Improved treatment of pelvis and inguinal nodes using modified segmental boost technique: dosimetric evaluation

Abstract

Purpose To describe a novel, yet simple, modified segmental boost technique (MSBT) and to compare the dosimetry of our method with that of other traditional methods of treatment for the pelvis and inguinal nodes. Methods and materials We developed a radiotherapy technique that uses linear accelerators with multileaf collimators to treat the pelvis and sequentially boost the inguinal regions, while minimizing “hot spots” across the match-line. This was achieved by angling the gantry for the inguinal fields so that their medial borders aligned with the divergence of the posterior pelvic field. Film dosimetry was performed to compare the MSBT with the traditional segmental boost technique, partial transmission block, and photon/electron combination techniques. These treatment techniques were scored on the basis of the dose homogeneity index, defined as the ratio of match-line maximum dose to the average dose at a given depth in the groin treatment area. Results The values of the dose homogeneity index were the same (1.04) for MSBT and partial transmission block, and 1.21, 1.39, and 1.18 for the segmental boost technique, photon pelvis with electron tags, and photon pelvis with electron boost, respectively. Conclusion The MSBT proved to be technically simple while optimizing dose homogeneity compared with the other techniques and allows for maximum use of the features of modern linear accelerators.