Extracranial Tumors

E564 Purpose/Objective(s): The outcomes of particle therapy using protons or carbon ions for cancer patients with cardiac implantable electronic devices (CIEDs) were evaluated. Materials/Methods: From April 2001 to March 2013, 19,585 patients were treated with proton beam therapy (PBT) or carbon ion therapy (CIT) in eight Japanese institutions. Of these, 70 patients (0.36%, PBT [47] and CIT [23]) with CIEDs (65 pacemakers [PMs], 4 implantable cardioverter defibrillators [ICDs], and 1 with a cardiac resynchronization therapy defibrillator [CRT-D]) were retrospectively reviewed. Control patients were selected at random from the patients without CIEDs treated with particle therapy at these facilities in the same period and with follow-up periods of at least one year. Local control rates (LC), progression-free survival rates (PFS), and overall survival rates (OS) in stage I hepatocellular carcinoma (HCC), stage IA non-small-cell lung cancer (NSCLC), or stage I-III prostate cancer patients with CIEDs and the control group were calculated and compared. Results: The median age was 81 years (60-96). Tumor locations included liver (26), lungs (20), prostate (15), and others (9). The median prescribed dose was 70.0 GyE (36.3-88.0) for PBT and 57.6 GyE (28.0-77.0) for CIT. Ten device malfunctions (7 electrical resets and 3 over-sensings) occurred in 6 patients (13%, 4 PMs, 1 ICD, and 1 CRT-D) treated with PBT, and there were no device malfunctions observed in the patients treated with CIT (Pearson’s chi-square test, pZ0.073). No permanent device malfunctions were observed. At a median follow-up of 41 months (17-118), 3year LC, PFS, and OS of 100%, 60%, and 36% vs. 83%, 60%, and 79% (log-rank test, pZ0.32, pZ0.26, and pZ0.20) in stage I HCC; 100%, 83%, and 100% vs. 100%, 91%, and 83% (pZn/a, pZ0.75, and pZ0.59) in stage IA NSCLC; and 100%, 100%, and 100% vs. 95%, 91%, and 100% (pZ0.50, pZ0.84, and pZ0.43) in stage I-III prostate cancer, for the patients with CIEDs and the control group, respectively. Conclusion: Device malfunctions induced by particle therapy on the CIEDs are rare, but are an inevitable and unpredictable phenomenon. The frequency of occurrence of device malfunctions were higher for patients treated with PBT than for patients treated with CIT, however there was no significant difference between the incidences of occurrence. Although the number of cases was limited, wearing CIEDs was not associated with poorer LC, PFS, and OS in stage I HCC, stage IA NSCLC, or stage I-III prostate cancer patients treated with particle therapy. Author Disclosure: T. Hashimoto: None. Y. Demizu: None. T. Isobe: None. H. Numajiri: None. S. Fukuda: None. M. Wakatsuki: None. H. Yamashita: None. S. Murayama: None. S. Takamatsu: None. H. Katoh: None. K. Murata: None. R. Kohno: None. T. Arimura: None. T. Matsuura: None. Y.M. Ito: None.

3416 A Dosimetric Study of an Advanced SRS/SRT System for Intra/ Extracranial Tumors C.M.C. Ma,1 C. Li,2 A. ElDib,1 O. Chibani,1 G. Mora,3 J. Li,1 and L. Chen1; 1Fox Chase Cancer Center, Philadelphia, PA, 2Renmin Hospital, Wuhan, China, 3University of Lisbon - Center for Nuclear Physics, Lisbon, Portugal Purpose/Objective(s): Several specialty machines are available clinically for stereotactic radiosurgery/radiation therapy (SRS/SRT). Gamma Knife provides superior delivery accuracy for intracranial lesions and CyberKnife allows accurate SRS/SRT treatments for extracranial tumors with real-time image guidance and respiratory tracking. This work investigates a new SRS/SRT system that provides both superior dose conformity/ gradient and accurate stereotaxy for intra/extracranial treatments. Materials/Methods: The CybeRay system (Cyber Medical Corp., China) consists of a ring gantry with a treatment head containing 16 gamma sources with a span of 33 in the superior-inferior direction, each focusing at the isocenter with 4 collimators measuring 4, 8, 16 and 32mm diameter. The treatment head can also swing 35 in the superior direction, allowing a total of 68 non-coplanar beam incident. The treatment couch provides 6degrees-of-freedom motion compensation and the kV cone-beam CT

International Journal of Radiation Oncology  Biology  Physics Poster Viewing Abstracts 3416; Table 1 Later Tumor Site Number Size (cm) Brain, H&N Thorax Abdomen Pelvis Spine Other

8 79 17 7 10 4

32.9  10.9 36.5  4.5 33.1  4.4 39.4  6.0 36.3  5.3 43.9  7.6

Body Weight (lb)

Target Arc Volume (cc) Arrangements

169.9  49.6 55.0  56.1 161.0  41.9 44.6  47.7 166.0  45.5 144.6  162.6 198.4  44.0 40.3  43.4 183.3  38.5 69.0  53.2 161.0  37.7 108.6  112.7

Full Arc Half/Full Half/Full Half/Full Full Arc Half/Full

Arc Arc Arc Arc

system has a spatial resolution of 0.4mm for target localization. Monte Carlo simulations were used to compute dose distributions and compare with measurements. A retrospective study of 125 previously treated SBRT patients was performed to evaluate the dosimetric characteristics of the CybeRay system in comparison with existing SBRT systems. Results: Monte Carlo results confirmed the CybeRay design parameters including output factors and 3D dose distributions. Its beam penumbra/ dose gradient is similar to that of Gamma Knife and its stereotaxy/isocenter accuracy is 0.3mm. Compared to the 6 MV beams of the CyberKnife, Co-60 beams produce lower-energy secondary electrons that exhibit better dose properties in low-density lung tissues. Because of their rapid depth dose falloff, Co-60 beams are ideal for peripheral lung tumors with half-arc arrangements to spare the opposite lung and other critical structures. The table below shows the patient lateral size, body weight and target volume (mean1SD) for the 125 patients investigated. Superior dose distributions have been obtained for brain, head and neck, breast, spine and lung tumors with half/full arc arrangements. Conclusion: The unique dosimetric properties of Co-60 sources and its accurate stereotaxy/dose delivery make CybeRay an ideal system for SRS/ SRT of small (up to 100cc) intra/extracranial tumors. A clinical investigation of ablative treatment for multiple (1-3) discrete lung metastases with a single fraction of 25Gy is being conducted. Author Disclosure: C. Ma: None. C. Li: None. A. ElDib: None. O. Chibani: None. G. Mora: None. J. Li: None. L. Chen: None.

3417 Is Magnetic Resonance Imaging for Prostate Bed Radiation Therapy Planning Useful? M. Barkati,1 G. Delouya,2 D. Simard,1 and D. Taussky2; 1Centre Hospitalier de l’Universite´ de Montre´al (CHUM), Montreal, QC, Canada, 2 Centre Hospitalier de l’Universite de Montreal, Montreal, QC, Canada Purpose/Objective(s): To assess the inter- and intra-observer variability in contouring the prostate bed for radiation therapy (RT) planning using magnetic resonance imaging (MRI) compared to computed tomography (CT). Materials/Methods: We randomly selected 15 patients with prior radical prostatectomy for prostate cancer treated at our department with adjuvant or salvage RT. All had CT and MRI simulation for planning purposes with the same recommendation regarding bladder and bowel preparation. Image fusions were done between CT and MRI. Three radiation oncologists with several years of experience in prostate RT contoured the prostate bed first on CT and then on a T2 weighted MRI sequence without consulting the other imaging modality. Before contouring, each radiation oncologist had to review the RTOG guidelines for postoperative radiation therapy. Only the pathology report was available while contouring. Volume of the prostate bed as contoured on MRI was compared for inter-observer variability. This was repeated for CT. Intra-observer variability for each radiation oncologist between CT and MRI were compared. The agreement between volumes was calculated using the Dice similarity coefficient (DSC), defined as the intersection volume between two volumes divided by the mean of volumes. The closer this value is to 1, the higher the agreement between the