Dosimetric and Cost Analysis of Treatment Methods for Whole Brain Radiation Therapy: 3D-CRT versus HA-IMRT

Summary: Purpose Whole brain radiotherapy (WBRT) is a cornerstone in the management of brain metastasis. Indications for stereotactic radiosurgery (SRS) have expanded; however, the vast number of patients still undergo WBRT using 3D techniques. Our purpose was to compare four WBRT delivery types: classic opposed lateral (OL) 3D-CRT, a novel opposed lateral sparing 3D-CRT technique (OLS) involving MLC modifications to protect the lacrimal and parotid glands, 3D optimized dynamic conformal arcs (optDCA), and hippocampal avoidant IMRT (HA-IMRT). We hypothesized that OLS can lead to significant organ at risk (OAR) sparing over OL planning, and that optDCA planning will approximate OAR doses seen in HA-IMRT, while being similar in cost to other 3D techniques. Methodology Ten patients who previously underwent HA-IMRT according to RTOG 0933 protocol were retrospectively planned using OL, OLS, and optDCA techniques. OLS technique involved MLC modifications to protect the lacrimal and parotid glands. Optimized DCA technique was inverse-planned 3D-CRT with dynamic conformal arcs optimized for PTV coverage and homogeneity. No attempt was made to spare OARs. Treatment planning was conducted to deliver 30Gy in 10 fractions. PTV coverage, conformity indices, and heterogeneity indices were compared. Dosage to OARs including cochlea, lacrimal glands, lens, parotid glans, and scalp were compared between plans, and a cost analysis was performed. Results PTV coverage to prescription dose between 3D planning techniques was not significantly different between OL and OLS techniques (96.8 vs 96.6, p=0.86), or between OL, OLS, and optDCA (95.0%) techniques (p=0.079). There was no difference in PTV coverage to 95% of the prescription dose between the 3D plans (99.9 vs. 99.7 vs. 99.7%, p=0.40). There was no difference in the heterogeneity index between 3D plans (p=0.48), and all were less heterogeneous than HA-IMRT plans (p<.001). Optimized DCA was more conformal than OL and OLS, and similar in conformity to HA-IMRT. OLS achieved significant sparing of lacrimal and parotid glands over OL in terms of mean dose, maximum dose, and volumetric doses. There were significant step-function reductions in OAR dose when comparing OL to OLS to optDCA to HA plans. Additionally, optDCA plans spared the scalp significantly compared to OL and OLS. The cost to deliver optDCA and HA-IMRT was increased by 13.9% and 57.1% compared to OL and OLS plans, respectively. Conclusions We showed adequate and equivalent target coverage using OL, OLS, and optDCA techniques. Lacrimal and parotid dosages can be greatly reduced with the implementation of minor MLC adjustments. Optimized DCA therapy represented a further improvement of these modifications in the delivery of WBRT, and was comparable to HA-IMRT in terms of OAR dose, while being about two-thirds the cost. Further study is warranted to determine the clinical significance of these findings.