- Email: [email protected]
3D Anatomy-Based Planning Optimization for HDR Brachytherapy of Cervix Cancer
Abstracts / Brachytherapy 10 (2011) S14eS101 Interstitial Template were included in the study. All procedures were done by radiation oncologists with 6 or more years of experience in brachytherapy. Implanted volume comprised of gross tumour with an additional 2e3 cm margin in superoinferior (SI) direction and 1 cm margin in mediolateral (ML) direction. All patients underwent CT scans for brachytherapy planning. CT cuts were obtained with patients in supine position with pelvic ring and arms on chest. Imaged volume encompassed the entire pelvis along with implanted needles at an inter-slice thickness of 3 mm (SomatomÒ). CT scans were repeated at every alternate fraction. All images were transferred to CoherenceÒ for quality evaluation. A reproducible, relocatable bony point coordinate was localized at pubic symphysis for all patients. The accuracy of reference point localisation was confirmed using repeat measures method. All displacements i.e SI, anteroposterior (AP) and ML were calculated in reference to this point. While SI displacement was calculated in each needle for all patients, anterior-most and lateral-most needles were used as surrogate for calculating AP and ML displacements. Inter-fraction maximum displacement was calculated for each patient and average was obtained across all the patients. The calculated average represented the planned target volume (PTV) margins for multifractionated brachytherapy implantation. Results: Ten patients were included in this study. While 7 patients received brachytherapy as boost (20 Gy/5# over 3 days), 3 underwent radical reirradiation (36 Gy/10# over 6 days). Eight patients had 3 scans and 2 scans were available for another 2 patients. The reference point localisation error was 0.1mm, 0.17mm, 0.05mm in ML, SI and AP direction. The mean displacement of needles in superior, inferior, anterior, posterior, right and left direction was 4.8 mm (0e15), 19.5 mm (0e33), 2.0 mm (0e2), 4.9 mm (2.2e9.5), 4.4 mm (0.6e9.3), and 5.2 mm (2.6e7.8), respectively. The displacements in patient undergoing radical re-irradiation (10 fractions) were no greater than those undergoing boost brachytherapy. Conclusions: Clinically significant inferior displacements occur during multifractionated pelvic brachytherapy. The displacements observed in this study provide guidance for PTV margins for preplanning brachytherapy during multifractionated brachytherapy.
PD51 Retrospective Analysis of Late Toxicity in Cervical Cancer Patients Treated With CT-Based High-Dose-Rate Brachytherapy Krystine K. Lupe, Carmen Popescu, Abe S. Alexander, MD, Hosam A. Kader, Cheryl Alexander, Caroline L. Holloway, MD. British Columbia Cancer Agency, Vancouver Island Centre, BC, Canada. Purpose: The purpose of this study was to (1) compare volumetric (D2cc) and ICRU point doses delivered to the bladder and rectum with CT based intracavitary brachytherapy (BT) and (2) evaluate late toxicity relative to total linear quadratic equivalent dose in 2Gy per fraction (LQED2) to bladder and rectum using volumetric and point based methods of dose reporting. Materials and Methods: This retrospective study evaluated 22 women treated for cervical cancer at our institution with external beam radiation (EBRT) and CT based high-dose-rate (HDR) intracavitary BT. All patients were followed for a minimum of two years, with the exception of those who developed toxicity but died within two years of treatment. Patient, treatment and toxicity data were extracted from paper and electronic charts. During the study period, CT images were acquired at the time of each BT insertion and BT plans were evaluated and approved using ICRU point dose tolerances. To allow evaluation of D2cc doses, organs at risk (bladder and rectum) were retrospectively contoured on the original CT images by one radiation oncologist (RO) and reviewed by a second RO. The position of the ICRU bladder and rectal points were reviewed by a single medical physicist. Dose to the bladder and rectum was evaluated for each fraction of BT using volumetric (D2cc) and point dose (ICRU) methods of dose reporting. Total LQED2 (EBRT þ BT) to point A, bladder and rectum was calculated using an a/b of 3 for normal tissue and 10 for tumor. Late toxicity was graded as per the common
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terminology criteria for adverse events version 3.0 (CTCAE). Correlative analysis was performed to determine association between late toxicity and total LQED2 to organs at risk. Results: Twenty-two women received a total of 88 HDR intracavitary insertions. The median age was 50 years and the median followup was 48.8 months. All patients were treated with 45Gy in 25 fractions to the pelvis; nine patients (41%) received an external beam boost to involved nodes and/or parametria (range:5.4Gy/3 e 9Gy/5). BT was delivered with tandem and ovoid applicators and the most common fractionation for BT was 26Gy in 4 fractions (82%). The mean dose per fraction to point A was 6.39Gy and the mean total LQED2 to point A was 79.2Gy. The mean dose per fraction to the ICRU rectal point and D2cc rectum was 4.1Gy and 3.3Gy; corresponding values for the bladder were 4.6Gy and 5.8Gy. The mean total LQED2 to the ICRU rectal point and D2cc rectum were 66.7Gy and 60.4Gy respectively; corresponding values for the bladder were 72.5Gy and 85.0Gy. Ten women (45%) experienced a total of fourteen grade 1/2 late gastrointestinal (GI) toxicities. Eleven women (50%) experienced a total of sixteen grade1/2, and three grade 3/4 late genitourinary (GU) toxicities. The three grade 3/4 toxicities (dysuria, frequency and vesicovaginal fistula) occurred in a single patient (ICRU bladder 103.0Gy, D2cc bladder 88.3Gy). There was no correlation between toxicity and total LQED2 to D2cc bladder or rectum, nor was there correlation between toxicity and total LQED2 to ICRU bladder or rectal points (all r2 !0.07). Conclusions: Similar to previously published studies, the ratio of mean D2cc/ICRU dose to bladder and rectum in our series was 1.3 and 0.82, respectively. We found no correlation between late toxicity and total LQED2 to bladder and rectum using either point dose or volumetric evaluation of organs at risk. Large prospective studies are needed to evaluate late toxicity relative to total LQED2 to bladder and rectum in the definitive treatment of cervical cancer.
PD52 3D Anatomy-Based Planning Optimization for HDR Brachytherapy of Cervix Cancer Yasir A. Bahadur, FRCP1, Camelia Constantinescu, PhD3, Mohamad E. El Sayed, MD2,3, Noor Ghassal, BSc3. 1Radiology, King Abdul Aziz University, Jeddah, Saudia Arabia; 2Radiation Oncology, National Cancer Institute, Cairo University, Cairo, Egypt; 3Oncology, King Faisal Specialist Hospital & Research Center, Jeddah, Saudia Arabia. Purpose: To evaluate the dosimetric superiority of inverse planning optimization and isodose line manually optimization (both 3D planning methods) versus conventional treatment plan (point A planning method), using various dosimetric indices in HDR brachytherapy planning for cervical carcinoma. Materials and Methods: Data from 10 patients treated with HDR brachytherapy for cervical cancer using tandem and ovoids were analyzed. Target and organ at risk volumes were defined using systematic guidelines. Dose distributions were created according to three different dose calculation protocols: point A, isodose line manually optimization, and inverse planning and doseevolume histograms from these plans were analyzed, and all plans were evaluated for V100%, V95%, the conformity index CI 5 V100%/VCTV, and the dose homogeneity index DHI 5 (V100% -V150%)/ V100% for target. For rectum D5cc, V50%, V70% and V100% of prescription dose were evaluated. For bladder D5cc, V50%, V80% and V100% of prescription dose were evaluated. Results: Both 3D planning methods showed significant better target coverage compared with point A calculation: average 85.65% isodose manually shaping vs. 48.43% point A calculation (p ! 0.003) and 90.33% inverse planning vs. 48.43% point A calculation (p ! 0.001) for V7Gy. Dose homogeneity was better for both 3D planning protocols: average 0.33% isodose manually shaping vs. 0.39% point A calculation (p ! 0.008) and 0.31% inverse planning vs. 0.39% point A calculation (p ! 0.031) for DHI. For organs at risk, point A calculation average was 4.29 Gy vs. 4.99 Gy isodose manually shaping (p ! 0.037) and 4.29 Gy point A calculation
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vs. 5.14 Gy inverse planning (p ! 0.013) for D5cc of rectum; and average 4.88 Gy point A calculation vs. 6.32 Gy isodose manually shaping (p ! 0.019) and 4.88 Gy point A calculation vs. 5.78 Gy inverse planning (p ! 0.019) for D5cc of bladder. Conclusions: The 3D planning methods improve dose conformity and homogeneity of target coverage while minimizing dose to critical structures by chosen the appropriate priorities and allows for easy comparison between patients.
PD53 Preoperative High-Dose-Rate Brachytherapy for Clinical Stage IIB Endometrial Carcinoma Gaurav Shukla, BSE1, Sushil Beriwal, MD2, Thomas C. Krivak, MD3, Joseph L. Kelley, MD3, Paniti Sukumvanitch, MD3, Robert P. Edwards, MD3, Scott Richard, MD3, Alexander Olawaiye, MD3, Kristen K. Zorn, MD3. 1School of Medicine, University of Pittsburgh, Pittsburgh, PA; 2 Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA; 3Gynecologic Oncology, University of Pittsburgh Medical Center, Pittsburgh, PA. Purpose: To evaluate pathological response, tolerance, and outcome after preoperative (neoadjuvant) high-dose-rate brachytherapy in a small series of patients with clinical stage IIB endometrial carcinoma. Materials and Methods: Nine women clinically diagnosed with clinical stage IIB endometrial carcinoma from 1999e2008 treated with preoperative radiation therapy were analyzed. All patients had biopsyconfirmed endometrial cancer and had pretreatment CT scan and/or MRI for staging. The dose of external beam (EBRT) was 45e50.4 Gy in 25 to 28 fractions followed by HDR brachytherapy. The HDR brachytherapy was done with placement of a Smit sleeve and tandem and ring applicator. A dose of 4e5.5 Gy in 3e4 fractions was prescribed to point A. Three of the 9 patients had 3D CT scan image-based dosimetric planning with the clinical target volume being the entire uterus and cervix. Extrafascial hysterectomy with lymph node sampling was performed 4e8 weeks after the last brachytherapy treatment. The pathological response and outcome data were extracted and analyzed. The total doses from EBRT and brachytherapy were summated and normalized to a biologically equivalent dose of 2 Gy per fraction (EQD2) using the linear quadratic model and a/b 5 10 Gy. All patients were followed every three months for the first two years, and every six months thereafter, with vaginal cytology at each surveillance visit. Results: The median age was 64 (range 49e76) with median body mass index (BMI) of 32.6 (range 29e45). All patients completed the planned course of preoperative radiation therapy with a median EQD2 dose of 66.31 Gy (range 59e75.4 Gy). No patient developed acute grade three or higher toxicity. All patients had surgery done with uneventful recovery from the operation. Complete pathological response (pCR) was seen in two patients (22%) while three patients (33%) had only microscopic residual disease confined to either the endometrium or cervical glands. Two patients were found to have para-aortic disease and received adjuvant para-aortic radiation. Two patients with high grade pathology (one each with serous and clear cell histology) also received adjuvant chemotherapy after surgery. At a median followup of 24 months (3e86 months), one patient has developed recurrence at the vaginal apex six months after completing initial therapy, while another has developed a lung recurrence at 28 months. Both of these patients are alive with disease at 69 and 32 months, respectively. One patient developed a second primary lung carcinoma that was treated surgically. One patient has died of comorbidities at 86 months with no evidence of disease at last followup. No patient developed late grade three or higher radiation treatment-related morbidity. Two-year disease-free and cause-specific survivals were 85.7% and 100%, respectively. Conclusions: Our small study shows that the HDR fractionation schedule as done in our series for preoperative radiation therapy for clinical stage II endometrial cancer is well tolerated with good clinical response and outcome and would be an option for patients treated with neoadjuvant radiation therapy.
POSTER DISCUSSION: PHYSICS Friday April 15, 2011 1:30 PMe3:00 PM PD54 Clinical Treatment Planning Using a Non-invasive Image-Guided Conical Breast Brachytherapy Applicator Yun Yang, PhD1,2, Mark J. Rivard, PhD1. 1Radiation Oncology, Tufts University School of Medicine, Boston, MA; 2Biomedical Engineering and Biotechnology, Univeristy of Massachusetts Lowell, Lowell, MA. Purpose: AccuBoost applicators are designed to deliver whole breast irradiation (WBI) boost dose in a non-invasive manner instead of conventional WBI electron boost. In order to irradiate the target volume while providing additional dose sparing to critical structures like the skin, the current round applicator design has been augmented through addition of an internally-truncated cone shield. Brachytherapy dose distributions for the new cone applicator were simulated using model Monte Carlo (MC) methods for radiation transport and a conventional treatment planning system (TPS), and the dose distributions compared to the unmodified round applicator. Materials and Methods: Dosimetry parameters for the 6 cm and 7 cm diameter round and conical applicators (6R/7R/6C/7C) were deduced from MC simulations (MCNP5) and entered into the Pinnacle3 TPS (v8.0m). The radial dose function g(r) data were in the range 1.0 # r #15.4 cm and 2D anisotropy function F(x, z) data were in the ranges 0.0 # x # 12.5 cm and 2.675 # z # 10.675 cm. With 0.05 cm increments, 161 and 40411 data points were used for g(r) and F(x, z) characterization, respectively. Treatment plans were generated using both 6R and 6C applicators for single patients with the same treatment setup. Dose was normalized to the breast center along the central axis. The maximum dose (DMAX) to skin, chest wall, and lung, tumor DMEAN, the percentage of prescription dose delivered to the planning tumor volume (PTV) (D10, D50, D90, D100), and the percentage of volume receiving a percentage of the prescription dose (V90, V100, V110) were then compared for the four applicators. Dose volume histograms (DVH) were obtained for all salient structures for several patient plans using the four applicators. Results: The conical applicators reduced the skin, chest wall, and lung DMAX by an additional 38%, 10%, and 5%, respectively for the 6 cm applicator, and 34%, 9%, and 6% for the 7 cm applicator compared to the unmodified applicators. Differences between the 6C and 6R applicators for D10 and D100 were about 5%, with similar differences for D50 and D90 of less than 2%. Comparable results were observed for the 7 cm applicators. On average, V90, V100, and V110 decreased by 7% when using the conical applicators with the 7C applicator providing more uniform PTV coverage (see Figure). This improved coverage was at the expense of higher average skin dose due to the larger 7 cm aperture. When using a 4-field AccuBoost beam arrangement, these parameters are considerably more favorable when compared to conventional WBI electron boost (Sioshansi et al. IJROBP in press, DOI: 10.1016/j.ijrobp.2010.01.052).
PD51 Retrospective Analysis of Late Toxicity in Cervical Cancer Patients Treated With CT-Based High-Dose-Rate Brachytherapy Krystine K. Lupe, Carmen Popescu, Abe S. Alexander, MD, Hosam A. Kader, Cheryl Alexander, Caroline L. Holloway, MD. British Columbia Cancer Agency, Vancouver Island Centre, BC, Canada. Purpose: The purpose of this study was to (1) compare volumetric (D2cc) and ICRU point doses delivered to the bladder and rectum with CT based intracavitary brachytherapy (BT) and (2) evaluate late toxicity relative to total linear quadratic equivalent dose in 2Gy per fraction (LQED2) to bladder and rectum using volumetric and point based methods of dose reporting. Materials and Methods: This retrospective study evaluated 22 women treated for cervical cancer at our institution with external beam radiation (EBRT) and CT based high-dose-rate (HDR) intracavitary BT. All patients were followed for a minimum of two years, with the exception of those who developed toxicity but died within two years of treatment. Patient, treatment and toxicity data were extracted from paper and electronic charts. During the study period, CT images were acquired at the time of each BT insertion and BT plans were evaluated and approved using ICRU point dose tolerances. To allow evaluation of D2cc doses, organs at risk (bladder and rectum) were retrospectively contoured on the original CT images by one radiation oncologist (RO) and reviewed by a second RO. The position of the ICRU bladder and rectal points were reviewed by a single medical physicist. Dose to the bladder and rectum was evaluated for each fraction of BT using volumetric (D2cc) and point dose (ICRU) methods of dose reporting. Total LQED2 (EBRT þ BT) to point A, bladder and rectum was calculated using an a/b of 3 for normal tissue and 10 for tumor. Late toxicity was graded as per the common
S61
terminology criteria for adverse events version 3.0 (CTCAE). Correlative analysis was performed to determine association between late toxicity and total LQED2 to organs at risk. Results: Twenty-two women received a total of 88 HDR intracavitary insertions. The median age was 50 years and the median followup was 48.8 months. All patients were treated with 45Gy in 25 fractions to the pelvis; nine patients (41%) received an external beam boost to involved nodes and/or parametria (range:5.4Gy/3 e 9Gy/5). BT was delivered with tandem and ovoid applicators and the most common fractionation for BT was 26Gy in 4 fractions (82%). The mean dose per fraction to point A was 6.39Gy and the mean total LQED2 to point A was 79.2Gy. The mean dose per fraction to the ICRU rectal point and D2cc rectum was 4.1Gy and 3.3Gy; corresponding values for the bladder were 4.6Gy and 5.8Gy. The mean total LQED2 to the ICRU rectal point and D2cc rectum were 66.7Gy and 60.4Gy respectively; corresponding values for the bladder were 72.5Gy and 85.0Gy. Ten women (45%) experienced a total of fourteen grade 1/2 late gastrointestinal (GI) toxicities. Eleven women (50%) experienced a total of sixteen grade1/2, and three grade 3/4 late genitourinary (GU) toxicities. The three grade 3/4 toxicities (dysuria, frequency and vesicovaginal fistula) occurred in a single patient (ICRU bladder 103.0Gy, D2cc bladder 88.3Gy). There was no correlation between toxicity and total LQED2 to D2cc bladder or rectum, nor was there correlation between toxicity and total LQED2 to ICRU bladder or rectal points (all r2 !0.07). Conclusions: Similar to previously published studies, the ratio of mean D2cc/ICRU dose to bladder and rectum in our series was 1.3 and 0.82, respectively. We found no correlation between late toxicity and total LQED2 to bladder and rectum using either point dose or volumetric evaluation of organs at risk. Large prospective studies are needed to evaluate late toxicity relative to total LQED2 to bladder and rectum in the definitive treatment of cervical cancer.
PD52 3D Anatomy-Based Planning Optimization for HDR Brachytherapy of Cervix Cancer Yasir A. Bahadur, FRCP1, Camelia Constantinescu, PhD3, Mohamad E. El Sayed, MD2,3, Noor Ghassal, BSc3. 1Radiology, King Abdul Aziz University, Jeddah, Saudia Arabia; 2Radiation Oncology, National Cancer Institute, Cairo University, Cairo, Egypt; 3Oncology, King Faisal Specialist Hospital & Research Center, Jeddah, Saudia Arabia. Purpose: To evaluate the dosimetric superiority of inverse planning optimization and isodose line manually optimization (both 3D planning methods) versus conventional treatment plan (point A planning method), using various dosimetric indices in HDR brachytherapy planning for cervical carcinoma. Materials and Methods: Data from 10 patients treated with HDR brachytherapy for cervical cancer using tandem and ovoids were analyzed. Target and organ at risk volumes were defined using systematic guidelines. Dose distributions were created according to three different dose calculation protocols: point A, isodose line manually optimization, and inverse planning and doseevolume histograms from these plans were analyzed, and all plans were evaluated for V100%, V95%, the conformity index CI 5 V100%/VCTV, and the dose homogeneity index DHI 5 (V100% -V150%)/ V100% for target. For rectum D5cc, V50%, V70% and V100% of prescription dose were evaluated. For bladder D5cc, V50%, V80% and V100% of prescription dose were evaluated. Results: Both 3D planning methods showed significant better target coverage compared with point A calculation: average 85.65% isodose manually shaping vs. 48.43% point A calculation (p ! 0.003) and 90.33% inverse planning vs. 48.43% point A calculation (p ! 0.001) for V7Gy. Dose homogeneity was better for both 3D planning protocols: average 0.33% isodose manually shaping vs. 0.39% point A calculation (p ! 0.008) and 0.31% inverse planning vs. 0.39% point A calculation (p ! 0.031) for DHI. For organs at risk, point A calculation average was 4.29 Gy vs. 4.99 Gy isodose manually shaping (p ! 0.037) and 4.29 Gy point A calculation
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Abstracts / Brachytherapy 10 (2011) S14eS101
vs. 5.14 Gy inverse planning (p ! 0.013) for D5cc of rectum; and average 4.88 Gy point A calculation vs. 6.32 Gy isodose manually shaping (p ! 0.019) and 4.88 Gy point A calculation vs. 5.78 Gy inverse planning (p ! 0.019) for D5cc of bladder. Conclusions: The 3D planning methods improve dose conformity and homogeneity of target coverage while minimizing dose to critical structures by chosen the appropriate priorities and allows for easy comparison between patients.
PD53 Preoperative High-Dose-Rate Brachytherapy for Clinical Stage IIB Endometrial Carcinoma Gaurav Shukla, BSE1, Sushil Beriwal, MD2, Thomas C. Krivak, MD3, Joseph L. Kelley, MD3, Paniti Sukumvanitch, MD3, Robert P. Edwards, MD3, Scott Richard, MD3, Alexander Olawaiye, MD3, Kristen K. Zorn, MD3. 1School of Medicine, University of Pittsburgh, Pittsburgh, PA; 2 Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA; 3Gynecologic Oncology, University of Pittsburgh Medical Center, Pittsburgh, PA. Purpose: To evaluate pathological response, tolerance, and outcome after preoperative (neoadjuvant) high-dose-rate brachytherapy in a small series of patients with clinical stage IIB endometrial carcinoma. Materials and Methods: Nine women clinically diagnosed with clinical stage IIB endometrial carcinoma from 1999e2008 treated with preoperative radiation therapy were analyzed. All patients had biopsyconfirmed endometrial cancer and had pretreatment CT scan and/or MRI for staging. The dose of external beam (EBRT) was 45e50.4 Gy in 25 to 28 fractions followed by HDR brachytherapy. The HDR brachytherapy was done with placement of a Smit sleeve and tandem and ring applicator. A dose of 4e5.5 Gy in 3e4 fractions was prescribed to point A. Three of the 9 patients had 3D CT scan image-based dosimetric planning with the clinical target volume being the entire uterus and cervix. Extrafascial hysterectomy with lymph node sampling was performed 4e8 weeks after the last brachytherapy treatment. The pathological response and outcome data were extracted and analyzed. The total doses from EBRT and brachytherapy were summated and normalized to a biologically equivalent dose of 2 Gy per fraction (EQD2) using the linear quadratic model and a/b 5 10 Gy. All patients were followed every three months for the first two years, and every six months thereafter, with vaginal cytology at each surveillance visit. Results: The median age was 64 (range 49e76) with median body mass index (BMI) of 32.6 (range 29e45). All patients completed the planned course of preoperative radiation therapy with a median EQD2 dose of 66.31 Gy (range 59e75.4 Gy). No patient developed acute grade three or higher toxicity. All patients had surgery done with uneventful recovery from the operation. Complete pathological response (pCR) was seen in two patients (22%) while three patients (33%) had only microscopic residual disease confined to either the endometrium or cervical glands. Two patients were found to have para-aortic disease and received adjuvant para-aortic radiation. Two patients with high grade pathology (one each with serous and clear cell histology) also received adjuvant chemotherapy after surgery. At a median followup of 24 months (3e86 months), one patient has developed recurrence at the vaginal apex six months after completing initial therapy, while another has developed a lung recurrence at 28 months. Both of these patients are alive with disease at 69 and 32 months, respectively. One patient developed a second primary lung carcinoma that was treated surgically. One patient has died of comorbidities at 86 months with no evidence of disease at last followup. No patient developed late grade three or higher radiation treatment-related morbidity. Two-year disease-free and cause-specific survivals were 85.7% and 100%, respectively. Conclusions: Our small study shows that the HDR fractionation schedule as done in our series for preoperative radiation therapy for clinical stage II endometrial cancer is well tolerated with good clinical response and outcome and would be an option for patients treated with neoadjuvant radiation therapy.
POSTER DISCUSSION: PHYSICS Friday April 15, 2011 1:30 PMe3:00 PM PD54 Clinical Treatment Planning Using a Non-invasive Image-Guided Conical Breast Brachytherapy Applicator Yun Yang, PhD1,2, Mark J. Rivard, PhD1. 1Radiation Oncology, Tufts University School of Medicine, Boston, MA; 2Biomedical Engineering and Biotechnology, Univeristy of Massachusetts Lowell, Lowell, MA. Purpose: AccuBoost applicators are designed to deliver whole breast irradiation (WBI) boost dose in a non-invasive manner instead of conventional WBI electron boost. In order to irradiate the target volume while providing additional dose sparing to critical structures like the skin, the current round applicator design has been augmented through addition of an internally-truncated cone shield. Brachytherapy dose distributions for the new cone applicator were simulated using model Monte Carlo (MC) methods for radiation transport and a conventional treatment planning system (TPS), and the dose distributions compared to the unmodified round applicator. Materials and Methods: Dosimetry parameters for the 6 cm and 7 cm diameter round and conical applicators (6R/7R/6C/7C) were deduced from MC simulations (MCNP5) and entered into the Pinnacle3 TPS (v8.0m). The radial dose function g(r) data were in the range 1.0 # r #15.4 cm and 2D anisotropy function F(x, z) data were in the ranges 0.0 # x # 12.5 cm and 2.675 # z # 10.675 cm. With 0.05 cm increments, 161 and 40411 data points were used for g(r) and F(x, z) characterization, respectively. Treatment plans were generated using both 6R and 6C applicators for single patients with the same treatment setup. Dose was normalized to the breast center along the central axis. The maximum dose (DMAX) to skin, chest wall, and lung, tumor DMEAN, the percentage of prescription dose delivered to the planning tumor volume (PTV) (D10, D50, D90, D100), and the percentage of volume receiving a percentage of the prescription dose (V90, V100, V110) were then compared for the four applicators. Dose volume histograms (DVH) were obtained for all salient structures for several patient plans using the four applicators. Results: The conical applicators reduced the skin, chest wall, and lung DMAX by an additional 38%, 10%, and 5%, respectively for the 6 cm applicator, and 34%, 9%, and 6% for the 7 cm applicator compared to the unmodified applicators. Differences between the 6C and 6R applicators for D10 and D100 were about 5%, with similar differences for D50 and D90 of less than 2%. Comparable results were observed for the 7 cm applicators. On average, V90, V100, and V110 decreased by 7% when using the conical applicators with the 7C applicator providing more uniform PTV coverage (see Figure). This improved coverage was at the expense of higher average skin dose due to the larger 7 cm aperture. When using a 4-field AccuBoost beam arrangement, these parameters are considerably more favorable when compared to conventional WBI electron boost (Sioshansi et al. IJROBP in press, DOI: 10.1016/j.ijrobp.2010.01.052).