Comparison of value of biologically equivalent dose (BED) in clinical target volume (CTV) and surrounding healthy organs after PDR and HDR brachytherapy

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Abstracts / Brachytherapy 6 (2007) 77e118

delivered doses with standard deviations of 0.34% and 0.53% at 50 and 40 kVp, respectively. All authors are employees of Xoft, Inc. PO-37 Positron-emitting microspheres for assessing dose distributions in liver microsphere brachytherapy Reed G. Selwyn, M.A.1 Miguel A. Avila-Rodriguez, M.S.1 Robert J. Nickles, Ph.D.1 Bruce R. Thomadsen, Ph.D.1,2 James S. Welsh, M.D., F.A.C.R.O.2 1Medical Physics, University of Wisconsin, Madison, WI; 2 Human Oncology, University of Wisconsin, Madison, WI. Purpose: Microsphere brachytherapy, also known as selective internal radiation therapy (SIRT), is a brachytherapy technique in which radiation is delivered by microspheres injected into regions of the liver intraarterially. The radioisotope, 90Y, is either surface loaded on resin spheres (SIR-SpheresÒ, Sirtex Medical) or impregnated in glass spheres (TherasphereÒ, M.D.S. Nordion). The therapy is FDA approved for unresectable hepatocellular carcinoma and metastatic hepatic cancer. This treatment has shown promise but presently there is difficulty in demonstrating a clear relationship between administered activities and patient outcome. The minuscule gamma radiation of 90Y makes assessing the in vivo distribution of 90Y-labeled microspheres difficult and, for simplification, homogeneous distributions are typically assumed. Research on explanted livers has shown that microspheres preferentially deposit in tumors with uptake ratios ranging between 1:1 and 200:1. These ratios are not utilized when calculating tumor and liver doses, however, and can lead to the underestimation of tumor dose and overestimation of liver dose. The purpose of this research is to develop positron-emitting microspheres that will accurately assess the in vivo distribution of 90Y-labeled microspheres. Methods and Materials: 18F (t1/2 5 1.8 h) produced via the 18O(p,n) reaction was tagged to yttrium loaded SIR-SpheresÒ using a ‘shake and bake’ approach and the stability of the radiolabeling was evaluated in HSA and canine serum at 37  C for several hours. A GE Discovery LS PET/CT scanner was used to assess the activity concentration of 18F while in the presence of 90Y bremsstrahlung. Results: The radiolabeling efficiency of 18F was nearly quantitative and the in vitro stability was O99%. The radiolabeling method developed in this study is quick and suitable to be performed by a nuclear pharmacist. The presence of 25 mCi of 90Y-labeled microspheres in the PET field of view was insignificant on the quantification of 1 mCi of 18F. Conclusions: The use of 18F-labeled SIR-SpheresÒ to mimic the in vivo distribution of 90Y-labeled SIR-SpheresÒ holds great potential for accurate and quantitative pre-assessment and post-assessment of SIRT treatments and could be used for treatment optimization. A commercial device that is approved by the FDA has been radiolabeled with a positron emitter. The PET-labeled device is not approved by the FDA and is for investigational use only. PO-38 Monte Carlo characterization of Cs-131 brachytherapy source Mark J. Rivard, Ph.D. Radiation Oncology, Tufts-New England Medical Center, Boston, MA. Purpose: Currently there is one publication, Murphy et al., which presents dosimetry results and the brachytherapy dosimetry parameters for the IsoRay Medical model CS-1 Cs-131 brachytherapy source. Murphy et al. included a TLD-measured value for the dose rate constant which differed substantially from that subsequently published by Chen et al. Upon comparison of Murphy et al. measured and calculated radial dose function results, significant differences were observed at large distances from the source. This study aims to a) resolve those differences, b) present Monte Carlo-derived brachytherapy dosimetry parameters, and c) assess a variety of radiological properties of Cs-131 for comparison with established low-energy sources such as I-125 and Pd-103. Methods and Materials: Preceding Monte Carlo calculations, dimensions and construction of the source capsule and internal components were compared to manufacturer-provided dimensions and tolerances. The

MCNP5 radiation transport code was used to calculate dose rate distributions for the model CS-1 source from 0.05 to 15 cm typically with 1 mm increments and from 0 < q < 180 in liquid water, Solid Water, and Plastic Water. The Cs-131 photon spectrum was characterized as 6 discrete photons, E1-E6. In addition to determining the TG-43 dosimetry parameters, dependence of results on source orientation, cross-section library, and photon energy was assessed. The dose rate constant was determined in vacuo through multiplication of the *F4 cell energy fluence estimator by energy-specific Hubbell and Seltzer men/r coefficients. Results: Radial dose function results for the Cs-131 spectrum, E1-E6, and the averaged mono-energetic source showed a small dependence of results on energy. In liquid water, we obtained g(0.05) 5 1.05, g(0.1) 5 0.96, g(0.5) 5 1.01, g(2) 5 0.91, g(5) 5 0.52, g(10) 5 0.15, and g(15) 5 0.04. Substantial differences in gL(r) were observed for the MCPLIB03p and MCPLIB04p cross-section libraries, explaining results obtained by Murphy et al. to within 1%. Capsule orientation produced changes within 5% for everything except MCF(r!1 cm,q) and only within 10 of the source long axis due to the 0.16 mm offset possible with the tightlywelded capsule. Modeling Cs-131 emissions as a mono-energetic photon source differed by >2% from the more detailed spectrum only for r > 13 cm. Our MCL value of 1.046  0.019 cGy h 1 U 1 was within 2% of that determined by Chen et al. and by Wittman and Fisher. Conclusions: This comprehensive analysis of the IsoRay Medical model CS-1 Cs-131 brachytherapy source demonstrated good agreement of MCgL(r) and MCF(r,q) results in Virtual WaterÔ with uncorrected ExPgL(r) and MCF(r,q) results in Virtual WaterÔ by Murphy et al. Similar good agreement of our MCL with ExPL in liquid water from Chen et al. and MCL from Wittman and Fisher was observed. Prof. Rivard has received financial support for this research. PO-39 Comparison of value of biologically equivalent dose (BED) in clinical target volume (CTV) and surrounding healthy organs after PDR and HDR brachytherapy Janusz Skowronek, M.D., Ph.D.1 Julian Malicki, Asst Prof.2 1 Brachytherapy, Greatpoland Cancer Center, Poznan, Poland; 2Medical Physics, Greatpoland Cancer Center, Poznan, Poland. Purpose: Pulsed-dose-rate (PDR) treatment is a new brachytherapy modality that combines the physical advantages of high-dose-rate (HDR) technology (isodose optimization and radiation safety) with the radiobiological advantages of low-dose-rate (LDR) brachytherapy. In many locations the same tumors can be treated by PDR or HDR brachytherapy. The aim of this work is to compare PDR and HDR doses calculated in clinical target volume (CTV) and surrounding healthy organs. Influence of optimization on dose value was analyzed. Methods and Materials: Fifty-one patients treated in Greatpoland Cancer Center from May 1999 to December 2002 were qualified for calculations. There were 22 males (43.1%) and 29 females (56.9%). Age ranged from 22 to 85 years, median 53 years. Doses calculation were made in 15 patients with head and neck cancer, 23 patients with brain tumor, 8 patients with breast cancer, 3 patients with sarcoma, 1 with penile cancer and 1 with rectal cancer. Doses were calculated using PLATO planning system (Nucletron) in prescribed reference point (CTV) and in chosen critical points in surrounded health organs. For all treatment plans doses were compared using BED formula. In every case optimization on distance and on volume were fulfilled and, then, doses compared. The Friedman ANOVA test and Kendall ratio were used for statistical analysis. Results: Dose value analysis after PDR brachytherapy shows unexpected growth (from 1.9 Gy till 13.4 Gy) in most critical points in healthy organs after optimization (Kendall 5 from 0.48 to 1.0, p 5 from 0.002 to 0.00001). This could lead to an increased risk of late complications. After conversion of PDR and HDR doses differences in CTV and healthy tissues doses were observed. The median value of BED in chosen critical points was statistically related to the methoddit was lower in HDR then in PDR method. We noted that for equal biological effect in CTV we should probably decrease total doses in case of replace PDR by HDR brachytherapy and in case of increase of HDR fraction dose, too. For example, replacing PDR by HDR (fraction of 4 Gy daily) indicates decreasing of total dose up to 81.4% PDR dose.

Abstracts / Brachytherapy 6 (2007) 77e118 Conclusions: Optimization in PDR improve homogeneity in CTV but probably cause unexpected, clinically and statistically unfavorable dose growth in surrounded health organs. The risk of late complications probably increase. Conversion of PDR and HDR doses using BED formula could be useful in daily clinical practice. Treatment plan should contain calculations of doses value in surrounded health organs, especially in those responsible for higher risk of late complications. PO-40 Breast permanent seed implant as a boost Nicolas Jansen, M.D., Philippe Nickers, M.D., Ph.D. Radiation Oncology, Liege University Hospital (Sart Tilman), Liege, Belgium. Purpose: To evaluate the feasibility of a permanent seed implant technique for breast brachytherapy and to report short-term toxicity. This experience was based on 15 boost treatments. Methods and Materials: During adjuvant external whole breast radiotherapy (50 Gy in 25 fractions) a simulation was organized for 15 patients with an indication for boosting. The breast was fixed with a thermoplastic sheet and a ‘template bridge’ was applied, mildly compressing the breast. The needle guiding bridge was placed in such a way that the tumor bed was covered by the template under fluoroscopic control and reference points were placed on the sheet and patient. A CT/MRI scan was obtained and the image set rotated to get images perpendicular to the implant axis. A 4e5 mm thick skin layer, ipsilateral lung, heart (for left sided breasts) and CTV were delineated. For this boost series the CTV was defined as the tumor bed plus a margin of >2 cm, amounting in practice to the volume of a breast quadrant. A preplan was made prescribing a very low dose rate dose of 50 Gy to the CTV, using ProwessÒ v4.2. For early/tumor effects, this dose is considered biologically equivalent to a 16 Gy boost in 8 fractions. Skin doses should be below 30 Gy. The breast was immobilized in the same position using the reference points and under general anesthesia 8e20 needles were placed and 29e80 0.3 mCi Iodine-125 seeds in strands (InterstrandÒ, IBt, Seneffe, Belgium) were implanted through the template. A short fluoroscopy at the end of the implant was done to check implant consistency. The implant results were verified with a postplan scan 2 weeks later, on which the CTV was not contoured because of a different breast orientation and absence of markers in some patients. Results: The simulation and implant procedure were feasible and well tolerated: no short term toxicity over grade I after a mean followup of 18 months (range 6e21) except for one case of transient grade III arm neuropathy. Grade I toxicity included mild edema or hyperpigmentation, possibly related to previous external radiotherapy. Fluoroscopy showed good strand insertion, with the exception of a mild shift in a few strands. The preplan and dose volume histogram showed a good CTV coverage (CTV V100% 5 97  3.8%). Organs at risk were well spared: the mean postplan for skin, heart and lung V30 Gy were 2, 0, and 4 mL, respectively. The postplan showed a mild seed dispersion because of breast edema and relaxation after sheet removal. No local recurrences were observed. Conclusions: The described technique is feasible and offers good protection or organs at risk. It is too early to evaluate late or cosmetic results, but at 18-month mean followup very little local toxicity was seen except one Grade III transient neurological problem. A trial testing this approach for partial breast irradiation has started. The seed strands used for these treatments were made available free of charge by IBT, who also provided an unrestricted grant. PO-41 Outpatient brachytherapy in 37 patients with brain tumors using the GliaSiteÔ radiation therapy system Kazumi Chino, M.D.1 Baldassarre Stea, M.D., Ph.D.1 Daniel Silvain, M.S.2 Ana Grace, M.D.3 1Radiation Oncology, University of Arizona, Tucson, AZ; 2Radiation Control Office, University of Arizona, Tucson, AZ; 3 Radiation Oncology, Los Angeles, CA. Purpose: Temporary low-dose-rate brachytherapy to the margins of resected brain tumors, using a balloon catheter system (GliaSite Radiation Therapy System) and liquid I-125 radiation source (Iotrex) began in 2002

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at the University of Arizona Medical Center. Initially, all patients were treated on an in-patient basis. For patient convenience and reimbursement issues, we converted to outpatient therapy, after the radiation safety concerns were reviewed thoroughly by the Radiation Safety officer. To date, 37 patients have been safely treated on an outpatient basis at this institution; in this paper we review the exposure data and safety history pertaining to this group of patients. Methods and Materials: Proper patient selection and instruction is crucial to having a successful outpatient brain tumor brachytherapy program. A set of evaluation criteria and patient instructions were developed and used in implementing this program. The criteria and instructions were developed in compliance with the U.S. Nuclear Regulatory Commission’s document, NUREG-1556 Volume 9 (Appendix U) and Arizona State Nuclear regulatory guidelines. In general, patients must be able to care for themselves and agree to several restrictions on activities, mainly related to minimizing potential exposure of other people to radiation. Results: Most patients had either recurrent glioblastoma multiforme (GBM) (n 5 26) or metastatic brain tumors (n 5 5), and 6 patients were treated for primary GBM. All 37 patients evaluated for release during brachytherapy, and their primary caregiver, gave signed agreement to follow a specific set of instructions and were released for the duration of brachytherapy (3e7 days). The typical prescription dose was 60 Gy delivered at 0.5 cm from the balloon surface. Afterloaded activities in these patients ranged from 90.9 mCi to 750.0 mCi and measured exposure rates at 1 meter from the head were less than 14 mR/hr. The mean dose to the caretaker measured by dosimetry for 25 caretakers was found to be 9.6 mR. All patients completed brachytherapy without serious adverse events or radiation safety violations and returned to the department on time for retrieval of the radioactive source material. Conclusions: Our experience in treating post-resection brain tumor patients with GliaSiteÔ brachytherapy, as outpatients, has been successful and uneventful. For properly selected patients, outpatient therapy provides a simple, safe means of completing this form of brachytherapy. Finally, outpatient treatment is more convenient for the patient and, in our experience, can be successfully reimbursed. PO-42 An analysis of clinical outcomes in patients with stage IB endometrial cancer treated with vaginal brachytherapy only Virginia M. Diavolitsis, M.D., John Lurain, M.D., Julian Schinck, M.D., Diljeet Singh, M.D., Barbara Buttin, M.D., William Small, M.D. Radiation Oncology, Northwestern University, Chicago, IL. Purpose: This analysis was undertaken to determine patterns of recurrence and survival in patients with endometrial cancer, Stage IB, treated with vaginal brachytherapy only. Methods and Materials: All patients treated with hysterectomy for endometrial cancer at Northwestern Memorial Hospital between 1979 and 2005 were identified and those treated with vaginal brachytherapy only were included in this report. All patients had adenocarcinoma histology, clear cell and serous histologies were excluded. All patients had Stage IB disease. Ninety patients were identified and included in this analysis. Results: The median followup for the entire group was 118 months (1e265). The mean age was 59 (std dev 11, range 38e72). The majority underwent lymph node staging. 45 had Grade 1 disease, 38 had Grade 2 disease, and seven had Grade 3 disease. The mean number of days to first dose of radiation therapy was 47. The total prescribed brachytherapy dose was most commonly 2100 cGy in three fractions prescribed to 0.5 cm from the vaginal mucosa for high-dose-rate brachytherapy. For low-dose-rate brachytherapy, the most common prescription was 7000 cGy at 100 cGy per hour using Cesium afterloading techniques. Four patients (4.4%) had a recurrence. Of these patients, two had Grade 1 histology, one had Grade 2 histology, and one had Grade 3 histology. Two patients had lymphatic permeation, none had vascular permeation of the tumor. Two of these patients had lymph node staging. Recurrences were noted 16, 18, 39, and 100 months after surgery. Location of the initial sites of recurrences were pelvic (3), inguinal lymph node (1), upper abdomen (2), and lung (1). Two patients had multiple sites of initial recurrence. No patient had a vaginal cuff