Leakage dose reduction using modified midline block technique in the treatment of cervical cancer

This study aimed to evaluate the usefulness of multileaf collimator (MLC) and jaw shielding in the midline block (MLB) plan for radiation treatment of cervical cancer. The shape of the MLC opening was considered in the MLB treatment plan to close the jaw in cases treated with the Varian linear accelerators (Linac) and to close the diaphragm in cases treated with the Elekta Linac. To evaluate the radiation dose to unintended areas, the Exradin A19 Ion Chamber was used to assess the calibrated EBT3 film. For the MLB treatment plan, approximately 60% of the applied dose was received at unintended locations due to the gap of leaf in the Elekta Linac. Approximately 30% dose leakage was measured with the Varian Linac. Comparing the treatment plans, the mean dose to the rectum is reduced by roughly 30%, and that to the bladder is reduced by approximately 4% when shielded fields are used for both Elekta and Varian Linac. In MLB boost treatment, the plan needs to consider using a shield in accordance with the characteristics of the Linac to reduce unintended radiation to the central block.