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Evaluation of Applicator Geometry and Impact on Reference Point and Organ Volume Dose (D2cc) in the Era of 3-Dimensional Imaging for Cervical Cancer Brachytherapy
E262
International Journal of Radiation Oncology Biology Physics
2651
patients with cervical cancer. Criteria for proper placement have been described based on 2-dimensional imaging. In the era of 3-dimensional (3D) imaging, both International Commission on Radiation Units and Measurements (ICRU) reference points and minimum dose to 2 cc volume receiving the highest dose (D2cc) are used to evaluate postimplant dosimetry. The purpose of this study was to evaluate the impact of applicator position in the pelvis and patient anatomy on ICRU reference point dose and OAR D2cc using 3D imaging in cervical cancer patients. Materials/Methods: Forty-five thin-slice pelvic computed tomography (CT) scans from 15 patients with cervical cancer (1 IB1, 3 IB2, 1 IIA1, 3 IIA2, 6 IIB, and 1 IIIB) having 3 high-dose-rate ICBT applications of 8 Gy to point A following external beam radiation therapy (EBRT) were reviewed. Applicator consisted of Fletcher tandem and ovoids. Applicator geometry was evaluated using consensus guideline parameters. Anatomic parameters included uterus thickness and uterus and bladder volume. Dose to rectal (RP) and bladder (BP) ICRU reference point and physiciancontoured OAR (bladder, rectum, small bowel, and sigmoid colon) D2cc were determined for each fraction. Mixed linear regression model with Bonferroni correction was used to determine the effect of applicator position and patient anatomy on OAR D2cc and ratio of OAR reference point dose and D2cc. Results: Median tandem length, curvature, and ovoid size were 6 cm, 30 degrees, and 2.5 cm, respectively. Increased uterus volume decreased small bowel D2cc (PZ.002). Increased uterus thickness decreased RP dose (P<.001) and bladder D2cc (P<.001). Increased rectal packing decreased RP dose (P<.001). Mean ratio of bladder point dose to D2cc was 0.760.39. Mean ratio of rectum point dose to D2cc was 1.210.58. Increased cranial distance of the applicator from symphysis pubis (distance from the flange to the top of the symphysis pubis) decreased BP dose (P<.001) and the ratio between BP and bladder D2cc (P<.001) without significantly changing bladder D2cc or any other organ dose. Posterior sagittal rotation of the applicator (distance from symphysis pubis to the tandem) decreased ratio of BP and bladder D2cc (P<.001) and increased ratio of RP and rectum D2cc (PZ.001). Conclusion: This study confirms the importance of applicator geometry and its effect on point dose and D2cc. Increased cranial distance of the applicator from symphysis pubis significantly decreases the ratio between BP dose and D2cc without negatively impacting dose to other OARs. In addition, uterus size and shape have significant impact on both OAR reference point dose and D2cc. Author Disclosure: C. Dulaney: None. A.S. Wallace: None. O.L. Burnett: None. M. Huang: None. Z. Wang: None. S. Shen: None. R.Y. Kim: None.
The Effect of Anatomical Changes on Target Coverage in Intensity Modulated Proton Therapy for Cervical Cancer D. Wang,1 S.K. Bhatia,1 N.K. Felderman,1 E. Dinges,1 S.C. Patel,1 J. Buatti,2 and S.M. McGuire1; 1University of Iowa, Iowa City, IA, 2 University of Iowa Hospitals and Clinics, Iowa City, IA Purpose/Objective(s): Intensity modulated proton therapy (IMPT) is a promising radiation therapy (RT) modality for cervical cancer treatment, especially for its potential role in reducing hematologic toxicity. IMPT dose distribution is known to be sensitive to patient anatomical changes during the treatment course. This study quantifies the effect of the anatomical change on IMPT’s target coverage for cervical cancer treatment. Materials/Methods: In this IRB-approved study, 3-beam IMPT plans were generated on the planning computed tomography (CT) image for 6 enrolled patients. Three or 4 weekly CT images were obtained for each patient using the same imaging protocol in subsequent weeks after the simulation day, for a total of 21 weekly CT images. CTs of the same patient were rigidly registered to the planning CT by matching bony anatomy. The geometric cervical and nodal target volumes were the same in subsequent CTs as in the planning CT, while major organs-at-risk including bowel, bladder, and rectum were re-contoured on each weekly CT. Patient body weights at the time of each weekly CT scan were also recorded. Dose from the IMPT plan was recomputed on these weekly CTs. Dose received by at least 95% of the cervical and nodal internal target volumes (Cervical DITV95% and Nodal DITV95%, respectively) were compared to their planned values. Univariate analysis was performed to discover the correlation between DITV95% to the relative changes of various anatomical factors, as well as the correlation between the anatomical factors. Results: Body weight increase was found to be significantly correlated to the decrease of both Cervical DITV95% (Spearman rank correlation coefficient SCCZ-0.653, PZ.001) and Nodal DITV95% (SCCZ-0.713, P<.001). Bowel volume increase was found to be significantly correlated to the decrease of Nodal DITV95% only (SCCZ-0.502, PZ.020), but not Cervical DITV95% (SCC Z -0.260, PZ.256). The correlations between bladder or rectum changes and target coverage were not statistically significant. Yet, there was also a significant correlation between bowel volume and body weight (SCCZ0.576, PZ.006). By deducting the bowel and bladder volume change, body weight increase was still found to be significantly correlated to the decrease of both Cervical DITV95% (SCCZ0.613, PZ.003) and Nodal DITV95% (SCCZ-0.646, PZ.002). Conclusion: The decrease of target coverage in IMPT for cervical cancer was found to be significantly correlated to mainly the increase of body weight, although intercorrelations between the changes of bladder, rectum, bowel, and body weight also existed. Multivariate analysis is needed to further uncover the major anatomical factor that impacts IMPT target coverage so that patient surveillance or intervention may be applied to maintain IMPT’s superior dose distribution. Author Disclosure: D. Wang: Research Grant; IBA Proton Therapy. Licensee for Royalty Payment; IBA Proton Therapy. S.K. Bhatia: None. N.K. Felderman: Student Researcher; The University of Iowa. Intern; Zimmer Inc. E. Dinges: Student; The University of Iowa. S.C. Patel: None. J. Buatti: None. S.M. McGuire: Research Grant; NCI.
2652 Evaluation of Applicator Geometry and Impact on Reference Point and Organ Volume Dose (D2cc) in the Era of 3-Dimensional Imaging for Cervical Cancer Brachytherapy C. Dulaney,1 A.S. Wallace,2 O.L. Burnett, III,1 M. Huang,1 Z. Wang,3 S. Shen,1 and R.Y. Kim1; 1University of Alabama at Birmingham, Birmingham, AL, 2University of Alabama Medical Center, Birmingham, AL, 3Duke University, Durham, NC Purpose/Objective(s): Optimal brachytherapy applicator placement is important in improving local control and organ at risk (OAR) sparing in
2653 Outcome of Patients With Local Recurrent Gynecologic Malignancies After Resection Combined With Intraoperative Radiation N. Arians,1 R. Fo¨rster,1 M. Uhl,2 J. Rom,3 J. Debus,4 and K. Lindel5; 1 University Hospital Heidelberg, Heidelberg, Germany, 2University of Heidelberg, Heidelberg, Germany, 3Univeristy Hospital Heidelberg, Heidelberg, Germany, 4Univesity Hospital Heidelberg, Heidelberg, Germany, 5University Heidelberg, Heidelberg, Germany Purpose/Objective(s): Treatment of patients with recurrent gynecologic malignancies remains challenging. Pelvic exenteration is one of the last options and associated with many intra- and postoperative complications. The aim of this study was to investigate clinical features and outcomes of patients with recurrent gynecologic malignancies who underwent resection including intraoperative radiation therapy (IORT) at a University Hospital between 2002 and 2014. Materials/Methods: A total of 36 patients (recurrent cervical [nZ18], endometrial [nZ12], or vulvar [nZ6] cancer were retrospectively identified through hospital databases. For IORT, a linear accelerator with electron fields was used with a mean dose of 15 Gray (10-18 Gy). Patient characteristics and patient outcomes (locoregional progression-free
International Journal of Radiation Oncology Biology Physics
2651
patients with cervical cancer. Criteria for proper placement have been described based on 2-dimensional imaging. In the era of 3-dimensional (3D) imaging, both International Commission on Radiation Units and Measurements (ICRU) reference points and minimum dose to 2 cc volume receiving the highest dose (D2cc) are used to evaluate postimplant dosimetry. The purpose of this study was to evaluate the impact of applicator position in the pelvis and patient anatomy on ICRU reference point dose and OAR D2cc using 3D imaging in cervical cancer patients. Materials/Methods: Forty-five thin-slice pelvic computed tomography (CT) scans from 15 patients with cervical cancer (1 IB1, 3 IB2, 1 IIA1, 3 IIA2, 6 IIB, and 1 IIIB) having 3 high-dose-rate ICBT applications of 8 Gy to point A following external beam radiation therapy (EBRT) were reviewed. Applicator consisted of Fletcher tandem and ovoids. Applicator geometry was evaluated using consensus guideline parameters. Anatomic parameters included uterus thickness and uterus and bladder volume. Dose to rectal (RP) and bladder (BP) ICRU reference point and physiciancontoured OAR (bladder, rectum, small bowel, and sigmoid colon) D2cc were determined for each fraction. Mixed linear regression model with Bonferroni correction was used to determine the effect of applicator position and patient anatomy on OAR D2cc and ratio of OAR reference point dose and D2cc. Results: Median tandem length, curvature, and ovoid size were 6 cm, 30 degrees, and 2.5 cm, respectively. Increased uterus volume decreased small bowel D2cc (PZ.002). Increased uterus thickness decreased RP dose (P<.001) and bladder D2cc (P<.001). Increased rectal packing decreased RP dose (P<.001). Mean ratio of bladder point dose to D2cc was 0.760.39. Mean ratio of rectum point dose to D2cc was 1.210.58. Increased cranial distance of the applicator from symphysis pubis (distance from the flange to the top of the symphysis pubis) decreased BP dose (P<.001) and the ratio between BP and bladder D2cc (P<.001) without significantly changing bladder D2cc or any other organ dose. Posterior sagittal rotation of the applicator (distance from symphysis pubis to the tandem) decreased ratio of BP and bladder D2cc (P<.001) and increased ratio of RP and rectum D2cc (PZ.001). Conclusion: This study confirms the importance of applicator geometry and its effect on point dose and D2cc. Increased cranial distance of the applicator from symphysis pubis significantly decreases the ratio between BP dose and D2cc without negatively impacting dose to other OARs. In addition, uterus size and shape have significant impact on both OAR reference point dose and D2cc. Author Disclosure: C. Dulaney: None. A.S. Wallace: None. O.L. Burnett: None. M. Huang: None. Z. Wang: None. S. Shen: None. R.Y. Kim: None.
The Effect of Anatomical Changes on Target Coverage in Intensity Modulated Proton Therapy for Cervical Cancer D. Wang,1 S.K. Bhatia,1 N.K. Felderman,1 E. Dinges,1 S.C. Patel,1 J. Buatti,2 and S.M. McGuire1; 1University of Iowa, Iowa City, IA, 2 University of Iowa Hospitals and Clinics, Iowa City, IA Purpose/Objective(s): Intensity modulated proton therapy (IMPT) is a promising radiation therapy (RT) modality for cervical cancer treatment, especially for its potential role in reducing hematologic toxicity. IMPT dose distribution is known to be sensitive to patient anatomical changes during the treatment course. This study quantifies the effect of the anatomical change on IMPT’s target coverage for cervical cancer treatment. Materials/Methods: In this IRB-approved study, 3-beam IMPT plans were generated on the planning computed tomography (CT) image for 6 enrolled patients. Three or 4 weekly CT images were obtained for each patient using the same imaging protocol in subsequent weeks after the simulation day, for a total of 21 weekly CT images. CTs of the same patient were rigidly registered to the planning CT by matching bony anatomy. The geometric cervical and nodal target volumes were the same in subsequent CTs as in the planning CT, while major organs-at-risk including bowel, bladder, and rectum were re-contoured on each weekly CT. Patient body weights at the time of each weekly CT scan were also recorded. Dose from the IMPT plan was recomputed on these weekly CTs. Dose received by at least 95% of the cervical and nodal internal target volumes (Cervical DITV95% and Nodal DITV95%, respectively) were compared to their planned values. Univariate analysis was performed to discover the correlation between DITV95% to the relative changes of various anatomical factors, as well as the correlation between the anatomical factors. Results: Body weight increase was found to be significantly correlated to the decrease of both Cervical DITV95% (Spearman rank correlation coefficient SCCZ-0.653, PZ.001) and Nodal DITV95% (SCCZ-0.713, P<.001). Bowel volume increase was found to be significantly correlated to the decrease of Nodal DITV95% only (SCCZ-0.502, PZ.020), but not Cervical DITV95% (SCC Z -0.260, PZ.256). The correlations between bladder or rectum changes and target coverage were not statistically significant. Yet, there was also a significant correlation between bowel volume and body weight (SCCZ0.576, PZ.006). By deducting the bowel and bladder volume change, body weight increase was still found to be significantly correlated to the decrease of both Cervical DITV95% (SCCZ0.613, PZ.003) and Nodal DITV95% (SCCZ-0.646, PZ.002). Conclusion: The decrease of target coverage in IMPT for cervical cancer was found to be significantly correlated to mainly the increase of body weight, although intercorrelations between the changes of bladder, rectum, bowel, and body weight also existed. Multivariate analysis is needed to further uncover the major anatomical factor that impacts IMPT target coverage so that patient surveillance or intervention may be applied to maintain IMPT’s superior dose distribution. Author Disclosure: D. Wang: Research Grant; IBA Proton Therapy. Licensee for Royalty Payment; IBA Proton Therapy. S.K. Bhatia: None. N.K. Felderman: Student Researcher; The University of Iowa. Intern; Zimmer Inc. E. Dinges: Student; The University of Iowa. S.C. Patel: None. J. Buatti: None. S.M. McGuire: Research Grant; NCI.
2652 Evaluation of Applicator Geometry and Impact on Reference Point and Organ Volume Dose (D2cc) in the Era of 3-Dimensional Imaging for Cervical Cancer Brachytherapy C. Dulaney,1 A.S. Wallace,2 O.L. Burnett, III,1 M. Huang,1 Z. Wang,3 S. Shen,1 and R.Y. Kim1; 1University of Alabama at Birmingham, Birmingham, AL, 2University of Alabama Medical Center, Birmingham, AL, 3Duke University, Durham, NC Purpose/Objective(s): Optimal brachytherapy applicator placement is important in improving local control and organ at risk (OAR) sparing in
2653 Outcome of Patients With Local Recurrent Gynecologic Malignancies After Resection Combined With Intraoperative Radiation N. Arians,1 R. Fo¨rster,1 M. Uhl,2 J. Rom,3 J. Debus,4 and K. Lindel5; 1 University Hospital Heidelberg, Heidelberg, Germany, 2University of Heidelberg, Heidelberg, Germany, 3Univeristy Hospital Heidelberg, Heidelberg, Germany, 4Univesity Hospital Heidelberg, Heidelberg, Germany, 5University Heidelberg, Heidelberg, Germany Purpose/Objective(s): Treatment of patients with recurrent gynecologic malignancies remains challenging. Pelvic exenteration is one of the last options and associated with many intra- and postoperative complications. The aim of this study was to investigate clinical features and outcomes of patients with recurrent gynecologic malignancies who underwent resection including intraoperative radiation therapy (IORT) at a University Hospital between 2002 and 2014. Materials/Methods: A total of 36 patients (recurrent cervical [nZ18], endometrial [nZ12], or vulvar [nZ6] cancer were retrospectively identified through hospital databases. For IORT, a linear accelerator with electron fields was used with a mean dose of 15 Gray (10-18 Gy). Patient characteristics and patient outcomes (locoregional progression-free