Dosimetric analysis of treatment planning optimization techniques for CO-60 and IR-192 HDR brachytherapy sources in carcinoma cervix patients

Abstract

Introduction: The study was designed to dosimetrically compare the treatment planning optimization techniques to analyze the equivalence of Co-60 and Ir-192 HDR Brachytherapy sources. Further, the present study planned to analyze the equivalence on the basis of technical, logistical and clinical aspects for both the sources. Methods: Thirty-two patients with confirmed diagnosis of carcinoma cervix were included in the study. Comparative treatment plans were made for three different treatment planning optimization techniques for both the sources Co-60 and Ir-192 i.e. (a) plans with prescription on Point A (Manchester system) with identical dwell position, (b) plans with inverse planning and (c) plans with prescription on HR-CTV with manual optimization. Treatment plans were evaluated on the basis of clinical parameters HR-CTV V200%, V150%, V100%, D95%, D50%, D2cc Bladder, D2cc rectum and point dose on ICRU Rectum and Bladder reference point. Results: For the plans with prescription on Point A with identical dwell position, the average percentage difference were found HR-CTV V200% (6.3%), V150% (5.1%), V100% (1.8%), D2cc rectum (2.3%) and ICRU Rectum reference point (2.1%) and all these parameters were statistically significant for both the sources. For the Plans with inverse planning optimization, these parameters were found significant with average percentage difference HR-CTV V200% (6.1%), V150% (4.9%), D50% (2.1%) and ICRU Rectum reference point (2.3%). For the plans with dose prescription on HR-CTV and manual optimization, most of the average percentage differences were found non-significant and clinical parameters were observed clinically comparable to each other for both the sources. Further, it was also observed that on an average Ir-192 source required only 42% of the treatment time required by Co-60 for the same treatment plan delivery. Conclusion: Among all the three planning techniques, the planning technique with prescription on HR-CTV & manual optimization was found to have comparable clinical quality for both the sources. This analysis revealed that geometry of source placement can overcome the differences in individual source characteristics.

Keywords

• cobalt-60
• iridium-192
• high dose rate brachytherapy
• cervical cancer