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Interstitial High-Dose-Rate Gynecological Brachytherapy: Dosimetric Impact of Catheter Deflection
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Abstracts / Brachytherapy 14 (2015) S11eS106
demonstrated the dosimetric advantage of multi-channel applicator. The single-use disposable mold applicator provides an inexpensive alternative to other multi-channel vaginal cylinder applicators available on market for infrequent use. PO19 CT Planned Interstitial Brachytherapy for Cancers of the Female Reproductive Tract Mark Amsbaugh, MD1, Neal Bhatt, MD1, Lynn Parker, MD2, Daniel Metzinger, MD2, Jeremy Gaskins, PhD3, Moataz El-Ghamry, MD1. 1 Radiation Oncology, University of Louisville, Louisville, KY, USA; 2 Obstetrics, Gynecology, and Women’s Health, University of Louisville, Louisville, KY, USA; 3Department of Bioinformatics and Biostatistics, University of Louisville, Louisville, KY, USA. Purpose: To report predictors of toxicity and preliminary outcomes of treatment with interstitial brachytherapy (ISBT) for cancers of the female reproductive tract. Materials and Methods: All patients who received ISBT at our institution were retrospectively reviewed. Patients were treated between January 2009 and September 2014. Demographic, disease specific, treatment, toxicity and outcome data were collected. Kaplan-Meier and proportional hazard models were used to estimate survival, and logistic regression to model toxicity. A least absolute shrinkage and selection operator (LASSO) penalty was used to identify relevant predictors of outcome and toxicity. Results: Seventy-three patients received ISBT at our institution. Twentyone patients were treated for cancer recurrence and 52 were treated at first presentation. Median age of patients was 56 years (range 27 - 87 years). Median Karnofsky Performance Status was 90%. Thirty-six patients had cervical cancer, 16 had vaginal cancer, 13 had uterine cancer, and eight had vulvar cancer. The indication for ISBT was vaginal or vulvar involvement in 40 patients, pelvic sidewall involvement in 19 patients, anatomy not suitable for tandem and ovoid in ten patients, and doseescalation and dose shaping in four patients. Median tumor size was 4.0 cm (range 0.0 to 10.0 cm). ISBT was performed using Iridium-192 sources (27 low dose rate, 46 high dose rate). Median low dose rate dose was 40.0 Gy (range 16.0 to 55.0 Gy). Low dose rate treatment was delivered over 37.5 - 88.0 hours (median 85.0 hours). Median high dose rate dose was 25.0 Gy (range 12.0 - 29.0 Gy). High dose rate treatment was delivered over three to five fractions, twice-daily fractions (median 5). Each procedure used a median of ten interstitial needles (range 3 - 18 needles). Sixty-two patients received external beam irradiation in addition to ISBT. One year actuarial freedom from local-regional failure (FLRF), progression free survival (PFS), and overall survival (OS) were 75.1%, 62.2%, and 80.2% respectively. There were no differences in FLRF (p 5 0.436), PFS (p50.612), and OS (p 5 0.333) between patients treated for first cancer occurrence or recurrent cancer. Patients with uterine cancer had improved OS compared to those with cervical cancer (HR 0.142 95% CI 0.033 - 0.616). Grade 3 or higher toxicity was experienced by 26.0% of patients (6 vaginal, 2 urinary, 4 rectal). Three out of 73 patients developed a deep vein thrombosis or pulmonary embolism either during or shortly following brachytherapy. Grade 2 or higher vaginal, urinary, and rectal toxicity occurs in 57.5% (95% CI 45.4 - 68.8), 31.5% (95% CI 21.4 - 43.6%) and 17.8% (95% CI 10.2 - 28.9%) of patients respectively. Conclusions: CT planned ISBT is safe and effective. Patients with recurrent cancer selected for ISBT have similar survival local control and survival outcomes to patients with first cancer occurrence. Extended follow-up is required to assess late failures and long-term toxicity. PO20 Interstitial High-Dose-Rate Gynecological Brachytherapy: Dosimetric Impact of Catheter Deflection Matt Wronski, PhD1, Eric Leung, MD2, Melanie Davidson, PhD1, Ananth Ravi, PhD1. 1Department of Medical Physics, Odette Cancer Centre, Toronto, ON, Canada; 2Department of Radiation Oncology, Odette Cancer Centre, Toronto, ON, Canada.
Purpose: The purpose of this study is to characterize the amount of catheter deflection and angulation during gynecological high-dose-rate (HDR) interstitial brachytherapy and the resulting implications on the planned dose distribution. In particular, the study investigates whether inverse planning could overcome deviation of the implanted catheters from their intended tracks. Materials and Methods: Four patients were treated using volumetric image-guided interstitial HDR gynecological brachytherapy using an intracavitary vaginal applicator and a Syed-Neblett template for interstitial catheter implantation. Pre-brachytherapy axial and sagittal T2-weighted MR images were acquired for each patient with the applicator and template in place and used to determine catheter template positions for implantation. For each patient, 8-14 6F plastic interstitial catheters were used. Determination of catheter implantation positions assumed ideal catheter tracks that are orthogonal to the template. Applicator and catheter insertion was performed a week later, followed by a CT scan for delineating the targets and organs at risk (OAR) as well as catheter reconstruction. All patients received 3 HDR fractions with a planned dose of 650 cGy per fraction to the gross target volume (GTV) and high-risk clinical target volume (HR-CTV) and 500 cGy per fraction to the intermediate risk CTV (IR-CTV). All implanted catheters presented some degree of deviation (deflection and angulation) within each patient and subsequent treatment planning using Inverse Planning Simulated Annealing (IPSA) took this into account (clinical plan). For each patient, an additional plan was retrospectively generated in which all catheter tracks were orthogonal to the template (reference plan). This reference plan represented the ideal case in which treatment planning was unaffected by catheter deviation. The clinical and reference plans were retrospectively compared to evaluate the extent to which IPSA could overcome catheter deviation. All plans achieved HR-CTV V100% $ 99%. Results: Our results based on four patients demonstrate a substantial discrepancy in the clinical catheter tracks as shown in the figure below. The mean value of the maximum catheter deflection at the level of the GTV was 9.1 3.2 mm (range 3.0 - 18.4 mm) in the direction parallel to the template. 77.5 3.5% of clinical catheter track segments were at an angle of 1-5 degrees to normal template incidence and 13.5 2.4% were at an angle of 6-10 degrees. Interestingly, 32/45 interstitial catheters were found to monotonically converge towards the central axis of the vaginal cylinder as a function of increasing depth in tissue. For all four patients, the IPSA-generated clinical plans yielded inferior target and OAR dose metrics compared to the reference plans with no catheter deflection, although the dose metrics were only at most 3.9% worse in 3/4 patients. One of the patients, however, demonstrated a stark difference in the achieved IPSA plans with a 43.8% higher rectal D2cc and a 46.8% larger HR-CTV V200%. For this patient, most of the interstitial catheters (8/11) diverged from the central axis of the vaginal cylinder, in contrast to the other patients. Presented results will be based on 10 patients and will stratify the relative dosimetric differences according to the level of catheter deflection. Conclusions: Our results demonstrate that interstitial gynecological HDR brachytherapy results in catheter deflections that can approach 2 cm at the level of the GTV. This may result in sub-optimal plan quality. IPSA-based planning can be used to mitigate some of the dosimetric impact arising from deviation of the implanted catheters from their intended tracks as was shown in 3/4 patients. Further strategies to mitigate interstitial catheter deviation such as real-time needle guidance during implantation may be necessary for some patients to ensure optimal plan quality.
Abstracts / Brachytherapy 14 (2015) S11eS106
demonstrated the dosimetric advantage of multi-channel applicator. The single-use disposable mold applicator provides an inexpensive alternative to other multi-channel vaginal cylinder applicators available on market for infrequent use. PO19 CT Planned Interstitial Brachytherapy for Cancers of the Female Reproductive Tract Mark Amsbaugh, MD1, Neal Bhatt, MD1, Lynn Parker, MD2, Daniel Metzinger, MD2, Jeremy Gaskins, PhD3, Moataz El-Ghamry, MD1. 1 Radiation Oncology, University of Louisville, Louisville, KY, USA; 2 Obstetrics, Gynecology, and Women’s Health, University of Louisville, Louisville, KY, USA; 3Department of Bioinformatics and Biostatistics, University of Louisville, Louisville, KY, USA. Purpose: To report predictors of toxicity and preliminary outcomes of treatment with interstitial brachytherapy (ISBT) for cancers of the female reproductive tract. Materials and Methods: All patients who received ISBT at our institution were retrospectively reviewed. Patients were treated between January 2009 and September 2014. Demographic, disease specific, treatment, toxicity and outcome data were collected. Kaplan-Meier and proportional hazard models were used to estimate survival, and logistic regression to model toxicity. A least absolute shrinkage and selection operator (LASSO) penalty was used to identify relevant predictors of outcome and toxicity. Results: Seventy-three patients received ISBT at our institution. Twentyone patients were treated for cancer recurrence and 52 were treated at first presentation. Median age of patients was 56 years (range 27 - 87 years). Median Karnofsky Performance Status was 90%. Thirty-six patients had cervical cancer, 16 had vaginal cancer, 13 had uterine cancer, and eight had vulvar cancer. The indication for ISBT was vaginal or vulvar involvement in 40 patients, pelvic sidewall involvement in 19 patients, anatomy not suitable for tandem and ovoid in ten patients, and doseescalation and dose shaping in four patients. Median tumor size was 4.0 cm (range 0.0 to 10.0 cm). ISBT was performed using Iridium-192 sources (27 low dose rate, 46 high dose rate). Median low dose rate dose was 40.0 Gy (range 16.0 to 55.0 Gy). Low dose rate treatment was delivered over 37.5 - 88.0 hours (median 85.0 hours). Median high dose rate dose was 25.0 Gy (range 12.0 - 29.0 Gy). High dose rate treatment was delivered over three to five fractions, twice-daily fractions (median 5). Each procedure used a median of ten interstitial needles (range 3 - 18 needles). Sixty-two patients received external beam irradiation in addition to ISBT. One year actuarial freedom from local-regional failure (FLRF), progression free survival (PFS), and overall survival (OS) were 75.1%, 62.2%, and 80.2% respectively. There were no differences in FLRF (p 5 0.436), PFS (p50.612), and OS (p 5 0.333) between patients treated for first cancer occurrence or recurrent cancer. Patients with uterine cancer had improved OS compared to those with cervical cancer (HR 0.142 95% CI 0.033 - 0.616). Grade 3 or higher toxicity was experienced by 26.0% of patients (6 vaginal, 2 urinary, 4 rectal). Three out of 73 patients developed a deep vein thrombosis or pulmonary embolism either during or shortly following brachytherapy. Grade 2 or higher vaginal, urinary, and rectal toxicity occurs in 57.5% (95% CI 45.4 - 68.8), 31.5% (95% CI 21.4 - 43.6%) and 17.8% (95% CI 10.2 - 28.9%) of patients respectively. Conclusions: CT planned ISBT is safe and effective. Patients with recurrent cancer selected for ISBT have similar survival local control and survival outcomes to patients with first cancer occurrence. Extended follow-up is required to assess late failures and long-term toxicity. PO20 Interstitial High-Dose-Rate Gynecological Brachytherapy: Dosimetric Impact of Catheter Deflection Matt Wronski, PhD1, Eric Leung, MD2, Melanie Davidson, PhD1, Ananth Ravi, PhD1. 1Department of Medical Physics, Odette Cancer Centre, Toronto, ON, Canada; 2Department of Radiation Oncology, Odette Cancer Centre, Toronto, ON, Canada.
Purpose: The purpose of this study is to characterize the amount of catheter deflection and angulation during gynecological high-dose-rate (HDR) interstitial brachytherapy and the resulting implications on the planned dose distribution. In particular, the study investigates whether inverse planning could overcome deviation of the implanted catheters from their intended tracks. Materials and Methods: Four patients were treated using volumetric image-guided interstitial HDR gynecological brachytherapy using an intracavitary vaginal applicator and a Syed-Neblett template for interstitial catheter implantation. Pre-brachytherapy axial and sagittal T2-weighted MR images were acquired for each patient with the applicator and template in place and used to determine catheter template positions for implantation. For each patient, 8-14 6F plastic interstitial catheters were used. Determination of catheter implantation positions assumed ideal catheter tracks that are orthogonal to the template. Applicator and catheter insertion was performed a week later, followed by a CT scan for delineating the targets and organs at risk (OAR) as well as catheter reconstruction. All patients received 3 HDR fractions with a planned dose of 650 cGy per fraction to the gross target volume (GTV) and high-risk clinical target volume (HR-CTV) and 500 cGy per fraction to the intermediate risk CTV (IR-CTV). All implanted catheters presented some degree of deviation (deflection and angulation) within each patient and subsequent treatment planning using Inverse Planning Simulated Annealing (IPSA) took this into account (clinical plan). For each patient, an additional plan was retrospectively generated in which all catheter tracks were orthogonal to the template (reference plan). This reference plan represented the ideal case in which treatment planning was unaffected by catheter deviation. The clinical and reference plans were retrospectively compared to evaluate the extent to which IPSA could overcome catheter deviation. All plans achieved HR-CTV V100% $ 99%. Results: Our results based on four patients demonstrate a substantial discrepancy in the clinical catheter tracks as shown in the figure below. The mean value of the maximum catheter deflection at the level of the GTV was 9.1 3.2 mm (range 3.0 - 18.4 mm) in the direction parallel to the template. 77.5 3.5% of clinical catheter track segments were at an angle of 1-5 degrees to normal template incidence and 13.5 2.4% were at an angle of 6-10 degrees. Interestingly, 32/45 interstitial catheters were found to monotonically converge towards the central axis of the vaginal cylinder as a function of increasing depth in tissue. For all four patients, the IPSA-generated clinical plans yielded inferior target and OAR dose metrics compared to the reference plans with no catheter deflection, although the dose metrics were only at most 3.9% worse in 3/4 patients. One of the patients, however, demonstrated a stark difference in the achieved IPSA plans with a 43.8% higher rectal D2cc and a 46.8% larger HR-CTV V200%. For this patient, most of the interstitial catheters (8/11) diverged from the central axis of the vaginal cylinder, in contrast to the other patients. Presented results will be based on 10 patients and will stratify the relative dosimetric differences according to the level of catheter deflection. Conclusions: Our results demonstrate that interstitial gynecological HDR brachytherapy results in catheter deflections that can approach 2 cm at the level of the GTV. This may result in sub-optimal plan quality. IPSA-based planning can be used to mitigate some of the dosimetric impact arising from deviation of the implanted catheters from their intended tracks as was shown in 3/4 patients. Further strategies to mitigate interstitial catheter deviation such as real-time needle guidance during implantation may be necessary for some patients to ensure optimal plan quality.