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Pelvic Radiation in Patients with a Pelvic Kidney: No Longer Playing with Fire
Proceedings of the 51st Annual ASTRO Meeting reduce the magnitude of hot regions. It therefore appears that this method of automated treatment planning is a good candidate to be further developed for several potential uses, including off-line adaptive re-planning, as a plan quality assurance check, or as a replacement for effort-intensive human planning. This research was supported by NIH grant R01 CA85181 and a research grant from TomoTherapy, Inc. Author Disclosure: J.O. Deasy, NIH R01 CA85181, B. Research Grant; Tomotherapy, Inc., B. Research Grant; Varian, Inc., B. Research Grant; V. Clark, None; Y. Chen, None; A. Apte, None; J.M. Michalski, None; J. Cui, None.
3067
Image Guided Radiotherapy after Radical Prostatectomy: A Report of Total Setup Error using Surgical Clips as Fiducials
S. Song, S. Liauw University of Chicago Medical Center, Chicago, IL Purpose/Objective(s): For post-prostatectomy radiation therapy (RT), the appropriate PTV expansion beyond the prostate bed is not well defined. The purpose of this study was to report (a) the total setup error in a cohort of patients undergoing image-guided radiation therapy (IGRT) using surgical clips to define the prostate bed, and (b) the feasibility of this image-guided approach using kilovoltage (kV) portal imaging. Materials/Methods: 7 patients were treated with post-prostatectomy RT; all had surgical clips in the prostate bed. The PTV was defined as the prostate bed (CTV) plus a 1cm uniform expansion. Surgical clips were delineated in each of the four outermost quadrants (right/left superolateral, right/left inferolateral) of the CTV. MV images were taken once a week to confirm position of bony anatomy. Orthogonal kV images were taken twice a week and were registered to digitally reconstructed radiographs (DRRs) created from the planning CT to relate the position of the four surgical clips. Translational shifts of the surgical clips in the left-right (LR), superior-inferior(SI), and anterior-posterior (AP) axis were calculated with respect to the treatment isocenter. If the suggested shifts were .1cm in any axis, applicable shifts were made based on the location of the surgical clips, and kV imaging was repeated daily thereafter. The mean shift, and standard deviation (SD), in each axis were determined for each and all patients. Cone beam CT (CBCT) was used for large shifts. Results: A total of 108 kV image pairs and 324 shifts were analyzed. Surgical clips were reproducibly identified in relationship to one another. No trend between shifts in any axis and treatment fraction was observed, suggesting no significant clip migration over a mean 48 days of treatment. The mean (± SD) shifts in the LR, SI, and AP axis were: -0.7mm ( ± 3.2mm), 1.2mm ( ± 2.5mm), and -3.8mm ( ± 5.3mm), respectively. In the LR axis, 64%, 97%, and 100% of the time, shifts were within 2mm, 6mm, and 10mm, respectively. In the SI axis, 66%, 98%, and 100% of the time, shifts were within 2mm, 6mm, and 10mm, respectively. In the AP axis, 39%, 69%, and 83% of the time, shifts were within 2mm, 6mm, and 10mm. Overall, a 1cm PTV expansion was adequate for 94% of the setups. Except for 1 patient, shifts were always within the PTV. This patient showed a .1 cm setup error posteriorly along the AP axis 46% of the time. CBCT revealed a discrepancy in bladder filling for this patient. Daily KV image fiducial guidance was used for the entire treatment in this case. Conclusions: Surgical clips in each of the 4 quadrants of the prostate bed can be used as reliable fiducial markers for IGRT. The largest shifts were predominantly posterior shifts in the AP direction. Bladder filling is an important consideration to ensure adequacy of PTV expansion. Author Disclosure: S. Song, None; S. Liauw, None.
3068
Pelvic Radiation in Patients with a Pelvic Kidney: No Longer Playing with Fire
D. M. Berlach, M. Brodeur, F. Cury McGill University Health Centre, Montreal, QC, Canada Purpose/Objective(s): With improvements in surgical techniques and better control of post transplantation complications, there are a growing number of long-term kidney transplantation survivors. Due to the emergence of prostate cancer screening the lifetime risk of developing prostate cancer has increased to 1 in 6. These advances have spawned a new subpopulation of patients with pelvic kidneys who are surviving long enough to develop malignancies such as prostate cancer. Classically, pelvic radiation therapy was contraindicated for patients with pelvic kidney due to the high sensitivity of the transplanted organ and its proximity to the prostate. Moreover, patients who have received transplantations are often poor surgical candidates due to their coexisting morbidities. With advances in radiation therapy over the past few decades, namely IMRT and IGRT, a pelvic kidney may no longer be a contraindication to pelvic radiation therapy. Materials/Methods: We present a series of treatment plans for patients with renal transplantation who developed prostate cancer and were treated with radical radiation therapy using IMRT technique delivered via Helical Tomotherapy (HT). Seven plans per patient were developed to illustrate circumstances when the pelvic nodes are or are not included in the treatment plan. We then compared the dosimetric aspects of the HT plans to 2D-conventional EBRT, 3D-CRT and LinAc-based IMRT. We treated the prostate, with or without the proximal seminal vesicles, using 0.7 cm margins to PTV, to a dose of 72 Gy delivered in 36 fractions. The internal and external iliac lymph nodes were treated to 46 Gy in the high-risk plans. Results: Dose-volume histograms demonstrating the doses received by the implanted kidney, as well as other normal structures, were well within acceptable limits, while targeted structures received near or full dose when utilizing HT or LinAc-based IMRT planning. This compared favorably to 2D or 3D CRT planning of the same cases. For high-risk plans, a reduction in mean maximum dose to the transplanted kidney from 50.9 Gy in the 3D CRT treatments to 13.9 Gy with HT is noticed. Similarly, a reduction in mean kidney V20 volume from 43.1% to 0% is observed. With nearly 2 years of follow-up we continue to see baseline kidney functioning and no evidence of disease recurrence in our patients. Conclusions: Radical radiation therapy via HT or LinAc-based IMRT can be safely utilized to treat low to high-risk prostate cancer in patients with a transplanted pelvic kidney. Author Disclosure: D.M. Berlach, None; M. Brodeur, None; F. Cury, None.
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3067
Image Guided Radiotherapy after Radical Prostatectomy: A Report of Total Setup Error using Surgical Clips as Fiducials
S. Song, S. Liauw University of Chicago Medical Center, Chicago, IL Purpose/Objective(s): For post-prostatectomy radiation therapy (RT), the appropriate PTV expansion beyond the prostate bed is not well defined. The purpose of this study was to report (a) the total setup error in a cohort of patients undergoing image-guided radiation therapy (IGRT) using surgical clips to define the prostate bed, and (b) the feasibility of this image-guided approach using kilovoltage (kV) portal imaging. Materials/Methods: 7 patients were treated with post-prostatectomy RT; all had surgical clips in the prostate bed. The PTV was defined as the prostate bed (CTV) plus a 1cm uniform expansion. Surgical clips were delineated in each of the four outermost quadrants (right/left superolateral, right/left inferolateral) of the CTV. MV images were taken once a week to confirm position of bony anatomy. Orthogonal kV images were taken twice a week and were registered to digitally reconstructed radiographs (DRRs) created from the planning CT to relate the position of the four surgical clips. Translational shifts of the surgical clips in the left-right (LR), superior-inferior(SI), and anterior-posterior (AP) axis were calculated with respect to the treatment isocenter. If the suggested shifts were .1cm in any axis, applicable shifts were made based on the location of the surgical clips, and kV imaging was repeated daily thereafter. The mean shift, and standard deviation (SD), in each axis were determined for each and all patients. Cone beam CT (CBCT) was used for large shifts. Results: A total of 108 kV image pairs and 324 shifts were analyzed. Surgical clips were reproducibly identified in relationship to one another. No trend between shifts in any axis and treatment fraction was observed, suggesting no significant clip migration over a mean 48 days of treatment. The mean (± SD) shifts in the LR, SI, and AP axis were: -0.7mm ( ± 3.2mm), 1.2mm ( ± 2.5mm), and -3.8mm ( ± 5.3mm), respectively. In the LR axis, 64%, 97%, and 100% of the time, shifts were within 2mm, 6mm, and 10mm, respectively. In the SI axis, 66%, 98%, and 100% of the time, shifts were within 2mm, 6mm, and 10mm, respectively. In the AP axis, 39%, 69%, and 83% of the time, shifts were within 2mm, 6mm, and 10mm. Overall, a 1cm PTV expansion was adequate for 94% of the setups. Except for 1 patient, shifts were always within the PTV. This patient showed a .1 cm setup error posteriorly along the AP axis 46% of the time. CBCT revealed a discrepancy in bladder filling for this patient. Daily KV image fiducial guidance was used for the entire treatment in this case. Conclusions: Surgical clips in each of the 4 quadrants of the prostate bed can be used as reliable fiducial markers for IGRT. The largest shifts were predominantly posterior shifts in the AP direction. Bladder filling is an important consideration to ensure adequacy of PTV expansion. Author Disclosure: S. Song, None; S. Liauw, None.
3068
Pelvic Radiation in Patients with a Pelvic Kidney: No Longer Playing with Fire
D. M. Berlach, M. Brodeur, F. Cury McGill University Health Centre, Montreal, QC, Canada Purpose/Objective(s): With improvements in surgical techniques and better control of post transplantation complications, there are a growing number of long-term kidney transplantation survivors. Due to the emergence of prostate cancer screening the lifetime risk of developing prostate cancer has increased to 1 in 6. These advances have spawned a new subpopulation of patients with pelvic kidneys who are surviving long enough to develop malignancies such as prostate cancer. Classically, pelvic radiation therapy was contraindicated for patients with pelvic kidney due to the high sensitivity of the transplanted organ and its proximity to the prostate. Moreover, patients who have received transplantations are often poor surgical candidates due to their coexisting morbidities. With advances in radiation therapy over the past few decades, namely IMRT and IGRT, a pelvic kidney may no longer be a contraindication to pelvic radiation therapy. Materials/Methods: We present a series of treatment plans for patients with renal transplantation who developed prostate cancer and were treated with radical radiation therapy using IMRT technique delivered via Helical Tomotherapy (HT). Seven plans per patient were developed to illustrate circumstances when the pelvic nodes are or are not included in the treatment plan. We then compared the dosimetric aspects of the HT plans to 2D-conventional EBRT, 3D-CRT and LinAc-based IMRT. We treated the prostate, with or without the proximal seminal vesicles, using 0.7 cm margins to PTV, to a dose of 72 Gy delivered in 36 fractions. The internal and external iliac lymph nodes were treated to 46 Gy in the high-risk plans. Results: Dose-volume histograms demonstrating the doses received by the implanted kidney, as well as other normal structures, were well within acceptable limits, while targeted structures received near or full dose when utilizing HT or LinAc-based IMRT planning. This compared favorably to 2D or 3D CRT planning of the same cases. For high-risk plans, a reduction in mean maximum dose to the transplanted kidney from 50.9 Gy in the 3D CRT treatments to 13.9 Gy with HT is noticed. Similarly, a reduction in mean kidney V20 volume from 43.1% to 0% is observed. With nearly 2 years of follow-up we continue to see baseline kidney functioning and no evidence of disease recurrence in our patients. Conclusions: Radical radiation therapy via HT or LinAc-based IMRT can be safely utilized to treat low to high-risk prostate cancer in patients with a transplanted pelvic kidney. Author Disclosure: D.M. Berlach, None; M. Brodeur, None; F. Cury, None.
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