S840 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

Conclusions: FP WBRT is superior to conventional WBRT in reducing dose inhomogeneity and tangential scalp doses. The dosewithin the dose build-up region/hair follicle location is also decreased with this technique. Considering the radiation dose-responserelationship for permanent alopecia has been shown to follow a sigmoidal curve with a D50 follicle dose of 43 Gy (2 Gy/fraction),incremental improvements in dosing may substantially decrease the risk of alopecia. Lessening dose delivered to these regionsshould result in both decreased alopecia and risk of brain injury without negatively impacting the intended outcomes of treatment.Follow-up in this study is currently too short to assess clinically meaningful outcome differences.

Author Disclosure: S. Karlovits, None; R. Fuhrer, None; B. Leicher, None; S. Gott, None; L. Miller, None; O. Gayou, None.

3422 Intensity Modulated or Volumetric Modulated Radiation Therapy (IMRT or VMAT) to Reduce Alopecia,

Xerostomia, and Otitis after Whole Brain Radiation Therapy for Brain Metastases: A Planning Analysis

B. R. Mancini, L. H. Kim, S. F. Shaitelman, D. Yan, L. L. Kestin, I. S. Grills

William Beaumont Hospital, Royal Oak, MI

Purpose/Objective(s): To investigate potential for reducing scalp, parotid, and ear dose via IMRT (IM) or VMAT (VM) vs. stan-dard opposed lateral (OL) beam setup to decrease incidence and severity of alopecia, xerostomia, and otitis after WBRT for brainmetastases.

Materials/Methods: Nine patients with brain metastases previously treated with standard OL WBRT using CT-planning were stud-ied. 4 new plans were created for each patient: 1) 4-beam IM, 2) 7-beam IM, 3) 13-beam IM and 4) VM (single arc technique) andcompared to the OL plan with respect to multiple normal tissue doses. IM plans included a mixture of coplanar and vertex beams set toavoid entry or exit through eyes, ears and mouth when possible. The PTV was defined as whole brain plus a 0.5cm uniform 3D ex-pansion and prescribed 37.5Gy in 15 fractions, volumetrically for IM or VM or to midplane for OL. All plans were optimized toachieve equivalent uniform PTV coverage and dose to lens, globe, brainstem, optic apparatus and cochlea while limiting dose to scalp(skin + 0.5cm depth), parotids and ears. Cochlear dose could not be reduced in this setting due to inclusion in the PTV (brain + 0.5cm).Multiple dose-volume histogram (DVH) parameters for PTV and organs at risk (OAR) were compared.

Results: All multi-beam IM or VM plans significantly reduced dose to scalp, ears and parotids without increasing dose to optic n,lens, cochlea or brainstem, while maintaining homogeneity in the whole brain (WB) PTV compared to OL plans. Exceptions wereincreased scalp low dose using VM (V5 +30%, V10 +10%) and increased mean lens dose with VM (7.4Gy v 4.8Gy OL). MeanPTV dose ranged from 39-40Gy for IM/VM plans vs. 38Gy for OL; PTV max dose was moderately higher for IM/VM (46-50Gy)vs. OL (42Gy). Mean dose to optic n, lens, and cochlea were 27Gy, 3.6Gy, and 33Gy and similar across plans. Improved scalpsparing was seen for low, intermediate, and high doses (V5, V10, V20, and V30) with 4- and 13-beam IM; intermediate andhigh doses with 7-beam IM (V10, V20, and V30) and only high doses with VM (V20 and V30) compared to OL. Dependingon the DVH parameter, IM/VM reduced scalp dose 10-70%, ear dose 2-96%, parotid dose 3-31%. Across all plans, 13-beamIM achieved the largest dose reduction for scalp (V10 -10%, V20 -30%, V30 -70%), ear (V5 -10%, V10 -32%, V20 -28%,V30 -96%), and parotid (-31% mean dose).

Conclusions: IMRT or VMAT provided sparing of scalp, ear and parotids compared to standard OL beams for WBRT. Such im-provement is promising and may decrease non-cognitive WBRT toxicities (alopecia, otitis, xerostomia). 13-beam IMRT planswere superior while VMAT increased low-dose scalp and lens dose. Future planning will attempt to reduce cochlear dose to avoidhearing loss but may require WB PTV modification.

Author Disclosure: B.R. Mancini, None; L.H. Kim, None; S.F. Shaitelman, None; D. Yan, None; L.L. Kestin, None; I.S. Grills,None.

3423 Evaluation of Two Brachytherapy Planning Methods for Accelerated Partial Breast Irradiation

using MammoSite

J. M. Pollard, S. Kirsner, B. Mason, C. Nelson, E. Bloom, K. Gifford

M. D. Anderson Cancer Center, Houston, TX

Purpose/Objective(s): APBI delivered via high dose rate brachytherapy with the use of the MammoSite device has become anincreasingly popular therapy for eligible breast cancer patients. Recently, we changed our planning technique from using 4 standarddwell positions with the Plato v14.3.5 TPS to using Oncentra MasterPlan 3.2 TPS with IPSA optimization. Consequently, wesought to evaluate the dosimetric differences between the two planning techniques for 22 of our previous MammoSite patients.

Materials/Methods: Twenty-two patients were planned with Plato and Oncentra. The Plato clinical plans were generated by usingfour fixed dwell positions, creating a series of calculation points on the surface of the expanded contour of the balloon plus 1 cm andprescribing 340 cGy to these points. Next, graphical optimization was employed to spare critical structures. Identical images, struc-ture sets and dose constraint criteria were used for each plan. In Oncentra, IPSA was used to spare critical structures and providea uniform dose to the PTV-EVAL. The two planning methods were evaluated by comparing the following parameters: (PTV-EVAL) receiving 90% of the target dose (V90), the percentage volume of target receiving 95% of the target dose (V95), the per-centage volume of target receiving 100% of the target dose (V100), the volume of target receiving 150% of the target dose (V150),the volume of target receiving 200% of the target dose (V200), maximum percentage of prescribed dose delivered to 0.1 cc and 1.0cc of both the skin and ribs.

Results: All plans evaluated met our dose constraints set by the protocols followed at our facility. Compared to the Plato plans, theOncentra plans provided a 0.6% higher V90, 1.5% higher V95, 2.1% higher V100, 2.5% higher V150, 20.9% lower V200, 57.1%lower 0.1 cc volume skin dose values, 212% lower 1.0 cc volume skin doses, 42.0% lower 0.1 cc volume rib doses and 40.9% lower1.0 cc volume rib doses.

Conclusions: The IPSA optimization utilized by Oncentra provided smaller V200 volumes and greatly reduced maximum skin andrib doses as well as equal to or better target coverage. If the MammoSite device is placed centrally in the breast, far away (. 5 mm)from both critical structures, the skin and ribs, then planning without IPSA on Plato v13.4 is sufficient. However, the majoradvantage of IPSA is its ability to spare critical structures and it should be utilized for this purpose when available.

Author Disclosure: J.M. Pollard, None; S. Kirsner, None; B. Mason, None; C. Nelson, None; E. Bloom, None; K. Gifford, None.