Proceedings of the 52nd Annual ASTRO Meeting S811

Conclusions: The new applicator once applied will overcome most of the disadvantages from the conventional FSD device andoffers numerous superior clinical advantages for patients with gynecological cancer. The applicator design, patient comfort studies,GYN dosimetric comparison to FSD will be presented.*This project is supported by Varian Medical System

Author Disclosure: Z. Zhang, None; E. Parsai, None; J.J. Feldmeier, None; W. Chen, None.

3357 A Hybrid IMRT Technique for High Dose Radiotherapy in Large-Volume Stage III Lung Tumors:

Planning Comparison with 3 Other Techniques

W. Verbakel, I. Ladenius-Lischer, B. J. Slotman, S. Senan

VU University Medical Center, Amsterdam 1007 MB, Netherlands

Purpose/Objective(s): The delivery of doses .60 Gy to large-volume Stage III lung tumors is difficult due to the need to limit lungdoses. Non-IMRT planning is time consuming but IMRT or volumetric modulated arc therapy may increase volumes of low doseirradiation in the lungs. We compared dose distributions in patients treated using a novel h-IMRT (hybrid) approach with fullIMRT, RapidArc and conventional static-field plans.

Materials/Methods: A h-IMRT technique was used to treat 15 patients, with an average PTV of 589 cc (range, 236-1258 cc), whounderwent concurrent chemo-radiotherapy to 66 Gy. Plans generally consisted of open fields of 15 MV photons from AP and PA,with an additional oblique PA field to avoid the spinal cord, planned up to an average PTV dose of 58 Gy (88% of prescribed dose),minimum 47 Gy. The IMRT component of h-IMRT consisted of 2 slightly angulated AP PA fields and 1 lateral of 6 MV, optimizedto 66 Gy using the Eclipse TPS (Varian Medical Systems), and taking into account the dose distribution from the static fields. H-IMRT planning objectives were: PTV V95 . 97%, hot spots receiving .107% of prescribed dose to\5 cm3, homogeneous PTVdose, spinal cord Dmax \50 Gy and total lung V20 and contralateral lung V5 as low as possible. All cases were retrospectivelyreplanned using either a full 3D conformal technique (3Dconf), applying 5-9 static fields, a 2-arc RapidArc (v10.0.11) or anIMRT technique, applying 6 fields of 6 MV chosen such that lung V5 and V20 was optimally spared. Dosimetric data for all planswere compared using the Wilcoxon paired signed rank test.

Results: H-IMRT plans consistently required around 1 hour per patient to achieve an acceptable plan. All other techniquesrequired between 1.5-5 planning hours. H-IMRT achieved the lowest V5 (32 ± 13%) compared to 3Dconf, IMRT and Rap-idArc, respectively (47 ± 17, 39 ± 14 and 50 ± 16%, all p\0.01), and lowest V20 (29 ± 7%) vs. 32 ± 7, 32 ± 7 and 30 ±7% (p = 0.001, 0.003 and 0.5). Hot spots of V107 were best minimized by h-IMRT (average 1 ± 1.5 cm3) compared toaverage 10 ± 13, 25 ± 27 and 9 ± 12 cm3, respectively (all p \ 0.03). Both conventional and full IMRT plans resulted inoccasional unacceptable hot spots outside the PTV. Surprisingly, 6 field IMRT did not achieve comparable results as h-IMRT, using the same 6 fields.

Conclusions: H-IMRT, using a small IMRT component of average 12%, allows large volume stage III lung tumors to be treated toa dose of 66 Gy. It is a fast planning technique and superior to full IMRT or RapidArc in reducing ipsilateral (V20) and contralateral(V5) lung doses and dose hot spots. The main AP-PA open fields permit the use of online dosimetry and position/gating verificationusing cine-EPI.The VUmc has a research agreement with Varian Medical Systems.

Author Disclosure: W. Verbakel, Varian Medical Systems, D. Speakers Bureau/Honoraria; I. Ladenius-Lischer, None; B.J. Slot-man, Varian Medical Systems, D. Speakers Bureau/Honoraria; S. Senan, Varian Medical Systems, D. Speakers Bureau/Honoraria.

3358 Beam Angle Selection (BAS) via Nested Partitions-based Global Search using a Fast Beam Set

Scoring Process

W. Chen1, H. H. Zhang2, R. R. Meyer1, L. Shi1, W. D. D’Souza2

1University of Wisconsin, Madison, WI, 2University of Maryland, Baltimore, MD

Purpose/Objective(s): To develop and evaluate a Nested Partitions BAS global search approach that combines single-beam datawith a ‘‘fast’’ beam set scoring process.

Materials/Methods: Locally advanced head and neck cases were selected for this study. The treatment targets involved primarytumor, high risk and low risk nodal volumes. Organs-at-risk (OARs) included both parotids and the spinal cord. For each case a col-lection of 11 seven-beam IMRT equi-spaced plans (e-plans) were generated using the Pinnacle3 planning system. This collectioncontained all 72 beam angles corresponding to 5 degree spacing. The Pinnacle3 planning system was then used to extract the dosedelivered from each of these 72 angles. This dose data was employed in a search process guided by the random-sample-basedNested Partitions global optimization framework. In this context a sample was a 7-beam set satisfying beam spacing constraints.The beams were selected by a biased-sampling procedure in which ‘‘good’’ angles had a higher selection probability. A fast methodwas used to obtain an approximate quality score for each beam set sample. This method simply added the dose matrices for thebeams in the sample, scaled the resulting total dose matrix in order to achieve the prescription dose on 95% of the PTV, andthen computed a DVH-based overdose/underdose score for the scaled dose matrix. This process enabled us to compute ‘‘fast’’scores for 3000 beam set samples in 100 seconds, and, although it did not optimize dose, our experience has shown that the elitesamples with the best 5-10 ‘‘fast’’ scores generally contain ‘‘improved’’ beam sets. (Improvement was measured by generatingoptimized Pinnacle plans for the best samples, applying the same scoring process described above to the optimized plans, andthen comparing these ‘‘true’’ scores with the best e-plan score.)

Results: Global beam angle search obtained quality beam sets for IMRT delivery. The overall treatment planning objective wasreduced 15% from the initial best e-plan. Individual OAR sparing was also achieved. In summary, parotid gland sparing was im-proved by 2-10% in comparison with the best e-plan. The most significant improvement was achieved in spinal cord, where themaximum dose was reduced by 40%. Dose homogeneity was higher for our approach for all PTvs. (tumor and nodes). Integraldose to non-PTV and non-OARs tissues was lower with BAS, which may have long-term implications for secondary cancer in-cidence. These improvements were significant comparing to the best e-plans (p \ 0.005).

S812 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

Conclusions: Our results suggest that a global beam angle search method combining single-beam dose data with a ‘‘fast’’ beam setscoring process yields superior beam sets.

Author Disclosure: W. Chen, None; H.H. Zhang, None; R.R. Meyer, NIH CA130814, B. Research Grant; L. Shi, NIH CA130814,B. Research Grant; W.D. D’Souza, NIH CA130814, B. Research Grant.

3359 Influence of Customized 125I Plaque Radiotherapy Design on Dosimetry Related to Iris Melanoma

J. Emrich1, L. Komarnicky1, C. L. Shields2, C. Bianciotto2, J. A. Shields2

1Drexel University College of Medicine, Philadelphia, PA, 2Wills Eye Institute, Thomas Jefferson University, Philadelphia, PA

Purpose/Objective(s): To evaluate the treatment of iris melanoma with 125Iodine plaque radiotherapy. Our group has previouslyreported (2003) on custom-built plaque radiotherapy for 38 iris melanoma patients. During the time period 2004-2009, 35 addi-tional patients were treated with the same diagnosis using customized 125I episcleral plaque radiotherapy.

Materials/Methods: The diagnosis of iris melanoma was documented after opthalmoscopic evaluation, fundus photography,ultrasound biomicroscopy, and demonstrable tumor enlargement over time. Patients were treated with customized episcleral125I plaque radiotherapy as an alternative to the surgical intervention that enucleation entails. Management of this tumor islargely dependent on tumor size and seeding. Tumor seeding often accompanies the spread of iris melanoma and invasive pro-cedures can shed malignant cells into the circulation. Iodine-125 seeds (Model 6711; Oncura) were affixed to the plaques todeliver a prescribed tumor apex dose of 70 Gy (TG-43 formalism). Small size plaques (10 mm) were loaded in a ladder design,while medium (15 mm) and large (18 mm) were symmetric pinwheel or outer circumference patterns. To achieve the prescrip-tion dose of 70 Gy (TG-43), seed strengths ranging from 1.98 to 4.84 mCi/seed were used and corresponding dose rates of58-75 cGy/hr were calculated. The plaques are typically planned, using the BEBIG treatment planning software, to deliverthe prescribed dose in 4 days.

Results: Iris melanoma patients, ranging in age from 15-82 years (median 63)were predominantly male (20 vs. 15 females) in thisfollow-up study. All patients were Caucasian except one Hispanic female. The iris melanoma affected the right eye in 14 patientsand the left eye in 21 patients. The mean tumor height was 4 mm and the largest tumor had a diameter of 15 mm. Round plaque innerdiameters included 10, 13, 15 and 18 mm, based on the tumor’s largest basal diameter. The tumor apex received doses of 67-71 Gy(TG-43) while the base received doses from 10.7-41 Gy, Doses to the optic disc ranged from nearly 3 Gy to less than 6 Gy andvalues for the fovea closely matched this dose range. Lens dose was highly dependent on tumor location and height and variedfrom 35 Gy to 105 Gy.

Conclusions: The major radiation-related complication from this procedure is cataractogenesis and elevated intraocular pressure.For nonresectable iris melanomas, plaque radiotherapy using 125I seeds provides a viable option for patients with minimal inva-siveness and surgical complications. All patients undergo continuing follow-up for tumor metastasis or recurrence.

Author Disclosure: J. Emrich, None; L. Komarnicky, None; C.L. Shields, None; C. Bianciotto, None; J.A. Shields, None.

3360 Management of Swallowing Motion with Prospective Gating in Head and Neck Cancer Radiotherapy

E. S. Paulson, A. Tai, X. Li

Medical College of Wisconsin, Milwaukee, WI

Purpose/Objective(s): Recently, we demonstrated the utility of dynamic MRI in determining patient-specific PTV margins forhead and neck cancer radiotherapy (RT) based on swallowing frequency, duration, and tumor displacement. Although the dosimet-ric impact of deglutition was found to be small for many patients, removing swallowing motion entirely during treatment deliverywould permit reduction of PTV margins. Since there is some degree of awareness and control over swallowing, we theorized thatpatients might be able to prospectively (manually) gate their own treatments. Specifically, when a patient feels the need to swallow,he or she would simply press and hold a momentary switch to pause the beam on the treatment machine. In this proof-of-principlestudy, we tested the feasibility of this prospective swallowing gating method.

Materials/Methods: One healthy volunteer was setup in treatment position on a 3T MRI scanner (Verio, Siemens). A ten min-ute dynamic time series of single-slice, sagittal, 2D FLASH images (6.67 frames/sec) was acquired to determine the volunteer’sactual swallowing frequency and duration. Prior to the scan, the volunteer was instructed to press a squeeze ball each time heswallowed, and keep the ball depressed for the entire swallow duration. The volunteer responses, time locked to the dynamicimage acquisition, were recorded using the scanner’s physiological monitoring software. The responses were then correlatedwith the imaging data to assess the volunteer’s awareness of his swallowing and, thus, feasibility of performing manually gatedRT. Manual gating on a linac (Artiste, Siemens) was tested via momentary switch interfaced to the gating portal equipped forrespiratory gating.

Results: The frequency of swallowing and mean swallowing duration were found to be 1.8 swallows/minute and 3.2 seconds. In allinstances of swallowing, movement of internal anatomy (soft palate) preceded movement of external anatomy, precluding the useof external surrogate-based gating methods. The volunteer responded for each swallow and the duration of each response exceededthe actual swallow event as visualized on dynamic MRI, demonstrating the feasibility of manual gating. On the linac, manual gatingwas successfully executed through the respiratory gating portal.

Conclusions: Acute awareness of swallowing implies that swallowing motion during RT can be managed/removed by manual(patient initiated) beam gating. Such manual gating can be achieved using existing respiratory gating capabilities on linacs. Asan alternative to estimating appropriate PTV margins based on swallowing frequency, duration, and tumor displacement, dynamicMRI permits assessment of swallowing awareness and, thus, determination of those patients capable of performing manual swal-lowing gating.

Author Disclosure: E.S. Paulson, MCW Merinez Fellowship, B. Research Grant; A. Tai, None; X. Li, Siemens Healthcare, B. Re-search Grant.