13 =30.2% (19.5–44.5%), V 20 =25.7% (16.1–36.1%), V 30 =21.7% (13.6–31.1%), NTCP 1 =10.7% (2.8–24.9%), NTCP 2 =6% (0.03–24.9%), NTCP 3 =36.5% (10.7–67.8%). Discussion and Conclusion: Results revealed that for heterogeneity non‐corrected plans, relative increase (with respect to −PTV definition) of V x s were 4.7%, 8.9%, 11.3%, 14.7%, and NTCPs were 32.6%, 193.4%, 32.8%; and similar increases were observed for heterogeneity corrected plans.