Trade-offs in proton and photon radiotherapy for pituitary adenomas

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.

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.

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_40% to the hippocampi. For the right hippocampus, median D_40% (EQD_Gy2) was 1.1 Gy with IMPT, compared with 4.9 Gy for coplanar and 3.2 Gy 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_40% of 0.7 Gy, compared with 5.0 Gy for coplanar and 2.7 Gy 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.

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.