Dosimetric evaluation of clinical target volume in the postimplant analysis of low-dose-rate brachytherapy for prostate cancer Nicola J. Nasser 1,2,y , Joshua Sappiatzer 1,y , Yinkun Wang 3 , Jette Borg 3 , Elantholi P. Saibishkumar 1,2, * 1 Department of Radiation Oncology, Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada 2 Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada 3 Department of Radiation Physics, Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada ABSTRACT PURPOSE: Brachytherapy is an effective single treatment modality for low- and intermediate-risk prostate cancer. In this study, we defined a clinical target volume (CTV) and evaluated its dosimetry 1 month after the low-dose-rate brachytherapy procedure. METHODS AND MATERIALS: One hundred ninety-eight consecutive patients treated for pros- tate cancer by iodine-125 seed brachytherapy were assessed. Prostate dosimetry was stratified ac- cording to British Columbia Cancer Agency criteria, with good implants having both V 100 (percentage of target volume that receives 100% of the prescribed dose) O 85% and D 90 (percent- age of the prescribed dose received by 90% of the target volume) O 90%, suboptimal implants with V 100 of 75e85%, or D 90 80e90%, whereas poor implants were defined as those with V 100 ! 75 or D 90 ! 80%. CTV dosimetry stratification was performed according to the same dose coverage criteria, albeit to the CTV. RESULTS: One hundred ninety-two patients (97%) had good prostate radiation coverage, whereas only 165 patients (83%) had good postimplant CTV dosimetry. Patients with suboptimal vs. good CTV dosimetry had prostate edema of 7.8  0.2% vs. 0.2  0.1%, respectively ( p 5 0.001). CONCLUSIONS: Prostate seed implants with optimal dosimetry to prostate may still have sub- optimal D 90 and V 100 for the CTV, especially in the presence of postimplant edema. A consensus is needed for definition and evaluation of CTV in postimplant setting for low-dose-rate prostate brachytherapy. Ó 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved. Keywords: Clinical target volume; Prostate; Dosimetry; Cancer Introduction Low-dose-rate (LDR) brachytherapy is widely used for treatment of low- and intermediate-risk prostate cancer (1e4). Extracapsular extension can occur in low- and intermediate-risk prostate cancer but is mostly confined within 3e5 mm (5). Hence, clinical target volume (CTV) in LDR brachytherapy should include the whole prostate and a margin around the prostate to account for possible extracapsular extension (6). Moreover, including a margin around the prostate allows for at least partial compensation for prostate edema, which usually occurs as a result of seed insertion (7e10). Preimplant planning usually ensures adequate coverage to the prostate CTV, whereas posttreatment dosimetry is usually limited to the prostate, rectum, and urethra, and prostate CTV dosimetry is not routinely performed. Moreover, there are no clear guidelines to evaluate the qual- ity of CTV dosimetry. Recently, we have shown that there are significant differences in dose coverage of different sectors of the prostate between preplan and postimplant dosimetry (11). In the present study, preimplant treatment plans and postimplant dosimetry are compared for patients treated with iodine-125 prostate brachytherapy at Princess Margar- et Cancer Centre (PMCC) to evaluate radiation dose coverage to the prostate and the prostate CTV. Received 7 June 2014; received in revised form 24 July 2014; accepted 4 August 2014. Conflict of interest statement: Authors have no financial disclosure or conflicts of interest to report. * Corresponding author. Department of Radiation Oncology, Princess Margaret Cancer Centre/University of Toronto, Toronto M5G 2M9, Ontar- io, Canada. Tel.: þ1-416-946-2919; fax: þ1-416-946-6561. E-mail address: saibish.elantholi@rmp.uhn.on.ca (E.P. Saibishkumar). y These authors contributed equally to this manuscript. 1538-4721/$ - see front matter Ó 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.brachy.2014.08.044 Brachytherapy 14 (2015) 189e196