Shalini Vinod1,2, Callie Choong1, Philip Vial1,2,3, Tomas Kron4,5, David Ball4,5. 1. Cancer Therapy Centre, Liverpool Hospital, Sydney, New South Wales, Australia. 2. South Western Sydney Clinical School, University of NSW, Sydney, New South Wales, Australia. 3. Institute of Medical Physics, School of Physics, University of Sydney, Sydney, New South Wales, Australia. 4. Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia. 5. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Victoria, Australia.
Abstract
INTRODUCTION: In the 4DCT era, the definition of lung organ-at-risk (OAR) volumes for dose-volume histogram (DVH) calculation is unclear, introducing potential for variability in practice. We aimed to identify definitions used clinically and evaluate the magnitude of DVH differences between these. METHODS: We surveyed Australian & New Zealand departments about lung radiotherapy protocols including lung OAR volume definition. We used these definitions to calculate lung DVHs on 10 patients prescribed lung IMRT (60-66 Gy/30-33 fractions). We calculated mean lung dose (MLD), V20 and V30 for 'Lungs - PTV', 'Lungs - CTV', 'Lungs - iGTV' (internal GTV in all respiratory phases) and 'Lungs - GTV_EX' (expiratory phase). RESULTS: The response rate was 39% (34/88). 14% and 29% of departments did not have a departmental protocol for OAR and tumour volume delineation, respectively. All permutations for lung OAR volumes were used with no clear preference. For conventional radiotherapy (n = 27), this included Lungs alone (n = 1), Lungs - PTV (n = 6), Lungs - CTV (n = 2), Lungs - iGTV (n = 6), Lungs - GTV in single phase (n = 5) and individual clinician preference (n = 7). The different lung OAR volumes resulted in MLD difference ranging from 0.9 to 4.15 Gy, V20 from 1.5% to 6.6% and V30 from 1.34% to 7.11%. The largest differences between subtraction of GTV_EX and iGTV were 0.32 Gy, 0.43% and 0.46% for MLD, V20 and V30, respectively. CONCLUSION: A significant number of departments lacked lung cancer radiotherapy contouring protocols. Lung OAR volume definition was variable between and within departments. Potentially clinically significant differences in lung DVH parameters were seen according to the volume used.
INTRODUCTION: In the 4DCT era, the definition of lung organ-at-risk (OAR) volumes for dose-volume histogram (DVH) calculation is unclear, introducing potential for variability in practice. We aimed to identify definitions used clinically and evaluate the magnitude of DVH differences between these. METHODS: We surveyed Australian & New Zealand departments about lung radiotherapy protocols including lung OAR volume definition. We used these definitions to calculate lung DVHs on 10 patients prescribed lung IMRT (60-66 Gy/30-33 fractions). We calculated mean lung dose (MLD), V20 and V30 for 'Lungs - PTV', 'Lungs - CTV', 'Lungs - iGTV' (internal GTV in all respiratory phases) and 'Lungs - GTV_EX' (expiratory phase). RESULTS: The response rate was 39% (34/88). 14% and 29% of departments did not have a departmental protocol for OAR and tumour volume delineation, respectively. All permutations for lung OAR volumes were used with no clear preference. For conventional radiotherapy (n = 27), this included Lungs alone (n = 1), Lungs - PTV (n = 6), Lungs - CTV (n = 2), Lungs - iGTV (n = 6), Lungs - GTV in single phase (n = 5) and individual clinician preference (n = 7). The different lung OAR volumes resulted in MLD difference ranging from 0.9 to 4.15 Gy, V20 from 1.5% to 6.6% and V30 from 1.34% to 7.11%. The largest differences between subtraction of GTV_EX and iGTV were 0.32 Gy, 0.43% and 0.46% for MLD, V20 and V30, respectively. CONCLUSION: A significant number of departments lacked lung cancer radiotherapy contouring protocols. Lung OAR volume definition was variable between and within departments. Potentially clinically significant differences in lung DVH parameters were seen according to the volume used.
Authors: Nicholas Bucknell; Nicholas Hardcastle; Price Jackson; Michael Hofman; Jason Callahan; Peter Eu; Amir Iravani; Rhonda Lawrence; Olga Martin; Mathias Bressel; Beverley Woon; Benjamin Blyth; Michael MacManus; Keelan Byrne; Daniel Steinfort; Tomas Kron; Gerard Hanna; David Ball; Shankar Siva Journal: BMJ Open Date: 2020-12-10 Impact factor: 2.692