The intricate interplay between cardiac and lung physiology is vital, governing processes within the cardiovascular and respiratory systems. The heart propels oxygenated blood rich in nutrients throughout the body while removing metabolic waste. Simultaneously, deoxygenated blood returns to the heart for oxygenation in the lungs. The lungs facilitate gas exchange, extracting oxygen and expelling carbon dioxide through breathing. This exchange occurs in the alveoli, tiny air sacs in the lungs. The interaction between the lung and the heart involves direct ventricular interaction, blood volume redistribution, and left ventricular afterload regarding the physiology 2 or through the relationship between pulmonary and cardiac diseases. 2 Assessing the heart's function involves gathering patient history, checking vital signs (blood pressure, heart rate) and examination. In examination, the peripheral pulses and jugular venous pressure are evaluated, and auscultation is performed to listen for heart sounds and blood flow. We can use many types of tests to assess heart functions. We can check its electricity (ECG), pumping capacity (Echocardiogram), cardio function under stress (Stress Test), cardiac enzyme markers, structural assessment (MRI or CT scan). Pulmonary function assessment includes both clinical and non-clinical modalities, similar to the approach taken in heart assessment. Clinical methodologies involve thorough patient history collection, evaluation of respiratory patterns, oxygen saturation, and physical examinations employing inspection, palpation, and auscultation. In the non-clinical techniques such as spirometry, peak flow rate measurement, X-ray and advanced imaging modalities like CT scans, MRI, PET and V/Q scans are employed to provide a thorough understanding of pulmonary function.

When lung function is not working well due to conditions like chronic bronchitis, pneumonia, or pneumonitis, the gas exchange becomes less efficient. This inefficiency leads to lower oxygen levels in the blood and a buildup of carbon dioxide, causing problems like difficulty breathing and reduced ability Editorial Open Access to exercise. At the same time, if the heart is not working properly due to issues like heart failure or coronary artery disease, it affects the flow of blood throughout the body. The heart, responsible for pumping oxygen-rich blood to different organs, struggles to meet the body's needs. This can result in tiredness, retaining fluids, and, in severe cases like organ failure. Of importance, there is considerable overlap in the assessment of the heart and pulmonary symptoms.

There are many factors that can damage lung and heart functions. They may be internal factor stemming from comorbidities which play a key role in developing long-term impacts on the lungs and heart, such as diabetes, cardiac disease, hypertension, previous surgeries 4 and systemic treatment. 3 They can be external such as pollution, smoking and substance expose (asbestosis or coal), even common environmental exposes via the link with extracellular vesicles causing chronic systemic lung and heart diseases. 4 As a reminder, the lungs have been dramatically at the forefront during the COVID-19 pandemics, stressing the importance of sparing the lungs. 567 The overall message is that lung and heart physiology are complex. Relying on a single "toxicity grade" might be misleading. The functional evaluation is multidimensional. We will refer to that later.

It has been known over a hundred years ago, almost immediately after Roentgen discovery of Xrays, as early as 1909, that radiation was efficient to control breast cancer and reduce recurrence. 89 However, a favorable effect on survival has long been elusive. It was shown in 1987 that excess deaths occurred among patients receiving post-operative radiotherapy. 10 Building on the 1995 meta-analysis of the Early Breast Cancer Trialists' Collaborative Group (EBCTCG), 11

were the first to demonstrate a significant overall survival benefit, 12 which the EBCTCG acknowledged soon after. 15 Van de Steene et al. stressed that the benefit was contingent on the use of current techniques to reduce cardiovascular and other toxicities. 12 The authors did not specify what they meant by "other toxicities". But to radiation oncologists at the time, lung damage was a wellknown major toxicity demonstrated in numerous studies. 13141516 A subsequent pooled analysis for breast conserving surgery found in 2004 a two-third proportional reduction of local-regional recurrences, but with a small benefit in overall survival, 17 Reducing lung-heart toxicity with modern radiotherapy The signposts recalled above led to the design of TomoBreast, a randomized clinical trial conducted in 2007-2011 that compared hypofractionated image guided radiation therapy (H-IGRT), delivered with the tomotherapy system, with normofractionated conventional radiation therapy (CRT), delivered with 3D conformal therapy. 18 H-IGRT patients received 42 Gy to the breast/chest wall with/without nodal irradiation and simultaneous integrated boost to 51 Gy in 15 fractions over 3 weeks. CRT patients received 50 Gy to the breast/chest wall with/without nodal irradiation in 25 fractions over 5 weeks and 16 Gy sequential boost in 8 fractions over 1.6 weeks. The trial hypothesized that H-IGRT could provide a significant reduction in lung and heart toxicity, as compared with CRT. Reminding that lung and heart assessments are multidimensional, measurements were made using patient reported outcome (PRO), Radiation Therapy Oncology Group (RTOG) toxicity score, left ventricular ejection fraction (LVEF), and pulmonary function tests (PFT). In an intention-totreat analysis at 12 years median follow-up, the survival time free from alteration in any of the measured outcomes was significantly improved with H-IGRT, P=0.041, providing a gain of restricted mean survival time free of alteration of 1.46 years as compared with CRT. This study is the only one to date that demonstrates the positive impact of H-IGRT globally on cardio-vascular, pulmonary function and quality of life in breast cancer adjuvant radiotherapy, without causing disease-free survival reduction.

TomoBreast is a proof of concept that technology matters in the radiotherapy of breast cancer. There are, however, drawbacks to the tomotherapy system: notably treatment duration is long, 19 and the system cannot manage breathing control which has attracted considerable attention. 20 Beyond tomotherapy, the current challenge is to identify the most cost-effective technique to improve the balance of tumor control and avoidance of toxicity. Another challenge is that most of the later decade has been devoted to reducing the risk of heart toxicity with little attention to the lungs.

It is not the purpose of this commenting editorial to review or to advocate any particular technique, but to point out that the lungs have an intertwined physiological importance in tandem with the heart. Future research will have to consider not the heart or the lungs exclusively, but both the lungs and the heart.

The editorial was written based on experience and knowledge of the team without receiving any commercial or financial relationships which can potentially create conflicts of interest.