low malignancy and complete surgical resection is the primary curativestrategy. Long-term follow up is advisable with high 5-year survival rate.The study demonstrated highest positive rate of progesterone receptor (PR),suggesting that progesteronemight have played a role in the genesis of SPT.

Author Disclosure Block: X. Chengqian: None. X. Zhao: None.

125

CT Findings, Clinicopathologic Features, and Treatment Modalities ofAnorectal Melanoma: A Report of 10 CasesX. Chengqian, X. Zhao, Cancer Institute and Hospital, Chinese Academyof Medical Sciences, Beijing, China

Purpose/Objectives: To retrospectively evaluate CT findings and clinico-pathologic features in patients with pathologically proved anorectalmelanoma, and to discuss the diagnosis and treatment modalities of thisentity.Materials/Methods: Clinicopathologic features, diagnosis, treatmentmodalities and survival of 10 patients (four men and six women; agerange, 41–75 years; mean age, 61 years) with anorectal melanoma inCIAMS from 2006 to 2011, were analyzed. CT scans were evaluated bytwo radiologists for the involved site, size, morphology, infiltration,lymphadenopathy and metastasis.Results: The most common presentation was rectal bleeding (n = 8),followed by tenesmus (n = 5) and Dyschezia (n = 3). Distant metastasiswas noted in 2 patients. The approximate mean length of the tumors was3.1 cm (range, 1.9-7.7 cm) and the diameter was 2.5 cm (range,1-7 cm).All of the tumors appeared as polypoid or fungating intraluminalneoplasm. Perirectal infiltration could extended to the presacral space (n= 2). 3 patients had lymphadenopathy, involving the perirectal, presacraland iliac vessel lymph node stations. There was no evidence ofobstruction in any patients. 6 underwent abdominoperineal resection, 2underwent local excision, 1 underwent sigmoid colostomy and 1underwent adjuvant immunotherapy and chemotherapy. Most of thetumors invaded the dentate line confirmed by postoperative pathology(n = 6). All 9 cases stained for HMB-45 and S-100. 8 stained for Melan A.7 died with the median survival time of 24 months (range, 8–70 months).1 is undergoing palliative therapy, approaching her end and 2 are understable condition 21 months and 31 months after surgery.Conclusions: On CT scans, anorectal melanoma appeared as intraluminalfungating masses, expanding the lumen without causing obstruction, withperirectal infiltration and lymphadenopathy. The preoperative staging hasan important role in influencing treatment decisions and abdominoper-ineal resection may be considered as the first choice for the anorectalmelanoma patients without distant metastasis.

Author Disclosure Block: X. Chengqian: None. X. Zhao: None.

IMAGE GUIDED THERAPEUTIC TECHNIQUES

126

See Oral Abstract Presentation #3

127

See Oral Abstract Presentation #10

128

See Oral Abstract Presentation #6

129

See Oral Abstract Presentation #1

130

See Oral Abstract Presentation #2

131

See Oral Abstract Presentation #5

132

Dosimetric Impact of Intrafraction Prostate Motion Using a NewContour Shifting MethodM.K. Khan 2, S. Shin 1, A. Magnelli 1, P. Xia 1, 1Cleveland Clinic,Cleveland, OH, 2Emory University School of Medicine, Atlanta, GA

Purpose/Objectives: To use a newly developed in-house organ contourshifting algorithm to evaluate optimal planning treatment (PTV) marginsusing daily real-time intra-fraction organ tracking for prostate cancerpatients undergoing intensity modulated radiotherapy (IMRT).Materials/Methods: The dose matrices, planning CT images, andphysician defined organ contours were exported from the treatmentplanning system into a newMATLAB algorithm. The new algorithm shiftsthe prostate organ contours according to real-time intra-fraction prostatetracking data (Calypso® Medical, Seattle, WA). The average prostatemotion over each 30 second increment is used to shift the prostate contourswithin a static dose cloud to generate a composite dose volume histogram(cDVH) for an entire treatment plan (typically 38–39 fractions, eachlasting about 10 minutes). The adequacy of the standard PTV margins (6mm around the prostate and 4 mm posterior to the prostate) was comparedagainst a smaller PTV margin (uniform 2 mm around the prostate). Thedose to 90% (D90), 95% (D95), and 99% (D99) of the prostate werecompared among the two different treatment margin schemes.Results: Ten patients underwent IMRT (7600–7800 cGy in 38–39fractions). Most (8) were either intermediate or high risk with six of thesepatients receiving androgen deprivation therapy. Each patient underwentdaily Calypso alignment and prostate tracking during IMRT. The averageprostate motion in the Superior-Inferior, Anterior-Posterior, and Right-Left directions were: 0.69 ± 0.8 mm, 0.38 ± 0.8 mm, and 0.11 ± 0.6 mm,respectively. The average magnitude vector was 1.55 ± 0.7 mm. For 6/4and 2-mm PTV margins, adequate treatment was achieved in 10 out of 10patients. The percent differences between the 6/4 and 2-mm plans forD90, D95, and D99 were negligible - less than 1.5% in all cases.Conclusions: Our preliminary analysis is consistent with other reportsthat suggest that 2 mm PTV margins may be adequate with the use ofintra-fraction real-time prostate tracking with little impact on the radiationdoses delivered. Future work should address the biochemical outcome aswell as the reduction in toxicity to surrounding normal organs whenreduced PTV margins are employed.

Author Disclosure Block: M.K. Khan: None. S. Shin: None. A.Magnelli: None. P. Xia: None.

133

Use of Implanted Gold Fiducial Markers With MV-CBCT Image GuidedIMRT for Pancreatic TumorsM. Packard, A. Kirichenko, O. Gayou, B. Weiss, S. Thakkar, E.D. Werts,Allegheny General Hospital, Pittsburgh, PA

S14 Poster Presentations Practical Radiation Oncology: April-June Supplement 2013