Review the case below and weigh in on how you would contour this case. 

Case Review

78-year-old male with a 30 pack-year history of smoking and previously diagnosed with Stage IIIA (T4 N0 M0) non-small cell lung carcinoma status post RUL/RLL bilobectomy two years ago and subsequently developed biopsy proven recurrence in right hilar and subcarinal lymph nodes. Definitive chemoradiation to 60 Gray with outback durvalumab is recommended after multi-disciplinary discussion. 


The patient has no known history of cardiac disease, but the presence of coronary calcium is noted on your planning CT scans (4D-CT without contrast and free-breathing CT with contrast).

 

Which cardiac contour(s) would be most appropriate for planning?  

A)  Whole heart contour

B)  Left anterior descending (LAD) coronary artery or left-sided coronary arteries (including left main, LAD, and left circumflex coronary arteries) 

C)  Heart base 

D)  A and B or C

Respond in the Academy poll  or on X and LinkedIn with the answer you would choose for today's contouring the Case of the Day. 


Our experts, Drs. Atkins, Walls and Mak, weigh in...

There is growing awareness of the impact of cardiac sub-structure radiation dose exposure on the risk of cardiac injury in lung cancer patients. Historically, the whole heart has been contoured, and the standard of care (such as NCCN guidelines) remains to constrain the whole heart (e.g. mean heart dose < 20 Gy) in the setting of definitive RT for lung cancer. Whole heart dose has been associated with survival (e.g. RTOG 0617), but a survival endpoint is multi-factorial and does not fully capture the cardiac impact of thoracic RT [1]. Emerging data suggests cardiac sub-structure radiation exposure may be more highly associated with specific cardiac toxicity events.  For example, intermediate dose to the left-sided coronary arteries (e.g. V15) has been associated with the risk of coronary-related toxicity (e.g. major cardiovascular adverse events including MI, heart failure, coronary stenosis requiring intervention, and sudden cardiac death), while pulmonary vein dose has been associated with the risk of atrial fibrillation [2–5]. Thus, the ability to contour cardiac sub-structures at risk will be an important skill set for lung cancer RT moving forward.

Contouring cardiac sub-structures at risk: How we do it

While the whole heart is still important for planning optimization, we recommend contouring additional cardiac sub-structures to protect the coronary arteries and potentially decrease the risk of the most serious class of cardiac toxicity events: coronary events and cardiac death. We typically contour the left-sided coronaries (left main, left anterior descending, and left circumflex) using the substructure atlas developed by Duane et al, practically modified for lung cancer RT to enlarge the brush to 8-mm (to accommodate respiratory/cardiac motion uncertainties) and we contour on the average intensity projection (AIP) of the 4D-CT to encompass respiratory motion, using a contrast-enhanced CT for guidance [6]. Coronary calcifications as observed in this case, can also provide useful landmarks for the location of the coronaries within the interventricular groove for the LAD and atrioventricular groove for the left circumflex.

An alternative approach includes contouring the ‘heart base’, which has varying definitions, but defined by Walls et al. (in the first studying linking heart base dose specifically to cardiac events) as a Boolean of left main, proximal LAD and right coronary arteries, the right atria, superior vena cava, and aortic root [7]. This structure may achieve a similar dosimetric effect for sparing the proximal coronaries and reducing centralized cardiopulmonary dose.

While national guidelines for constraints to these sub-structures are still evolving, clinicians who would like to practice at the leading edge of cardiac-sparing planning, can place an optimization priority on whole heart and their choice of cardiac substructure to minimize unnecessary dose to these critical regions. As we typically prioritize target coverage over cardiac sub-structure sparing when not fully achievable, the exposure (or exceeded constraint) may serve as an alert to considering referring patient back to their primary care physician or to a cardiologist for guidelines-based cardiovascular risk optimization and surveillance

References:

  1. Bradley JD, Paulus R, Komaki R, Masters G, Blumenschein G, Schild S, et al. Standard-dose versus high-dose conformal radiotherapy with concurrent and consolidation carboplatin plus paclitaxel with or without cetuximab for patients with stage IIIA or IIIB non-small-cell lung cancer (RTOG 0617): a randomised, two-by-two factorial phase 3 study. Lancet Oncol. 2015;16: 187–199.
  2. Atkins KM, Zhang SC, Kehayias C, Guthier C, He J, Gasho JO, et al. Cardiac substructure radiation dose and associations with tachyarrhythmia and bradyarrhythmia after lung cancer radiotherapy. CardioOncology. 2024;6: 544–556.
  3. Walls GM, McCann C, O’Connor J, O’Sullivan A, I Johnston D, McAleese J, et al. Pulmonary vein dose and risk of atrial fibrillation in patients with non-small cell lung cancer following definitive radiotherapy: An NI-HEART analysis. Radiother Oncol. 2024;192: 110085.
  4. Atkins KM, Chaunzwa TL, Lamba N, Bitterman DS, Rawal B, Bredfeldt J, et al. Association of Left Anterior Descending Coronary Artery Radiation Dose With Major Adverse Cardiac Events and Mortality in Patients With Non-Small Cell Lung Cancer. JAMA Oncol. 2020;7:206-219.
  5. No HJ, Guo FB, Park NJ-I, Kastelowitz N, Rhee J-W, Clark DE, et al. Predicting adverse cardiac events after radiotherapy for locally advanced non–small cell lung cancer. JACC CardioOncol. 2023;5: 775–787.
  6. Duane F, Aznar MC, Bartlett F, Cutter DJ, Darby SC, Jagsi R, et al. A cardiac contouring atlas for radiotherapy. Radiother Oncol. 2017;122: 416–422.
  7. Walls GM, O’Connor J, Harbinson M, Duane F, McCann C, McKavanagh P, et al. The association of incidental radiation dose to the heart base with overall survival and cardiac events after curative-intent radiotherapy for non-small cell lung cancer: results from the NI-HEART Study. Clin Oncol. 2024;36:119-127.

Acknowledgements

Thank you to the experts below for putting this case together.

  • Katelyn Atkins, MD/PhD – Cedars-Sinai Medical Center
  • Gerard Walls, FRCR PhD – Patrick G. Johnston Centre for Cancer Research
  • Raymond Mak, MD – Memorial Sloan Kettering Cancer Center