Abstract
Purpose: The aim of this investigation was to measure the gain in DVH indices when the recently developed MLC was used for Cobalt-60 treatments. Methods: A prototype multileaf collimator (MLC) that was retrofitted to telecobalt-60 therapy machine was reported and is currently proposed for clinical trials in our institution. Ten patients’ plans that were previously planned through an ECLIPSE ® treatment planning system and were treated with open beams from Cobalt-60 machine were imported into Radiation Oncology Planning System [ROPS] and the dose calculations and dose volume histogram (DVH) analysis were performed. The plans were re-planned using the Cobalt-MLC, a feature available in the ROPS planning system. The DVH analysis consisted of conformity index (CI), homogeneity index (HI) and conformation number (CN). The results of this study are presented in this paper. The analysis specifically aimed at measuring the gain in these indices when the MLC was compared with open beams. Results: DVH Comparison of ten sites using open and Cobalt MLC fields showed that the use of MLC results in reduced normal tissue dose, while maintaining the GTV dose. Lower value of CI for normal structures was observed demonstrating the sparing of critical organs when MLC was used. The index HI was studied to show the significance of hot spots outside the PTV. Hot spots were observed even with MLC beams for some cases due to less number of fields. Conclusion: It has been demonstrated through DVH analysis that the use of the recently developed MLC for Cobalt Teletherapy machine results in benefit for the treatment of patients.
Highlights
Cobalt-60 treatment machines are still used in developing countries all over the world
While 95% isodose line is used as a standard isodose line for the definition of the indices, for cobalt-60, we have considered 90% isodose line since 95% cannot cover the target volume (TV) in some cases
It can be seen that the use of multileaf collimator (MLC) results in reduced normal tissue dose, while maintaining the gross tumor volume (GTV) dose
Summary
Cobalt-60 treatment machines are still used in developing countries all over the world. In India there are over 200 Co-60 machines are still in operational. The benefit of using MLC for cobalt-60 was referred by several investigators[2,3,4,5,6,7,8]. The overall goal of our MLC project is to develop the MLC as a retrofit attachment to the existing cobalt machines, and to provide a controller and a low cost treatment planning system (TPS) such as Radiation Oncology Planning System [ROPS] from TJCS (Tirumala Jyothi Computer Systems, Secunderabad, India). Figure[1] shows the Cobalt machine and the attached MLC
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