TARGET VOLUME DEFINITION FOR 3-DIMENSIONAL CONFORMAL RADIATION-THERAPY OF LUNG-CANCER

Three-dimensional conformal radiation therapy (3DCRT) is a mode of hig h precision radiotherapy which has the potential to improve the therap eutic ratio of radiation therapy for locally advanced non-small cell l ung cancer. The preliminary clinical experience with 3DCRT has been pr omising and justifies further endeavour to refine its clinical applica tion and ultimately test its role in randomized trials. There are seve ral steps to be taken before 3DCRT evolves into an effective single mo dality for the treatment of lung cancer and before it is effectively i ntegrated with chemotherapy. This article addresses core issues in the process of target volume definition for the application of 3DCRT tech nology to lung cancer. The International Commission on Radiation Units and Measurements Report no. 50 definitions of target volumes are used to identify the factors influencing target volumes in lung cancer. Th e rationale for applying 3DCRT to lung cancer is based on the frequenc y of failure to eradicate gross tumour with conventional approaches. I t may therefore be appropriate to ignore subclinical or microscopic ex tensions when designing a clinical target volume, thereby restricting target volume size and allowing dose escalation. When the clinical tar get volume is expanded to a planning target volume, an optimized margi n would result in homogeneous irradiation to the highest dose feasible within normal tissue constraints. To arrive at such optimized margins , multiple factors, including data acquisition, data transfer, patient movement, treatment reproducibility, and internal organ and target vo lume motion, must be considered. These factors may vary significantly depending on technology and techniques, and published quantitative ana lyses are no substitute for meticulous attention to detail and audit o f performance.