- Email: [email protected]
18FDG PET CT Metabolic Parameters as Useful Prognostic Factors in Cervical Cancer Patients Treated With Chemoradiation Therapy
E272
International Journal of Radiation Oncology Biology Physics
of treatment were then simulated for each patient, based on the use of the different planning, after a pelvic bone registration. Two scenarios corresponded to the intermediate bladder plans (i.e., the standard treatment without ART), with standard and reduced margins. The 2 others corresponded to ART, with standard and reduced margins. The choice of the most appropriate ART planning for each CBCT was based on dosimetric criteria: privileging first the CTV coverage and then, the organ at risk (OAR) sparing. For each scenario, the cumulated doses in the OAR were finally estimated by deforming the dose according to the anatomical variations estimated by deformable image registration (demon algorithm). Wilcoxon test was used to compare values from the different scenarios. Results: The table displays the estimated percentage of the OARs receiving 45 Gy (V45), depending on the treatment scenarios after dose accumulation, for the 8 patients. The sigmoid V45 and the CTV V99 were calculated, from the CBCT, without deformable registration.
coverage was quantified by the ratio of the HR-CTV D90 to the dose delivered to Point A. Results: Mean HR-CTV volumes in the small lesion group and large lesion groups were 13.2 cc (median 11.2 cc) and 56.0 cc (median 48.1 cc), respectively. See table below for the HR-CTV and OAR dosimetric parameters. OAR doses were significantly different when comparing the D90 and point-based plans, with lower OAR doses in the D90 plans for small targets and higher OAR doses in the same plans for large targets. The mean-ratio of the D90 dose to Point A dose was significantly different in the small group (1.43, P<.01) and the large group (0.78, P<.01). Conclusion: For plans prescribed to point A, the HR-CTV D90 was significantly different for both the small and large target groups. For Point A planning, small lesions showed overcoverage of the target, while larger lesions showed undercoverage of the target. In addition to the target overcoverage, the small lesion group OARs showed significantly higher doses when planned to Point A. These results exemplify the shortcomings of the use of a point-based prescription system and reinforce the role of image guided brachytherapy.
Poster Viewing Abstracts 2677; Table 1 Anatomical structures and V45 or V99 (%) (median) Scenarios and margins Planning
Non ART (cumulated)
ART(cumulated)
Standard margins Reduced margins Standard margins Reduced margins Standard margins Reduced margins
Rectum V45
Bladder V45
Small bowel V45
Sigmoid V45
CTV T V99
58,2
27,3
9,1
38,3
100
29,8
11,9
7,9
18,2
100
63,1
22,6
9,78
38,6
99,6
19,7
10,6
6,6
22,5
94,6
60,4
20,9
10,8
33,0
99,7
22,4
9,3
5,6
19,2
98,6
The doses in the OARs are significantly lower in case of ART with reduced margins compared with non-ART with standard margins.
Conclusion: Compared to a standard non-ART, ART with reduced margins in LACC reduces dramatically the dose in the OARs, while treating properly the CTV, and may therefore decrease the risk of genitourinary and gastrointestinal toxicities. Author Disclosure: M. Gobeli: None. A. Simon: None. M. Ge´tain: None. E. Dardelet: None. C. Lafond: None. D. Williaume: None. E. Lahlou: None. R. De Crevoisier: None. J. Leseur: None.
Poster Viewing Abstracts 2678; Table 1 Small Lesions (<25cc)
Point A HRCTV D90 D100 Bladder D2cc D0.1cc Rectum D2cc D0.1cc Sigmoid D2cc D0.1cc
Large Lesions (>25 cc)
Prescription to Point A (Gy)
Prescription to D90 (Gy)
Prescription to Point A (Gy)
Prescription to D90 (Gy)
6.9 0.4
4.8 0.6*
6.6 0.4
9.2 1.8*
9.8 1.1 6.4 1.0
6.9 0.4* 4.6 0.3*
5.2 1.3 2.7 0.8
6.6 0.4* 3.4 0.6*
6.8 2.0 9.0 1.3
4.8 1.1* 6.3 1.8*
5.3 1.2 7.0 1.9
7.2 2.5* 9.7 3.7*
4.3 1.6 5.5 1.1
3.4 0.8* 4.5 1.1*
4.1 1.0 5.4 1.7
5.0 1.4* 6.5 2.1*
3.8 2.8 5.9 1.7
2.6 1.1* 4.0 1.8*
3.98 1.2 5.56 2.0
5.6 2.0 8.0 3.6
(*) indicates p<0.05
Author Disclosure: G. Harmon: None. A.M. Diak: None. S.M. Shea: None. J.H. Yacoub: None. W. Small: None. M.M. Harkenrider: None.
2679 18
2678 Point A Versus D90 in MR-Guided Cervical Brachytherapy of Small and Large Lesions: A Dosimetric Study G. Harmon,1 A.M. Diak,2 S.M. Shea,2 J.H. Yacoub,2 W. Small, Jr,2 and M.M. Harkenrider3; 1Loyola University Chicago, Maywood, IL, 2 Loyola University Medical Center, Maywood, IL, 3Stritch School of Medicine, Loyola University Chicago, Maywood, IL Purpose/Objective(s): To compare tumor coverage and organ-at-risk (OAR) doses in plans prescribed to Point A versus plans prescribed to D90 high-risk clinical target volume (HR-CTV) for patients with either small or large tumors at time of brachytherapy (BT). Materials/Methods: Nine patients with 14 total implants received magnetic resonance (MR)-guided BT for cervical cancer. Patients initially presented for MR-guided BT in which the planning goal was to cover 90% of the HR-CTV with the prescription dose. We retrospectively created alternate plans to deliver the same prescribed dose to Point A by rescaling the plan and adjusting ovoid weighting to match the initial plan. The patients were split into 2 groups: small (<25 cc, NZ8) and large (>25 cc, NZ6) volume HR-CTV. Dosimetric parameters (HR-CTV D90, D100 and OAR D0.1cc, D2cc) were compared between Point A versus HR-CTV plans for both small and large tumor groups. The degree of HR-CTV
FDG PET CT Metabolic Parameters as Useful Prognostic Factors in Cervical Cancer Patients Treated With Chemoradiation Therapy T. Breuneval,1 F. Herrera,1 J.O. Prior,2 J. Bourhis,2 and E.M. Ozsahin1; 1 Lausanne University Hospital, Lausanne, Switzerland, 2Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland Purpose/Objective(s): We compared the prognostic value of different anatomical and functional metabolic parameters determined using 18fluorodeoxyglucose positron emission tomography computed tomography (18FDG PET CT) with other important clinical and pathologic prognostic parameters in cervical cancer. Materials/Methods: Between 2004 and 2014, 38 patients with cervical cancer were treated with chemoradiation therapy (CRT). All patients underwent pre- and post-CRT 18FDG PET CT. Various metabolic/volumebased 18FDG PET CT parameters including tumor standardized uptake values (SUVmax/mean), metabolic tumor volume (MTV), and tumor volume glycolysis (TVG) were measured before CRT. The pre-CRT SUVmean of the total bone marrow was recorded and the post-CRT metabolic response was evaluated. These parameters were compared to other patient and tumor prognostic factors. Survival curves were estimated using the Kaplan Meier method and compared using the log-rank test. To determine the independent contribution of each prognostic factor, Cox regression analysis was performed. Linear regression analysis was used to test the association of different parameters.
Volume 93 Number 3S Supplement 2015 Results: After a median follow-up of 37 months (range, 12-106), overall survival (OS) was 71% (95% confidence interval [CI], 54%-88%), diseasefree survival (DFS) was 61% (95% CI, 44%-78%) and locoregional control (LRC) was 76% (95% CI, 62%-90%). In univariate analyses, 18FDG PET CT parameters unfavorably influencing OS, DFS, and LRC were pre-CRT TVG cutoff 562 g (37% vs 76%, PZ.01; 36% vs 88%, PZ.004; and 65% vs 88%, PZ.04, respectively), pre-CRT tumor SUVmean cutoff 5 (57% vs 86%, PZ.03; 36% vs 88%, PZ.004; 65% vs 88%, PZ.04, respectively) and a partial tumor metabolic response post-CRT (9% vs 29%, PZ.0008; 0 vs 83%, P<.0001; 22% vs 96%, P<.0001, respectively). The pre-CRT total bone marrow metabolism (SUVmean cutoff 0.9) had a statistically significant negative effect on DFS (47% vs 71%, PZ.01). Patients with squamous cell carcinoma had a statistically significant better clinical outcome than patients with adenocarcinoma (OS: 75% vs 50%, PZ.02, DFS 65% vs 26%, PZ.02). After multivariate analyses, post-CRT response measured by 18FDG PET CT uptake remained as an independent prognostic factor negatively influencing OS and LRC (RR 7.7, P.0001, and RR 22.6, PZ.0003, respectively) while the pre-CRT TVG cutoff 562g negatively influenced DFS (RR 2.75, PZ.05). The pre-CRT total bone marrow metabolism increased when the pre-CRT tumor metabolism increased (PZ.002). Conclusion: Parameters capturing the pre-CRT glycolytic volume and metabolic activity of 18FDG positive disease as well as bone marrow metabolism provide important prognostic information in patients with cervical cancer treated with CRT. The post-CRT 18FDG uptake is predictive of disease outcome. Author Disclosure: T. Breuneval: None. F. Herrera: None. J.O. Prior: None. J. Bourhis: None. E. Ozsahin: None.
2680 Analyzing the Correlation Between Pretreatment Rectal Fullness and Dose Delivered to the Rectum When Using HDR-VB in Women With Endometrial Cancer J. Gruhl,1 D. Zheng,1 J.M. Longo,2 C.A. Enke,1 and A.O. Wahl1; 1 University of Nebraska Medical Center, Omaha, NE, 2Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): To determine the association between pretreatment rectal fullness and dose delivered to the rectum in postoperative endometrial cancer patients receiving high-dose-rate vaginal brachytherapy (HDR-VB). Materials/Methods: Seventeen patients received postoperative HDR-VB using a vaginal cylinder and were retrospectively analyzed under IRB approval. The prescription (Rx) dose ranged from 500 to 700 cGy/fraction at 5-mm depth for 3 to 4 fractions, using 25- to 35-mm diameter cylinders treating upper 35 to 55 mm. Prior to each fraction, a CT simulation was performed and treatment planning was completed. The rectum was contoured for each fraction. To represent rectal fullness, the rectal volume on a single slice (all scans had the same 2-mm slice thickness) with the largest rectal diameter identified within the Rx length along the cylinder was chosen. After normalizing the results based on varied Rx doses, the D50, D2cc, D1cc, D0.1cc, and V100 of the rectum were analyzed based on the chosen maximum-diameter rectal volume (VmaxD) using Pearson’s Correlation Coefficient. The data were then grouped into two groups: those fractions with the rectal VmaxD <2cm3, and those >2cm3. The mean D50, D2cc, D1cc, D.1cc, and V100 were calculated for the two separate groups and compared. Results: Fifty-nine fractions were available for analysis. There was a weak positive correlation between increasing rectal fullness (measured by the rectal diameter/volume at the largest point within the treatment cylinder range) for D2cc (correlation coefficientZ.10), D1CC (correlation coefficientZ.09), D.1cc (correlation coefficientZ.07), V100 (correlation coefficientZ.03). There was a negative correlation between increasing rectal fullness and D50 (correlation coefficientZ-.40). For the fractions in the “less full rectum” group (VmaxD<2cm3) the mean D50 rectumZ184.88
Poster Viewing Session E273 cGy, D2ccZ532.51 cGy, D1ccZ572.37 cGy, D.1ccZ688.94 cGy, and V100Z1.00%. For the fractions in the “full rectum group” (VmaxD>2cm3) the mean D50 rectumZ155.91 cGy, D2ccZ549.55cGy, D1ccZ599.19cGy, D.1ccZ703.56cGy, and V100Z1.19%. On average, the dose delivered to the rectum was higher for the “full rectum group” for D2cc (+17.04 cGy), D1cc (+26.82 cGy), D.1cc (+14.62 cGy), V100 (+.19%). However, the average D50 rectum was 28.97cGy lower in the “full rectum group.” Conclusion: It may be unnecessary for patients who receive adjuvant HDR-VB for endometrial cancer to be routinely treated with an empty rectum, based on the weak correlation between rectal fullness and dose delivered to rectum. Although the average dose delivered to the rectum was higher in the “full rectum group,” the differences were quite small (1530 cGy) and the published toxicity rates are low. In disease sites where external beam radiation therapy is combined with HDR-VB, it may be prudent to monitor rectal filling. Author Disclosure: J. Gruhl: None. D. Zheng: None. J.M. Longo: None. C.A. Enke: None. A.O. Wahl: None.
2681 Using 3T MRI to Assess Interfractional Variation of the HR-CTV for HDR Brachytherapy of Cervix Cancer: Is Optimizing Based on the First HR-CTV Appropriate for All Patients? C. Dempsey,1,2 S. Oultram,2 S. Dempsey,1 G. Govindarajulu,2 S. Sridharan,2 P.C. O’Brien,2 and A.L. Capp2; 1University of Newcastle, Newcastle, Australia, 2Calvary Mater Newcastle Hospital, Newcastle, Australia Purpose/Objective(s): Magnetic resonance imaging (MRI)-based highdose-rate (HDR) brachytherapy treatment planning for cervix cancer was introduced in the department in 2011. Since that time, all patients have had MRI for every fraction of treatment. A study has been conducted to determine the physical changes to the size of the high-risk clinical target volume (HR-CTV) as brachytherapy treatment progresses and any changes to dosimetry as a result. Materials/Methods: The treatment records of 56 patients who received HDR brachytherapy using MRI-based treatment planning were assessed. Each patient received 3 fractions, 1 per week of HDR treatment with a total of 168 plans studied. MRI-based plans were generated using a single 3T MR image set (with axis parallel to the intrauterine tube and perpendicular to the ovoids or ring). HR-CTV data as well as dosimetric qualities for each patient plan were gathered and compared for inter-fractional variation. The HR CTV was considered in terms of size and volume with bladder, rectal and sigmoid D2ccdoses also collected. A previous study has already reported that the inter-observer mean variation in HR-CTV contours for the department was 9.2% with a conformity index of 0.80. This has been incorporated into the uncertainty of the statistics presented. Results: On average, the size of the HR-CTV decreased by 5.6 cm3 over the course of brachytherapy, equating to a 22% reduction in the HR-CTV size. This was determined as statistically significant (p<0.02). Only 20% of patients had volumes which increased between fractions however the increase in size was within the measure of uncertainty for HR-CTV contouring in the department. As each fraction was independently planned and optimized for the specific HR-CTV, the HR-CTV D90, bladder, and sigmoid D2cc doses did not significantly change between fractions. Rectal D2cc dose reduced by 9% between brachytherapy fractions. This could be associated with the reduction of the HR-CTV or may be due to changes in rectal filling over the course of treatment. Conclusion: The assumption that the HR-CTV from fraction 1 can be transferred to all HDR brachytherapy fractions may be misguided. In this study, a significant reduction in the HR-CTV was seen between treatment fractions. If this reduction was not taken into consideration during the course of HDR brachytherapy there may have been implications to the organs at risk which lie adjacent to the HR-CTV with an increased risk of over exposing these organs to excessive radiation.
International Journal of Radiation Oncology Biology Physics
of treatment were then simulated for each patient, based on the use of the different planning, after a pelvic bone registration. Two scenarios corresponded to the intermediate bladder plans (i.e., the standard treatment without ART), with standard and reduced margins. The 2 others corresponded to ART, with standard and reduced margins. The choice of the most appropriate ART planning for each CBCT was based on dosimetric criteria: privileging first the CTV coverage and then, the organ at risk (OAR) sparing. For each scenario, the cumulated doses in the OAR were finally estimated by deforming the dose according to the anatomical variations estimated by deformable image registration (demon algorithm). Wilcoxon test was used to compare values from the different scenarios. Results: The table displays the estimated percentage of the OARs receiving 45 Gy (V45), depending on the treatment scenarios after dose accumulation, for the 8 patients. The sigmoid V45 and the CTV V99 were calculated, from the CBCT, without deformable registration.
coverage was quantified by the ratio of the HR-CTV D90 to the dose delivered to Point A. Results: Mean HR-CTV volumes in the small lesion group and large lesion groups were 13.2 cc (median 11.2 cc) and 56.0 cc (median 48.1 cc), respectively. See table below for the HR-CTV and OAR dosimetric parameters. OAR doses were significantly different when comparing the D90 and point-based plans, with lower OAR doses in the D90 plans for small targets and higher OAR doses in the same plans for large targets. The mean-ratio of the D90 dose to Point A dose was significantly different in the small group (1.43, P<.01) and the large group (0.78, P<.01). Conclusion: For plans prescribed to point A, the HR-CTV D90 was significantly different for both the small and large target groups. For Point A planning, small lesions showed overcoverage of the target, while larger lesions showed undercoverage of the target. In addition to the target overcoverage, the small lesion group OARs showed significantly higher doses when planned to Point A. These results exemplify the shortcomings of the use of a point-based prescription system and reinforce the role of image guided brachytherapy.
Poster Viewing Abstracts 2677; Table 1 Anatomical structures and V45 or V99 (%) (median) Scenarios and margins Planning
Non ART (cumulated)
ART(cumulated)
Standard margins Reduced margins Standard margins Reduced margins Standard margins Reduced margins
Rectum V45
Bladder V45
Small bowel V45
Sigmoid V45
CTV T V99
58,2
27,3
9,1
38,3
100
29,8
11,9
7,9
18,2
100
63,1
22,6
9,78
38,6
99,6
19,7
10,6
6,6
22,5
94,6
60,4
20,9
10,8
33,0
99,7
22,4
9,3
5,6
19,2
98,6
The doses in the OARs are significantly lower in case of ART with reduced margins compared with non-ART with standard margins.
Conclusion: Compared to a standard non-ART, ART with reduced margins in LACC reduces dramatically the dose in the OARs, while treating properly the CTV, and may therefore decrease the risk of genitourinary and gastrointestinal toxicities. Author Disclosure: M. Gobeli: None. A. Simon: None. M. Ge´tain: None. E. Dardelet: None. C. Lafond: None. D. Williaume: None. E. Lahlou: None. R. De Crevoisier: None. J. Leseur: None.
Poster Viewing Abstracts 2678; Table 1 Small Lesions (<25cc)
Point A HRCTV D90 D100 Bladder D2cc D0.1cc Rectum D2cc D0.1cc Sigmoid D2cc D0.1cc
Large Lesions (>25 cc)
Prescription to Point A (Gy)
Prescription to D90 (Gy)
Prescription to Point A (Gy)
Prescription to D90 (Gy)
6.9 0.4
4.8 0.6*
6.6 0.4
9.2 1.8*
9.8 1.1 6.4 1.0
6.9 0.4* 4.6 0.3*
5.2 1.3 2.7 0.8
6.6 0.4* 3.4 0.6*
6.8 2.0 9.0 1.3
4.8 1.1* 6.3 1.8*
5.3 1.2 7.0 1.9
7.2 2.5* 9.7 3.7*
4.3 1.6 5.5 1.1
3.4 0.8* 4.5 1.1*
4.1 1.0 5.4 1.7
5.0 1.4* 6.5 2.1*
3.8 2.8 5.9 1.7
2.6 1.1* 4.0 1.8*
3.98 1.2 5.56 2.0
5.6 2.0 8.0 3.6
(*) indicates p<0.05
Author Disclosure: G. Harmon: None. A.M. Diak: None. S.M. Shea: None. J.H. Yacoub: None. W. Small: None. M.M. Harkenrider: None.
2679 18
2678 Point A Versus D90 in MR-Guided Cervical Brachytherapy of Small and Large Lesions: A Dosimetric Study G. Harmon,1 A.M. Diak,2 S.M. Shea,2 J.H. Yacoub,2 W. Small, Jr,2 and M.M. Harkenrider3; 1Loyola University Chicago, Maywood, IL, 2 Loyola University Medical Center, Maywood, IL, 3Stritch School of Medicine, Loyola University Chicago, Maywood, IL Purpose/Objective(s): To compare tumor coverage and organ-at-risk (OAR) doses in plans prescribed to Point A versus plans prescribed to D90 high-risk clinical target volume (HR-CTV) for patients with either small or large tumors at time of brachytherapy (BT). Materials/Methods: Nine patients with 14 total implants received magnetic resonance (MR)-guided BT for cervical cancer. Patients initially presented for MR-guided BT in which the planning goal was to cover 90% of the HR-CTV with the prescription dose. We retrospectively created alternate plans to deliver the same prescribed dose to Point A by rescaling the plan and adjusting ovoid weighting to match the initial plan. The patients were split into 2 groups: small (<25 cc, NZ8) and large (>25 cc, NZ6) volume HR-CTV. Dosimetric parameters (HR-CTV D90, D100 and OAR D0.1cc, D2cc) were compared between Point A versus HR-CTV plans for both small and large tumor groups. The degree of HR-CTV
FDG PET CT Metabolic Parameters as Useful Prognostic Factors in Cervical Cancer Patients Treated With Chemoradiation Therapy T. Breuneval,1 F. Herrera,1 J.O. Prior,2 J. Bourhis,2 and E.M. Ozsahin1; 1 Lausanne University Hospital, Lausanne, Switzerland, 2Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland Purpose/Objective(s): We compared the prognostic value of different anatomical and functional metabolic parameters determined using 18fluorodeoxyglucose positron emission tomography computed tomography (18FDG PET CT) with other important clinical and pathologic prognostic parameters in cervical cancer. Materials/Methods: Between 2004 and 2014, 38 patients with cervical cancer were treated with chemoradiation therapy (CRT). All patients underwent pre- and post-CRT 18FDG PET CT. Various metabolic/volumebased 18FDG PET CT parameters including tumor standardized uptake values (SUVmax/mean), metabolic tumor volume (MTV), and tumor volume glycolysis (TVG) were measured before CRT. The pre-CRT SUVmean of the total bone marrow was recorded and the post-CRT metabolic response was evaluated. These parameters were compared to other patient and tumor prognostic factors. Survival curves were estimated using the Kaplan Meier method and compared using the log-rank test. To determine the independent contribution of each prognostic factor, Cox regression analysis was performed. Linear regression analysis was used to test the association of different parameters.
Volume 93 Number 3S Supplement 2015 Results: After a median follow-up of 37 months (range, 12-106), overall survival (OS) was 71% (95% confidence interval [CI], 54%-88%), diseasefree survival (DFS) was 61% (95% CI, 44%-78%) and locoregional control (LRC) was 76% (95% CI, 62%-90%). In univariate analyses, 18FDG PET CT parameters unfavorably influencing OS, DFS, and LRC were pre-CRT TVG cutoff 562 g (37% vs 76%, PZ.01; 36% vs 88%, PZ.004; and 65% vs 88%, PZ.04, respectively), pre-CRT tumor SUVmean cutoff 5 (57% vs 86%, PZ.03; 36% vs 88%, PZ.004; 65% vs 88%, PZ.04, respectively) and a partial tumor metabolic response post-CRT (9% vs 29%, PZ.0008; 0 vs 83%, P<.0001; 22% vs 96%, P<.0001, respectively). The pre-CRT total bone marrow metabolism (SUVmean cutoff 0.9) had a statistically significant negative effect on DFS (47% vs 71%, PZ.01). Patients with squamous cell carcinoma had a statistically significant better clinical outcome than patients with adenocarcinoma (OS: 75% vs 50%, PZ.02, DFS 65% vs 26%, PZ.02). After multivariate analyses, post-CRT response measured by 18FDG PET CT uptake remained as an independent prognostic factor negatively influencing OS and LRC (RR 7.7, P.0001, and RR 22.6, PZ.0003, respectively) while the pre-CRT TVG cutoff 562g negatively influenced DFS (RR 2.75, PZ.05). The pre-CRT total bone marrow metabolism increased when the pre-CRT tumor metabolism increased (PZ.002). Conclusion: Parameters capturing the pre-CRT glycolytic volume and metabolic activity of 18FDG positive disease as well as bone marrow metabolism provide important prognostic information in patients with cervical cancer treated with CRT. The post-CRT 18FDG uptake is predictive of disease outcome. Author Disclosure: T. Breuneval: None. F. Herrera: None. J.O. Prior: None. J. Bourhis: None. E. Ozsahin: None.
2680 Analyzing the Correlation Between Pretreatment Rectal Fullness and Dose Delivered to the Rectum When Using HDR-VB in Women With Endometrial Cancer J. Gruhl,1 D. Zheng,1 J.M. Longo,2 C.A. Enke,1 and A.O. Wahl1; 1 University of Nebraska Medical Center, Omaha, NE, 2Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): To determine the association between pretreatment rectal fullness and dose delivered to the rectum in postoperative endometrial cancer patients receiving high-dose-rate vaginal brachytherapy (HDR-VB). Materials/Methods: Seventeen patients received postoperative HDR-VB using a vaginal cylinder and were retrospectively analyzed under IRB approval. The prescription (Rx) dose ranged from 500 to 700 cGy/fraction at 5-mm depth for 3 to 4 fractions, using 25- to 35-mm diameter cylinders treating upper 35 to 55 mm. Prior to each fraction, a CT simulation was performed and treatment planning was completed. The rectum was contoured for each fraction. To represent rectal fullness, the rectal volume on a single slice (all scans had the same 2-mm slice thickness) with the largest rectal diameter identified within the Rx length along the cylinder was chosen. After normalizing the results based on varied Rx doses, the D50, D2cc, D1cc, D0.1cc, and V100 of the rectum were analyzed based on the chosen maximum-diameter rectal volume (VmaxD) using Pearson’s Correlation Coefficient. The data were then grouped into two groups: those fractions with the rectal VmaxD <2cm3, and those >2cm3. The mean D50, D2cc, D1cc, D.1cc, and V100 were calculated for the two separate groups and compared. Results: Fifty-nine fractions were available for analysis. There was a weak positive correlation between increasing rectal fullness (measured by the rectal diameter/volume at the largest point within the treatment cylinder range) for D2cc (correlation coefficientZ.10), D1CC (correlation coefficientZ.09), D.1cc (correlation coefficientZ.07), V100 (correlation coefficientZ.03). There was a negative correlation between increasing rectal fullness and D50 (correlation coefficientZ-.40). For the fractions in the “less full rectum” group (VmaxD<2cm3) the mean D50 rectumZ184.88
Poster Viewing Session E273 cGy, D2ccZ532.51 cGy, D1ccZ572.37 cGy, D.1ccZ688.94 cGy, and V100Z1.00%. For the fractions in the “full rectum group” (VmaxD>2cm3) the mean D50 rectumZ155.91 cGy, D2ccZ549.55cGy, D1ccZ599.19cGy, D.1ccZ703.56cGy, and V100Z1.19%. On average, the dose delivered to the rectum was higher for the “full rectum group” for D2cc (+17.04 cGy), D1cc (+26.82 cGy), D.1cc (+14.62 cGy), V100 (+.19%). However, the average D50 rectum was 28.97cGy lower in the “full rectum group.” Conclusion: It may be unnecessary for patients who receive adjuvant HDR-VB for endometrial cancer to be routinely treated with an empty rectum, based on the weak correlation between rectal fullness and dose delivered to rectum. Although the average dose delivered to the rectum was higher in the “full rectum group,” the differences were quite small (1530 cGy) and the published toxicity rates are low. In disease sites where external beam radiation therapy is combined with HDR-VB, it may be prudent to monitor rectal filling. Author Disclosure: J. Gruhl: None. D. Zheng: None. J.M. Longo: None. C.A. Enke: None. A.O. Wahl: None.
2681 Using 3T MRI to Assess Interfractional Variation of the HR-CTV for HDR Brachytherapy of Cervix Cancer: Is Optimizing Based on the First HR-CTV Appropriate for All Patients? C. Dempsey,1,2 S. Oultram,2 S. Dempsey,1 G. Govindarajulu,2 S. Sridharan,2 P.C. O’Brien,2 and A.L. Capp2; 1University of Newcastle, Newcastle, Australia, 2Calvary Mater Newcastle Hospital, Newcastle, Australia Purpose/Objective(s): Magnetic resonance imaging (MRI)-based highdose-rate (HDR) brachytherapy treatment planning for cervix cancer was introduced in the department in 2011. Since that time, all patients have had MRI for every fraction of treatment. A study has been conducted to determine the physical changes to the size of the high-risk clinical target volume (HR-CTV) as brachytherapy treatment progresses and any changes to dosimetry as a result. Materials/Methods: The treatment records of 56 patients who received HDR brachytherapy using MRI-based treatment planning were assessed. Each patient received 3 fractions, 1 per week of HDR treatment with a total of 168 plans studied. MRI-based plans were generated using a single 3T MR image set (with axis parallel to the intrauterine tube and perpendicular to the ovoids or ring). HR-CTV data as well as dosimetric qualities for each patient plan were gathered and compared for inter-fractional variation. The HR CTV was considered in terms of size and volume with bladder, rectal and sigmoid D2ccdoses also collected. A previous study has already reported that the inter-observer mean variation in HR-CTV contours for the department was 9.2% with a conformity index of 0.80. This has been incorporated into the uncertainty of the statistics presented. Results: On average, the size of the HR-CTV decreased by 5.6 cm3 over the course of brachytherapy, equating to a 22% reduction in the HR-CTV size. This was determined as statistically significant (p<0.02). Only 20% of patients had volumes which increased between fractions however the increase in size was within the measure of uncertainty for HR-CTV contouring in the department. As each fraction was independently planned and optimized for the specific HR-CTV, the HR-CTV D90, bladder, and sigmoid D2cc doses did not significantly change between fractions. Rectal D2cc dose reduced by 9% between brachytherapy fractions. This could be associated with the reduction of the HR-CTV or may be due to changes in rectal filling over the course of treatment. Conclusion: The assumption that the HR-CTV from fraction 1 can be transferred to all HDR brachytherapy fractions may be misguided. In this study, a significant reduction in the HR-CTV was seen between treatment fractions. If this reduction was not taken into consideration during the course of HDR brachytherapy there may have been implications to the organs at risk which lie adjacent to the HR-CTV with an increased risk of over exposing these organs to excessive radiation.