Abstract
(1) Background: Selecting patients that will benefit the most from proton radiotherapy (PRT) is of major importance. This study sought to assess dose reductions to numerous organs-at-risk (OARs) with PRT, as compared to three-dimensional conformal radiotherapy (3DCRT) and volumetric-modulated arc therapy (VMAT), as a function of tumor location. (2) Materials/Methods: Patients with intracranial neoplasms (all treated with PRT) were stratified into five location-based groups (frontal, suprasellar, temporal, parietal, posterior cranial fossa; n = 10 per group). Each patient was re-planned for 3DCRT and intensity-modulated radiotherapy (IMRT) using similar methodology, including the originally planned target and organ-at-risk (OAR) dose constraints. (3) Results: In parietal tumors, PRT showed the most pronounced dose reductions. PRT lowered doses to nearly every OAR, most notably the optical system and several contralateral structures (subventricular zone, thalamus, hippocampus). For frontal lobe cases, the greatest relative dose reductions in mean dose (Dmean) with PRT were to the infratentorial normal brain, contralateral hippocampus, brainstem, pituitary gland and contralateral optic nerve. For suprasellar lesions, PRT afforded the greatest relative Dmean reductions to the infratentorial brain, supratentorial brain, and the whole brain. Similar results could be observed in temporal and posterior cranial fossa disease. (4) Conclusions: The effectiveness and degree of PRT dose-sparing to various OARs depends on intracranial tumor location. These data will help to refine selection of patients receiving PRT, cost-effectiveness, and future clinical toxicity assessment.
Highlights
Radiotherapy (RT) for intracranial neoplasms, many of which are benign and/or have good long-term prognosis, is inherently associated with a risk of damaging normal brain parenchyma and causing late toxicities [1,2]
The latest effort to deliver highly conformal RT and potentially decrease chronic adverse effects of cerebral irradiation in appropriate patients is manifested by the rapid rise of proton radiotherapy (PRT)
PRT offers a unique dose deposition known as the Bragg peak, before and beyond which there is only limited dose absorption [3] in the normal tissue, and only limited effects in non-target tissue
Summary
Radiotherapy (RT) for intracranial neoplasms, many of which are benign and/or have good long-term prognosis, is inherently associated with a risk of damaging normal brain parenchyma and causing late toxicities [1,2]. The latest effort to deliver highly conformal RT and potentially decrease chronic adverse effects of cerebral irradiation in appropriate patients is manifested by the rapid rise of proton radiotherapy (PRT). A central question facing radiation oncology is the assessment of which patients will benefit most from PRT. It has been posited by Zietman et al that PRT may be most advantageous based on the location and anatomic considerations of the tumor with surrounding tissue [12]. Dosimetric differences as compared to photon-based techniques vary greatly based on location. Tumors abutting the optic apparatus or the brainstem, especially if dose-escalation is warranted, may show the most striking dosimetric differences between PRT and photons. It is likely that tumors that are relatively away from dose-limiting structures may have negligible dosimetric differences
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