873 ISSN 1479-6694 Future Oncol. (2017) 13(10), 873–874 REVIEW part of 10.2217/fon-2016-0535 © 2017 Future Medicine Ltd In our recent article published in Future Oncology [1] , we reported the outcomes of radiation therapy administered to 195 liver cancer patients. In addition to traditional patient specific parameters, such as age, sex, Child-Pugh (CP) class [2] , we included dosi- metric data. To our surprise, the volume of normal liver receiving more than 24 Gy (V24) correlated positively with disease- free survival for rotational modalities of radiation delivery (volumetric-modulated arc therapy and TomoTherapy), but not for the patients treated with fixed-beams inten- sity-modulated radiation therapy. This finding indicates that relatively large doses delivered in the area adjacent to the tumor in an isotropic manner are able to eradi- cate microscopic spread of malignant cells, while fixed-beam delivery misses these cells in the regions between the beams. In radiation therapy literature, the main focus is on motion and margins [3,4] . The clinical tumor volume created to account for all microscopic spread has not been established for secondary and primary liver disease. Indeed, in many studies, a mar- gin for clinical tumor volume is not added based on the assumption that microscopic disease is of minor importance in this dis- ease site. This is at odds with surgical data where margin beyond the gross tumor has been shown to be independently associated with overall survival [5,6] . Another reason for limiting margins is that with more encompassing treatment, there is an increased risk of radiation- induced liver disease (RILD). Indeed, land- mark work by the Michigan group on whole liver radiation plus a boost resulted in signif- icant RILD [7] . This concern for RILD has led to the modern management philosophy to use stereotactic body radiation therapy to focus on the gross disease. This has allowed very safe dose escalation using partial vol- ume tolerance data. The effect of low-dose spillage was shown to be dependent on patient characteristics: CP class A patients were not affected, while CP class B patients experiencing grade III/IV liver toxicity had significantly higher mean liver dose, higher dose to a-third normal liver, and larger vol- umes of liver receiving doses <2.5–15 Gy in 2.5-Gy increments [8] . Therefore, emphasiz- ing avoidance of low dose spillage may not be necessary in patients with certain known parameters, especially in the absence of liver parenchymal disease. We hypothesize that the density of neo- plastic cells is decreasing gradually with distance from the gross tumor. The lower is the density of malignant cells, the bet- ter is their oxygenation The density of cancerous cells is so low further from the tumor that the patient’s immune system or targeted chemotherapy [9] can eliminate residual disease. However, one may need to LETTER TO THE EDITOR Potential beneft of rotational radiation therapy Jason Vickress 1 , Michael Lock 1,2,3 , Simon Lo 4 & Slav Yartsev* ,1,2,3 1 Department of Medical Biophysics, Western University, London, ON, Canada 2 Department of Oncology, Western University, London, ON, Canada 3 London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada 4 Department of Radiation Oncology, University of Washington School of Medicine, Seattle, WA, USA *Author for correspondence: Tel.: +1 519 685 8605; Fax: +1 519 685 8658; slav.yartsev@lhsc.on.ca KEYWORDS • hepatocellular carcinoma • radiotherapy • stereotactic body radiation therapy • treatment outcomes First draft submitted: 7 December 2016; Accepted for publication: 14 December 2016; Published online: 9 January 2017 For reprint orders, please contact: reprints@futuremedicine.com