Abstract
Purpose: To evaluate the influence of collimator rotation in IMRT planning with respect to the target coverage and dose to critical structures. In addition, the delivery efficiency of desired fluence with collimator rotation is assessed. Methods : The computed tomography (CT) datasets of 5 patients with parotid cancer were employed for this study. Dynamic IMRT plans were generated with a dose prescription of 60 Gy in 30 fractions. IMRT plans were generated with five unilateral fields using 6MV X-rays. Four different plans were generated for each patient by keeping the collimator angle at 0, 30, 60, and 90 degree. All plans were analyzed using dose volume histogram. Conformity index (CI) and heterogeneity index (HI) were calculated. The total monitor units (MU) required to deliver one fraction were noted and compared. To verify the delivery efficiency; the measured fluence on IBA I’mRT MatriXX ionization chamber array detector was compared with the TPS dose plan with 2D gamma evaluation. Results: There is not much difference in the PTV Dmax and Dmean with respect to the different collimator angles. The PTV coverage is best at collimator angle of 0 degree. A slight reduction in CI was observed with plans at other collimator angles as compared to 0 degree. The HI values were almost similar for plans with collimator angle 0, 30, and 60 degree. The plan with 90 degree collimator showed a slightly higher heterogeneity for the PTV. A slight reduction in the average Dmax to spinal cord was observed for the plan with collimator angle 30 degree as compared to other angles whereas maximum value of Dmax to spinal cord was at collimator angle 60 degree. No clinically relevant difference was observed among the plans with respect to brainstem and mandible Dmax. An increase in average of oral cavity Dmax and Dmean was observed for collimator angle 60 and 90 degree as compared to collimator angle 0 and 30 degree. Not much difference was observed with respect to Dmax and Dmean for contralateral parotid and cochlea with plans at different collimator angles. A decrease in MU required to deliver a fraction was observed for the plan with collimator angle 30 degree as compared to other angles. The plan with 90 degree collimator required maximum MU. The 2D γ index evaluation of planned and delivered fluence showed almost similar results for plans with different collimator angles. Conclusion: An individual case-specific collimator rotation may aid in achieving the desired dose distribution and relative sparing of critical structures in IMRT.
Highlights
In the era of modern radiotherapy techniques day to day new and advance techniques of radiotherapy are being implemented like intensity modulated radiotherapy (IMRT), image guided radiotherapy (IGRT), rapid arc therapy and flattening filter free (FFF)
The new algorithm Acuros XB (AXB) has been introduced with ECLIPSE treatment planning system (TPS) which is considered similar to Monte Carlo, few authors have already presented AXB more accurate algorithm compare to analytical algorithm (AAA).[6, 7]
Plan quality assurance (QA) plan done on Slab phantom
Summary
In the era of modern radiotherapy techniques day to day new and advance techniques of radiotherapy are being implemented like intensity modulated radiotherapy (IMRT), image guided radiotherapy (IGRT), rapid arc therapy and flattening filter free (FFF). With the superposition of doses of the photon and electron convolutions the resultant dose distribution is achieved.[3, 4] still researchers are doing work on many codes of Monte Carlo, they advocate that Monte Carlo consider more accurately the higher level of scattering and effect of heterogeneity.[5] Recently the new algorithm Acuros XB (AXB) has been introduced with ECLIPSE TPS which is considered similar to Monte Carlo, few authors have already presented AXB more accurate algorithm compare to AAA.[6, 7] The research in this direction of developing new radiotherapy modalities with more accurate dose calculating algorithms is going on
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: International Journal of Cancer Therapy and Oncology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
