Impact of 6 MV photons and mixed beam (6 MV and 15 MV) photons on the dose distribution in high-grade gliomas using three-dimensional conformal radiotherapy technique - A Retrospective Analysis

Abstract

Background and Aim: The present study focused on the impact of 6 MV photons and mixed beam (6 MV and 15 MV) photons on dose distribution in high-grade gliomas using three-dimensional conformal radiotherapy (3DCRT) technique. The suitability of using different photon beam energies was evaluated with respect to dose distribution. Materials and Methods: A total of 24 patients of high-grade glioma treated on linear accelerator were enrolled and evaluated in this retrospective study. All patients had undergone total/subtotal resection of tumor. These patients were treated with postoperative adjuvant external beam radiotherapy on a linear accelerator using 3DCRT technique. Treatment plans were generated using 6 MV and a combination of both 6 MV and 15 MV photon beams. All plans were generated using suitable planning objectives, and dose constraints which were identical across the plans, except the beam energy. The plans were analyzed in terms of their target coverage, conformity, and normalized dose range. Results: In 16 patients out of 24, the treatment plans were generated using 6 MV photons, the normalization dose was well within 5%–7% of the dose prescribed. In the remaining 8 patients, the normalized dose was >107%, and in these cases, the use of mixed beam plans yielded a better dose distribution with normalized dose between 101% and 105%. Conformity index (CI) values were between 1.2 and 1.98. CI mean was 1.59. Conclusions: The use of mixed beams in 3DCRT technique may be considered as an alternative, especially in a scenario where pure 6 MV photons do not yield homogeneous dose distribution within the normalized range, and in centers where intensity-modulated radiation therapy and field-in-field technique are not available.