Hypofractionated Intensity Modulated Radiation Therapy for Localized Prostate Cancer: Long-term Outcomes and a Comparison to Standard Dose-Escalated RT

S152

International Journal of Radiation Oncology  Biology  Physics

treated with VMAT and IMRT. This method could be utilized routinely for complex treatment validations. Author Disclosure: M. Lin: None. L. Jinsheng: None. C. M. Charlie Ma: None.

Purpose/Objective(s): The goal of this study was to investigate systematically the imaging dose to the cardiac implantable electronic devices (CIEDs) from routine kilo-voltage cone-beam CT (kVCBCT) scans and its dependence on the patient dimension, the scan protocol as well as the location of CIED. Materials/Methods: For the patients with CIEDs who receive frequent image guidance during their radiation therapy treatments, x-rays from kVCBCT scans could pose a risk of CIED malfunction. Three patients with pacemakers scanned by a kVCBCT scanner were selected for this study. The pacemaker, along with other critical structures such as the heart, the lungs, the trachea, the esophagus and the spinal cord were delineated on a commercial treatment planning system. For each patient this data was then converted to patient CT phantom for Monte Carlo simulations with an in-house DICOM utility tool. A benchmarked EGS4 Monte Carlo code was used to calculate the 3D dose distributions in the patients scanned with three different protocols provided by the manufacturer: low-dose thorax, pelvis and high-quality head. Any correlations between the mean dose to the pacemaker and the following parameters were investigated: (i) the patient size (calculated as the square root of the product of AP and LAT), (ii) the scan protocol and (iii) the distance from the scan center to the CIED along superior-inferior direction. Results: The mean dose to the CIED per kVCBCT scan was found to be 1.5, 6.2, and 0.9 cGy in the low-dose thorax, pelvis and high-quality head protocols, respectively. Our results indicate that the CIED dose decreased exponentially with the distance measured from the scan center to the center of device, both superiorly and inferiorly. There was a sizable difference (up to 12%) in the CIED doses between the two directions, with higher doses scored inferiorly due to the increased scatter from the patient. A linearly decreasing correlation was observed between the patient size and the kVCBCT-contributed imaging doses, with lower doses in larger-size patients. Conclusions: While mega-voltage photon beams contribute approximately 2.0 to 9.0 cGy scattered dose to the CIED per fraction around the chest, each kVCBCT scan could deposit 0.6 to 7.1 cGy additional dose to the CIED depending on the scan scenarios and patient size. Combining the contributions from kVCBCT scans and MV photon beams in a typical IGRT treatment course (45 Gy in 18 fractions with 18 kVCBCT scans), the total dose to the pacemaker was as high as 190 cGy in one of the 3 patients studied. This is quite close to the threshold dose of 1 to 5 Gy suggested by various CIED manufacturers. Hence, it is important to include the kVCBCT-deposited dose to the pacemaker and other CIEDs in treatment planning and take appropriate precautions during IGRT. Author Disclosure: X. Ming: None. Y. Feng: None. Z. Chen: None. Y. Zhang: None. R. Nath: None. J. Deng: None.

1011 Establishment of an Easy-to-Handle Quality Assurance (QA) Tool Using Plastic Scintillator for Dynamic Parameters of VMAT S. Akita,1 H. Takei,2 F. Matsubayashi,3 H. Asai,4 Y. Kamikubo,5 S. Nakamura,6 K. Sakata,1 Y. Nakayama,1 K. Maruyama,7 and K. Hayakawa7; 1Kanagawa Cancer Center, Kanagawa, Japan, 2Keio University, Tokyo, Japan, 3The Cancer Institute Hospital of JFCR, Tokyo, Japan, 4National Cancer Center Hospital East, Chiba, Japan, 5Kyosai Tachikawa Hospital, Tokyo, Japan, 6National Cancer Center Hospital, Tokyo, Japan, 7Kitasato University, Kanagawa, Japan Purpose/Objective(s): Radiographic film and the four-dimensional (4D) detector are used as the QA tools for VMAT. These tools are unable to evaluate variations in the dynamic parameters, such as the dose rate and the gantry speed, as a function of the rotational angle. A plastic scintillator (PS) that is sensitive to the dynamic movement of the irradiation can be used for the measurement of these parameters. We compared the parameters measured using a PS with those measured with the 4D detector and those in the log file. The purpose of this study is to establish an easy-tohandle QA tool that is able to evaluate the dynamic parameters of VMAT. Materials/Methods: A 20-cm diameter and 10-cm thick PS disk was placed on the beam axis. A digital video camera recorded the scintillation light. The experiment was performed using 6 MV X-rays. The gantry rotation angle was 360 and the irradiation field was 2 2 cm2. The dose rate, angular dependence, and systematic setup errors were evaluated. The same geometric configuration and irradiation conditions of the 4D detector and the PS disc were used for the measurement of the dynamic parameters. In order to evaluate linearity of the dose rate, the PS light yield, and the counts of the 4D detector, irradiation of the static gantry was performed with a varying dose rate of 100-600 MU/min. Various gantry speeds (Sset) for rotation irradiation were established at 1.8, 2.3, 3.0, and 4.5 /s with a constant dose rate Ds of 600 MU/min. The log file recorded the gantry rotation angle and monitor units (MUs) every 50 ms. Results: The light yield of the PS and the counts of the 4D detector were proportional to the dose rate. The average measurement error of the gantry speed with the PS was 0.23 /s. The dose rate and the gantry speed measured by the PS were compared to those in the log file and those measured by the 4D detector. The differences between the PS and the log file (YPS,log) and the PS and the 4D detector (YPS,Arc) were calculated for each irradiation condition. Maximum mean values and standard deviations (ss) for the dose rate at YPS,log and YPS,Arc were 19.2  34.3 MU/min and 26.6  38.4 MU/min, respectively. Maximum mean values and ss for the gantry speed at YPS,log and YPS,Arc were 0.0  0.2 /s and 0.1  0.6 /s, respectively. These experimental findings suggest that the measurement accuracies for the dynamic parameters with the PS are equal to those of the 4D detector. Measurements of these parameters using the PS were possible at all angles under fundamental clinical conditions. Conclusions: We established an easy-to-handle QA tool with a PS disk that can evaluate the dynamic parameters of VMAT. The experimental results suggest that it is possible to evaluate the dose rate and the gantry speed with accuracies of 26.6 MU/min and 0.1 /s, respectively. Author Disclosure: S. Akita: None. H. Takei: None. F. Matsubayashi: None. H. Asai: None. Y. Kamikubo: None. S. Nakamura: None. K. Sakata: None. Y. Nakayama: None. K. Maruyama: None. K. Hayakawa: None.

1012 Monte Carlo Estimation of Dose to the Cardiac Implantable Electronic Devices From a kVCBCT System Used in Image Guided Radiation Therapy X. Ming,1,2 Y. Feng,1 Z. Chen,2 Y. Zhang,1,2 R. Nath,2 and J. Deng2; 1 Tianjin University, Tianjin, China, 2Yale University, New Haven, CT

1013 Hypofractionated Intensity Modulated Radiation Therapy for Localized Prostate Cancer: Long-term Outcomes and a Comparison to Standard Dose-Escalated RT M.A. Weller,1 P.A. Kupelian,2 C.A. Reddy,1 R. Kotecha,1 J.P. Ciezki,1 E.A. Klein,1 K.L. Stephans,1 and R.D. Tendulkar1; 1Cleveland Clinic, Cleveland, OH, 2University of California Los Angeles Health System, Los Angeles, CA Purpose/Objective(s): To study the long term outcomes in patients treated for localized prostate cancer (PCA) with a hypofractionated regimen of 70 Gy at 2.5 Gy/fraction, in comparison to those treated with 78 Gy at 2.0 Gy/fraction. Materials/Methods: The study sample included 1410 patients with PCA treated between 1996 and 2009 at a single institution: 822 patients received hypofractionated radiation (HYPO) with 70 Gy delivered at 2.5 Gy/fraction using intensity modulated radiation therapy (IMRT), and 588 patients received standard fractionated (SFX) RT with 78 Gy delivered at 2.0 Gy/ fraction using either 3D conformal therapy or IMRT. Kaplan-Meier analysis was used to calculate biochemical relapse free survival (bRFS, Phoenix definition), distant metastasis free survival (DMFS), and overall

Volume 87  Number 2S  Supplement 2013 survival (OS). Prostate cancer specific mortality (PCSM) rates were calculated using cumulative incidence methods. Cox proportional hazards regression was used to identify factors predictive of bRFS, DMFS, and OS. Fine and Gray regression was used to identify factors predictive of PCSM. Results: The median follow-up for all patients was 86 months (103 months for HYPO vs 71 months for SFX). For all patients, 10-yr bRFS rates for HYPO vs SFX were 70% vs 65% (p Z 0.65); 10-yr DMFS rates were 86% vs 81% (p Z 0.45); 10-yr OS rates were 72% vs 70% (p Z 0.37); 10-yr PCSM rates were 7% vs 8% (p Z 0.89), respectively. For high risk, 10-yr bRFS rates for HYPO vs SFX were 41% vs 52% (p Z 0.003); 10-yr DMFS rates were 68% vs 71% (p Z 0.06); 10-yr OS rates were both 63% (p Z 0.56); 10-yr PCSM rates were both 15% (p Z 0.11), respectively. For intermediate risk, 10-yr bRFS rates for HYPO vs SFX were 74% vs 70% (p Z 0.70); 10-yr DMFS rates were 90% vs 84% (p Z 0.61); 10-yr OS rates were both 72% (p Z 0.56); 10-yr PCSM rates were both 5% (p Z 0.86), respectively. For low risk, 10-yr bRFS rates for HYPO vs SFX were 87% vs 85% (p Z 0.95); 10-yr DMFS rates were 97% vs 93% (p Z 0.54); 10-yr OS rates were 78% vs 76% (p Z 0.71); 10-yr PCSM rates were 3% vs 2% (p Z 0.91), respectively. Fewer patients in the HYPO group received androgen deprivation therapy, 61% vs 67% (p Z 0.02). On multivariate analysis, dose was a significant predictor of bRFS, but not DMFS, OS, or PCSM. Conclusions: After a median follow-up of nearly 9 years, the outcomes after hypofractionated radiation were acceptable and comparable to a modern series using standard fractionation in the dose-escalation era. Outcomes across risk groups were equivalent between both fractionation schemes in all endpoints, with the exception of bRFS, which showed an advantage for standard fractionation in the high risk group. Potential explanations for this difference may include uneven follow-up times, increased utilization of androgen deprivation in the SFX group, and differences in technique. A toxicity analysis will be conducted separately. Author Disclosure: M.A. Weller: None. P.A. Kupelian: None. C.A. Reddy: None. R. Kotecha: None. J.P. Ciezki: None. E.A. Klein: None. K.L. Stephans: None. R.D. Tendulkar: None.

1014 High-Dose Moderately Hypofractionated Tomotherapy for Prostate Cancer: 5-Year Results N.G. Di Muzio, C. Fiorino, A. Fodor, B. Noris Chiorda, G. Berardi, C. Cozzarini, M. Pasetti, S. Broggi, P. Mangili, and R. Calandrino; Scientific Institute S. Raffaele, Milan, Italy Purpose/Objective(s): To report the 5-year biochemical relapse-free survival (bRFS) and late toxicity of the first 99 prostate cancer (PCa) pts treated within a Phase I-II study with moderately hypofractionated imageguided helical tomotherapy (HTT). Materials/Methods: From January 2006 to July 2009, 99 PCa pts with median age of 73 yrs (56-89 yrs) underwent HTT. Forty-five pts were low risk (LR), 45 intermediate risk (IR), and 9 high risk (HR), according to NCCN staging system. LR pts were treated with 71.4 Gy/28 fr on the prostate and seminal vesicles, while IR and HR pts were treated with 51.8 Gy/ 28 fr on the pelvic lymph nodes and SIB to 74.2 Gy on the prostate. The median follow-up was 5.2 yrs (range, 4.9-5.6). Neoadjuvant and/or concomitant and/or adjuvant deprivation therapy (ADT) was prescribed in 69 pts (25 LR, 37 IR, and 7 HR pts). Late toxicities were evaluated based on RTOG/EORTC scale. Biochemical relapses (BRs) were defined according to the ASTRO definition. Results: Three pts in the LR group died for causes other than cancer. Among the 42 alive LR pts, no BRs were seen. Three pts in the IR+HR group died, one with BR, the other two for other causes; three pts were lost to follow-up. Three BRs were seen in the alive IR+HR patients (one IR and two HR patients). In total, 47 of 51 of the evaluable IR+HR patients showed to be BR-free (92.2%). In the five yrs of follow-up, 4 of 99 (4%) pts developed G3 GU late toxicity: two in the LR group were cured with catheterization/dilatation, and now G0; two in the IR+HR group improved

Digital Poster Discussion Abstracts S153 Digital Poster Abstract 1014; Table Toxicity G0GU G1GU G2GU G0GI G1GI G2GI

Low risk group (42 evaluable pts) 30/42 9/42 3/42 35/42 6/42 1/42

(71.4%) (21.4%) (7.1%) (83.3%) (14.3%) (2.4%)

Intermediate risk group (40 evaluable pts) 22/40 13/40 5/40 34/40 3/40 3/40

(55%) (32.5%) (12.5%) (85%) (7.5%) (7.5%)

High risk group (8 evaluable pts) 6/8 (75%) 2/8 (25%) 0 7/8 (87.5%) 1/8 (12.5%) 0

to last follow-up. G3GI late toxicity was experienced by 5 of 99 pts (5%): Four were cured with argon laser therapy (and now G0), one improved without therapy. The prevalence of the toxicities at the last follow-up in the evaluable patients is reported in the Table. Conclusions: This study shows excellent results regarding the 5 year biochemical control of our high-dose moderately hypo-fractionated schedule, with 0/45 BR in the LR group and 4/51 BR in the IR+HR group. Late toxicities are acceptable: G3 toxicities are manageable and all G3 patients improved their symptoms at the last follow-up. Author Disclosure: N.G. Di Muzio: None. C. Fiorino: None. A. Fodor: None. B. Noris Chiorda: None. G. Berardi: None. C. Cozzarini: None. M. Pasetti: None. S. Broggi: None. P. Mangili: None. R. Calandrino: None.

1015 Stereotactic Radiosurgery Versus Intensity Modulated Radiation Therapy for Prostate Cancer: Comparison of Early Toxicity J.B. Yu,1 L.D. Cramer,2 J. Herrin,2 P.R. Soulos,2 A.L. Potosky,3 and C.P. Gross4; 1Department of Therapeutic Radiology, Yale School of Medicine, and the Cancer Outcomes, Public Policy, and Effectiveness Research (COPPER) Center at Yale, New Haven, CT, 2Cancer Outcomes, Public Policy, and Effectiveness Research (COPPER) Center at Yale, New Haven, CT, 3Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 4Yale University School of Medicine, Cancer Outcomes, Public Policy, and Effectiveness Research (COPPER) Center at Yale, New Haven, CT Purpose/Objective(s): Stereotactic radiosurgery (SRS) is a recent innovation in the treatment of prostate cancer that has begun to disseminate into national practice. Compared to intensity modulated radiation therapy (IMRT), SRS is both technologically more intensive and less expensive due to its shorter treatment length. Although it is suggested that SRS delivers a greater biologically effective dose of radiation than IMRT, with the potential for improved cancer control, a comparative examination of toxicity has not been performed. Materials/Methods: We performed a retrospective study using the Medicare Chronic Condition Warehouse of all Medicare beneficiaries aged 66 years old who received only SRS alone or IMRT alone as primary treatment for prostate cancer during 2008 through 2010, with at least 6 months of available follow-up. Each SRS patient was matched to two IMRT patients with similar follow-up (6 or 12 months) and clinical and sociodemographic characteristics. We assessed toxicity by searching Medicare claims based on insights from prior studies for procedure or diagnosis codes indicative of radiation therapy treatment-related toxicity. We used a conditional logit model to compare the likelihood of genitourinary (GU) and gastrointestinal (GI) toxicity at 6 and 12 months after the initiation of treatment between the SRS and IMRT treatment groups. Results: The study sample consisted of 748 SRS patients matched to 1,496 IMRT patients. After 6 months, there was no significant difference in either GU complications (12.1% for IMRT vs 13.8% for SRS, p Z .26) or GI complications (4.5% for IMRT vs 5.7% for SRS, p Z .19). However, among the 1,938 patients with 12 months of follow-up, GU complications were significantly more likely among patients who received SRS (19.7% for IMRT vs 25.1% for SRS, p < .01); there was no difference in GI complications (11.5% for IMRT vs 11.3% for SRS, p Z .92). The greater