CT-based Inverse Treatment Planning In HDR-intracavitary ...

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Total 40 plans were created. Dose received by 1 cc volume (V1), 2cc (V2), 5cc (V5) and. 10cc (V10) of bladder and rectum was calculated. Volume of target that ...
I. J. Radiation Oncology d Biology d Physics

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Volume 78, Number 3, Supplement, 2010

brachytherapy groups. Dose volume histograms from the conformal/IMRT boost were within normal tissue constraints as demonstrated by a median bladder dose of 13.75Gy, median rectal dose of 8.58Gy, median small bowel dose of 6.89 Gy, and median femoral head dose of 4.25Gy. Conclusions: Conformal external beam or IMRT boosts offer a safe alternative to HDR brachytherapy for the treatment of inoperable endometrial cancer. This non-invasive approach achieves excellent disease-specific survival and similar toxicity. No significant differences were observed between the groups. Larger studies will be required to increase study power and confirm these results. Author Disclosure: A.K. Olson, None; S. Bhatia, None; C. Duncan, None; V. Betts, None; B. Smith, None; G. Jacobson, None.

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Predicting the Risk of Pelvic Nodal Metastasis in T1 Endometrial Carcinoma

B. Liu, H. Liang, E. Scosyrev University of Rochester, Rochester, NY Purpose/Objective(s): The MRC ASTEC trial showed no benefit from lymphadenectomy in patients with early endometrial cancer. We developed a model to predict the risk of pelvic lymph node metastasis in T1 endometrial carcinoma. Materials/Methods: Data were collected from the Surveillance, Epidemiology, and End Results (SEER) program between 2004 and 2006. 3807 patients diagnosed with T1 endometrial uterine carcinoma with known pathologic T stage (T1A-C)/histology grade (G1-3), who underwent hysterectomy and nodal dissection with at least 8 documented lymph nodes were included in this study. The effect of T stage, grade, tumor size, age, the number of nodes examined (NNE), and race on the risk of nodal metastases was examined. A nonparametric logistic model was used to quantify the relationship between the positive probability and risk factors. Results: The median number of lymph nodes examined was 13, and the mean 15. Overall, 4.4% of the patients had positive nodal involvement. Younger age, higher tumor grade, deeper tumor invasion, and larger tumor size were significantly associated with increased risk of nodal metastasis. Race and NNE had no effect on the risk of nodal involvement. Conclusions: The predictive model can accurately estimate the risk of pelvic nodal metastasis in T1 endometrial carcinoma. This tool may provide information for adjuvant therapy especially in patients without complete pelvic nodal dissection. Author Disclosure: B. Liu, None; H. Liang, None; E. Scosyrev, None.

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Rectal and Bladder Toxicity in Patients Receiving CT-guided HDR Interstitial Brachytherapy for Gynecologic Malignancies

E. M. Wiebe1,2, K. Surry2,1, D. P. D’Souza2 1

University of Western Ontario, London, ON, Canada, 2London Regional Cancer Program, London, ON, Canada

Purpose/Objective(s): To correlate toxicity outcomes with dose volume parameters in patients treated with CT-guided high dose rate (HDR) gynecologic interstitial brachytherapy (IBT). Materials/Methods: 40 patients received IBT for malignancy involving gynecologic organs between August 2004 and October 2008. 37 patients had a single IBT implant procedure with 15-24 Gy HDR radiation over 2-4 fractions. 3 patients had a second IBT implant. 38 patients also received external beam radiation therapy (EBRT) with a median EBRT dose of 45 Gy. Implant quality assessment and brachytherapy planning was performed with CT imaging. Dose Volume Histograms (DVHs) were computed for the bladder and rectum, and the dose to the 2 cm3 volume (D2cc) determined. Cumulative biologically equivalent dose (BED) was calculated from EBRT and IBT dose contributions. Cumulative BED was normalized to the equivalent dose in 2 Gy per fraction (EQD2). Results: The mean brachytherapy prescription volume (V100%) was 91.6 cc (SD 38.6 cc). The mean cumulative EQD2 to D2cc of bladder and rectum, respectively, was 60.1 Gy (SD 16.8 Gy) and 60.4 Gy (SD 12.0 Gy). The mean cumulative EQD2 to tumor was 69.5 Gy (SD 12.0 Gy). Median follow-up was 27.2 months. Nineteen patients were identified to have tumor recurrence, with median time to recurrence of 21.5 months. There were 7 late Grade 3/4 GI and GU toxicities in 5 patients: proctitis (4), diarrhea (1), recto-vaginal fistula (1), and vesico-vaginal fistula (1). Additionally, 2 patients had Grade 3 radiation necrosis. Mean EQD2 rectal D2cc in patients with GI toxicity was 65.2 Gy. The vesico-vaginal fistula occurred in a patient with EQD2 bladder D2cc of 87 Gy. The mean tumor EQD2 in patients with radiation necrosis was 72.7 Gy. Conclusions: Rectal and bladder doses were reasonable in this series of patients receiving extensive treatment for locally advanced gynecologic malignancy. Despite volumetric planning and the utilization of standard bladder and rectum dose constraints, there was a trend toward GI and GU toxicity occurring in patients with higher cumulative radiation doses. Author Disclosure: E.M. Wiebe, None; K. Surry, None; D.P. D’Souza, None.

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CT-based Inverse Treatment Planning In HDR-intracavitary Brachytherapy for Cervical Cancer: Impact of Point A and Target-based Dosimetric and Dose Prescription Methods

R. Madan, V. Subramani, S. Pathy, S. Sharma, D. Manigandan, M. Sujith Kumar, B. K. Mohanti AIIMS, Delhi, India Purpose/Objective(s): To evaluate the potential of inverse planning technique in HDR intracavitary brachytherapy (ICRT) with conventional 2D planning technique for cervical cancer in terms of tumor coverage and toxicity profile.

Proceedings of the 52nd Annual ASTRO Meeting Materials/Methods: Ten patients of Carcinoma cervix stage IIB to IIIB, who underwent 3 sessions of ICRT at weekly interval after EBRT were included. CT/MRI compatible tandem-ovoids applicators were used. Both X-ray and CT simulation was done. Images were transferred to Plato TPS. For X-ray based planning, 7 Gy was prescribed to point A. Dose was calculated for bladder and rectal ICRU-38 points. For CT-based planning, target volume, bladder and rectum were contoured. For each patient, CT plan- Point A based (Plan A), CT plan-target based (Plan B) and IPSA plan-target based (Plan C) were generated. Total 40 plans were created. Dose received by 1 cc volume (V1), 2cc (V2), 5cc (V5) and 10cc (V10) of bladder and rectum was calculated. Volume of target that received 100%, 95% and 90% of the prescribed dose (D100), (D95) and (D90) respectively was calculated. All plans were compared. Paired-t test was used to analyze the statistical significance. Results: For D100, difference in Plan A and Plan B was 27.3%,-25.9% and -24.7% and difference in Plan A and Plan C was -27.6%, -26.4% and -25.9% for all 3 sessions respectively (p \ 0.001). For D100, interfraction difference between 1st and 2nd fraction and 1st and 3rd fraction was 1.38% and 4% respectively (p \ 0.06) for Plan A;6.28% and 21.3% respectively (p \ 0.001) for Plan B and 5.4% and 20% respectively (p \ 0.001) for Plan C. In bladder, the difference between Plan A and Plan B was 10%, 8.6%, 6.8% and -6.18% for V1, V2, V5 and V10 respectively. The maximum interfraction difference among 3 fractions was found to be 30-32% (p \ 0.001). In rectum, the difference in Plan A and Plan B were 11%, 10.3%, 9.4% and 8.5% for V1, V2, V5 and V10 respectively. The maximum interfraction difference among 3 fraction was found to be 3-5%. Conclusions: With reference to CT plan-Point A based, CT plan-target based was better in terms of target coverage and OAR sparing. There was no much difference in CT plan-target based and IPSA plan-target based. However, IPSA plan was superior to CT plan-Point A based. Between the 1st and 2nd fraction no significant dosimetric difference was noticed for target and bladder but the difference was significant between 1st and 3rd fractions, Rectal doses remained similar during all fractions This study points to the volumetric and dosimetric changes that occur between fractions which assumes importance especially during transition from point A based to target based treatment planning in Carcinoma Cervix. Author Disclosure: R. Madan, None; V. Subramani, None; S. Pathy, None; S. Sharma, None; D. Manigandan, None; M. Sujith Kumar, None; B.K. Mohanti, None.

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Ultrasound-based Determination of Vaginal Wall Thickness in Postoperative Vaginal Brachytherapy for Endometrial Cancer

B. Zobec Logar, B. Segedin, R. Hudej, P. Petric Institute of Oncology, Ljubljana, Slovenia Purpose/Objective(s): Standard dose prescription in postoperative vaginal brachytherapy (BT) of endometrial cancer is at 5 mm depth from the applicator surface at the reference plane. Individual clinical determination of prescription depth reduces morbidity without increasing vaginal recurrence rate (Onsrud, IJROBP 2001; 49(3):749-55). We report on updated results of a feasibility study, evaluating an innovative technique for ultrasound (US) based determination of prescription depth in distended vagina, simulating treatment conditions. Materials/Methods: 32 patients with stage I-II endometrial cancer, treated postoperatively with fractionated high dose rate BT, were included in this study. Prior to first application, condom-covered Foley catheter was inserted into vagina. Catheter balloon was hyper inflated and pulled to vaginal entrance to obstruct it. US probe was inserted into rectum and vagina fully distended under US control with gel, injected through catheter. Diameter of vaginal lumen and thickness of vaginal wall were measured and catheter removed. Procedure time was recorded and patient comfort assessed, using a 10-tiered visual analogue scale (VAS: 0-no discomfort, 10-extreme discomfort). Size of vaginal cylinder was chosen according to lumen diameter, assuring close contact of applicator with mucosa. Two (combination with external beam radiotherapy) or 4 fractions (BT alone) of 5 Gy were applied to upper 1/3 of vagina. Prescription depth was defined according to vaginal wall thickness. Results: Mean time to perform the measurement procedure was 10 (8-17) minutes. Discomfort during procedure was kept below level 3 on VAS in all patients. Mean diameter of vaginal lumen and thickness of vaginal wall were 28 +/- 6 and 4 +/- 1 mm, respectively. In 13 patients, vaginal wall thickness was up to 3 mm and in remaining 19 patients 4-6 mm. Conclusions: US-based determination of prescription depth is feasible, well tolerated and enables individualized tailoring of postoperative vaginal BT. Further follow-up is needed to assess clinical implications of the described technique. Author Disclosure: B. Zobec Logar, None; B. Segedin, None; R. Hudej, None; P. Petric, None.

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Prognostic Role of Pathologic Complete Response to Chemoradiation in FIGO IB2 Cervical Cancer

S. V. Dandapani, J. J. Kang, J. E. Shriki, P. G. Pagnini University of Southern California, Los Angeles, CA Purpose/Objective(s): Localized early stage cervical cancer is treated with either radical hysterectomy or definitive radiation and patients have excellent cure rates. However patients with bulky FIGO IB2 cervical carcinoma have less local control and decreased overall survival. At our institution we treat high risk FIGO IB2 patients with preoperative chemoradiation followed by adjuvant hysterectomy. This retrospective review evaluated the pathological response, local control and toxicities. Materials/Methods: FIGO IB2 cervical cancer patient records were provided by the LA county cancer registry. Patients were treated with chemoradiation followed by adjuvant hysterectomy from 2000-2009. Patients received whole pelvic radiation using a four field approach (45Gy) followed by low dose rate intracavitary brachytherapy (point A median dose 75Gy) concurrently with cisplatin. Median follow-up was 3.5 yrs (8mos - 9 yrs). Results: 30 female patient charts were reviewed. Median age at diagnosis was 48 years old (range 28-60). 73% had squamous cell, 17% adenocarcinoma, and 10% glassy cell. 12/30 (40%) had pathologic complete response (pCR) and 4/30 (13%) had only microscopic residual disease (\0.5mm). 12/30 (40%) patients had partial response and 2/30 (7%) had no response. Higher tumor

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