Principles of radiation oncology in older adults

Introduction Radiation therapy (RT) plays a central role in the definitive treatment and palliation of many different cancers. RT is recommended for patients across the entire spectrum of ages, from neuroblastoma diagnosed in an infant to glioblastoma diagnosed in an octogenarian. Generally speaking, the fundamental principles of radiation therapy, such as dose, fractionation, tumor targeting, and integration with systemic therapy, are similar for both young and old. In addition, the primary goal of radiation therapy – obtaining local-regional control with acceptable morbidity – is the same for all age groups. Given these similarities, there is not a coherent set of radiation therapy principles solely applicable to older adults. Nevertheless, a nuanced understanding of the importance of age as a factor associated with tumor behavior, response to treatment, and treatment tolerance is critically important to ensure that older adults receive optimal treatment that achieves the appropriate balance of local-regional control with morbidity. For example, older age is associated with a decreased risk of local-regional recurrence in breast cancer but an increased risk of local-regional recurrence in endometrial cancer. Age-specific differences such as these may influence clinical decision making for older adults. In addition, older adults may have a decreased functional reserve that can modulate the risk of normal tissue toxicity incurred by radiotherapy. For example, the risk of clinically significant lung damage may be much greater for an older adult with abnormal pulmonary function as compared to a younger adult with normal pulmonary reserve, and such considerations may therefore influence selection of radiotherapy dose and volume in older adults.