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Dosimetric Feasibility Of VMAT And SBRT versus Interstitial Brachytherapy Boost For Recurrent Endometrial Carcinoma
I. J. Radiation Oncology d Biology d Physics
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Volume 81, Number 2, Supplement, 2011
brachytherapy (VB) (20.8%), EBRT plus VB (26.3%), and chemotherapy (C) (44%), with IRB approval for data collection. Treatment included lymph node (LN) dissection in 66.7% (mean 15 LNs removed), EBRT median dose of 45 Gy (range, 35 - 50.4 Gy) and VB median dose of 21 Gy (range, 7 - 60 Gy). Patient FIGO stages I, II, III, and IV were 30.6%, 22.2%, 30.6%, and 16.7%, respectively. The endpoints examined were pattern of recurrence, overall survival (OS) and freedom from locoregional failure (pelvis or vagina) (FFLF). Univariate and multivariate analysis were performed with log rank and Cox proportional hazards model respectively. Results: Mean age was 68.3 years (range, 45 - 88 years). Mean follow up time was 34.5 months (range, 5.5 - 126.5 months) and mean time to first recurrence after completion of curative treatment was 10.3 months (range, 0 - 54 months). Initial failure rates were 12.5% local and 37.5% distant, overall. Of 36 failures at last follow-up, 25% were locoregional and 75% were distant, initially. Four PS, 5 MHG, and 0 CC endometrial cancer patients failed locally. 9% (2/22) stage I patients, 12.5% (2/16) stage II, 18.2% (4/22) stage III, and 8.3% (1/12) stage IV patients failed locally. On univariate analysis, smoking, BMI, race, stage, LN dissection, definitive surgery, VB, and the use of C were not significantly associated with FFLF. Peritoneal washings (p = 0.05) and EBRT (p = 0.0072) were found to be associated with FFLF, and remained significant on multivariate analysis (p = 0.025). Eight of the 9 initial LF patients did not receive EBRT, 8/9 patients did undergo LN dissections, and 4/9 underwent VB. 66.7% (6/9) of local failures occurred in the vagina. 55.6% (5/9) of patients who recurred locally died of disease. Median survival times for PS, CC, and MHG histologies were 28.7, 37.6, and 40 months, respectively. The overall survival (OS) by histology was not found to be significantly different (p = 0.5376). Conclusions: Our data suggests that distant failures predominate after curative treatment of PS, CC, and MHG endometrial cancers, implicating the need for intensified C. Furthermore, while local recurrences most commonly occur in the vagina, this does not negate the need for EBRT for local control. Author Disclosure: M.B. Goldberg: None. P. Dorn: None. E. Lengyel: None. N.K. Lee: None. D. Yamada: None. Y. Hasan: None.
2556
Adjuvant Vaginal Brachytherapy and Chemotherapy in the Management of High-Intermediate Risk Early-stage Endometrial Cancer: A Single Institutional Report
A. J. Iglesias, A. H. Wolfson, L. Portelance, W. Zhao, J. Stine, P. Yali, J. Lucci, S. Schuman University of Miami, Miami, FL Purpose/Objective(s): Currently, the Gynecologic Oncology Group (GOG) is conducting a phase III trial (GOG #249) comparing pelvic external beam irradiation versus vaginal brachytherapy (VBT) and chemotherapy (CT) for endometrial cancer (EC) patients with stage I and high-intermediate risk (H-IR) factors or stage II disease. Since January 2006, we adopted a unified treatment policy at our institution in which all such patients were offered adjuvant CT and VBT. We now report the preliminary results of this group of patients. Materials/Methods: From January 2006 until November 2009, 31 patients underwent surgical staging with hysterectomy/bilateral salpingo-oophorectomy, retroperitoneal nodal sampling, and collection of pelvic washings followed by adjuvant VBT with Carboplatin/Paclitaxel CT. HR factors for this study included increased age, grade 2 or 3, papillary serous or clear cell carcinoma, invasion of the outer third of the myometrium and positive lymph-vascular space invasion. Results: Of the 31 study patients, 71% (n = 22) had FIGO stage I and 29% (n = 9) stage II disease. Histology included 64% (n = 20) endometrioid carcinomas and 36% (N = 11) papillary serous/clear cell carcinomas. There were 19% (n = 6) grade 1, 26% (n = 8) grade 2, and 55% (n = 17) grade 3 lesions. Lymphovascular space invasion was present in 65% (n = 20) of patients, while outer one-third myometrial invasion was present in 48% (n = 22). Twenty-nine patients received VBT (55% low-dose-rate [LDR]; 45% high-dose-rate [HDR]. Thirty patients received generally six cycles of carboplatin (AUC 5 - 6) and paclitaxel (175mg/m2) every 21 days. Two patients received adjuvant CT but no VBT, and one patient received VBT but declined CT. None of our patients had vaginal, pelvic, or abdominal recurrences. However, one patient had a distant relapse. With median follow-up of 1.8 years (range: 0.3 - 4.1 years), no deaths have been reported. Conclusions: Adjuvant VBT and CT for H-IR early-stage EC demonstrates a potential treatment approach for this group of patients. The results of GOG #249 are eagerly awaited to confirm the efficacy of this treatment regimen. Author Disclosure: A.J. Iglesias: None. A.H. Wolfson: None. L. Portelance: None. W. Zhao: None. J. Stine: None. P. Yali: None. J. Lucci: None. S. Schuman: None.
2557
Dosimetric Feasibility Of VMAT And SBRT versus Interstitial Brachytherapy Boost For Recurrent Endometrial Carcinoma
E. M. Wiebe, G. Hajdok, D. Hoover, D. D’Souza, K. Surry London Regional Cancer Program, London, ON, Canada Purpose/Objective(s): A comparison of boost plans for endometrial carcinoma recurrence using delivered interstitial brachytherapy (IBT) versus advanced external beam techniques. Materials/Methods: Five patients with recurrent endometrial carcinoma in the vaginal vault were treated with pelvic external beam radiotherapy plus an IBT boost of 6 Gy x 3. The dosimetric feasibility of delivering a similar boost was examined for single arc VMAT, and for SBRT with 7 fixed coplanar beams. To minimize the PTV margin required for external beam planning, a vaginal cylinder was assumed for cone-beam image guidance, and to provide local tissue immobilization. The CTV defined for IBT was expanded isotropically by 5mm to create a PTV. The mean CTV and PTV were 51.8 ± 13.3 cc, and 103.8 ± 23 cc. Optimized plans were compared with respect to conformality index (CI), R50, and dose to regional OARs. A CI was calculated for all plans using the definition of CI = cover factor x spill factor. R50 was calculated as the ratio of the 50% isodose volume to the CTV volume. Dose-volume parameters for bladder, rectum, sigmoid and small bowel were assessed and converted to equivalent 2 Gy doses, assuming an a/b ratio of 3 (EQD2Gy3).
Proceedings of the 53rd Annual ASTRO Meeting Results: The CI is 0.7 ± 0.1 for the CTV using IBT, 0.8 ± 0.0 and 0.7 ± 0.1 for the PTV using VMAT and SBRT. The R50 for external beam techniques is 6.6 ± 0.3 and 8.8 ± 0.8, compared to 2.8 ± 0.4 obtained with IBT. VMAT and SBRT produce more homogeneous irradiation of the PTV, with average maximum point doses of 2111 ± 25 cGy and 2067 ± 55 cGy. In comparison, within the IBT plans, a mean volume of 2.7 ± 2.6 cc receives the 250% dose of 4500 cGy. Doses to organs at risk increase by 29 to 66% with VMAT, and by 24 to 93% with SBRT compared to IBT plans. The highest organ at risk doses were to the bladder, where the EQD2Gy3 for D2cc is 72.7 ± 4.5 Gy3 and 72.4 ± 3.0 Gy3 with VMAT and SBRT, compared to 57.3 ± 4.2 Gy3 for IBT. Conclusions: VMAT and SBRT produce highly conformal and homogenous boost dose to the target using image guidance, although with greater spread of the 50% dose region than IBT. Despite limiting the PTV expansion, VMAT and SBRT result in higher doses to the regional organs at risk. Consequently, advanced external beam techniques confer a higher risk of toxicity to proximal organs at risk compared with ‘gold standard’ IBT boost techniques. Author Disclosure: E.M. Wiebe: None. G. Hajdok: None. D. Hoover: None. D. D’Souza: None. K. Surry: None.
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Overall Interval Brachytherapy Treatment Time In High Dose Rate Brachytherapy (HDRBT) For Endometrial Carcinoma (EC)
A. Rovirosa1, C. Ascaso2, I. Valduvieco1, B. Carlos1, A. Herreros1, M. Arenas3, A. Biete1,4 1 Radiation Oncology Department, Hospital Clinic i Universitari Barcelona, Barcelona 08036, Spain, 2Public Health Department Medicine Faculty., Barcelona University, Spain, 3Radiation Oncology Department, Hospital Sant Joan de Reus, Tarragona, Spain, 4Medicine Faculty, Barcelona University, Spain
Purpose/Objective(s): To evaluate the HDRBT results in postoperative treatment of EC using a schedule of 3 or 4 fractions/week. Materials/Methods: From June 03 to December 08, 164 patients (pts) were treated with HDRBT (HDR Ir192, MicroHDR Nucletron projector) after surgery for EC. After surgery patients were staged using 2002 FIGO classification: 2 IA, 48 IB, 72 IC, 8 IIA, 12 IIB, 9 IIIA, 2 IIIB, 11 IIIC. Pathology: 130 endometrioid, 8 serous, 2 clear cell, 21 mixed types, 3 miscellaneous. Radiotherapy: 124/164 pts. received external beam irradiation (EBI) plus HDRBT (Group 1) and 40/164 pts. received exclusive HDRBT (Group 2). Group 1: mean EBI dose was 45 Gy (range 44 - 50), 1.8 - 2 Gy/day, using 6 or 18 MV photons from a Linac; after EBI pts received HDRBT with 3 fractions of 4 to 5 Gy. Group 2: Pts received 6 fractions of 4 to 5 Gy. HDRBT dose was prescribed at 5 mm from vaginal surface and the applicators were colpostats in 8/164 cases and cylinders in 156/164 cases (cylinder diameters were 2, 2.5, 3 and 3.5 cm). HDRBT was administered 3 or 4 days per week regime when possible. Overall treatment time with HDRBT. Group 1: HDRBT was completed in a mean time of 4 days in 66 pts (range 3 to 5) and in more than 5 days in 58 pts, mean 8 days (range 6 - 13). Group 2: HDRBT was completed in #10 days in 14 pts, mean 8 days (range 6 - 10) and, in more than 11 days in 26 pts, mean 17 days (range 11 to 28). Toxicity was evaluated using RTOG scores for rectum and bladder. Vaginal toxicity was evaluated using the objective scores of LENT-SOMA. Statistics: Variance, Student’s t-test, Chi-square test. Results: Pts mean follow-up was 48 months (range 9 - 91). Only 2/164 pts had vaginal relapse and died and 7/164 pts were lost to follow-up. Early G1-G2 toxicity appeared in 28/164 (17%) pts and was resolved; late toxicity appeared in 42/164 (25%): vaginal mucosa 21 G1, 11G2, 1G4; bladder 2G1; rectal 5G1, 2G2. No differences in toxicity were found in relation to the overall treatment interval time in Groups 1 and 2. Conclusions: Three fractions of 4 - 5 Gy administered in 3 to 5 days after EBI or 6 fractions in less than 10 days in patients receiving HDRBT alone seems to be safe in relation to toxicity and local control for EC. 2) These results suggest that toxicity in HDRBT is not related to the overall interval treatment time. Author Disclosure: A. Rovirosa: None. C. Ascaso: None. I. Valduvieco: None. B. Carlos: None. A. Herreros: None. M. Arenas: None. A. Biete: None.
2559
Dosimetric Analysis of Inter fractional Dose and Volume Changes in Bladder and Rectum during Intensity Modulated Radiation Therapy for Gynecological Cancers with Daily Cone Beam CT guidance
H. Kim, S. Beriwal, S. Parikh, C. Houser Magee Women’s Hospital of UPMC, Pittsburgh, PA Purpose/Objective(s): To assess the changes in dose volume histograms from inter fractional changes in bladder and rectum as evaluated by daily KV cone beam CT (CBCT) during Intensity Modulated Radiation Therapy (IMRT) for post operative endometrial cancers. Materials/Methods: A total of 134 CBCT images from 7 patients who had adjuvant pelvic radiation after surgery for endometrial cancer were analyzed. Prescription dose was 1.8Gy per fraction for a total of 25 - 28 fractions with IMRT. Each of these patients had at least 3 CBCT images per week for setup verification before the radiation treatment. Daily setup shifts in translational directions (Superior-Inferior, Medial-Lateral, Anterior-Posterior) were applied before radiation treatment delivery by combination of soft tissue and bony anatomy match (3D- 3D match). Retrospectively, bladder and rectum volumes were contoured on daily CBCT images and treatment fields from the reference CT plan were applied to generate dose volume histograms (DVH) in each CBCT image. Cumulative DVHs from all image guided fractions per patient were calculated and compared with the planned DVH (comparison for V10 through V90: V10 and V90 are a volume covered by 10% and 90% of prescription dose, respectively). Also, CTV was drawn on daily CBCT images and DVH was generated for each image guided fraction to see if target coverage was still adequate during treatment course. CTV dose coverage (D95) was evaluated for each CBCT fraction and average CTV coverage of those was compared to the one in the reference CT plan. Results: For whole patient group, the cumulative DVH (V10 through V90) of bladder and rectum dose had a minimal difference from the planned DVH (range: 0- 4.7% for bladder, 0- 3.3% for rectum). However, for individual fractions, there were significant
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Volume 81, Number 2, Supplement, 2011
brachytherapy (VB) (20.8%), EBRT plus VB (26.3%), and chemotherapy (C) (44%), with IRB approval for data collection. Treatment included lymph node (LN) dissection in 66.7% (mean 15 LNs removed), EBRT median dose of 45 Gy (range, 35 - 50.4 Gy) and VB median dose of 21 Gy (range, 7 - 60 Gy). Patient FIGO stages I, II, III, and IV were 30.6%, 22.2%, 30.6%, and 16.7%, respectively. The endpoints examined were pattern of recurrence, overall survival (OS) and freedom from locoregional failure (pelvis or vagina) (FFLF). Univariate and multivariate analysis were performed with log rank and Cox proportional hazards model respectively. Results: Mean age was 68.3 years (range, 45 - 88 years). Mean follow up time was 34.5 months (range, 5.5 - 126.5 months) and mean time to first recurrence after completion of curative treatment was 10.3 months (range, 0 - 54 months). Initial failure rates were 12.5% local and 37.5% distant, overall. Of 36 failures at last follow-up, 25% were locoregional and 75% were distant, initially. Four PS, 5 MHG, and 0 CC endometrial cancer patients failed locally. 9% (2/22) stage I patients, 12.5% (2/16) stage II, 18.2% (4/22) stage III, and 8.3% (1/12) stage IV patients failed locally. On univariate analysis, smoking, BMI, race, stage, LN dissection, definitive surgery, VB, and the use of C were not significantly associated with FFLF. Peritoneal washings (p = 0.05) and EBRT (p = 0.0072) were found to be associated with FFLF, and remained significant on multivariate analysis (p = 0.025). Eight of the 9 initial LF patients did not receive EBRT, 8/9 patients did undergo LN dissections, and 4/9 underwent VB. 66.7% (6/9) of local failures occurred in the vagina. 55.6% (5/9) of patients who recurred locally died of disease. Median survival times for PS, CC, and MHG histologies were 28.7, 37.6, and 40 months, respectively. The overall survival (OS) by histology was not found to be significantly different (p = 0.5376). Conclusions: Our data suggests that distant failures predominate after curative treatment of PS, CC, and MHG endometrial cancers, implicating the need for intensified C. Furthermore, while local recurrences most commonly occur in the vagina, this does not negate the need for EBRT for local control. Author Disclosure: M.B. Goldberg: None. P. Dorn: None. E. Lengyel: None. N.K. Lee: None. D. Yamada: None. Y. Hasan: None.
2556
Adjuvant Vaginal Brachytherapy and Chemotherapy in the Management of High-Intermediate Risk Early-stage Endometrial Cancer: A Single Institutional Report
A. J. Iglesias, A. H. Wolfson, L. Portelance, W. Zhao, J. Stine, P. Yali, J. Lucci, S. Schuman University of Miami, Miami, FL Purpose/Objective(s): Currently, the Gynecologic Oncology Group (GOG) is conducting a phase III trial (GOG #249) comparing pelvic external beam irradiation versus vaginal brachytherapy (VBT) and chemotherapy (CT) for endometrial cancer (EC) patients with stage I and high-intermediate risk (H-IR) factors or stage II disease. Since January 2006, we adopted a unified treatment policy at our institution in which all such patients were offered adjuvant CT and VBT. We now report the preliminary results of this group of patients. Materials/Methods: From January 2006 until November 2009, 31 patients underwent surgical staging with hysterectomy/bilateral salpingo-oophorectomy, retroperitoneal nodal sampling, and collection of pelvic washings followed by adjuvant VBT with Carboplatin/Paclitaxel CT. HR factors for this study included increased age, grade 2 or 3, papillary serous or clear cell carcinoma, invasion of the outer third of the myometrium and positive lymph-vascular space invasion. Results: Of the 31 study patients, 71% (n = 22) had FIGO stage I and 29% (n = 9) stage II disease. Histology included 64% (n = 20) endometrioid carcinomas and 36% (N = 11) papillary serous/clear cell carcinomas. There were 19% (n = 6) grade 1, 26% (n = 8) grade 2, and 55% (n = 17) grade 3 lesions. Lymphovascular space invasion was present in 65% (n = 20) of patients, while outer one-third myometrial invasion was present in 48% (n = 22). Twenty-nine patients received VBT (55% low-dose-rate [LDR]; 45% high-dose-rate [HDR]. Thirty patients received generally six cycles of carboplatin (AUC 5 - 6) and paclitaxel (175mg/m2) every 21 days. Two patients received adjuvant CT but no VBT, and one patient received VBT but declined CT. None of our patients had vaginal, pelvic, or abdominal recurrences. However, one patient had a distant relapse. With median follow-up of 1.8 years (range: 0.3 - 4.1 years), no deaths have been reported. Conclusions: Adjuvant VBT and CT for H-IR early-stage EC demonstrates a potential treatment approach for this group of patients. The results of GOG #249 are eagerly awaited to confirm the efficacy of this treatment regimen. Author Disclosure: A.J. Iglesias: None. A.H. Wolfson: None. L. Portelance: None. W. Zhao: None. J. Stine: None. P. Yali: None. J. Lucci: None. S. Schuman: None.
2557
Dosimetric Feasibility Of VMAT And SBRT versus Interstitial Brachytherapy Boost For Recurrent Endometrial Carcinoma
E. M. Wiebe, G. Hajdok, D. Hoover, D. D’Souza, K. Surry London Regional Cancer Program, London, ON, Canada Purpose/Objective(s): A comparison of boost plans for endometrial carcinoma recurrence using delivered interstitial brachytherapy (IBT) versus advanced external beam techniques. Materials/Methods: Five patients with recurrent endometrial carcinoma in the vaginal vault were treated with pelvic external beam radiotherapy plus an IBT boost of 6 Gy x 3. The dosimetric feasibility of delivering a similar boost was examined for single arc VMAT, and for SBRT with 7 fixed coplanar beams. To minimize the PTV margin required for external beam planning, a vaginal cylinder was assumed for cone-beam image guidance, and to provide local tissue immobilization. The CTV defined for IBT was expanded isotropically by 5mm to create a PTV. The mean CTV and PTV were 51.8 ± 13.3 cc, and 103.8 ± 23 cc. Optimized plans were compared with respect to conformality index (CI), R50, and dose to regional OARs. A CI was calculated for all plans using the definition of CI = cover factor x spill factor. R50 was calculated as the ratio of the 50% isodose volume to the CTV volume. Dose-volume parameters for bladder, rectum, sigmoid and small bowel were assessed and converted to equivalent 2 Gy doses, assuming an a/b ratio of 3 (EQD2Gy3).
Proceedings of the 53rd Annual ASTRO Meeting Results: The CI is 0.7 ± 0.1 for the CTV using IBT, 0.8 ± 0.0 and 0.7 ± 0.1 for the PTV using VMAT and SBRT. The R50 for external beam techniques is 6.6 ± 0.3 and 8.8 ± 0.8, compared to 2.8 ± 0.4 obtained with IBT. VMAT and SBRT produce more homogeneous irradiation of the PTV, with average maximum point doses of 2111 ± 25 cGy and 2067 ± 55 cGy. In comparison, within the IBT plans, a mean volume of 2.7 ± 2.6 cc receives the 250% dose of 4500 cGy. Doses to organs at risk increase by 29 to 66% with VMAT, and by 24 to 93% with SBRT compared to IBT plans. The highest organ at risk doses were to the bladder, where the EQD2Gy3 for D2cc is 72.7 ± 4.5 Gy3 and 72.4 ± 3.0 Gy3 with VMAT and SBRT, compared to 57.3 ± 4.2 Gy3 for IBT. Conclusions: VMAT and SBRT produce highly conformal and homogenous boost dose to the target using image guidance, although with greater spread of the 50% dose region than IBT. Despite limiting the PTV expansion, VMAT and SBRT result in higher doses to the regional organs at risk. Consequently, advanced external beam techniques confer a higher risk of toxicity to proximal organs at risk compared with ‘gold standard’ IBT boost techniques. Author Disclosure: E.M. Wiebe: None. G. Hajdok: None. D. Hoover: None. D. D’Souza: None. K. Surry: None.
2558
Overall Interval Brachytherapy Treatment Time In High Dose Rate Brachytherapy (HDRBT) For Endometrial Carcinoma (EC)
A. Rovirosa1, C. Ascaso2, I. Valduvieco1, B. Carlos1, A. Herreros1, M. Arenas3, A. Biete1,4 1 Radiation Oncology Department, Hospital Clinic i Universitari Barcelona, Barcelona 08036, Spain, 2Public Health Department Medicine Faculty., Barcelona University, Spain, 3Radiation Oncology Department, Hospital Sant Joan de Reus, Tarragona, Spain, 4Medicine Faculty, Barcelona University, Spain
Purpose/Objective(s): To evaluate the HDRBT results in postoperative treatment of EC using a schedule of 3 or 4 fractions/week. Materials/Methods: From June 03 to December 08, 164 patients (pts) were treated with HDRBT (HDR Ir192, MicroHDR Nucletron projector) after surgery for EC. After surgery patients were staged using 2002 FIGO classification: 2 IA, 48 IB, 72 IC, 8 IIA, 12 IIB, 9 IIIA, 2 IIIB, 11 IIIC. Pathology: 130 endometrioid, 8 serous, 2 clear cell, 21 mixed types, 3 miscellaneous. Radiotherapy: 124/164 pts. received external beam irradiation (EBI) plus HDRBT (Group 1) and 40/164 pts. received exclusive HDRBT (Group 2). Group 1: mean EBI dose was 45 Gy (range 44 - 50), 1.8 - 2 Gy/day, using 6 or 18 MV photons from a Linac; after EBI pts received HDRBT with 3 fractions of 4 to 5 Gy. Group 2: Pts received 6 fractions of 4 to 5 Gy. HDRBT dose was prescribed at 5 mm from vaginal surface and the applicators were colpostats in 8/164 cases and cylinders in 156/164 cases (cylinder diameters were 2, 2.5, 3 and 3.5 cm). HDRBT was administered 3 or 4 days per week regime when possible. Overall treatment time with HDRBT. Group 1: HDRBT was completed in a mean time of 4 days in 66 pts (range 3 to 5) and in more than 5 days in 58 pts, mean 8 days (range 6 - 13). Group 2: HDRBT was completed in #10 days in 14 pts, mean 8 days (range 6 - 10) and, in more than 11 days in 26 pts, mean 17 days (range 11 to 28). Toxicity was evaluated using RTOG scores for rectum and bladder. Vaginal toxicity was evaluated using the objective scores of LENT-SOMA. Statistics: Variance, Student’s t-test, Chi-square test. Results: Pts mean follow-up was 48 months (range 9 - 91). Only 2/164 pts had vaginal relapse and died and 7/164 pts were lost to follow-up. Early G1-G2 toxicity appeared in 28/164 (17%) pts and was resolved; late toxicity appeared in 42/164 (25%): vaginal mucosa 21 G1, 11G2, 1G4; bladder 2G1; rectal 5G1, 2G2. No differences in toxicity were found in relation to the overall treatment interval time in Groups 1 and 2. Conclusions: Three fractions of 4 - 5 Gy administered in 3 to 5 days after EBI or 6 fractions in less than 10 days in patients receiving HDRBT alone seems to be safe in relation to toxicity and local control for EC. 2) These results suggest that toxicity in HDRBT is not related to the overall interval treatment time. Author Disclosure: A. Rovirosa: None. C. Ascaso: None. I. Valduvieco: None. B. Carlos: None. A. Herreros: None. M. Arenas: None. A. Biete: None.
2559
Dosimetric Analysis of Inter fractional Dose and Volume Changes in Bladder and Rectum during Intensity Modulated Radiation Therapy for Gynecological Cancers with Daily Cone Beam CT guidance
H. Kim, S. Beriwal, S. Parikh, C. Houser Magee Women’s Hospital of UPMC, Pittsburgh, PA Purpose/Objective(s): To assess the changes in dose volume histograms from inter fractional changes in bladder and rectum as evaluated by daily KV cone beam CT (CBCT) during Intensity Modulated Radiation Therapy (IMRT) for post operative endometrial cancers. Materials/Methods: A total of 134 CBCT images from 7 patients who had adjuvant pelvic radiation after surgery for endometrial cancer were analyzed. Prescription dose was 1.8Gy per fraction for a total of 25 - 28 fractions with IMRT. Each of these patients had at least 3 CBCT images per week for setup verification before the radiation treatment. Daily setup shifts in translational directions (Superior-Inferior, Medial-Lateral, Anterior-Posterior) were applied before radiation treatment delivery by combination of soft tissue and bony anatomy match (3D- 3D match). Retrospectively, bladder and rectum volumes were contoured on daily CBCT images and treatment fields from the reference CT plan were applied to generate dose volume histograms (DVH) in each CBCT image. Cumulative DVHs from all image guided fractions per patient were calculated and compared with the planned DVH (comparison for V10 through V90: V10 and V90 are a volume covered by 10% and 90% of prescription dose, respectively). Also, CTV was drawn on daily CBCT images and DVH was generated for each image guided fraction to see if target coverage was still adequate during treatment course. CTV dose coverage (D95) was evaluated for each CBCT fraction and average CTV coverage of those was compared to the one in the reference CT plan. Results: For whole patient group, the cumulative DVH (V10 through V90) of bladder and rectum dose had a minimal difference from the planned DVH (range: 0- 4.7% for bladder, 0- 3.3% for rectum). However, for individual fractions, there were significant
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