Purpose: To investigate cumulative doses of soft tissue anatomy from ultrasound (US) guided HDR interstitial brachytherapy boost and external beam pelvic IMRT using deformable registration.Materials and Methods: 10 patients previously treated with EB-IMRT and IG-BT boost were retrospectively evaluated for deformation and dose accumulation.Patients were treated with whole-pelvis EBRT (46.0 Gy in 2 Gy fractions) and an ultrasound-guided HDR implant with real-time dosimetry (21.0 Gy in10.5 Gy fractions).3 gold visicoil markers (4 cm in length) are placed at the same time as the HDR catheters and are used as a localization tool for both HDR fractions and IMRT delivery.A post-implant CT without the US probe and with catheters in place was alsoobtained as a verification scan for these patients.For soft tissue anatomy, a finite element based image registration method was applied to obtain the deformation of each voxel of the region of interest on the US image.Because of US probe in the rectum and a limited field of view, US image is limited in deforming only the prostate.Post-implant CT was therefore used to deform all the soft-tissue anatomy such as bladder, rectal wall and urethra.The deformation vector field generated after deforming postimplant CT contours was used to deform the BT dose grid on to the EB CT grid and the cumulative dose was calculated.A linear-quadratic model was applied to calculate the total equivalent dose in 2Gy fractions (EQD2) with a/b51.5 for prostate and 3 for prostatic urethra, bladder and rectal wall.Cumulative EQD2 to 99 %, 95 % and 50% volume were determined for prostate.Cumulative dose-volume parameters such as V80, V100, V125 and V150 were evaluated for urethra, bladder and rectal wall.Results: EQD2 for HDR fractionation with an a/b51.5 and 3 was 72 Gy and 56.7 Gy, respectively.The mean prostate volume for EB and BT fractions were 55.4 AE 13.2 cc and 45.7 AE 9.6 cc.The mean difference between EB and BT prostate volume was 6.0 AE 10.3 cc.The average cumulative EQD2 to 99 %, 95 % and 50% of prostate volume based on rigid and deformable registration was 84.0 AE 12.9, 94.1 AE 15.6, 131.1 AE 7 Gy and 116.6 AE 12.6, 123.1 AE 7.5, 141.9 AE 6.0 Gy, respectively.The mean V80, V100, V125 and V150 based on cumulative doses for urethra were 98.6 AE 3.1, 92.9 AE 6.9, 3.2 AE 7.7, 1.2 AE 3.0 %.Conclusions: Large deformations exist in soft tissue anatomy between BT and EB fractions that have a significant impact on cumulative dose distribution.Mean variations of up to 28 % were seen for cumulative doses in prostate based on rigid and deformable registration.Ongoing work will evaluate the effect of delivered brachytherapy dose in adaptive planning optimization of external beam IMRT planning.

Purpose: Patient specific needle deflection, during transperineal needle insertion, often leads to unnecessary added trauma due to the need for repeated corrections. In the absence of real-time imaging during MRI-guided procedures, deflections may also translate to longer procedure times. This study aims to test the performance of a navigation strategy whereby deflection of the first and second needle is used to re-calibrate the stereotactic transperineal grid projection, with the goal of improving subsequent needle targeting accuracy. Materials and Methods: Patients were enrolled on a prospective clinical trial of MRI-guided transperineal mapping prostate biopsy to guide subsequent tumor-targeted HDR brachytherapy. A customized system (Aegis with Prostate) was utilized to permit transperineal needle insertion under MRI-guidance. A stereotactic transperineal grid is rigidly affixed perpendicularly to an endorectal imaging coil (ERC), and registered to images using manually defined reference landmarks filled with water-based lubricant. As in standard TRUS-guided techniques, grid coordinates are chosen to achieve target prostate locations during needle insertion. After needle insertion, an axial T2 weighted fast spin echo (FSE) verification image was acquired to determine the actual location of the needle in x and y planes. Corrections were based on the error identified with the first inserted needle as well as the mean error of the first 2 needles inserted in opposite sides of the gland. A correction based on the mean error for the entire cohort was also explored. Results: Targeting accuracy data from 19 patient procedures was analyzed, with a mean of 11 biopsies per patient (range= 6–14 biopsies). The mean in-plane vector error for all 207 biopsies was 2.8mm (SD =1.6mm). The mean lateral displacement (x) was 0.3mm (SD=2.3mm), and mean AP displacement (y) was biased posteriorly at 1.7mm (SD=1.6). Correction based on the first needle improved AP mean accuracy (0.1, SD 1.7), but reduced lateral accuracy (mean -0.6, SD 2.2). Using the mean error of the first 2 needles inserted in opposing lateral lobes of the prostate marginally improved the in-plane vector error to 2.3mm (SD 1.9mm), but eliminated bias (mean(x/y)= -0.10/-0.04, SD(x/y)= 2.33/1.61). Systematic correction utilizing the global measured mean in-plane error also showed promise in increased targeting accuracy by improving the deflection error in 16/19 patients. Conclusions: Correcting for the average targeting error of the first 2 inserted needles reduces patient-specific deflection bias in transperineal procedures as does a systematic correction based on the global measured mean in-plane error. Prospective evaluation of these navigation strategies are currently underway.

Purpose: To investigate cumulative doses of soft tissue anatomy from ultrasound (US) guided HDR interstitial brachytherapy boost and external beam pelvic IMRT using deformable registration.Materials and Methods: 10 patients previously treated with EB-IMRT and IG-BT boost were retrospectively evaluated for deformation and dose accumulation.Patients were treated with whole-pelvis EBRT (46.0 Gy in 2 Gy fractions) and an ultrasound-guided HDR implant with real-time dosimetry (21.0 Gy in10.5 Gy fractions).3 gold visicoil markers (4 cm in length) are placed at the same time as the HDR catheters and are used as a localization tool for both HDR fractions and IMRT delivery.A post-implant CT without the US probe and with catheters in place was alsoobtained as a verification scan for these patients.For soft tissue anatomy, a finite element based image registration method was applied to obtain the deformation of each voxel of the region of interest on the US image.Because of US probe in the rectum and a limited field of view, US image is limited in deforming only the prostate.Post-implant CT was therefore used to deform all the soft-tissue anatomy such as bladder, rectal wall and urethra.The deformation vector field generated after deforming postimplant CT contours was used to deform the BT dose grid on to the EB CT grid and the cumulative dose was calculated.A linear-quadratic model was applied to calculate the total equivalent dose in 2Gy fractions (EQD2) with a/b51.5 for prostate and 3 for prostatic urethra, bladder and rectal wall.Cumulative EQD2 to 99 %, 95 % and 50% volume were determined for prostate.Cumulative dose-volume parameters such as V80, V100, V125 and V150 were evaluated for urethra, bladder and rectal wall.Results: EQD2 for HDR fractionation with an a/b51.5 and 3 was 72 Gy and 56.7 Gy, respectively.The mean prostate volume for EB and BT fractions were 55.4 AE 13.2 cc and 45.7 AE 9.6 cc.The mean difference between EB and BT prostate volume was 6.0 AE 10.3 cc.The average cumulative EQD2 to 99 %, 95 % and 50% of prostate volume based on rigid and deformable registration was 84.0 AE 12.9, 94.1 AE 15.6, 131.1 AE 7 Gy and 116.6 AE 12.6, 123.1 AE 7.5, 141.9 AE 6.0 Gy, respectively.The mean V80, V100, V125 and V150 based on cumulative doses for urethra were 98.6 AE 3.1, 92.9 AE 6.9, 3.2 AE 7.7, 1.2 AE 3.0 %.Conclusions: Large deformations exist in soft tissue anatomy between BT and EB fractions that have a significant impact on cumulative dose distribution.Mean variations of up to 28 % were seen for cumulative doses in prostate based on rigid and deformable registration.Ongoing work will evaluate the effect of delivered brachytherapy dose in adaptive planning optimization of external beam IMRT planning.