Secondary malignancies Estimation of risk of radiation-induced carcinogenesis in adolescents with nasopharyngeal cancer treated using sliding window IMRT Shamurailatpam Dayananda Sharma a, * , Ritu Raj Upreti a , Siddhartha Laskar b , Chandrashekhar M. Tambe a , Deepak D. Deshpande a , Shyam K. Shrivastava b , Ketayun A. Dinshaw b a Department of Medical Physics, and b Radiation Oncology, Tata Memorial Hospital, Parel, Mumbai, India Abstract Purpose: To estimate the risk of radiation-induced carcinogenesis based on whole-body dose measurement on adolescent patients undergoing intensity-modulated radiotherapy (IMRT). Methods and materials: Ten adolescent patients with nasopharyngeal cancer were planed and treated to a dose of 70.2 Gy using sliding window IMRT. Peripheral dose (PD) was measured using thermoluminescent dosimeters kept at anterior, lateral and posterior positions of each axial plane at the level of xiphoid process, umbilicus and gonads of every patient. The associated risk of radiation-induced carcinogenesis was estimated based on the measured whole-body dose and using age- and sex-specific ICRP-60 nominal probability coefficient of 7.5% (boys) and 9.5% (girls) per Sv. Results: In all patients, measured PD per monitor unit (MU) decreases almost exponentially with out-of-field distance and varies with gantry angle. Highest whole-body dose equivalent ranged from 0.5318 to 0.9867 Sv (mean = 0.8141 Sv, SD = 0.138) which was measured posteriorly at the level of xiphoid process. Whole-body dose was represented by the average dose at xiphoid process and all measurement positions ranged from 0.3661 to 0.8766 Sv (mean = 0.658 Sv, SD = 0.16) and 0.2267 to 0.5277 Sv (mean = 0.3859 Sv, SD = 0.09), respectively. The associated mean risk of radiation- induced carcinogenesis estimated based on different representation of mean whole-body dose was 6.57%, 5.3% and 3.11%, respectively. Higher mean risk of 7.32% was estimated among girls as compared to 6.25% for boys. Conclusions: Knowledge of risk of secondary malignancy is particularly important in adolescents and should be considered when choosing the optimal treatment technique and delivery system.  c 2007 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 86 (2008) 177–181. Keywords: Intensity-modulated radiotherapy; Peripheral dose; Second malignancy; Adolescents Intensity-modulated radiotherapy (IMRT) is widely adopted in the treatment of several types of cancers in adult and elderly patients because of its potential to reduce normal tissue complication probability. In the recent past, increasing interest has been shown in the use of this tech- nique for adolescent patients. Review of published data on IMRT in adolescent patients reveals significant reduction of dose to lens, optic nerve, optic chiasm, spinal cord and cochlea as compared to conventional radiotherapy in a ser- ies of adolescent patients treated for various intracranial tumors [12]. However, despite the promises, two major concerns often raised on the use of IMRT are the increase in whole-body dose due to the increase in the number of monitor units (MU) per target dose and larger volume of nor- mal tissue irradiated at lower radiation dose as compared to conventional radiotherapy [1–4,6,8,10,13,16]. These two factors can potentially increase the risk of radiation-in- duced carcinogenesis, particularly in long-term survivors [1–4,6–8,10,16]. The whole-body dose and associated risk of radiation-in- duced second malignancies have been reported from adult and elderly patients treated using various methods of IMRT [1,2,7,8,10,16]. Radiotherapy of adolescent patients using IMRT needs special consideration as the issue related to radiation-induced carcinogenesis is more pronounced in this patient population because (a) adolescents are more sensi- tive to radiation-induced cancer than are adults and (b) they may survive long enough after disease control [4]. More- over, risk of carcinogenesis reported so far in the literature was based on the estimate using the nominal probability coefficient of International Commission on Radiological Pro- tection (ICRP) Report No. 60 and National Council on Radia- Radiotherapy and Oncology 86 (2008) 177–181 www.thegreenjournal.com 0167-8140/$ - see front matter  c 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2007.11.019