Japanese Journal of Clinical Oncology Advance Access originally published online on January 22, 2008
Japanese Journal of Clinical Oncology 2008 38(2):158-163; doi:10.1093/jjco/hym167
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© The Author (2008). Published by Oxford University Press. All rights reserved
Performance Evaluation of Field-In-Field Technique for Tangential Breast Irradiation
1 Department of Radiation Oncology, School of Medicine, Konkuk University, Konkuk University Hospital, Seoul, Republic of Korea
2 Department of Biomedical Engineering, School of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
3 Department of Radiation Oncology, College of Medicine, Ajou University Hospital, Gyeonggi-do, Republic of Korea
4 Department of Radiation Oncology, Seoul National University Bundang Hospital, Gyeonggi-do, Republic of Korea
5 Department of Radiation Oncology, National Cancer Center, Gyeonggi-do, Republic of Korea
For reprints and all correspondence: Semie Hong, Department of Radiation Oncology, School of Medicine, Konkuk University, Konkuk University Hospital 4-12 Hwayang-dong, Gwangjin-gu, Seoul, 143-729, Republic of Korea. E-mail: semiehong{at}kuh.ac.kr
Received October 2, 2007; accepted November 21, 2007
Conventional hard or dynamic wedge systems are commonly applied to reduce the dose inhomogeneity associated with whole breast irradiation. We evaluated the dosimetric benefits of the field-in-field (FIF) technique by comparing it with the electronic compensator (EC), Varian enhanced dynamic wedge (EW) and conventional hard wedge (HW) techniques. Data were obtained from 12 patients who had undergone breast-conserving surgery (six left-sided and six right-sided). For these patients, the average breast planning target volume (PTV) was 447.4 cm3 (range, 211.6–711.8 cm3). For the experiments, a 6 MV photon beam from a Varian 21 EX was used, the HW and EW angles were applied from 15 to 45 degrees, while 40–50% isodose values were chosen to achieve the best dose distribution for electronic compensation. In applying the FIF technique, we used two or three subfields for each portal. To evaluate the performance for each planning technique, we analysed a dose-volume histogram (DVH) for the PTV and organs-at-risk (OARs). To evaluate the effects of these techniques on dose inhomogeneity, we defined the PTV Dose Improvement (PDI) index, which was derived from a PTV volume between 97–103% of the differential DVHs. In addition, we compared the average monitor units (MUs) for each technique. The average PDI index with FIF is 76.4%, while the PDI indices for other treatments were 65.8, 41.8 and 50.9% for EC, EW and HW, respectively. This study demonstrated an improved performance using the FIF technique compared with the conventional HW/EW system, as well as a new modality for EC. We demonstrated that FIF is a very useful technique for improving PTV conformity, while protecting the OARs from breast tangential irradiation.
Key Words: breast irradiation • field-in-field technique • dose compensation • PTV Dose Improvement Index (PDI index)