J Kim

Cyclooxygenase-2 Expression in Postmastectomy Chest Wall Relapse

Purpose: Cyclooxygenase-2 (COX-2) expression has been shown to be associated with radiation resistance, which theoretically could be overcome with the use of COX-2 inhibitors. The purpose of this study was to assess the prognostic significance and clinical correlations of COX-2 expression (COX) in a cohort of patients treated with radiation for postmastectomy chest wall relapse. Experimental Design: Between 1975 and 1999, 113 patients were treated for isolated postmastectomy chest wall relapse. All patients were treated with biopsy and/or excision of the chest wall recurrence followed by radiation therapy. Median follow-up was 10 years. All clinical data, including demographics, pathology, staging, receptor status, HER-2/neu status, and adjuvant therapy, were entered into a computerized database. Paraffin-embedded chest wall recurrence specimens were retrieved from 42 patients, of which 38 were evaluated, created into a tissue microarray, stained by immunohistochemical methods for COX, and graded 0 to 3+. A score of 2 to 3+ was considered positive. Results: Overall survival from original diagnosis for entire cohort was 44% at 10 years. Survival rate after chest wall recurrence was 28% at 10 years. The distant metastasis-free survival rate after chest wall recurrence was 40% at 10 years. Local-regional control of disease was achieved in 79% at 10 years after chest wall recurrence. COX was considered positive in 13 of 38 cases. COX was inversely correlated with estrogen receptor (P = 0.045) and progesterone receptor (P = 0.028), and positively correlated with HER-2/neu (P = 0.003). COX was also associated with a shorter time to postmastectomy chest wall relapse. The distant metastasis-free rate for COX-negative patients was 70% at 10 years, compared with 31% at 10 years for COX-2–positive patients (P = 0.029). COX positive had a poorer local-regional progression-free rate of 19% at 10 years, compared with 81% at 10 years for COX negative. This was of high statistical significance with a P value of 0.003. Conclusions: Outcome following radiation therapy for postmastectomy chest wall relapse is relatively poor. Positive COX correlated with other markers of poor outcome, including a shorter time to local relapse, negative estrogen receptor/progesterone receptor, and positive Her-2/neu status. Positive COX correlated with higher distant metastasis and lower local-regional control of disease. If confirmed with larger studies, these data have implications with respect to the concurrent use of COX-2 inhibitors and radiation for postmastectomy chest wall relapse.

MO‐F‐108‐07: Impact of Additional Intensity Modulation On Arc‐Based Stereotactic Body Radiotherapy (SBRT) for Lung Cancer

PURPOSE A single-isocenter multi-segment dynamic conformal arc technique (SiMs-arc) has been used in our department in the past three years for efficient planning and delivery of over 200 lung SBRT treatments. The purpose of this study is to investigate the impact of additional intensity-modulation made available by Varian RapidArc on the dosimetric quality and delivery efficiency of arc-based lung SBRT. METHODS Four patients previously treated with lung SBRT using SiMs-arc were selected. SiMs-arc plans were generated with the isocenter located in the geometric center of patient axial plane (to allow for collision-free gantry rotation around the patient) and six 60°-arc segments spanning from 1° to 359°. Two RapidArc plans, one using the same arc geometry as SiMs-arc and the other using typical partial arcs (210°) with the isocenter inside PTV, were generated for each patient. All plans, generated using Eclipse V10.0, were normalized with PTV V100 to 95%. PTV coverage, dose to organs-at-risk and total MUs were compared to assess the impact of additional intensity-modulation provided in RapidArc. RESULTS RapidArc plans produced higher PTV D99 (by 1.0%-3.1%) and minimum dose (by 2.4% to 9.8%); better PTV conformality index (by 1%-8%); and less volume of 50% dose outside 2cm from PTV (by 0-20.8cc) than the corresponding SiMs-arc plans. No significant dose differences were observed for lungs, trachea, chest wall and heart. RapidArc using partial-arcs had lowest maximum dose to spinal cord. RapidArc plans required 1.5 to 1.91 times more MUs than SiMs-arc plans to deliver the same dose. CONCLUSION Additional intensity-modulation enlisted by RapidArc produces modest dosimetric improvements over conformal arcs for lung SBRT, but requires more MUs (by a factor > 1.5) to deliver. The dosimetric improvements, most notably in PTV minimum dose and in dose conformality for irregularly shaped PTVs, may outweigh the increased MUs in using RapidArc.

SU-E-T-181: Feasibility and Robustness of Using Overlapping VMAT Arcs for Conformal Irradiation of Large Irregular PTVs

PURPOSE To investigate the feasibility and robustness of using multiple overlapping arcs for delivering volumetric modulated arc therapy (VMAT) to irregular PTVs with large superior-inferior (SI) dimensions. METHODS A patient with stage IV alveolar rhabdomyosarcoma, with a combined PTV length of 56 cm in SI direction, was planned and treated in our department using two VMAT arcs overlapped along the SI direction to take advantage of the much needed dose sculpting capabilities of VMAT. The overlapping VMATs, each consisted of two arcs, were optimized simultaneously using Varian Eclipse system. The susceptibility of the resulting plan to uncertainties associated the set up of two separate isocenters during treatment was investigated by comparing the dose distributions resulted from small shifts introduced into the isocenter position. The robustness of this technique was further assessed for plans generated using different amount of overlap between the overlapping arcs. RESULTS When the plan was generated with 6 cm overlap between adjacent arcs, maximum dose variations observed near overlapping edges was up to 9.2%, 10%, and 26.7% for setup uncertainties of 2 mm, 3 mm, and 5 mm, respectively. By increasing the junction overlap to 16 cm, maximum dose variations was reduced to 4.2%, 6.5%, and 10.2% for setup uncertainties of 2 mm, 3 mm, and 5 mm, respectively. In general, dose variation was found to increase dramatically with increasing magnitude of setup uncertainty. The technique can be made more robust against setup uncertainty by using large overlap between adjacent VMAT arcs. CONCLUSION Overlapping VMAT arcs can be used effectively for conformal irradiation of PTVs with large SI dimension. The dosimetric impact of uncertainties in required isocenter shifts can be minimized by planning with large overlap between adjacent arcs and by keeping setup uncertainty ≤ 2mm.

SU‐E‐T‐25: Investigating the Impact of Polymer‐Coating On the Dosimetric Characteristics of a 103Pd Brachytherapy Source Using Photon Spectroscopy

Purpose: Synthetic polymers have been used to coat the surface of existing low‐energy brachytherapy sources to improve their fixity in tissue in order to minimize seed migration in the patient. The purpose of this study was to evaluate the effects of the polymer‐coating on the photon energy spectra emitted by Pd‐103 seeds and to estimate its impact on the dosimetric characteristics of these seeds. Methods: Two Pd‐103 AnchorSeeds (Biocompatibles, Inc) and two Pd‐103 TheraSeeds (Theragenics Corporation) were used in this study. The AnchorSeed is made from the TheraSeed by coating its surface with bio‐absorbable polymeric anchoring rings and ribs. Photon energy spectra emitted by these seeds were measured using a high‐resolution, high‐purity Germanium (HPGe) photon spectrometer. The effects of polymer coating on the dose rate constant were quantified by comparisons of the coated seed with a non‐coated seed. Results: The relative photon energy spectrum emitted by the AnchorSeed was nearly identical to that emitted by the TheraSeed without polymer coating. The dose‐rate constants determined from the emitted photon energy spectra for the two seed models were identical to the third digit after the decimal point (0.679 ± 0.037 cGyh‐1U‐1). Because the basic dosimetric property of a brachytherapy seed is fundamentally determined by the photon characteristics emitted by the seed, effects of the polymer‐coating on the relative dosimetry data of TheraSeed is also expected to be minimal. Using a preexisting photon spectrometer, these measurements and calculations were completed in about 10 working hours. Conclusion: The polymer coating used in the AnchorSeed has minimal impact on its dosimetric characteristics compared to the non‐coated TheraSeed. We also demonstrate that photon spectroscopy provides a ready tool for the evaluation of impact of various coatings or other material changes in the seed manufacture process.

SU-E-T-198: Patient Scheduling Monitor (PSM)-A New Tool for Radiation Therapy Patient Scheduling and Workflow Management in an Increasingly Digital Environment

PURPOSE To develop an easy-to-use and customizable Patient Scheduling Monitor for 1) active monitoring of radiation therapy workflow from CT simulation to the start of treatment and 2) for optimizing the workflow based on treatment complexity. METHODS Microsoft Access database and Visual Basic language were used to create an in-house software application, Patient Scheduling Monitor (PSM). The PSM was designed with three functional modules: a patient schedule calculator, a workflow progress tracker, and a workflow evaluator. The PSM divides the radiation treatment workflow into 6 tasks including image acquisition/fusion, target delineation, dosimetry planning, MD review, physics QA and RTT QA. On the day of CT simulation, the scheduling calculator generates a planned timeline for each task based on the CT-simulation date and the default standard established for each given task and treatment type. Each task within the PSM can also be individualized as needed. After simulation, the progress tracker enables staff to actively monitor the workflow. The workflow evaluator will query the database and analyze the planned versus actual timeline and provide data for future workflow analysis. RESULTS We have used the PSM since Nov, 2011 for 186 patients. The PSM has allowed us to provide patient start times at the completion of simulation. It has helped to improve patient satisfaction. The workflow progress tracker enabled us to actively manage the workflow. Currently, for patients managed using the PSM, no rescheduling has been required. The use of PSM has reduced the average CT simulation to treatment start times. It also has improved intradepartmental communications. CONCLUSIONS An easy-to-use patient scheduling monitor has been developed. The PSM has been shown to be an efficient and effective tool in managing, assessing and improving the radiation therapy workflow and will be useful in managing the timelines in an increasingly dynamic working environment.