Introduction of Image‑Guided Pencil Beam for Skull Base Tumors in India: A Report of Two Cases and a Brief Review of the Literature.

Chordoma and chondrosarcoma are locally aggressive tumors occurring in one-third cases at the base of the skull. These tumors often recur locally with significant morbidity and mortality. The mainstay of treatment is maximal safe tumor debulking. However, in spite of gross total resection, these tumors are likely to recur. Hence, adjuvant radiation is provided to reduce the risk of local recurrence and to improve outcomes. These tumors are considered relatively radioresistant; hence, high doses of radiation are generally required during treatment. However, the presence of several important structures around the lesion poses a major challenge with respect to covering the target with the prescribed high dose. In this regard, protons, for their physical and dosimetric advantages, have become the accepted modality of treatment in these tumors. With the evolution of proton beam therapy (PBT) over the years, especially pencil beam scanning techniques; which result in an extremely high conformal intensity-modulated proton beam therapy (IMPT), robust and Monte Carlo optimization, computational algorithms, and biological modelling are the significant advances which have further enhanced the value of this technology and have improved outcomes. Herein, we would like to report our experience of two cases of skull base tumors treated with intensity-modulated proton therapy at our center along with a review of the literature.