- Email: [email protected]
Quality Assurance of Multifractionated Pelvic Interstitial Brachytherapy for Gynecologic Cancers
S60
Abstracts / Brachytherapy 10 (2011) S14eS101
HDR BT treatment are similar. However, the employment of PDR BT is beneficial due to a statistically significant reduction in the number of late radiation morbidity, compared with high-dose- rate brachytherapy (p 5 0.0376).
PD48 CT-Based 3-Dimensional Dose Planning in the Delivery of Vaginal Brachytherapy: New Instrumentation and Technique Rakesh Patel, MD1, Robert Sinha, MD1, Jennifer Scharff, MS1, Gail Lebovic, MD2. 1El Camino Hospital Cancer Center, Mountain View, CA; 2 American Society of Breast Disease, Dallas, TX. Purpose: CT-based 3-dimensional volumetric dose planning, when used with multichannel brachytherapy applicators, has demonstrated utility in certain settings such as in the post-lumpectomy treatment of breast cancer. A parallel situation exists for patients in need of transvaginal brachytherapy (e.g. post-hysterectomy for endometrial cancer). The purpose of this study is to evaluate the feasibility of this approach, using a new flexible, expandable applicator for vaginal cuff brachytherapy. Materials and Methods: Patients were identified as candidates for transvaginal brachytherapy in accordance with current FIGO guidelines. In 14 cases, a flexible, multi-lumen expandable vaginal applicator (CAPRI applicator) was inserted into the introitus in a low profile configuration, advanced to the vaginal vault and then expanded in-situ with saline until the device was held firmly in the vaginal canal. A pelvic brachytherapy external compression garment was used to help secure the applicator in position. No Foley or rectal catheters were used. The pelvic area was imaged via CT and a 3-dimensional dose plan was created, using an evenly spaced array of up to 13 available source lumens within the applicator. Bladder and rectum were fully contoured. The target volume was nominally a 5mm expansion of the applicator surface, with localized reductions (2e4mm expansions) at regions immediately adjacent to the bladder and rectum. Coverage was 90/100. After simulation, the patient returned on subsequent alternate days for applicator placement and dose delivery. Applicator position was monitored closely, with regard to any potential intra-fraction changes in applicator depth, rotation, fill volume and diameter. Dose was delivered via a remote high-dose-rate afterloader in accordance with relevant dose and fractionation schemes (e.g. 700cGy to depth x 3). Results: CTebased 3-dimensional dose planning with the flexible, expandable multi-lumen applicator provided for an anatomically conformal dose delivery. Monitoring of applicator position confirmed intra-fraction consistency, thereby allowing the same dose plan to be administered to that patient on subsequent fractions. Simulation and dose delivery were well tolerated by the patients and were easily adopted by the nursing, dosimetry and physics staff. Avoidance of the rigid applicator clamp and other indwelling catheters expedited applicator placement and contributed to patient comfort. Conclusions: CTebased 3-dimensional dose planning, when used with a new flexible, expandable multi-lumen vaginal applicator is feasible and allows for highly conformal dose delivery to the targeted tissue. Well received by patients and brachytherapy technical staff, this approach may play an increasing role in the treatment of endometrial cancers and other cancers that benefit from vaginal brachytherapy.
PD49 A New Predictive Model for Target Tissue and Critical Sturcture Dosimetry in the Application of ABS Guidelines for HDR Brachytherapy for Cervical Cancer Moataz N. El-Ghamry, MD1, Jianmin Pan, PhD2, Anthony E. Dragun, MD1, Shesh N. Rai, PhD2, Keith Sowards, MS1. 1Radiation Oncology, University of Louisville, Brown Cancer Center, Louisville, KY; 2 Biostatistics, University of Louisville, Brown Cancer Center, Louisville, KY. Purpose: HDR brachytherapy has been widely used in the past 2 decades in the management of cervical cancer. ABS and GEC-ESTRO HDR guidelines
are widely used for optimal treatment planning. The purpose of this study is to generate a comprehensive predictive model for target tissue and critical structure dosimetry in the application of HDR brachytherapy for cervical cancer using ABS guidelines. Materials and Methods: Using a model CT scan of a previously treated patient, we performed virtual HDR planning for 36 different scenarios when using the covariates: tandem lengths (TL) of 4.0, 6.0, and 8.0cm; tandem angles in relation to the patient’s central axis (TA) of 00, 150, and 300; and ovoid sizes (OS) of 1.6 cm (mini); 2.0 cm (small); 2.5 cm (medium); and 3.0 cm (Large). Dosimetric points for nine separate response variables were captured, including the ICRU points for bladder, rectal, bilateral vaginal and bilateral ‘‘point B,’’ as well as the D2cc of rectum, bladder and sigmoid colon. All plans optimized to 700cGy to ABS point H. Generalized Linear Model (GLM) was used to examine the effect of combinations. Results: Table 1 outlines the coefficients of the relationship between the covariates (TL, TA, OS) and the variable responses (point doses for ICRU and D2cc). The variable responses could be predicted by the following formula (response5intercept þxTLþyTAþzOS), e.g., D2cc bladder when using TL 6 cm, TA 150 and medium OS 5 386.64þ2.63þ28.95þ45 5 463cGy. By using bladder D2cc values as an example of correlation between the actual values and the predicted values. We found a linear relationship between the actual bladder D2cc and the predicted D2cc (R2 50.87). Response Bladder Rectum Sigmoid Vaginal Vaginal Point Covariate D2cc D2cc D2cc RT LT B Lt Intercept TL 4cm TL 6cm TL 8cm TA 0 deg TA 15 deg TA 30 deg mini ovd. small ovd. Medium ovd Large ovd.
386.64 -3.20 2.63 0 -16.89 28.95 0 -45.58 0 45.00
300.72 4.90 4.07 0 -5.67 15.16 0 -47.34 0 71.11
243.58 -46.95 -13.20 0 24.36 -16.89 0 -3.36 0 7.78
92.87
138.68
14.53
Point B Rt
1212.57 1190.28 258.87 214.40 3.82 30.39 -81.67 -25.33 3.66 12.53 -25.76 -6.58 0 0 0 0 -33.14 26.65 -41.48 18.86 -4.14 -31.64 66.52 -9.56 0 0 0 0 90.06 91.52 -5.83 -15.05 0 0 0 0 -59.42 -74.75 10.56 21.89 -109.64 -148.84
24.93 49.36
Conclusions: The GLM and the above mentioned formula is a clinicallypractical predictive tool for the evaluation of HDR treatment plans using ABS criteria. This model may be most useful in detecting faulty optimization processes during routine HDR treatment planning. Further clinical study is warranted for validation of this model.
PD50 Quality Assurance of Multifractionated Pelvic Interstitial Brachytherapy for Gynecologic Cancers Pragya Shukla, MD1, Supriya Chopra, MD2, Reena Engineer, DNB1, Umesh Mahantshetty, MD1, Jamema Sv, DRP1, Shyam Kishore Shrivastava, MD1. 1Radiation Oncology and Medical Physics, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India; 2 Radiation Oncology, Advanced Centre for Cancer Treatment Education and Research (ACTREC), Tata Memorial Centre, Navi Mumbai, Maharashtra, India. Purpose: Multifractionated pelvic interstitial brachytherapy is used either for boost or for radical re-irradition of gynecologic cancers. This study was designed to prospectively evaluate 3-D displacements during brachytherapy. Materials and Methods: From Nov. ‘09- Sept. ‘10 patients scheduled to undergo boost or re-irradiation with Martinez Universal Perineal
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
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
Abstracts / Brachytherapy 10 (2011) S14eS101
HDR BT treatment are similar. However, the employment of PDR BT is beneficial due to a statistically significant reduction in the number of late radiation morbidity, compared with high-dose- rate brachytherapy (p 5 0.0376).
PD48 CT-Based 3-Dimensional Dose Planning in the Delivery of Vaginal Brachytherapy: New Instrumentation and Technique Rakesh Patel, MD1, Robert Sinha, MD1, Jennifer Scharff, MS1, Gail Lebovic, MD2. 1El Camino Hospital Cancer Center, Mountain View, CA; 2 American Society of Breast Disease, Dallas, TX. Purpose: CT-based 3-dimensional volumetric dose planning, when used with multichannel brachytherapy applicators, has demonstrated utility in certain settings such as in the post-lumpectomy treatment of breast cancer. A parallel situation exists for patients in need of transvaginal brachytherapy (e.g. post-hysterectomy for endometrial cancer). The purpose of this study is to evaluate the feasibility of this approach, using a new flexible, expandable applicator for vaginal cuff brachytherapy. Materials and Methods: Patients were identified as candidates for transvaginal brachytherapy in accordance with current FIGO guidelines. In 14 cases, a flexible, multi-lumen expandable vaginal applicator (CAPRI applicator) was inserted into the introitus in a low profile configuration, advanced to the vaginal vault and then expanded in-situ with saline until the device was held firmly in the vaginal canal. A pelvic brachytherapy external compression garment was used to help secure the applicator in position. No Foley or rectal catheters were used. The pelvic area was imaged via CT and a 3-dimensional dose plan was created, using an evenly spaced array of up to 13 available source lumens within the applicator. Bladder and rectum were fully contoured. The target volume was nominally a 5mm expansion of the applicator surface, with localized reductions (2e4mm expansions) at regions immediately adjacent to the bladder and rectum. Coverage was 90/100. After simulation, the patient returned on subsequent alternate days for applicator placement and dose delivery. Applicator position was monitored closely, with regard to any potential intra-fraction changes in applicator depth, rotation, fill volume and diameter. Dose was delivered via a remote high-dose-rate afterloader in accordance with relevant dose and fractionation schemes (e.g. 700cGy to depth x 3). Results: CTebased 3-dimensional dose planning with the flexible, expandable multi-lumen applicator provided for an anatomically conformal dose delivery. Monitoring of applicator position confirmed intra-fraction consistency, thereby allowing the same dose plan to be administered to that patient on subsequent fractions. Simulation and dose delivery were well tolerated by the patients and were easily adopted by the nursing, dosimetry and physics staff. Avoidance of the rigid applicator clamp and other indwelling catheters expedited applicator placement and contributed to patient comfort. Conclusions: CTebased 3-dimensional dose planning, when used with a new flexible, expandable multi-lumen vaginal applicator is feasible and allows for highly conformal dose delivery to the targeted tissue. Well received by patients and brachytherapy technical staff, this approach may play an increasing role in the treatment of endometrial cancers and other cancers that benefit from vaginal brachytherapy.
PD49 A New Predictive Model for Target Tissue and Critical Sturcture Dosimetry in the Application of ABS Guidelines for HDR Brachytherapy for Cervical Cancer Moataz N. El-Ghamry, MD1, Jianmin Pan, PhD2, Anthony E. Dragun, MD1, Shesh N. Rai, PhD2, Keith Sowards, MS1. 1Radiation Oncology, University of Louisville, Brown Cancer Center, Louisville, KY; 2 Biostatistics, University of Louisville, Brown Cancer Center, Louisville, KY. Purpose: HDR brachytherapy has been widely used in the past 2 decades in the management of cervical cancer. ABS and GEC-ESTRO HDR guidelines
are widely used for optimal treatment planning. The purpose of this study is to generate a comprehensive predictive model for target tissue and critical structure dosimetry in the application of HDR brachytherapy for cervical cancer using ABS guidelines. Materials and Methods: Using a model CT scan of a previously treated patient, we performed virtual HDR planning for 36 different scenarios when using the covariates: tandem lengths (TL) of 4.0, 6.0, and 8.0cm; tandem angles in relation to the patient’s central axis (TA) of 00, 150, and 300; and ovoid sizes (OS) of 1.6 cm (mini); 2.0 cm (small); 2.5 cm (medium); and 3.0 cm (Large). Dosimetric points for nine separate response variables were captured, including the ICRU points for bladder, rectal, bilateral vaginal and bilateral ‘‘point B,’’ as well as the D2cc of rectum, bladder and sigmoid colon. All plans optimized to 700cGy to ABS point H. Generalized Linear Model (GLM) was used to examine the effect of combinations. Results: Table 1 outlines the coefficients of the relationship between the covariates (TL, TA, OS) and the variable responses (point doses for ICRU and D2cc). The variable responses could be predicted by the following formula (response5intercept þxTLþyTAþzOS), e.g., D2cc bladder when using TL 6 cm, TA 150 and medium OS 5 386.64þ2.63þ28.95þ45 5 463cGy. By using bladder D2cc values as an example of correlation between the actual values and the predicted values. We found a linear relationship between the actual bladder D2cc and the predicted D2cc (R2 50.87). Response Bladder Rectum Sigmoid Vaginal Vaginal Point Covariate D2cc D2cc D2cc RT LT B Lt Intercept TL 4cm TL 6cm TL 8cm TA 0 deg TA 15 deg TA 30 deg mini ovd. small ovd. Medium ovd Large ovd.
386.64 -3.20 2.63 0 -16.89 28.95 0 -45.58 0 45.00
300.72 4.90 4.07 0 -5.67 15.16 0 -47.34 0 71.11
243.58 -46.95 -13.20 0 24.36 -16.89 0 -3.36 0 7.78
92.87
138.68
14.53
Point B Rt
1212.57 1190.28 258.87 214.40 3.82 30.39 -81.67 -25.33 3.66 12.53 -25.76 -6.58 0 0 0 0 -33.14 26.65 -41.48 18.86 -4.14 -31.64 66.52 -9.56 0 0 0 0 90.06 91.52 -5.83 -15.05 0 0 0 0 -59.42 -74.75 10.56 21.89 -109.64 -148.84
24.93 49.36
Conclusions: The GLM and the above mentioned formula is a clinicallypractical predictive tool for the evaluation of HDR treatment plans using ABS criteria. This model may be most useful in detecting faulty optimization processes during routine HDR treatment planning. Further clinical study is warranted for validation of this model.
PD50 Quality Assurance of Multifractionated Pelvic Interstitial Brachytherapy for Gynecologic Cancers Pragya Shukla, MD1, Supriya Chopra, MD2, Reena Engineer, DNB1, Umesh Mahantshetty, MD1, Jamema Sv, DRP1, Shyam Kishore Shrivastava, MD1. 1Radiation Oncology and Medical Physics, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India; 2 Radiation Oncology, Advanced Centre for Cancer Treatment Education and Research (ACTREC), Tata Memorial Centre, Navi Mumbai, Maharashtra, India. Purpose: Multifractionated pelvic interstitial brachytherapy is used either for boost or for radical re-irradition of gynecologic cancers. This study was designed to prospectively evaluate 3-D displacements during brachytherapy. Materials and Methods: From Nov. ‘09- Sept. ‘10 patients scheduled to undergo boost or re-irradiation with Martinez Universal Perineal
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
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