Cardiac substructure avoidance in lung cancer using photon vs proton radiotherapy: A planning study
Banfill, Kathryn Wood, Joe Charlwood, Frances C Lines, D. Rompokos, V. Hiley, C. van Herk, Marcel Faivre-Finn, Corinne Schmitt, M. Salem, Ahmed
Banfill, Kathryn
Wood, Joe
Charlwood, Frances C
Lines, D.
Rompokos, V.
Hiley, C.
van Herk, Marcel
Faivre-Finn, Corinne
Schmitt, M.
Salem, Ahmed
Citations
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Abstract
Purpose or Objective
Higher radiotherapy dose to selected cardiac structures is associated with cardiac events and death in patients
with lung cancer. Studies reveal a dose response relationship for structures at the base of the heart including
the right atrium and ascending aorta, with a significant dose threshold of 23Gy (McWilliam et al, 2020). Our
objective was to define a cardiac avoidance area and investigate the ability of optimised photon and proton
plans to spare these structures compared to standard photon radiotherapy.
Materials and Methods
A cardiac avoidance area (CAA) was defined, based on previous studies, comprising the superior vena cava,
right atrium, aortic root, and proximal coronary arteries (figure 1). 12 patients with stage 3 NSCLC treated at
2 UK centres who had a 4D planning CT and ITV within 5cm of the heart were selected.
Plans were generated in Raystation v7R to achieve a dose of 66Gy in 33fractions using standard dose
parameters. Cases were re-planned using an additional dose constraint of D1cc<23Gy to the CAA for optimised
photon plans. For pencil beam scanning proton (PBSP) plans Varian Eclipse (v13.7) was used for replanning.
Photon plans used VMAT with two 360° arcs. PBSP plans used single field optimisation with 3 or 4 fields. PBSP
plans were robustly optimised for ITV as target using 5mm setup error and 5% range uncertainty. Plans were
compared using analysis of variance and pairwise comparisons.Results
Mean ITV volume 219cc (SD 66cc) and 6 ITVs were right sided. The median mean heart dose (MHD) was
significantly lower in PBSP plans compared to photon plans (7Gy v 14Gy v 17Gy, p<0.001). CAA was an average
of 15% (SD 2%) of the heart volume. Maximum D1cc to CAA was significantly lower with both photon and PBSP
cardiac avoidance plans compared to standard plans without cardiac avoidance (19Gy v 22Gy v 41Gy, p=0.003)
(figure 2). There was no difference in ITV D95% between the 3 planning strategies. Median mean lung dose
(MLD) was 16Gy for standard and cardiac avoidance photon plans; MLD was significantly lower at 9Gy with
PBSP (p<0.01).
Ability to achieve D1cc<23Gy to CAA depended on the location of the ITV. If CAA>5mm from ITV then D1cc was
already <23Gy in standard photon plans. No reduction to CAA D1cc was possible with either PBSP or photons if
ITV and CAA overlapped. 9 plans where ITV was on the same axial plane but not overlapping the CAA were
analysed. The mean dose reduction in D1cc to the CAA in these patients was 24Gy (SD10Gy) with photons and
26Gy (SD 13Gy) with PBSP. Conclusion
In this cohort, dose reduction to a cardiac avoidance area can be achieved with photons and protons without
compromising ITV coverage or increasing MLD. Protons did not allow more reduction to D1cc than photons. The
location of the ITV determines the maximum dose reduction that can be achieved, allowing selection of
patients that could benefit from this strategy.
Description
Date
2021
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Banfill K, Wood J, Charlwood F, Lines D, Rompokos V, Hiley C, et al. Cardiac substructure avoidance in lung cancer using photon vs proton radiotherapy: A planning study. Radiotherapy and Oncology. 2021;161:S497-S8.