Estimating Potential Benefits to Neurocognition with Proton Therapy in Adults with Brain Tumors.

Purpose: Photon radiation therapy (RT) is important in the treatment of many brain tumors but can negatively affect neurocognition. Proton therapy (PT) can reduce doses to normal brain structures. We compared photon and proton plans to estimate the potential benefit in cognition if the patient were treated with PT. Materials and Methods: We analyzed 23 adult patients with proton and photon plans for the treatment of a primary brain tumor. Cognitive outcomes were predicted using converted equivalent dose (EQD2) with an α/ß ratio of 3 to left temporal lobe and normal brain tissue. Risks of cognitive decline on 2 specific tests, the Controlled Oral Word Association Test (COWAT [letter S], a test of verbal fluency) and the Wechler Adult Intelligence Scale (WAIS-IV Coding Test, a test of processing speed) were derived from a previously published model. Results: Dose reductions to left temporal lobe and normal brain tissue translated into lower estimated probabilities of impairment in specific neurocognitive test scores after PT. With a mean dose reduction from 1490 to 1092 cGy in EQD2 to the left temporal lobe (P < .001), there was reduction in probability of impairment in the COWAT (Letter S) test from 6.8% to 5.4%. Similar results were seen with the normal brain (750 to 451 cGy in EQD2, P < .001), with reduction in probability of impairment in the WAIS-IV Coding test from 5% to 4.1%. Other structures experiencing dose reduction with PT included each cochlea, posterior fossa, each temporal lobe, and each hippocampus. Conclusion: We confirmed an association between PT and lower doses to brain substructures, which is expected to result in a modest decrease in probability of impairment in neurocognitive test scoring. These findings should be confirmed in prospective cohorts of patients treated with PT.

Simple and effective immobilization for radiation treatment of choroidal melanoma.

At our institution, patients diagnosed with choroidal melanoma requiring external beam radiation therapy are treated with two 6 MV volumetric-modulated arcs delivering 50 Gy over 5 daily fractions. The patient is immobilized using an Orfit head and neck mask and is directed to look at a light emitting diode (LED) during CT simulation and treatment to minimize eye movement. Patient positioning is checked with cone beam computed tomography (CBCT) daily. Translational and rotational displacements greater than 1 mm or 1° off the planned isocenter position are corrected using a Hexapod couch. The aim of this study is to verify that the mask system provides adequate immobilization and to verify our 2-mm planning target volume (PTV) margins are sufficient. Residual displacements provided by pretreatment verification and post-treatment CBCT data sets were used to assess the impact of patient mobility during treatment on the reconstructed delivered dose to the target and organs at risk. The PTV margin calculated using van Herk's method1 was used to assess patient motion plus other factors that affect treatment position, such as kV-MV isocenter coincidence. Patient position variations were small and were shown to not cause significant dose variations between the planned and reconstructed dose to the target and organs at risk. The PTV margin analysis showed patient translational motion alone required a PTV margin of 1 mm. Given other factors that affect treatment delivery accuracy, a 2-mm PTV margin was shown to be sufficient for treatment of 95% of our patients with 100% of dose delivered to the GTV. The mask immobilization with LED focus is robust and we showed a 2-mm PTV margin is adequate with this technique.

Dosimetric and clinical impact of 3D vs. 2D planning in palliative radiotherapy for bone metastases.

PURPOSE: The incorporation of three-dimensional (3D) planning for the treatment of bone metastases has been embraced in many North American practices with assumed superior tumor targeting, sparing of normal structures, and improvement in patient outcomes. The goal of our project was to evaluate the dosimetric and clinical impact of 3D vs. two-dimensional (2D) planning for patients who require simple palliative radiotherapy techniques (≤ 2 beams) for bone metastases. METHODS: Patients undergoing palliative radiation therapy for bone metastases were eligible. The study oncologists first documented the intended treatment target, defined the treatment target/field using digital radiographs (2D), followed by using full 3D planning computerized tomography volumetric datasets. Treatment plans were compared dosimetrically, and patient-reported outcomes (pain, fatigue, anorexia, and nausea) were compared against a historical cohort treated with 2D plans. RESULTS: Eighty-five patients were enrolled in the study group. Review of the 3D datasets led to changes in the target area of interest in 44/85 (52 %) of cases, of which 21/85 (25 %) were clinically significant. 3D plans resulted in superior target coverage and normal tissue sparing. There was no significant difference in patient-reported outcomes however. CONCLUSION: 3D radiotherapy planning resulted in superior treatment plans but we were unable to demonstrate a significant benefit in clinical outcomes. Prospective study designs are needed to describe the contemporary expectation of palliative radiotherapy for bone metastases in the modern era of 3D planning.