Trade-offs in proton and photon radiotherapy for pituitary adenomas

Background and Purpose: Pituitary Adenomas (PAs) are tumours proximal to sensitive organs of interest (OOIs). These tumours may be well-suited for proton therapy due to the Bragg peak. Few studies have evaluated the potential dose-volume benefits of protons for PAs in the pencil beam scanning era. Materials and Methods: Treatment plans for 15 PA patients were made using intensity modulated proton therapy (IMPT), coplanar- and- non-coplanar photon therapy. Dose distributions to OOIs were compared using the Radiation Oncology Collaborative Comparison Group’s (ROCOCO) Performance Scoring System (RPSS), which estimates adverse event (AE) burden. Results: Proton therapy resulted in significantly lower overall estimated AE burden than both photon modalities (median RPSS: 1.09 vs. 1.24; p < 0.005). This reduction was due to significantly lower D<inf>40%</inf> to the hippocampi. For the right hippocampus, median D<inf>40%</inf> (EQD<inf>Gy2</inf>) was 1.1Gy with IMPT, compared with 4.9Gy for coplanar and 3.2Gy for non-coplanar photons. Doses with protons and non-coplanar photons were significantly lower than those for coplanar photons (p < 0.001). For the left hippocampus, IMPT achieved a median D<inf>40%</inf> of 0.7Gy, compared with 5.0Gy for coplanar and 2.7Gy for non-coplanar photons. Non-coplanar was significantly lower than coplanar (p < 0.001), while IMPT was significantly lower than both photon modalities (p < 0.001). Protons delivered higher doses to the brainstem, optic nerves, chiasm, and the hypothalami. Conclusions: These findings indicate that IMPT can significantly reduce AEs to critical brain structures. Although considerations of cost, accessibility, and clinical validation remain, IMPT may offer a meaningful therapeutic advantage.