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EP-1935: Clinical evaluation of HIPO algorithm for HDR prostate cancer brachytherapy
ESTRO 33, 2014 evaluated:VlOO, Vl50, V200, D90. The relation of D90 for the postimplant dosimetry and the V150 parameter at the implantation have been evaluated. Results: The relation of post- and intra- implant D90 which represents a quality factor of the precision of the implant was 0.9 on average for small and large prostates.The median D90 was 157Gy (108% of prescribed dose) and does not change significantly (1%) with the prostate volume. The 82% (V>45cm3) and 94% (V<45cm3) of implant cases showed a D90 higher than 140Gy. The median V150 was 55% for large prostates, increasing slightly up to 58% for small volumes. On the other hand, this parameter was always higher in the postimplant dosimetry than during the implantation, but it did not exceed the 61%. The postimplant V150 changed up to 2% (on average) compared to the one obtained at the implant day. Conclusions: The relationship between dosimetric parameters of real implant and posterior outcomes has been established. Our preliminary results suggest that a V150 between 55 – 60% during implantation can translate in a better quality of the implant, achieving with a high probability a D90 of at least of 140Gy in the postimplant dosimetry. Future initiatives involve performing this evaluation in correlation with clinical factors as urinary morbidity, rectal morbidity, PSA values or posterior patient complications. EP-1935 Clinical evaluation of HIPO algorithm for HDR prostate cancer brachytherapy C. Alves de Oliveira1, A. Matos1, H. Azevedo2, M.C. Lopes1 1 Instituto Portugues de Oncologia de Coimbra, Medical Physics, Coimbra, Portugal 2 Universidade de Coimbra, physics, Coimbra, Portugal Purpose/Objective: Evaluate in a retrospective study the efficiency, main strengths and limitations of the Hybrid Inverse Treatment Planning and Optimization (HIPO) algorithm, available in Oncentra Prostate software, v 4.1.3., from Elekta, in the determination of optimal catheter position and source loading in real-time, Ultrasound based, HDR prostate brachytherapy treatment (BT) plans. Materials and Methods: In our clinical routine HDR BT are delivered to high risk prostate cancer patients as a boost (two implants, 15 days apart, with a total prescribed dose of 19 Gy). Catheters distribution within the prostate is decided manually and the treatment planning and optimization is performed using an inverse optimization algorithm followed by a graphical optimization tool. Based on anatomical and dosimetric constraints, the HIPO algorithm is capable to provide optimized catheters distribution to meet the required dose-volume criteria Nine patients (18 implants) already treated with HDR BT were randomly chosen. For each of the corresponding implants, different treatment plans were calculated based on HIPO purposed solutions: i) imposing the same number of catheters used to treat the patients, ii) using the number of catheters suggested by HIPO and iii) reducing it further. The treatment plans assessment was performed based on the dose distributions and on the dose-volume quality indexes: D90 and V100, (D90>90% , V100>95% of the prescribed dose), for the prostate , D10 and Dmáx for both the urethra (D10<13.5Gy, Dmáx<15.75Gy) and rectum (D10<6.75Gy, Dmáx<7.6Gy) as organs at risk (OR). The reference treatment plan was considered to be the one approved to treat the patient. Results: HIPO treatment plans were comparable to the reference plans in what concerns both the dose distributions and the dose-volume quality indexes. The best results were achieved for prostate volumes higher than 23 cm3 where a significant reduction (<5) in the number of catheters was achieved without compromising the treatment plan quality. For smaller prostate glands calculated dose distributions often show very large high-dose volumes within the anterior part of the prostate because of the dose contribution from the upper catheters. Conclusions: Especially for prostate volumes higher than 23cm3, HIPO performance allows, within acceptable calculation times, to achieve dose distribution and Dose-Volume quality indexes comparable to approved plans with a lower number of catheters. Nevertheless, it is important to further test its performance in clinical environment especially because a lower number of catheters raise the need for a precise implantation.
S335 EP-1936 Gamma H2AX and 53BP1 foci in lymphocytes correlate with rectal dosimetry in low dose rate I125 prostate brachytherapy D. Brady1, S. Horn1, D. Mitchell2, K. Prise1, J. O'Sullivan1 1 Queens University Belfast, Centre for Cancer Research and Cell Biology, Belfast, United Kingdom 2 Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, Belfast, United Kingdom Purpose/Objective: Current dosimetric estimations for low dose rate brachytherapy post seed implantation are calculated upon CT image derived models. While blood derived radiation biomarkers can provide an in vivo estimation of dose for large volume acute radiation exposures their utility for the small volume prolonged low dose rate exposures seen with LDR brachytherapy has yet to be established. The histone H2AX is phosphorylated to gamma H2AX at the sites of radiation induced DNA double stranded breaks where it co-localises with the DNA repair protein 53BP1 forming distinct nuclear foci. In this pilot study we investigated whether the use of these radiation biomarkers correlates with the CT derived physical dose. Materials and Methods: 10 patients with low risk prostate cancer treated with low dose rate I125 brachytherapy were recruited. Peripheral venous blood was sampled baseline prior to brachytherapy and at 1 hour, 4 hours, 24 hours and 4 weeks post seed implantation. Samples where immediately placed on ice before the peripheral blood lymphocytes (PBL) were separated from whole blood, fixed and stained with immunofluorescent antibodies for gamma H2AX and 53BP1. Individual gamma H2AX and 53BP1 foci which co-localised were counted using fluoresce microscopy. Patient dosimetry was calculated at a 4 week post implantation CT scan. Results: Mean gamma H2AX-53BP1 foci counts increased significantly above baseline for all time points sampled post implantation, peaking at 4 weeks. There was a significant positive correlation between mean PBL foci count at 24 hours and V100 to rectum (two tailed Spearman correlation coefficient 0.758, p=0.011). Conclusions: Evidence of DNA damage can be detected in PBLs from as early as 1 hour post seed implantation in patients undergoing low dose rate I125 prostate brachytherapy. Mean gamma H2AX-53BP1 foci count in PBL at 24 h post implantation warrants further investigation as an in vivo biomarker for rectal dose. EP-1937 Migration of coated and non-coated seed types at day zero and after four weeks after LDR prostate implant F.A. Siebert1, A. Arndt1, P. Jiang1, J. Dunst1 1 University Clinic of Schleswig-Holstein, Clinic of Radiotherapy, Kiel, Germany Purpose/Objective: To investigate the migration of coated and noncoated seed types in low dose rate brachytherapy of the prostate. Materials and Methods: Two different seed models were implanted in prostate cancer patients between 2006 and 2012. Either the seed model IsoSeed-S17 (Eckert&Ziegler Bebig, Berlin,Germany) or the AnchorSeed (BioCompatibles Inc., Oxford, UK) was used for one patient. The AnchoSeed type has a bio compatible coating to minimize seed migration. In our cohort 55 patients were implanted with the S17 type, 46 with the AnchorSeed; both as single seed implant by a Mick applicator. One experienced operator performed all implants with a prescription dose of 145 Gy and single activity per seed of 0.5 mCi. Post planning CT scans were acquired for all patients one to four hours after the implant (CT1), followed by another CT scan after four weeks (CT2). Seed reconstruction in the CT data sets was carried out using the VariSeed 8 (Varian Medical Systems, Palo Alto, CA) treatment planning software. The coordinates of the seed centers were exported and loaded to an in-house MATLAB routine (Mathworks, Natick, MA). In that software theEuclidian distance between migrated seeds outside the implanted 'seed cloud' in cranial direction was determined. The minimal distance when a source was labeled 'migrated' was set at 1.0 cm. Locations and distances to the 'seedcloud' were evaluated for all migrated sources for the two CT data sets. Results: Seed migrations were found in 21 (S17), resp. 12 (AnchorSeeds), patients in the two cohorts for CT1. For the CT2 13 patients showed migrated seeds for both source types. Mean number of migrated seeds was 1.67, resp. 1.92, for CT1 and 1.92, resp. 1.62 for CT2. In the table below the mean distances of migrated sources to the'seed cloud' are shown. It is remarkable that mean distances for the AnchorSeed type are smaller than for the IsoSeed S16. Moreover the standard deviations for this parameter are higher for the S17 model.
S335 EP-1936 Gamma H2AX and 53BP1 foci in lymphocytes correlate with rectal dosimetry in low dose rate I125 prostate brachytherapy D. Brady1, S. Horn1, D. Mitchell2, K. Prise1, J. O'Sullivan1 1 Queens University Belfast, Centre for Cancer Research and Cell Biology, Belfast, United Kingdom 2 Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, Belfast, United Kingdom Purpose/Objective: Current dosimetric estimations for low dose rate brachytherapy post seed implantation are calculated upon CT image derived models. While blood derived radiation biomarkers can provide an in vivo estimation of dose for large volume acute radiation exposures their utility for the small volume prolonged low dose rate exposures seen with LDR brachytherapy has yet to be established. The histone H2AX is phosphorylated to gamma H2AX at the sites of radiation induced DNA double stranded breaks where it co-localises with the DNA repair protein 53BP1 forming distinct nuclear foci. In this pilot study we investigated whether the use of these radiation biomarkers correlates with the CT derived physical dose. Materials and Methods: 10 patients with low risk prostate cancer treated with low dose rate I125 brachytherapy were recruited. Peripheral venous blood was sampled baseline prior to brachytherapy and at 1 hour, 4 hours, 24 hours and 4 weeks post seed implantation. Samples where immediately placed on ice before the peripheral blood lymphocytes (PBL) were separated from whole blood, fixed and stained with immunofluorescent antibodies for gamma H2AX and 53BP1. Individual gamma H2AX and 53BP1 foci which co-localised were counted using fluoresce microscopy. Patient dosimetry was calculated at a 4 week post implantation CT scan. Results: Mean gamma H2AX-53BP1 foci counts increased significantly above baseline for all time points sampled post implantation, peaking at 4 weeks. There was a significant positive correlation between mean PBL foci count at 24 hours and V100 to rectum (two tailed Spearman correlation coefficient 0.758, p=0.011). Conclusions: Evidence of DNA damage can be detected in PBLs from as early as 1 hour post seed implantation in patients undergoing low dose rate I125 prostate brachytherapy. Mean gamma H2AX-53BP1 foci count in PBL at 24 h post implantation warrants further investigation as an in vivo biomarker for rectal dose. EP-1937 Migration of coated and non-coated seed types at day zero and after four weeks after LDR prostate implant F.A. Siebert1, A. Arndt1, P. Jiang1, J. Dunst1 1 University Clinic of Schleswig-Holstein, Clinic of Radiotherapy, Kiel, Germany Purpose/Objective: To investigate the migration of coated and noncoated seed types in low dose rate brachytherapy of the prostate. Materials and Methods: Two different seed models were implanted in prostate cancer patients between 2006 and 2012. Either the seed model IsoSeed-S17 (Eckert&Ziegler Bebig, Berlin,Germany) or the AnchorSeed (BioCompatibles Inc., Oxford, UK) was used for one patient. The AnchoSeed type has a bio compatible coating to minimize seed migration. In our cohort 55 patients were implanted with the S17 type, 46 with the AnchorSeed; both as single seed implant by a Mick applicator. One experienced operator performed all implants with a prescription dose of 145 Gy and single activity per seed of 0.5 mCi. Post planning CT scans were acquired for all patients one to four hours after the implant (CT1), followed by another CT scan after four weeks (CT2). Seed reconstruction in the CT data sets was carried out using the VariSeed 8 (Varian Medical Systems, Palo Alto, CA) treatment planning software. The coordinates of the seed centers were exported and loaded to an in-house MATLAB routine (Mathworks, Natick, MA). In that software theEuclidian distance between migrated seeds outside the implanted 'seed cloud' in cranial direction was determined. The minimal distance when a source was labeled 'migrated' was set at 1.0 cm. Locations and distances to the 'seedcloud' were evaluated for all migrated sources for the two CT data sets. Results: Seed migrations were found in 21 (S17), resp. 12 (AnchorSeeds), patients in the two cohorts for CT1. For the CT2 13 patients showed migrated seeds for both source types. Mean number of migrated seeds was 1.67, resp. 1.92, for CT1 and 1.92, resp. 1.62 for CT2. In the table below the mean distances of migrated sources to the'seed cloud' are shown. It is remarkable that mean distances for the AnchorSeed type are smaller than for the IsoSeed S16. Moreover the standard deviations for this parameter are higher for the S17 model.