OC-45 FEASIBILITY OF ADC MAPPING IN ASSESSMENT OF TUMOR RESPONSE IN MRI-BASED HDR BRACHYTHERAPY FOR CERVICAL CANCER

World Congress of Brachytherapy 2012 OC-44 MODELS FOR BRACHYTHERAPY DOSE DE-ESCALATION IN LOW RISK LOCALLY ADVANCED CERVICAL CANCER PATIENTS S. Mohamed1, K. Tanderup1, C. Kirisits2, R. Pötter2, J.C. Lindegaard1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark 2 Medical University of Vienna, Department of Radiotherapy, Vienna, Austria Purpose/Objective: Image guided adaptive brachytherapy (BT) delivers high doses to the tumor and high rates of local control have been achieved. The prospective EMBRACE study evaluates the outcome of image guided adaptive BT and one of the purposes of EMBRACE is to set up clinical models that allow risk stratification which can promote the development of new prospective clinical studies. This study explores the possibilities of dose de-escalation for selected low risk tumours in locally advanced cervical cancer. Materials and Methods: A low risk criteria was defined as tumours of <=5 cm width on MRI at time of diagnosis and no lymph node involvement. Radiotherapy was EBRT of 45Gy/25fx and PDR BT of 17.5 Gy * 2 fractions with tandem ring applicator ± interstitial needles. Vaginal points were appointed at the level of the ring on both lateral sides at the mucosal surface and at 5mm depth indepent from the ring loading. Dose volume histogram parameters (DVH) were compared for 3 plans: 1. Optimised plan (as delivered), 2. Low dose plan which is down scaled and normalised to 85Gy to D90 HR CTV, 3. Reduced vaginal loading plan where the dwell times in the ring were reduced and a vaginal mucosa dose constraint of 140% of 17.5 Gy was applied, which is 120 Gy in total EQD2. EBRT and BT doses were summated and normalised to a 2 Gy fraction size (EQD2) using the linear quadratic model (α/β=3 Gy for OARs, α/β=10 Gy for tumour, T½=1.5h). Results: Among 60 consecutive patients of locally advanced cervical cancer 12 were included for this analysis as low risk patients. Interstitial needles were used in 2 patients. Mean HR CTV volume was 26cc and 23cc for BT1 and BT2 respectively. Table 1 presents total EQD2 dose. Optimised plans delivered high doses to the HR CTV D90 with a mean dose of 94 Gy. The doses to the vaginal surface varied widely and reached high doses in some patients with a mean dose of 211 Gy [113 – 546 Gy]. When reducing the vaginal loading, comparable target doses were achieved with significantly lowered vaginal doses with a mean value of 102 Gy [82 – 119 Gy]. The low dose plan normalised to 85 Gy de-escalated the HR-CTV D90 by a mean of 9Gy while reducing dose to OARs by 3-6Gy, and point A doses lower than 70Gy were frequently observed. Median point A doses were 72Gy, 67Gy, and 72Gy in plan 1, 2 and 3, respectively. Table 1: Mean doses values + standard deviation of total EQD2 dose for EBRT + brachytherapy in Gy.

S 19 for small tumours at BT and reducing the vaginal loading may be a further step for better therapeutic gain. This hypothesis needs to be tested in a prospective clinical study. OC-45 FEASIBILITY OF ADC MAPPING IN ASSESSMENT OF TUMOR RESPONSE IN MRI-BASED HDR BRACHYTHERAPY FOR CERVICAL CANCER K. Hosseinzadeh1, M.S. Rajagopalan2, S. Beriwal2 1 University of Pittsburgh Medical Center, Radiology, Pittsburgh PA, USA 2 University of Pittsburgh Cancer Institute, Radiation Oncology, Pittsburgh PA, USA Purpose/Objective: GEC-ESTRO recommends T2-weighted MRI for assessment of residual disease and 3D high dose-rate brachytherapy (HDR-BT) planning for cervical cancer. It can be difficult to distinguish radiation changes from residual tumor on this sequence. Diffusionweighted imaging (DWI) is sensitive to diffusion of water molecules in tissue and has shown promise in characterizing pathological processes at a microscopic level. Tumor cell death and corresponding changes in water homeostasis are reflected in increased apparent diffusion coefficients (ADC) on DWI. The goal of this study was to determine the feasibility of ADC mapping with ring and tandem applicator in place and to compare the response to therapy with conventional T2weighted sequence. Materials and Methods: Patients diagnosed with cervical cancer underwent MRI-based HDR-BT. Pre-EBRT MRI (pre-RT MRI) was compared to the final treatment planning MRI during HDR-BT (post-RT MRI). Patients without T2 signal abnormality on any post-RT MRI were excluded from the study. All studies were interpreted by a board certified radiologist experienced in pelvic MRI. Signal intensity was measured in the tumor volume (T2-Tumor) and in the psoas muscle (T2-Psoas) by drawing a region-of-interest. In a similar fashion, corresponding tumor ADC values were measured. The T2 signal of the tumor was then normalized by calculating the ratio between T2Tumor and T2-Psoas (T2-Ratio). Treatment response was determined using a paired t-test for T2 Tumor, T2-ratio, and ADC values. Results: 11 patients with both pre-RT and post-RT MRI performed at the same institution were included. Average age was 48.9 years and 91% had squamous cell histology. In the post-RT images, T2-Tumor was significantly lower than that in the pre-RT images (418.5 vs. 605.6, p=0.03) and there was no difference in T2-Psoas. T2-Ratio demonstrated a statistically significant decrease with treatment (1.7 vs. 2.6, p=0.04). In three patients in whom the T2-Tumor increased in the post-RT study (mean: +37.8%), the T2-Ratio decreased (mean: 38.4%). ADC values demonstrated a highly significant increase with treatment (1509.9 vs. 1037.0, p<0.0001) in all patients. The average percentage change from pre-RT to post-RT for ADC was +46.4% (range: +11.1% – +81.0%) and for T2-Ratio -26.2% (range: -80.6% – +10.4%). Conclusions: This preliminary study demonstrates the feasibility for measuring the ADC values in treatment planning scans with applicator in place for patients undergoing HDR-BT. Normalization of T2-Tumor to T2-Psoas appears to more accurately reflect response to therapy than absolute T2 signal intensity. In addition, ADC values demonstrated a highly significant increase in post-RT images, also consistent with treatment response. Studies with larger cohorts are needed to establish optimal imaging parameters in defining residual disease at the time of brachytherapy and correlation with outcomes based on ADC values. OC-46 HIGH DOSE RATE (HDR) INTRAOPERATIVE BRACHYTHERAPY IN THE MANAGEMENT OF RECURRENT GYNECOLOGIC MALIGNANCIES L.M. Scala1, D. Chi2, B. Bochner2, V. Andikyan2, S. Gerst2, J. Sandhu2, P. Boland2, Y. Sonoda2, K. Alektiar1 1 Memorial Sloan-Kettering, Radiation Oncology, New York, USA 2 Memorial Sloan-Kettering, Surgery, New York, USA

Conclusions: In low risk patients it is possible to manipulate the source loading pattern to de-escalate doses to the vagina and still obtain comparable doses to the target volumes. Dose de-escalation and normalisation to a HR CTV D90 of 85 Gy resulted in low point A doses in a significant number of patients. Studying dose de-escalation

Purpose/Objective: To report a single institution experience with HDR intraoperative brachytherapy and radical resection in patients with recurrent gynecologic malignancy and to determine the influence of potential prognostic factors. Materials and Methods: Between 6/1993-12/2008, 72 patients with recurrent gynecologic malignancy underwent radical resection with