Thomas W. Zusag

Dose enhancement by a thin foil of high-Z material: A Monte Carlo study

The purpose of this work is to study the dose enhancement by a thin foil (thickness of 0.2-4 mm) of high-Z material in a water phantom, irradiated by high-energy photon beams. EGS4 Monte Carlo technique was used. Perturbations on the beam spectra due to the presence of the foils, and dose enhancement dependence of photon-beam quality, beam incident angle, atomic number (Z), the thickness and size of the foil, and the depth of the foil situated in the phantom were studied. Analysis of photon and secondary-electron spectra indicates that the dose enhancement near an inhomogeneity interface is primarily due to secondary electrons. A calculation for 1-mm-thick planar lead foil in a water phantom shows that the dose enhancements at 0.25, 1, 2 and 3 mm away from the foil in the backward region were 58%, 37%, 24% and 17%, respectively, for a 15 MV beam. Calculations for a variety of planar foils and photon beams show that dose enhancement: (a) increases with Z; (b) decreases with decreasing foil thickness when the foils are thinner than a certain value (1 mm for lead foil for 15 MV); (c) decreases with decreasing incident photon-beam energies; (d) changes slightly for beam incident angles less than 45 degrees and more prominently for larger angles; (e) increases with size of foil; and (f) is almost independent of the depth at which the foil is situated when the foil is placed beyond the range of secondary electrons. The dose enhancement calculation is also performed for a cylindrically shaped lead foil irradiated by a four-field-box. The dose enhancement of 34%/13% was obtained at 0.25/2 mm away from the cylindrical outer interface for a 15 MV four-field-box.

Adjunctive radiation therapy for rectal carcinoma.

From 1977 through 1985, 113 patients received radiati on therapy in conjunction with definitive surgery for adenocar-cinoma of the rectum. Posttreatment consisted of a minimum follow-up of 4 years. Radiation was given as postoperative (eight patients), short-course preoperative (2,000 cGy/5 fx, 21 patients), or as full-course preoperative treatment (4,500–5,000 cGy, 84 patients). Three patients received chemotherapy as part of the adjuvant treatment. The local control for the total group was 90% (local failures, 11 of 113), and the rate of recurrence at any site (distant or local) was 30% (34 of 113). Local failure was not significantly influenced by pre-treatment clinical findings, tumor grade, or surgical stage. Because of distant failures, overall recurrence was significantly associated with surgical stage—0% (0 of 15) for Astler-Coller A, 23% (7 of 30) for B1, 25% (7 of 28) for B2, and 50% (20 of 40) for B3 or C lesions (p < 0.01). Locally advanced pre-treatment clinical findings were not independent of surgical stage as predictors of outcome. In particular, 14 of the tumors that received full course preoperative radiation were initially either nearly obstructing, circumferential, or deeply fixed. However, by the time of surgery, they were A or B1 lesions (probably down-staged lesions). Only one of 14 (7%) ultimately failed with a local and distant recurrence. There were four cases (3.5%) of small bowel obstruction requiring surgical management. Overall, there were 12 complications (11%) requiring either surgical or major medical management. The complication rate was not associated with radiotherapeutic factors. A strong association was noted between complications and the surgeon. Of 66 patients who had surgery with two colorectal specialists, four (6%) had serious complications. Of the remaining 47 patients who had general surgeons, eight (17%) experienced serious complications.

Split-Course Chemoradiotherapy for Locally Advanced Non-small Cell Lung Cancer: A Single-Institution Experience of 144 Patients

Background: Concurrent chemoradiotherapy (CRT) is a standard of care in the treatment of unresectable locally advanced non-small cell lung cancer (NSCLC). At Rush University Medical Center, patients with locally advanced NSCLC are treated with split-course CRT in an attempt to maximize efficacy and tolerability. We reviewed our experience in advanced NSCLC since 1999. Subset analysis was performed on poor-risk patients. Methods: All patients with a diagnosis of stage IIIA/IIIB NSCLC and treated with definitive split-course CRT between January 1999 and December 2008 were included in this retrospective study. The primary end point was overall survival. Poor-risk patients were defined in accordance with ongoing cooperative group trials. Results: One hundred forty-four patients were identified, 35% stage IIIA and 65% stage IIIB. There were 52 poor-risk patients and 92 average-risk patients. Median survival for all patients was 20.4 months with an actuarial 32.1% 3-year overall survival rate. Poor-risk patients demonstrated a median survival of 22.1 months, statistically indistinguishable from the remainder of the cohort (p = 0.21). Acute esophagitis was mild, with a 3% rate of grade 3 esophagitis and no cases of grade 4 or 5. Conclusions: Split-course CRT appeared effective and was delivered with a favorable toxicity profile. Poor-risk patients experienced better than expected survival. Prospective evaluation of split-course CRT must be completed before it can be considered a standard treatment option in locally advanced NSCLC.

Weight Gain in Advanced Non-Small-Cell Lung Cancer Patients During Treatment With Split-Course Concurrent Chemoradiotherapy Is Associated With Superior Survival

BACKGROUND Preoperative concurrent chemoradiotherapy (CRT) is an accepted treatment for potentially resectable, locally advanced, non-small-cell lung cancer (NSCLC). We reviewed a decade of single institution experience with preoperative split-course CRT followed by surgical resection to evaluate survival and identify factors that may be helpful in predicting outcome. METHODS AND MATERIALS All patients treated with preoperative split-course CRT and resection at Rush University Medical Center (RUMC) between January 1999 and December 2008 were retrospectively analyzed. Endpoints included overall survival (OS), progression-free survival (PFS), local-regional progression-free survival (LRPFS), and distant metastasis-free survival (DMFS). Patient and treatment related variables were assessed for correlation with outcomes. RESULTS A total of 54 patients were analyzed, 76% Stage IIIA, 18% Stage IIIB, and 6% oligometastatic. The pathologic complete response (pCR) rate was 31.5%, and the absence of nodal metastases (pN0) was 64.8%. Median OS and 3-year actuarial survival were 44.6 months and 50%, respectively. Univariate analysis revealed initial stage (p < 0.01) and percent weight change during CRT (p < 0.01) significantly correlated with PFS/OS. On multivariate analysis initial stage (HR, 2.4; 95% CI, 1.18-4.90; p = 0.02) and percent weight change (HR, 0.79; 95% CI, 0.67-0.93; p < 0.01) maintained significance with respect to OS. There were no cases of Grade 3+ esophagitis, and there was a single case of Grade 3 febrile neutropenia. CONCLUSIONS The strong correlation between weight change during CRT and OS/PFS suggests that this clinical parameter may be useful as a complementary source of predictive information in addition to accepted factors such as pathological response.

Application of holographic display in radiotherapy treatment planning II: a multi-institutional study.

We hypothesized that use of a true 3D display providing easy visualization of patient anatomy and dose distribution would lead to the production of better quality radiation therapy treatment plans. We report on a randomized prospective multi‐institutional study to evaluate a novel 3D display for treatment planning. The Perspecta® Spatial 3D System produces 360° holograms by projecting cross‐sectional images on a diffuser screen rotating at 900 rpm. Specially‐developed software allows bi‐directional transfer of image and dose data between Perspecta and the Pinnacle planning system. Thirty‐three patients previously treated at three institutions were included in this IRB‐approved study. Patient data were de‐identified, randomized, and assigned to different planners. A physician at each institution reviewed the cases and established planning objectives. Two treatment plans were then produced for each patient, one based on the Pinnacle system alone and another in conjunction with Perspecta. Plan quality was then evaluated by the same physicians who established the planning objectives. All plans were viewable on both Perspecta and Pinnacle for review. Reviewing physicians were blinded to the planning device used. Data from a 13‐patient pilot study were also included in the analysis. Perspecta plans were considered better in 28 patients (61%), Pinnacle in 14 patients (30%), and both were equivalent in 4 patients. The use of non‐coplanar beams was more common with Perspecta plans (82% vs. 27%). The mean target dose differed by less than 2% between rival plans. Perspecta plans were somewhat more likely to have the hot spot located inside the target (43% vs. 33%). Conversely, 30% of the Pinnacle plans had the hot spot outside the target compared with 18% for Perspecta plans. About 57% of normal organs received less dose from Perspecta plans. No statistically significant association was found between plan preference and planning institution or planner. The study found that use of the holographic display leads to radiotherapy plans preferred in a majority of cases over those developed with 2D displays. These data indicate that continued development of this technology for clinical implementation is warranted. PACS numbers: 87.55.D

Upright 3D treatment planning using a vertical CT.

In this report, we describe a novel technique used to plan and administer external beam radiation therapy to a patient in the upright position. A patient required reirradiation for thymic carcinoma but was unable to tolerate the supine position due to bilateral phrenic nerve injury and paralysis of the diaphragm. Computed tomography (CT) images in the upright position were acquired at the Northern Illinois University Institute for Neutron Therapy at Fermilab. The CT data were imported into a standard 3-dimensional (3D) treatment planning system. Treatment was designed to deliver 24 Gy to the target volume while respecting normal tissue tolerances. A custom chair that locked into the treatment table indexing system was constructed for immobilization, and port films verified the reproducibility of setup. Radiation was administered using mixed photon and electron AP fields.

Comparison of Computed Tomography Scout Based Reference Point Localization to Conventional Film and Axial Computed Tomography

Identification of source positions after implantation is an important step in brachytherapy planning. Reconstruction is traditionally performed from films taken by conventional simulators, but these are gradually being replaced in the clinic by computed tomography (CT) simulators. The present study explored the use of a scout image-based reconstruction algorithm that replaces the use of traditional film, while exhibiting low sensitivity to metal-induced artifacts that can appear in 3D CT methods. In addition, the accuracy of an in-house graphical software implementation of scout-based reconstruction was compared with seed location reconstructions for 2 phantoms by conventional simulator and CT measurements. One phantom was constructed using a planar fixed grid of 1.5-mm diameter ball bearings (BBs) with 40-mm spacing. The second was a Fletcher-Suit applicator embedded in Styrofoam (Dow Chemical Co., Midland, MI) with one 3.2-mm-diameter BB inserted into each of 6 surrounding holes. Conventional simulator, kilovoltage CT (kVCT), megavoltage CT, and scout-based methods were evaluated by their ability to calculate the distance between seeds (40 mm for the fixed grid, 30-120 mm in Fletcher-Suit). All methods were able to reconstruct the fixed grid distances with an average deviation of <1%. The worst single deviations (approximately 6%) were exhibited in the 2 volumetric CT methods. In the Fletcher-Suit phantom, the intermodality agreement was within approximately 3%, with the conventional sim measuring marginally larger distances, with kVCT the smallest. All of the established reconstruction methods exhibited similar abilities to detect the distances between BBs. The 3D CT-based methods, with lower axial resolution, showed more variation, particularly with the smaller BBs. With a software implementation, scout-based reconstruction is an appealing approach because it simplifies data acquisition over film-based reconstruction without requiring any specialized equipment and does not carry risk of misreads caused by artifacts.