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Organ at Risk Dose in Cervical Cancer HDR Brachytherapy-Correlation between Predicted Dose on MRI Scan and Calculated Dose on CBCT
S120
Abstracts / Brachytherapy 15 (2016) S21eS204
translates into better local control and organ sparing. One may also conjecture that experienced practioners are more likely to properly place the applicators. Although 3D imaging modalities for ICBT planning facilitate actual anatomical brachytherapy planning and actual geometry of applicators in-situ with respect to the patient’s anatomy however in a high throughput Indian facility applicators are generally placed without any aid of image guidance and orthogonal X-ray film simulation is still standard method for dosimetric calculation of brachytherapy that completely lacks any information about positioning of applicators in-situ with regard to anatomical variations. The problem is further compounded in teaching training departments where applicators are implanted by variable trained individuals. Purpose/Aim of Study: The present service evaluation was carried out to document the inappropriate placement of tandem using CT simulation. Material and Methods: All radically treated histopathologically proven cervical cancer patients who underwent ICBT using CT simulation by varied in training practioners were studied. After brachytherapy applicator insertion, patients were shifted to CT scanner and whole pelvis non contrast CT images were acquired. After acquiring the axial CT images 3D reconstruction in axial, coronal and sagittal planes were performed and images were analyzed to assess proper placement of tandem during the first brachytherapy application as is the practice in the department to ensure precision of applicator placement before proceeding for dosimetric planning and treatment. In case of inappropriate applicator/tandem placement the procedure was either abandoned or applicator repositioned and corrected before acquiring the simulation image for dosimetric estimation and treatment or planning optimisation done based on individual case. Results: 84 patients of cervical cancer, FIGO Stage I-IV were radically treated by external radiation therapy with or without chemotherapy and HDR brachytherapy 6Gy/fraction in 3 to 4fraction. The mean age was 52.7þ9.5 years (range 34-78). About one third patients were premenopausal and nearly two third had parity of 3-5. Half of these patients had bulky disease and 30% had ulcero-infilterative or infilterative growth. Two thirds achieved near complete response on clinical examination post external therapy There was 24% inappropriate tandem placement documented with false track formation in 10 cases (11%) and perforation of tandem through uterus in 11 cases (13%) using CT stimulation wherein the applicator were either repositioned on same day or planning optimised based on individual case or plan abandoned. There was tendency of false track formation with ulcero-infilterative growth. Conclusions: This service evaluation suggests that CT simulation (imaging) should be a part of quality assurance in ICBT application as it allows visualization of improperly placed applicator with respect to the patient’s anatomy thereby preventing delivery of inappropriate dose to target and organ at risk especially in teaching training facility. PO41 Outcomes of Uterine Papillary Serous and Uterine Clear Cell Carcinoma Treated with Vaginal-Cylinder Brachytherapy Alone Linda P. Cho, BA1, Kanokpis Townamchai, MD1, Matthias Manuel, MPH1, Larissa J. Lee, MD1,2, Mandar Bhagwat, PhD1, Ivan Buzurovic, PhD1,2, Antonio Damato, PhD1,2, Thomas Harris, MS1, Desmond O’Farrell, MSC1, Akila N. Viswanathan, MD, MPH1,2. 1Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Boston, MA, USA; 2Harvard Medical School, Boston, MA, USA. Purpose: Uterine serous (USC) and clear-cell (CC) carcinomas are both aggressive uterine-cancer histologies. The aim of this study was to analyze local recurrence (LR), distant recurrence (DR), disease-free survival (DFS) and overall survival (OS) among women with those histologic subtypes who received high-dose-rate (HDR) brachytherapy alone as their radiation treatment. Materials and Methods: A total of 154 USC and 35 CC patients were treated with HDR brachytherapy þ/- surgery or chemotherapy from 8/2000 to 7/2014. Exclusions were: stage III disease (76), stage IV (7), and combined use of external beam radiation therapy (43) for a final study population of 63 women, all of whom were treated with CT-guided HDR brachytherapy between 11/2002 and 7/2014. Kaplan-Meier local
control (LC), DFS and OS estimates were calculated. Chi-square statistics were used to assess prognostic factors. Cox regression analyses were performed at a50.05 significance level using JMP PRO 12. Results: Patient and treatment characteristics for the 63 patients were as follows. Fifty (79%) had USC histology and 13 (21%) had CC. FIGO 2009 stages were IA (n546; 73%), IB (n512; 19%) and II (n55; 8%). Median age at diagnosis was 65 and 63 years for USC and CC, respectively. Median total brachytherapy dose was 24 Gy and dose per fraction was 4 Gy for both groups. There were no significant differences in pathologic features or radiation technique between the two groups. However, 67% of the USC and 11% of the CC group received chemotherapy (p50.03). Median follow-up time was 4.0 years (range, 0.21-9). Overall 15 patients (24%) had any recurrence. Of the 6 patients with a vaginal recurrence, 5 (8%) had USC and 1 (2%) had CC. There was 1 pelvic nodal non-vaginal recurrence in a USC patient. Of the 3 patients with para-aortic lymph node recurrence, 2 (3%) had USC and 1 (2%) had CC. Of the 13 women (20%) with any DR, 10 (16%) had USC and 3 (5%) had CC. Of the 11 deaths, 3 (5%) were not attributable to disease. The 4-year tumor control and survival rates for USC and CC, respectively, were: LC, 89% and 90%; DFS, 73% and 66%; and OS, 90% and 89% (all pO0.2). Age, as a continuous variable, was the only significant predictor for overall survival (p50.034, HR51.08, 95% CI51.01-1.17). For every one year increase in age, the risk for death increased by 8%. Age was not a significant predictor for recurrence. Myometrial invasion, stage, lymphovascular invasion, washings, presence of an endometrial polyp, median cylinder diameter, total brachytherapy dose, dose per fraction and the use of chemotherapy were not associated with recurrence or survival on univariate analysis. There were too few events to conduct a multivariate analysis. Conclusion: Given the aggressive nature of the USC and CC histologic subtypes, these results show excellent local control and overall survival for women who received HDR brachytherapy as the sole radiation treatment. Age was the only significant predictor for overall survival in the population as a whole. There was no difference in DFS or OS between USC and CC patients. Future studies with larger USC and CC populations are warranted.
PO42 Organ at Risk Dose in Cervical Cancer HDR Brachytherapy-Correlation between Predicted Dose on MRI Scan and Calculated Dose on CBCT Dorte Klitgaard, MSci, Trine Juhler-Nøttrup, PhD. Dept of Oncology, Copenhagen University Hospital, Herlev, Denmark. Purpose: MRI based IGRT is widely used for cervical cancer brachytherapy. This allows individual doseplanning taking into account both optimal target coverage and reduced dose to organs at risk. During the time gap between MRI and dose delivery the organs at risk may change shape and then alter the actual delivered dose. We hypothesize that the actual delivered dose to the organs at risk is a better predictor for toxicity than the predicted dose. Materials and Methods: The evaluated cases were obtained from our local brachytherapy database from 2013. Our doseschedule was based on EBRT 25 or 30 F, 2Gy/fx, 5f/w (all IMRT) and BT with HDR, 5F, 2f/w. Doseplanning aim for HR-CTV was D95O90Gy in EQD2. Our planning and algorithm was to make an MRI scan before the first treatment without an applicator for the purpose of a preplan. At the first treatment the preplanned dose was delivered and afterwards the patient was transferred immediately to the MRI scanner with the applicator in place. This MRI scan was used to evaluate if the preplan had sufficient target coverage and organ at risk sparring. Often modifications were made for the following four fractions. At every fraction immediately before treatment a CBCT was performed on the treatment couch with a C-arm. Contrast fluid was installed in the bladder (40 ml) and in the rectum (40 ml). The MRI scans and CBCT scans were imported into the OncentraÔ planning system. Organs at risk were contoured on the CBCT scan. All contours were made by the same observer. Results: 11 consecutive patients were evaluated retrospectively. Two patients only had an MRI scan without applicator and this scan was used for the predicted dose to OAR. Six patients had an MRI scan without
Abstracts / Brachytherapy 15 (2016) S21eS204 applicator and one MRI with applicator at the first treatment. For these six patients the preplan was applied on the MRI with the applicator and the actual dose to OAR was measured for fraction no. 1. If the plan was adapted then the adapted dose to OAR was used to predict OAR dose for fraction no. 2, 3, 4 and 5. Three patients had additional MRI scans because plan modifications were needed and the doses to the OAR from the modified plans were used in the calculations. Nine patients had CBCT scans before each of the 5 fractions, two patients missed one CBCT due to malfunctioning of the equipment. In the attached graph the predicted dose from the MRI scans and the actual delivered dose to the OAR are depicted. The predicted median dose to the bladder was 88.1Gy, the actual dose was 81.4Gy, for all but two patients the predicted dose was higher than the delivered dose. The median difference in bladder dose was þ9.2Gy. The predicted median dose to the rectum was 72.1Gy, the actual dose was 71.1Gy, there were an even distribution of over and under prediction of doses. The median difference in rectum dose was -0.4Gy. The predicted median dose to the sigmoid was 72Gy, the actual dose was 72.3Gy, there were an even distribution of over and under prediction of doses. The median difference in sigmoid dose was -0.3Gy. We found that bladder volume was very variable and might be the reason why the bladder dose was the most difficult to predict. Due to the small no. of patients and the retrospective design we did not correlate the toxicity to our findings. Conclusions: We found that predicted doses to rectum and sigmoid were closely correlated from planning MRI scans to CBCT at dose delivery in HDR for cervical cancer. We also found that predicted doses to bladder were higher than actual delivered doses in HDR for cervical cancer. This study leads us to optimize our bladder filling protocol and we are redoing our measures using more reproducible settings combined with prospective evaluations of Patient Reported Outcomes.
S121
Materials and Methods: Treatment planning on data sets with cylinder diameters 3.5, 3.0, 2.5, and 2.0 cm, a treatment length of 7.5 cm, and prescription to the cylinder surface was completed using Oncentra Brachy treatment planning system, Version 4.3.0.410 (Elekta Brachytherapy). On each data set a plan was created using standard optimization point distance from dwell positions mirroring the prescription depth. An alternative plan was created using optimization points placed 0.5 cm closer to the dwell positions. The surface of the treated area of the cylinder þ/- 0.1 cm was contoured as the cylinder surface, and the plans were evaluated for dose conformality to this structure. Results: The treatment plan with optimization points closer to the dwell positions appears to conform more precisely to the application surface. In particular, the 100% isodose line more closely follows the domed shape at the terminus of the cylinder (Figure 1). Quantitatively, the DVH reveals reduced hot spots on the cylinder surface. The volume of surface for the standard optimization receiving 110% and 125% dropped on average by 33.9% and 40.4%, respectively, with the new optimization. Low dose coverage changed as well, with the V80 decreasing on average by 0.8% under the alternative plan. This decrease in coverage occurs at the connector end of the cylinder. Conclusions: Default positioning of dose optimization points matching the prescription distance from dwell positions should be reconsidered in favor of that same depth minus 0.5 cm, which provides improved dose distributions. This conclusion can be generalized to other cylinder parameters.
PO44 PO43 Improved Dose Conformality in Non-Image Based Treatment Planning for Vaginal Cylinders Using Shallower Dose Optimization Points Thomas Harris, MS, Mandar Bhagwat, PhD, Antonio Damato, PhD, Desmond O’Farrell, MSc, Scott Friesen, MS, Jorgen Hansen, MS, Larissa Lee, MD, Akila Viswanathan, MD, MPH, Phillip Devlin, MD, Robert Cormack, PhD, Ivan Buzurovic, PhD. Radiation Oncology, Dana Farber/Brigham and Women’s Cancer Center, Boston, MA, USA. Purpose: Dose optimization for straight line vaginal cylinder treatment planning is generally accomplished by creating optimization points along the axis of the cylinder and matching the dwell positions at a distance corresponding to the prescription depth. This study investigates whether a different arrangement of optimization points can yield a more conformal dose distribution.
Dosimetric Analysis of an Additional Rectal Point in Cervical HDR Brachytherapy Claire Dempsey, PhD1, Lori Young, PhD1, Juergen Meyer, PhD1, Ning Cao, PhD1, Alan Kalet, PhD1, Myra Lavilla, CMD2, Hannah Richardson, CMD2, Darrin Nikolaisen, CMD2, Randall McClure, RTT2, Nina Mayr, MD1, Wui-Jin Koh, MD1. 1Department of Radiation Oncology, University of Washington, Seattle, WA, USA; 2Department of Radiation Oncology, Seattle Cancer Care Alliance, Seattle, WA, USA. Purpose: New GEC-ESTRO/ICRU/ABS recommendations continue to endorse reporting and plan optimization for the ICRU rectal point, while D2cc and D0.1cc volumetric doses to the rectum should also now be considered. Good correlation between the ICRU point dose and D2cc dose has been shown in the past but to date there has been no point-dose to volumetric-dose comparisons for other, single dose points in the rectum. This retrospective analysis aimed to test the correlation and
Abstracts / Brachytherapy 15 (2016) S21eS204
translates into better local control and organ sparing. One may also conjecture that experienced practioners are more likely to properly place the applicators. Although 3D imaging modalities for ICBT planning facilitate actual anatomical brachytherapy planning and actual geometry of applicators in-situ with respect to the patient’s anatomy however in a high throughput Indian facility applicators are generally placed without any aid of image guidance and orthogonal X-ray film simulation is still standard method for dosimetric calculation of brachytherapy that completely lacks any information about positioning of applicators in-situ with regard to anatomical variations. The problem is further compounded in teaching training departments where applicators are implanted by variable trained individuals. Purpose/Aim of Study: The present service evaluation was carried out to document the inappropriate placement of tandem using CT simulation. Material and Methods: All radically treated histopathologically proven cervical cancer patients who underwent ICBT using CT simulation by varied in training practioners were studied. After brachytherapy applicator insertion, patients were shifted to CT scanner and whole pelvis non contrast CT images were acquired. After acquiring the axial CT images 3D reconstruction in axial, coronal and sagittal planes were performed and images were analyzed to assess proper placement of tandem during the first brachytherapy application as is the practice in the department to ensure precision of applicator placement before proceeding for dosimetric planning and treatment. In case of inappropriate applicator/tandem placement the procedure was either abandoned or applicator repositioned and corrected before acquiring the simulation image for dosimetric estimation and treatment or planning optimisation done based on individual case. Results: 84 patients of cervical cancer, FIGO Stage I-IV were radically treated by external radiation therapy with or without chemotherapy and HDR brachytherapy 6Gy/fraction in 3 to 4fraction. The mean age was 52.7þ9.5 years (range 34-78). About one third patients were premenopausal and nearly two third had parity of 3-5. Half of these patients had bulky disease and 30% had ulcero-infilterative or infilterative growth. Two thirds achieved near complete response on clinical examination post external therapy There was 24% inappropriate tandem placement documented with false track formation in 10 cases (11%) and perforation of tandem through uterus in 11 cases (13%) using CT stimulation wherein the applicator were either repositioned on same day or planning optimised based on individual case or plan abandoned. There was tendency of false track formation with ulcero-infilterative growth. Conclusions: This service evaluation suggests that CT simulation (imaging) should be a part of quality assurance in ICBT application as it allows visualization of improperly placed applicator with respect to the patient’s anatomy thereby preventing delivery of inappropriate dose to target and organ at risk especially in teaching training facility. PO41 Outcomes of Uterine Papillary Serous and Uterine Clear Cell Carcinoma Treated with Vaginal-Cylinder Brachytherapy Alone Linda P. Cho, BA1, Kanokpis Townamchai, MD1, Matthias Manuel, MPH1, Larissa J. Lee, MD1,2, Mandar Bhagwat, PhD1, Ivan Buzurovic, PhD1,2, Antonio Damato, PhD1,2, Thomas Harris, MS1, Desmond O’Farrell, MSC1, Akila N. Viswanathan, MD, MPH1,2. 1Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Boston, MA, USA; 2Harvard Medical School, Boston, MA, USA. Purpose: Uterine serous (USC) and clear-cell (CC) carcinomas are both aggressive uterine-cancer histologies. The aim of this study was to analyze local recurrence (LR), distant recurrence (DR), disease-free survival (DFS) and overall survival (OS) among women with those histologic subtypes who received high-dose-rate (HDR) brachytherapy alone as their radiation treatment. Materials and Methods: A total of 154 USC and 35 CC patients were treated with HDR brachytherapy þ/- surgery or chemotherapy from 8/2000 to 7/2014. Exclusions were: stage III disease (76), stage IV (7), and combined use of external beam radiation therapy (43) for a final study population of 63 women, all of whom were treated with CT-guided HDR brachytherapy between 11/2002 and 7/2014. Kaplan-Meier local
control (LC), DFS and OS estimates were calculated. Chi-square statistics were used to assess prognostic factors. Cox regression analyses were performed at a50.05 significance level using JMP PRO 12. Results: Patient and treatment characteristics for the 63 patients were as follows. Fifty (79%) had USC histology and 13 (21%) had CC. FIGO 2009 stages were IA (n546; 73%), IB (n512; 19%) and II (n55; 8%). Median age at diagnosis was 65 and 63 years for USC and CC, respectively. Median total brachytherapy dose was 24 Gy and dose per fraction was 4 Gy for both groups. There were no significant differences in pathologic features or radiation technique between the two groups. However, 67% of the USC and 11% of the CC group received chemotherapy (p50.03). Median follow-up time was 4.0 years (range, 0.21-9). Overall 15 patients (24%) had any recurrence. Of the 6 patients with a vaginal recurrence, 5 (8%) had USC and 1 (2%) had CC. There was 1 pelvic nodal non-vaginal recurrence in a USC patient. Of the 3 patients with para-aortic lymph node recurrence, 2 (3%) had USC and 1 (2%) had CC. Of the 13 women (20%) with any DR, 10 (16%) had USC and 3 (5%) had CC. Of the 11 deaths, 3 (5%) were not attributable to disease. The 4-year tumor control and survival rates for USC and CC, respectively, were: LC, 89% and 90%; DFS, 73% and 66%; and OS, 90% and 89% (all pO0.2). Age, as a continuous variable, was the only significant predictor for overall survival (p50.034, HR51.08, 95% CI51.01-1.17). For every one year increase in age, the risk for death increased by 8%. Age was not a significant predictor for recurrence. Myometrial invasion, stage, lymphovascular invasion, washings, presence of an endometrial polyp, median cylinder diameter, total brachytherapy dose, dose per fraction and the use of chemotherapy were not associated with recurrence or survival on univariate analysis. There were too few events to conduct a multivariate analysis. Conclusion: Given the aggressive nature of the USC and CC histologic subtypes, these results show excellent local control and overall survival for women who received HDR brachytherapy as the sole radiation treatment. Age was the only significant predictor for overall survival in the population as a whole. There was no difference in DFS or OS between USC and CC patients. Future studies with larger USC and CC populations are warranted.
PO42 Organ at Risk Dose in Cervical Cancer HDR Brachytherapy-Correlation between Predicted Dose on MRI Scan and Calculated Dose on CBCT Dorte Klitgaard, MSci, Trine Juhler-Nøttrup, PhD. Dept of Oncology, Copenhagen University Hospital, Herlev, Denmark. Purpose: MRI based IGRT is widely used for cervical cancer brachytherapy. This allows individual doseplanning taking into account both optimal target coverage and reduced dose to organs at risk. During the time gap between MRI and dose delivery the organs at risk may change shape and then alter the actual delivered dose. We hypothesize that the actual delivered dose to the organs at risk is a better predictor for toxicity than the predicted dose. Materials and Methods: The evaluated cases were obtained from our local brachytherapy database from 2013. Our doseschedule was based on EBRT 25 or 30 F, 2Gy/fx, 5f/w (all IMRT) and BT with HDR, 5F, 2f/w. Doseplanning aim for HR-CTV was D95O90Gy in EQD2. Our planning and algorithm was to make an MRI scan before the first treatment without an applicator for the purpose of a preplan. At the first treatment the preplanned dose was delivered and afterwards the patient was transferred immediately to the MRI scanner with the applicator in place. This MRI scan was used to evaluate if the preplan had sufficient target coverage and organ at risk sparring. Often modifications were made for the following four fractions. At every fraction immediately before treatment a CBCT was performed on the treatment couch with a C-arm. Contrast fluid was installed in the bladder (40 ml) and in the rectum (40 ml). The MRI scans and CBCT scans were imported into the OncentraÔ planning system. Organs at risk were contoured on the CBCT scan. All contours were made by the same observer. Results: 11 consecutive patients were evaluated retrospectively. Two patients only had an MRI scan without applicator and this scan was used for the predicted dose to OAR. Six patients had an MRI scan without
Abstracts / Brachytherapy 15 (2016) S21eS204 applicator and one MRI with applicator at the first treatment. For these six patients the preplan was applied on the MRI with the applicator and the actual dose to OAR was measured for fraction no. 1. If the plan was adapted then the adapted dose to OAR was used to predict OAR dose for fraction no. 2, 3, 4 and 5. Three patients had additional MRI scans because plan modifications were needed and the doses to the OAR from the modified plans were used in the calculations. Nine patients had CBCT scans before each of the 5 fractions, two patients missed one CBCT due to malfunctioning of the equipment. In the attached graph the predicted dose from the MRI scans and the actual delivered dose to the OAR are depicted. The predicted median dose to the bladder was 88.1Gy, the actual dose was 81.4Gy, for all but two patients the predicted dose was higher than the delivered dose. The median difference in bladder dose was þ9.2Gy. The predicted median dose to the rectum was 72.1Gy, the actual dose was 71.1Gy, there were an even distribution of over and under prediction of doses. The median difference in rectum dose was -0.4Gy. The predicted median dose to the sigmoid was 72Gy, the actual dose was 72.3Gy, there were an even distribution of over and under prediction of doses. The median difference in sigmoid dose was -0.3Gy. We found that bladder volume was very variable and might be the reason why the bladder dose was the most difficult to predict. Due to the small no. of patients and the retrospective design we did not correlate the toxicity to our findings. Conclusions: We found that predicted doses to rectum and sigmoid were closely correlated from planning MRI scans to CBCT at dose delivery in HDR for cervical cancer. We also found that predicted doses to bladder were higher than actual delivered doses in HDR for cervical cancer. This study leads us to optimize our bladder filling protocol and we are redoing our measures using more reproducible settings combined with prospective evaluations of Patient Reported Outcomes.
S121
Materials and Methods: Treatment planning on data sets with cylinder diameters 3.5, 3.0, 2.5, and 2.0 cm, a treatment length of 7.5 cm, and prescription to the cylinder surface was completed using Oncentra Brachy treatment planning system, Version 4.3.0.410 (Elekta Brachytherapy). On each data set a plan was created using standard optimization point distance from dwell positions mirroring the prescription depth. An alternative plan was created using optimization points placed 0.5 cm closer to the dwell positions. The surface of the treated area of the cylinder þ/- 0.1 cm was contoured as the cylinder surface, and the plans were evaluated for dose conformality to this structure. Results: The treatment plan with optimization points closer to the dwell positions appears to conform more precisely to the application surface. In particular, the 100% isodose line more closely follows the domed shape at the terminus of the cylinder (Figure 1). Quantitatively, the DVH reveals reduced hot spots on the cylinder surface. The volume of surface for the standard optimization receiving 110% and 125% dropped on average by 33.9% and 40.4%, respectively, with the new optimization. Low dose coverage changed as well, with the V80 decreasing on average by 0.8% under the alternative plan. This decrease in coverage occurs at the connector end of the cylinder. Conclusions: Default positioning of dose optimization points matching the prescription distance from dwell positions should be reconsidered in favor of that same depth minus 0.5 cm, which provides improved dose distributions. This conclusion can be generalized to other cylinder parameters.
PO44 PO43 Improved Dose Conformality in Non-Image Based Treatment Planning for Vaginal Cylinders Using Shallower Dose Optimization Points Thomas Harris, MS, Mandar Bhagwat, PhD, Antonio Damato, PhD, Desmond O’Farrell, MSc, Scott Friesen, MS, Jorgen Hansen, MS, Larissa Lee, MD, Akila Viswanathan, MD, MPH, Phillip Devlin, MD, Robert Cormack, PhD, Ivan Buzurovic, PhD. Radiation Oncology, Dana Farber/Brigham and Women’s Cancer Center, Boston, MA, USA. Purpose: Dose optimization for straight line vaginal cylinder treatment planning is generally accomplished by creating optimization points along the axis of the cylinder and matching the dwell positions at a distance corresponding to the prescription depth. This study investigates whether a different arrangement of optimization points can yield a more conformal dose distribution.
Dosimetric Analysis of an Additional Rectal Point in Cervical HDR Brachytherapy Claire Dempsey, PhD1, Lori Young, PhD1, Juergen Meyer, PhD1, Ning Cao, PhD1, Alan Kalet, PhD1, Myra Lavilla, CMD2, Hannah Richardson, CMD2, Darrin Nikolaisen, CMD2, Randall McClure, RTT2, Nina Mayr, MD1, Wui-Jin Koh, MD1. 1Department of Radiation Oncology, University of Washington, Seattle, WA, USA; 2Department of Radiation Oncology, Seattle Cancer Care Alliance, Seattle, WA, USA. Purpose: New GEC-ESTRO/ICRU/ABS recommendations continue to endorse reporting and plan optimization for the ICRU rectal point, while D2cc and D0.1cc volumetric doses to the rectum should also now be considered. Good correlation between the ICRU point dose and D2cc dose has been shown in the past but to date there has been no point-dose to volumetric-dose comparisons for other, single dose points in the rectum. This retrospective analysis aimed to test the correlation and