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PO-351 RADIATION SAFETY: SOURCE POSITION INDICATOR AS A QUALITY ASSURANCE TOOL IN HIGH DOSE RATE (HDR) BRACHYTHERAPY
World Congress of Brachytherapy 2012 Purpose/Objective: This study presents the results of treatments of skin T Cell Lymphoma of two patients, one of them with multiple sites. The complex skin curvature associated with some sites are difficult to treat with LINAC based external beams, but easily managed with HDR brachytherapy when using soft moldable applicators that follow the shape of the anatomy. Materials and Methods: The first clinical case involved a seventy five year old woman who received HDR brachytherapy treatments to the base of the fourth finger on the palm side of the right hand. The second case involved the region of the left thumb and left foot of an eighty four year old man. The skin areas to be treated were first delineated with radiopaque wires. Individual complex custom molds were required to conform to these curved anatomical sites. For each case, a CT scan was performed in order to conduct accurate 3D treatment planning (Oncentra Masterplan Brachytherapy, version 3.3). This method of patient simulation clearly defined the target without any ambiguity and ensured that only the skin volume of interest is treated. A computerized treatment volume was created that had dimensions identical to the skin area defined by the radiopaque wires and a thickness equal to the prescription depth of 3 mm for the three sites presented here. The 100% isodose line was normalized to target points situated at the prescription depth around the treatment volume to ensure that the treatment volume was receiving adequate coverage. In the first case a 3 catheter Freiburg Flap applicator was used that had 17 dwell positions and covered an area of about 4.5 cm x 2 cm. In the second case a 15 catheter Freiburg Flap applicator with 164 dwell positions was used to cover the area around the thumb and a 16 catheter homemade mold with 307 dwell positions was used for the left foot. All treatments were delivered with a Nucletron Microselectron afterloader containing a HDR 192Ir source. Results: In all cases, a treatment of 800cGy was delivered in 2 fractions. The patients’ treatment responses were determined to be remarkable with complete resolution of pain and very good cosmetic outcome on follow up ranging from 1 - 10 months post treatment. Conclusions: T cell lymphoma responds very well to radiation. However, it can be very aggressive and debilitating if not treated. For complex geometries, small treatment areas and shallow (3-5mm) depths of treatment, HDR brachytherapy techniques will provide better coverage when compared to external beam. Clinical results for T cell skin lymphoma cases treated at our center with high dose rate brachytherapy were very successful in terms of improved cosmetics and decreased pain. The superior dose coverage obtained with moldable HDR brachytherapy applicators is not easily achievable with conventional LINAC based external radiation beams. The increased dose conformity around the skin allows radiation to be delivered to specific skin sites accurately with less dose to normal nearby region. PO-350 INTENSE LEARNING OUTCOMES BASED BRACHYTHERAPY TRAINING FOR RADIATION ONCOLOGY MEDICAL PHYSICISTS E. Flower1 1 Crown Princess Mary Cancer Centre Westmead, Radiation Oncology, Westmead, Australia Purpose/Objective: Training of Radiation Oncology Medical Physicists in Australia is conducted within the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) Training, Education and Accreditation Program (TEAP). The TEAP for Radiation Oncology includes brachytherapy as a core training module. For Radiation Oncology centres which do not provide a brachytherapy service (especially in rural areas), TEAP registrars must complete their practical brachytherapy training at a brachytherapy centre. To facilitate consistent, formal training, our centre was contracted to develop and conduct a learning outcome based training program. The contract is an initiative of NSW Health Statewide Services, facilitated by Newcastle Innovations (University of Newcastle) under a grant provided by the Commonwealth Department of Health and Ageing. Materials and Methods: Learning outcomes were established to fulfill the requirements of TEAP. A schedule was developed with prerequisite questions encompassing fundamental brachytherapy concepts. The registrar then attends a series of clinical placements, a
S 141 primary two week placement, followed by a three week placement, with the possibility of a tertiary one week placement if required. A range of assignments based on the learning outcomes follows the primary and secondary clinical placements. The primary clinical placement prepares the registrar for the written exam component of the program, covering brachytherapy theory, basic commissioning, quality assurance, planning and treatment delivery techniques. The final clinical placements provide more advanced skills and knowledge to be developed. As such this prepares the registrar for the final examinations of the program, leading to certification. The assignment completion, feedback and assessment continue following the clinical placements using an on-line Modular Object Oriented Dynamic Learning Environment (Moodle) package. Results: Registrars attend clinical placements and are exposed to a range of brachytherapy techniques. They have access to brachytherapy resources enabling them to complete assignments, gain practical experience and satisfy the learning outcomes. The assignments aid in providing evidence to satisfy the learning outcomes and to provide study material for exam preparation. All registrars who have participated in the program to date have provided positive feedback on the program. Conclusions: An intense learning outcome based brachytherapy training program focusing on clinical placements has been successfully developed. It enables registrars to become competent in brachytherapy physics, completing certification requirements. PO-351 RADIATION SAFETY: SOURCE POSITION INDICATOR AS A QUALITY ASSURANCE TOOL IN HIGH DOSE RATE (HDR) BRACHYTHERAPY E.O. Oyekunle1, R.I. Obed2 1 University College Hospital (UCH), Department of Radiotherapy and Oncology, Ibadan, Nigeria 2 University of Ibadan, Department of Physics, Ibadan, Nigeria Purpose/Objective: Equipment failure or malfunction is associated with high overexposure levels in radiotherapy. In addition to concern for patients undergoing high dose rate (HDR) brachytherapy, potential exposure from radiotherapy sources includes occupational exposures to staff and exposures to members of the public. This study investigates the relevance of source position indicator as a quality assurance (QA) tool and advises on how to promote radiation safety in high dose rate brachytherapy. Materials and Methods: Source position indicator attached to a network camera was employed for routine visual test of cobalt-60 source in Bebig HDR unit during morning quality assurance checks. Ambient radiation in treatment room during daily visual test was measured by Ludlum cylindrical radiation detector positioned 3.96 m (13 feet) away from the afterloader. This was connected to a digital area monitor mounted in the control (computer) room which is adjacent to the treatment room. Using Fluke Victoreen survey meter, instantaneous dose rate in HDR control room (6.10 m or 20 feet from source in afterloader) occupied by personnel was also established. During treatment with gynaecological catheters (ring applicators), scatter radiation measurements in both rooms were repeated as above and compared with corresponding QA readings over a period of 1 month. Source strength during duration of study was between 12031.8 cGy.cm2/hr. (39.32 GBq) and 11906.7 cGy.cm2/hr. (38.91 GBq). Results: In general, ambient radiation in treatment room while source drives out of afterloader during visual (single-channel) test ranged from 0.21 to 1.27 mSv/hr, irradiation at dwell points in source indicator had values ranging from 0.06 to 0.14 mSv/hr while readings were between 1.22 and 0.03 mSv/hr during source retraction. However, corresponding values during 3-channel gynecological treatment were 0.24 to 1.34 mSv/hr, 0.02 to 0.10 mSv/hr and 1.26 to 0.05 mSv/hr respectively. Moreover, radiation levels in control room during visual (positioning) test were as follow: source driving out: 0.6 to 2.0 µSv/hr, source within position indicator: 0.3 to 1.9 µSv/hr, source driving back: 0.8 to 2.2 µSv/hr. With ring applicator in place for intracavitary irradiation, these measurements were 0.4 to 1.8 µSv/hr, 0.3 to 2.2 µSv/hr and 0.7 to 2.5 µSv/hr respectively. By inverse square law calculations, using the highest value of 1.34 mSv/hr in treatment room, a maximum dose rate of 0.57 mSv/hr is expected at personnel position in control room. Practical
S142 measurements which however showed much reduced values (in µSv/hr) are a consequence of structural shielding by concrete walls and lead-embedded doors. Conclusions: It is essential to include checks of radiation levels in treatment and control rooms in daily quality assurance tests. Measurements while source position indicator was in use were comparable to corresponding irradiation values with ring applicators in patients. Therefore, radiation readings during source visual test should be given necessary attention as typical of likely measurements when brachytherapy irradiation of patients is actually in progress. PO-352 MODULATION RESTRICTIONS DO NOT NECESSARILY IMPROVE TREATMENT PLAN QUALITY FOR HDR PROSTATE BRACHYTHERAPY M. Balvert1, B. Gorissen1, D. den Hertog1, A. Hoffmann2 1 Tilburg University, Dept. Econometrics and Operations Research, Tilburg, The Netherlands 2 MAASTRO Clinic, Medical Physics, Maastricht, The Netherlands Purpose/Objective: Inverse optimization algorithms in interstitial HDR prostate brachytherapy may produce solutions with large dwell time variations within catheters. An undesirable property is that dominant dwell positions result in selective high-dose volumes (i.e., hot spots). A dwell time modulation restriction (DTMR) has been suggested and is used in planning software to eliminate this problem. Additionally, such DTMRs are used to reduce the sensitivity for uncertainties in dwell positions that inevitably result from catheter reconstruction errors and source positioning inaccuracy of the afterloader. The aim of this study is to quantify the reduction of hot spots and the robustness against these uncertainties by applying a DTMR to template-based HDR prostate brachytherapy implants. Materials and Methods: For catheter reconstruction, the measurement error in defining the tip was estimated to be 2 mm in any direction. An additional error due to the source positioning inaccuracy of the afterloader (±1 mm) was considered separately. Three different DTMRs were consecutively applied to existing dosebased and dose-volume based optimization models, limiting the relative differences, absolute differences, or summed squared differences between neighboring dwell positions. The models were solved for various restriction levels, ranging from no restriction to uniform dwell times within catheters. The errors were simulated uniformly at least 1.000 times on representative clinical cases. For each resulting dose distribution, hot spot indices and DVH statistics for the PTV, rectum and urethra were computed. These indices comprise global and local measures, respectively given by the dose homogeneity index (DHI) computed as (V100-V150)/V100, and the newly introduced V150c, being the largest contiguous volume receiving 150% of the prescribed dose. Results: None of the DTMRs could improve the nominal value, simulated sample mean or variance of DHI or V150c without simultaneously reducing V100. Moreover, the simulated sample variance of V100 was not decreased by any DTMR. Preliminary results for the afterloader inaccuracy are consistent with these results. Conclusions: No improvement in robustness against uncertainty in dwell position measurement and afterloader precision was obtained by applying a DTMR for the dose-based and dose-volume based optimization models. We recommend not to use any of the three DTMRs for inverse treatment planning optimization in HDR prostate brachytherapy implants. PO-353 CLINICAL ASSESSMENT OF THE HDR CAPRIÔ APPLICATOR B. Steffey1, O. Craciunescu1, J. Cai1, J. Adamson1, J. Chino1 1 Duke University Medical Center, Radiation Oncology, Durham NC, USA Purpose/Objective: The Capri™ applicator (Varian Corp.) is a new HDR CT-compatible brachytherapy (BT) applicator marketed to better sculpt the radiotherapy dose and improve patient comfort. It is a 13catheter balloon that is inflated upon insertion to conform to patient's anatomy. In this study we characterize this applicator by investigating the dosimetry as it compares with a stump vaginal cylinder, and the manufacturer's stated relative catheter positions.
World Congress of Brachytherapy 2012 Materials and Methods: Six patients received HDR brachytherapy using the Capri™ applicator for the treatment of vaginal (4), recurrent endometrial (1), and recurrent ovarian (1) cancers involving the vagina. All patients received external beam radiation therapy followed by 5 Gy x 4-5 fractions of HDR BT. For each insertion, MR/CT-based HRCTV volumes were delineated for treatment planning. GEC-ESTRO guidelines were followed for dose volume constraints for the organs at risk (OARs): bladder, rectum, sigmoid and bowel. The planning was done in BrachyVision using the volume optimization technique. Depending on the HRCTV shape and location, 4-11 catheters were used. Plans were calculated using the TG43 formalism and with ACUROS™, a model-based analytical solver that accounts for tissue inhomogeneities. Retrospectively, for dosimetry comparison, planning was also done using a 3.5 cm stump cylinder(SC) with the dose prescribed at 0.5 cm in tissue. HRCTV D90, bladder, rectum, sigmoid and bowel D2cc were compared between the two plans (CAPRI™ vs SC). Twenty-eight CAPRI™ applicators were imaged after TX and the relative positions between the distal ends of the catheters were measured and compared to manufacturer's stated values: 2 mm from central catheter to outer ring, and 10 mm from outer ring to inner ring. Results: The 3.5 cm SC could be used on only 22/29 fractions. The mean percent differences in HRCTV D90, and D2cc for bladder, rectum, sigmoid and bowel between the Capri™, used as reference,r and SC were, respectively: -19%±14, 39%± 29, 59%±44, 58%±37, and 41%±32 for TG43. Similar differences were found when ACUROS was used. For the Capri™ plans, the mean differences between TG43 and ACUROS for the same metrics were: -1.8%±0.5, 2.3%±0.6, 2.6%±0.6, 3.5%±1.1, and 3.4%±1.5 The distal measurements ranged 2.0 to 7.0 mm (avg 4.1 mm) from central catheter to outer ring, and 7.1 to 10.2 mm (avg 8.3 mm) from outer ring to inner ring. Conclusions: The new CAPRI™ applicator has several advantages: 1) better dose coverage for asymmetric and deep (> 0.5 cm) targets; 2) better OARs sparing; 3) increased patient comfort and immobilization due conformity to the vaginal vault. For catheter identification purposes, it is important for the user to be aware of the differences between the manufacturer's stated relative positions of the catheters and individual production CAPRI™s. Air in the balloon, when accounted for with ACUROS, impacts modestly on the dose metrics. PO-354 DOSIMETRIC IMPACTS OF UPGRADING FROM PLATO TO ONCENTRABRACHY IN A HIGH VOLUME PROSTATE HDR BRACHYTHERAPY CENTER F. Lacroix1, J. Morrier1, M.C. Lavallée1, S. Aubin1, W. Foster1, A.G. Martin1, E. Vigneault1, N. Varfalvy1, L. Beaulieu1 1 CHUQ, Radio-oncologie, Québec, Canada Purpose/Objective: To investigate the dosimetric impacts of upgrading from Plato to OncentraBrachy for HDR prostate planning. Materials and Methods: CHUQ is one of the highest volume prostate HDR brachytherapy centers in North America today. More than 800 prostate cancer patients have been treated with an HDR brachytherapy boost at Hôtel-Dieu de Québec (CHUQ) since 1999 and more than 200 in 2011 only. Our current procedure involves the insertion of 16-17 flexible plastic needles using ultrasound guidance. Computed tomography imaging is used for contouring. Planning was performed using Plato (Nucletron, BV, The Netherlands) until june 1 2011 but is now performed using OncentraBrachy. Inverse planning simulated annealing optimization is used for all cases. 81 patients were accrued from January 1 2011 to June 1 2011 and treated with Plato and 112 patients were treated from June 15 2011 to November 8 2011 using Oncentra. In this period, there were no modifications in the implant procedure itself, to the prescription dose, the contouring methods, or in the personnel performing the implant. Student’s t-test was performed on relevant dosimetric indices of the distributions to determine whether the averages of the distributions were different between the two periods. An F-test was also performed to determine whether the standard deviation of the distributions were significantly different. In addition, where differences where statistically significant (p<0.005), we have calculated the mean and the average of the standard deviations of both distributions.
S 141 primary two week placement, followed by a three week placement, with the possibility of a tertiary one week placement if required. A range of assignments based on the learning outcomes follows the primary and secondary clinical placements. The primary clinical placement prepares the registrar for the written exam component of the program, covering brachytherapy theory, basic commissioning, quality assurance, planning and treatment delivery techniques. The final clinical placements provide more advanced skills and knowledge to be developed. As such this prepares the registrar for the final examinations of the program, leading to certification. The assignment completion, feedback and assessment continue following the clinical placements using an on-line Modular Object Oriented Dynamic Learning Environment (Moodle) package. Results: Registrars attend clinical placements and are exposed to a range of brachytherapy techniques. They have access to brachytherapy resources enabling them to complete assignments, gain practical experience and satisfy the learning outcomes. The assignments aid in providing evidence to satisfy the learning outcomes and to provide study material for exam preparation. All registrars who have participated in the program to date have provided positive feedback on the program. Conclusions: An intense learning outcome based brachytherapy training program focusing on clinical placements has been successfully developed. It enables registrars to become competent in brachytherapy physics, completing certification requirements. PO-351 RADIATION SAFETY: SOURCE POSITION INDICATOR AS A QUALITY ASSURANCE TOOL IN HIGH DOSE RATE (HDR) BRACHYTHERAPY E.O. Oyekunle1, R.I. Obed2 1 University College Hospital (UCH), Department of Radiotherapy and Oncology, Ibadan, Nigeria 2 University of Ibadan, Department of Physics, Ibadan, Nigeria Purpose/Objective: Equipment failure or malfunction is associated with high overexposure levels in radiotherapy. In addition to concern for patients undergoing high dose rate (HDR) brachytherapy, potential exposure from radiotherapy sources includes occupational exposures to staff and exposures to members of the public. This study investigates the relevance of source position indicator as a quality assurance (QA) tool and advises on how to promote radiation safety in high dose rate brachytherapy. Materials and Methods: Source position indicator attached to a network camera was employed for routine visual test of cobalt-60 source in Bebig HDR unit during morning quality assurance checks. Ambient radiation in treatment room during daily visual test was measured by Ludlum cylindrical radiation detector positioned 3.96 m (13 feet) away from the afterloader. This was connected to a digital area monitor mounted in the control (computer) room which is adjacent to the treatment room. Using Fluke Victoreen survey meter, instantaneous dose rate in HDR control room (6.10 m or 20 feet from source in afterloader) occupied by personnel was also established. During treatment with gynaecological catheters (ring applicators), scatter radiation measurements in both rooms were repeated as above and compared with corresponding QA readings over a period of 1 month. Source strength during duration of study was between 12031.8 cGy.cm2/hr. (39.32 GBq) and 11906.7 cGy.cm2/hr. (38.91 GBq). Results: In general, ambient radiation in treatment room while source drives out of afterloader during visual (single-channel) test ranged from 0.21 to 1.27 mSv/hr, irradiation at dwell points in source indicator had values ranging from 0.06 to 0.14 mSv/hr while readings were between 1.22 and 0.03 mSv/hr during source retraction. However, corresponding values during 3-channel gynecological treatment were 0.24 to 1.34 mSv/hr, 0.02 to 0.10 mSv/hr and 1.26 to 0.05 mSv/hr respectively. Moreover, radiation levels in control room during visual (positioning) test were as follow: source driving out: 0.6 to 2.0 µSv/hr, source within position indicator: 0.3 to 1.9 µSv/hr, source driving back: 0.8 to 2.2 µSv/hr. With ring applicator in place for intracavitary irradiation, these measurements were 0.4 to 1.8 µSv/hr, 0.3 to 2.2 µSv/hr and 0.7 to 2.5 µSv/hr respectively. By inverse square law calculations, using the highest value of 1.34 mSv/hr in treatment room, a maximum dose rate of 0.57 mSv/hr is expected at personnel position in control room. Practical
S142 measurements which however showed much reduced values (in µSv/hr) are a consequence of structural shielding by concrete walls and lead-embedded doors. Conclusions: It is essential to include checks of radiation levels in treatment and control rooms in daily quality assurance tests. Measurements while source position indicator was in use were comparable to corresponding irradiation values with ring applicators in patients. Therefore, radiation readings during source visual test should be given necessary attention as typical of likely measurements when brachytherapy irradiation of patients is actually in progress. PO-352 MODULATION RESTRICTIONS DO NOT NECESSARILY IMPROVE TREATMENT PLAN QUALITY FOR HDR PROSTATE BRACHYTHERAPY M. Balvert1, B. Gorissen1, D. den Hertog1, A. Hoffmann2 1 Tilburg University, Dept. Econometrics and Operations Research, Tilburg, The Netherlands 2 MAASTRO Clinic, Medical Physics, Maastricht, The Netherlands Purpose/Objective: Inverse optimization algorithms in interstitial HDR prostate brachytherapy may produce solutions with large dwell time variations within catheters. An undesirable property is that dominant dwell positions result in selective high-dose volumes (i.e., hot spots). A dwell time modulation restriction (DTMR) has been suggested and is used in planning software to eliminate this problem. Additionally, such DTMRs are used to reduce the sensitivity for uncertainties in dwell positions that inevitably result from catheter reconstruction errors and source positioning inaccuracy of the afterloader. The aim of this study is to quantify the reduction of hot spots and the robustness against these uncertainties by applying a DTMR to template-based HDR prostate brachytherapy implants. Materials and Methods: For catheter reconstruction, the measurement error in defining the tip was estimated to be 2 mm in any direction. An additional error due to the source positioning inaccuracy of the afterloader (±1 mm) was considered separately. Three different DTMRs were consecutively applied to existing dosebased and dose-volume based optimization models, limiting the relative differences, absolute differences, or summed squared differences between neighboring dwell positions. The models were solved for various restriction levels, ranging from no restriction to uniform dwell times within catheters. The errors were simulated uniformly at least 1.000 times on representative clinical cases. For each resulting dose distribution, hot spot indices and DVH statistics for the PTV, rectum and urethra were computed. These indices comprise global and local measures, respectively given by the dose homogeneity index (DHI) computed as (V100-V150)/V100, and the newly introduced V150c, being the largest contiguous volume receiving 150% of the prescribed dose. Results: None of the DTMRs could improve the nominal value, simulated sample mean or variance of DHI or V150c without simultaneously reducing V100. Moreover, the simulated sample variance of V100 was not decreased by any DTMR. Preliminary results for the afterloader inaccuracy are consistent with these results. Conclusions: No improvement in robustness against uncertainty in dwell position measurement and afterloader precision was obtained by applying a DTMR for the dose-based and dose-volume based optimization models. We recommend not to use any of the three DTMRs for inverse treatment planning optimization in HDR prostate brachytherapy implants. PO-353 CLINICAL ASSESSMENT OF THE HDR CAPRIÔ APPLICATOR B. Steffey1, O. Craciunescu1, J. Cai1, J. Adamson1, J. Chino1 1 Duke University Medical Center, Radiation Oncology, Durham NC, USA Purpose/Objective: The Capri™ applicator (Varian Corp.) is a new HDR CT-compatible brachytherapy (BT) applicator marketed to better sculpt the radiotherapy dose and improve patient comfort. It is a 13catheter balloon that is inflated upon insertion to conform to patient's anatomy. In this study we characterize this applicator by investigating the dosimetry as it compares with a stump vaginal cylinder, and the manufacturer's stated relative catheter positions.
World Congress of Brachytherapy 2012 Materials and Methods: Six patients received HDR brachytherapy using the Capri™ applicator for the treatment of vaginal (4), recurrent endometrial (1), and recurrent ovarian (1) cancers involving the vagina. All patients received external beam radiation therapy followed by 5 Gy x 4-5 fractions of HDR BT. For each insertion, MR/CT-based HRCTV volumes were delineated for treatment planning. GEC-ESTRO guidelines were followed for dose volume constraints for the organs at risk (OARs): bladder, rectum, sigmoid and bowel. The planning was done in BrachyVision using the volume optimization technique. Depending on the HRCTV shape and location, 4-11 catheters were used. Plans were calculated using the TG43 formalism and with ACUROS™, a model-based analytical solver that accounts for tissue inhomogeneities. Retrospectively, for dosimetry comparison, planning was also done using a 3.5 cm stump cylinder(SC) with the dose prescribed at 0.5 cm in tissue. HRCTV D90, bladder, rectum, sigmoid and bowel D2cc were compared between the two plans (CAPRI™ vs SC). Twenty-eight CAPRI™ applicators were imaged after TX and the relative positions between the distal ends of the catheters were measured and compared to manufacturer's stated values: 2 mm from central catheter to outer ring, and 10 mm from outer ring to inner ring. Results: The 3.5 cm SC could be used on only 22/29 fractions. The mean percent differences in HRCTV D90, and D2cc for bladder, rectum, sigmoid and bowel between the Capri™, used as reference,r and SC were, respectively: -19%±14, 39%± 29, 59%±44, 58%±37, and 41%±32 for TG43. Similar differences were found when ACUROS was used. For the Capri™ plans, the mean differences between TG43 and ACUROS for the same metrics were: -1.8%±0.5, 2.3%±0.6, 2.6%±0.6, 3.5%±1.1, and 3.4%±1.5 The distal measurements ranged 2.0 to 7.0 mm (avg 4.1 mm) from central catheter to outer ring, and 7.1 to 10.2 mm (avg 8.3 mm) from outer ring to inner ring. Conclusions: The new CAPRI™ applicator has several advantages: 1) better dose coverage for asymmetric and deep (> 0.5 cm) targets; 2) better OARs sparing; 3) increased patient comfort and immobilization due conformity to the vaginal vault. For catheter identification purposes, it is important for the user to be aware of the differences between the manufacturer's stated relative positions of the catheters and individual production CAPRI™s. Air in the balloon, when accounted for with ACUROS, impacts modestly on the dose metrics. PO-354 DOSIMETRIC IMPACTS OF UPGRADING FROM PLATO TO ONCENTRABRACHY IN A HIGH VOLUME PROSTATE HDR BRACHYTHERAPY CENTER F. Lacroix1, J. Morrier1, M.C. Lavallée1, S. Aubin1, W. Foster1, A.G. Martin1, E. Vigneault1, N. Varfalvy1, L. Beaulieu1 1 CHUQ, Radio-oncologie, Québec, Canada Purpose/Objective: To investigate the dosimetric impacts of upgrading from Plato to OncentraBrachy for HDR prostate planning. Materials and Methods: CHUQ is one of the highest volume prostate HDR brachytherapy centers in North America today. More than 800 prostate cancer patients have been treated with an HDR brachytherapy boost at Hôtel-Dieu de Québec (CHUQ) since 1999 and more than 200 in 2011 only. Our current procedure involves the insertion of 16-17 flexible plastic needles using ultrasound guidance. Computed tomography imaging is used for contouring. Planning was performed using Plato (Nucletron, BV, The Netherlands) until june 1 2011 but is now performed using OncentraBrachy. Inverse planning simulated annealing optimization is used for all cases. 81 patients were accrued from January 1 2011 to June 1 2011 and treated with Plato and 112 patients were treated from June 15 2011 to November 8 2011 using Oncentra. In this period, there were no modifications in the implant procedure itself, to the prescription dose, the contouring methods, or in the personnel performing the implant. Student’s t-test was performed on relevant dosimetric indices of the distributions to determine whether the averages of the distributions were different between the two periods. An F-test was also performed to determine whether the standard deviation of the distributions were significantly different. In addition, where differences where statistically significant (p<0.005), we have calculated the mean and the average of the standard deviations of both distributions.