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Lung cancer radiotherapy increases the risk of acute and late cardiotoxicity. Increased radiation dose to the heart has been associated with poorer survival. This study aims to describe heart radiation doses exposure from lung cancer radiotherapy and to summarise the treatment strategies in the modern era leading to a reduction in such exposure.  

A systematic review of studies reporting heart radiation doses published between 2013-2020 was undertaken. Doses were compared according to laterality, region irradiated, treatment modality (stereotactic ablative body radiotherapy (SABR) or non-SABR), radiation modality (photon beam therapy or particle beam therapy), and use of respiratory motion management.  Dose optimisation objectives and dose volume constraints (DVCs) for the heart were extracted for intensity modulated radiotherapy and particle therapy regimens to determine the priority placed on the heart in inverse planning optimisation. 

The average mean whole heart dose (MHD) across 560 regimens in 140 studies was 8.4 Gy (range 0.1-48.4). Average exposure was not significantly different between left and right-sided tumours. For 392 non-SABR regimens in 105 studies, the average MHD was 10.3 Gy (range 0-48.4).  MHD was similar in the IMRT and  3DCRT groups (10.9 Gy versus 10.6 Gy) and lower in the particle therapy group (proton 7.0 Gy; carbon-ion 1.9 Gy) (Fig 1). MHD was lower in studies using respiratory motion management (7.4 Gy versus  11.4 Gy )  (Fig 2). 

For non-SAR studies, optimisation dose objectives were described in only 2 studies while heart DVCs were described in only 37% (23/62) of IMRT studies and 21% (3/14) particle therapy studies reporting mean and/or maximum heart dose. The most commonly described DVC was MHD <26 Gy.  

For 168 SABR regimens in 35 studies, the average MHD was 4.0 Gy (range 0.0-32.4) and lowest for carbon ion SABR regimens (0.5 Gy) (Fig 1). Dose optimisation objectives were described in only 1 study while heart DVCs were described in only 37% (23/62) of IMRT studies and 21% (3/14) particle therapy studies reporting mean and/or maximum heart dose. The dose received by 15cc of the heart was the commonly described DVC with the threshold dose dependant on the dose fractionation. MHD was lower in studies using active (2.4 Gy) compared to non-active (5.0Gy) respiratory motion management techniques (Fig 2).

In most lung cancer radiotherapy studies the planning priority is rarely placed on the heart. For IMRT, the most common technique used, more stringent planning optimisation objectives for the heart may decrease the delivered dose to the heart.  Advanced radiotherapy techniques and technologies including active respiratory motion management or particle-based therapy may be considered where  cardiac dose is high.