The effect of metallic tracheal stents on radiation dose in the airway and surrounding tissues.

BACKGROUND: Metallic airway stents are often used in the management of central airway malignancies. The presence of a metallic foreign body may affect radiation dose in tissue. We studied the effect of a metallic airway stent on radiation dose delivery in a phantom and an in vivo porcine model. METHODS: A metallic tracheal stent was fitted onto a support in a water phantom. Point dosimeters were positioned in the phantom around the support and the stent. Irradiation was then performed on a linear accelerator with and without the stent. Metallic tracheal stents were deployed in the trachea of three pigs. Dosimeters were implanted in the tissues near (Group 1) and away (Group 2) from the stent. The pigs were then irradiated, and the dose perturbation factor was calculated by comparing the actual dose detected by the dosimeters versus the planned dose. RESULTS: The difference in the dose detected by the dosimeters and the planned dose ranged from 1.8% to 6.1% for the phantom with the stent and 0%-5.3% for the phantom without the stent. These values were largely within the manufacturer's specified error of 5%. No significant difference was observed in the dose perturbation factor for Group 1 and Group 2 dosimeters (0.836 ± 0.058 versus 0.877 ± 0.088, P = 0.220) in all the three pigs. CONCLUSIONS: Metallic airway stents do not significantly affect radiation dose in the airway and surrounding tissues in a phantom and porcine model. Radiation treatment planning systems can account for the presence of the stent. External beam radiation can be delivered without concern for significant dose perturbation.

2D kV orthogonal imaging with fiducial markers is more precise for daily image guided alignments than soft-tissue cone beam computed tomography for prostate radiation therapy.

PURPOSE: The hypothesis is that 2-dimensional kV orthogonal imaging with fiducial markers (kV-FM) and soft-tissue cone beam computed tomography (ST-CBCT) are equally reproducible for daily positional alignments for image guided (IG) intensity modulated radiation therapy (IMRT) for prostate cancer. METHODS AND MATERIALS: Ten patients undergoing definitive treatment for prostate cancer with IG-IMRT were imaged daily with kV-FM and ST-CBCT. For each acquired kV and CBCT image, offline alignments to the digitally reconstructed radiograph or planning CT, respectively, were made twice by the same physician to assess intraobserver test-retest reproducibility. The 256 kV and 142 CBCT images were analyzed, and the test-retest analysis was performed again on a subset of images by another physician to verify the results. RESULTS: The results demonstrated that kV-FM had better intraobserver test-retest reproducibility in the anterior-posterior (AP; 95% confidence interval [CI] Pearson correlation coefficient [r], 0.987-0.991), left-right (LR; 95% CI r, 0.955-0.969), and superior-inferior (SI; 95% CI r, 0.971-0.980) directions for daily IG alignments compared with ST-CBCT (AP: 95% CI r, 0.804-0.877; LR: 95% CI r, 0.877-0.924; SI: 95% CI r, 0.791-0.869). Errors associated with intraobserver test-retest reproducibility were submillimeter with kV-FM (AP: 0.4 ± 0.7 mm; RL: 0.4 ± 1.0 mm; SI: 0.5 ± 0.7 mm) compared with ST-CBCT (AP: 2.1 ± 2.2 mm; LR: 1.3 ± 1.4 mm; SI: 1.2 ± 1.8 mm). The mean shift differences between kV-FM and ST-CBCT were 0.3 ± 3.8 mm for AP, -1.1 ± 8.5 mm for LR, and -2.0 ± 3.7 mm for SI. Dose-volume histograms were generated and showed that test-retest variability associated with ST-CBCT IG-alignments resulted in significantly increased dose to normal structures and a reduced planning target volume dose in many patients. CONCLUSIONS: The kV-FM-based daily IG alignment for IMRT of prostate cancer is more precise than ST-CBCT, as assessed by a physician's ability to reproducibly align images. Given the magnitude of the error introduced by inconsistency in making ST-CBCT alignments, these data support a role for daily kV imaging of FM to enhance the precision of external beam dose delivery to the prostate.

Linear accelerator-based flattening-filter-free stereotactic radiosurgery for trigeminal neuralgia: Feasibility and patient-reported outcomes.

PURPOSE: The purpose of this study was to assess the safety and outcomes of the clinical use of LINAC (linear accelerator)-based flattening-filter-free beams for delivering ablative stereotactic radiosurgery (SRS) for trigeminal neuralgia (TN). METHODS AND MATERIALS: Thirty-six consecutive patients (34 unique patients) followed up by a single neurosurgeon and diagnosed with medically refractory unilateral TN were treated with SRS. There were 14 left-sided cases (41%) and 20 right-sided cases (59%). Twenty-eight of the patients (82%) had type 1 TN, and 6 (18%) had type 2 TN. Previous treatments were as follows: 10 patients (29%) had SRS to the ipsilateral TN (8 with Gamma Knife, 2 with LINAC), 4 (12%) had percutaneous rhizotomy, and 3 (9%) had microvascular decompression. A median prescription dose of 75 Gy (range, 70-80 Gy), prescribed to the 100% isodose line, was delivered in a single fraction. Before treatment delivery, image guidance verified stereotactic frame placement, head position, and final isocenter. The volume of brainstem receiving ≥10 Gy was <0.5 cm(3). At each visit, patients prospectively reported outcomes using the Barrow Neurological Institute (BNI) pain scale. RESULTS: With a median follow-up of 3.1 months (range, 0.6-24.3; mean, 5.5 months), no patient experienced grade 1+ toxicities. There were no new episodes of dysesthesia, hypoesthesia, or long-term complications related to SRS. Median baseline (pre-SRS) BNI score was 5.0 (mean, 4.7). Clinical assessment at first follow-up (median, 1 month) demonstrated a median BNI score of 3.0 (mean, 3.1). When stratified by TN subtype, both type 1 and type 2 TN patients had a median BNI score of 3.0 at first follow-up. Thirty patients (88.2%) achieved a reduction in their BNI at their first follow-up, and 5 patients (15%) achieved a score <3, which represents medication-free pain relief. The median BNI at second follow-up (average, 6.3 months) was 2.5. CONCLUSIONS: We report our experience with modern LINAC-based SRS using flattening-filter-free beams for TN. This treatment appears to be a safe and effective technique, although longer follow-up is needed to confirm durability. This modality may prove to be a viable treatment alternative for TN.

Phase I/II prospective trial of cancer-specific imaging using ultrasound spectrum analysis tissue-type imaging to guide dose-painting prostate brachytherapy.

PURPOSE: To assess the technical feasibility, toxicity, dosimetry, and preliminary efficacy of dose-painting brachytherapy guided by ultrasound spectrum analysis tissue-type imaging (TTI) in low-risk, localized prostate cancer. METHODS AND MATERIALS: Fourteen men with prostate cancer who were candidates for brachytherapy as sole treatment were prospectively enrolled. Treatment planning goal was to escalate the tumor dose to 200% with a modest de-escalation of dose to remaining prostate compared with our standard. Primary end points included technical feasibility of TTI-guided brachytherapy and equivalent or better toxicity compared with standard brachytherapy. Secondary end points included dose escalation to tumor regions and de-escalated dose to nontumor regions on the preimplant plan, negative prostate biopsy at 2 years, and freedom from biochemical failure. RESULTS: Thirteen of fourteen men successfully completed the TTI-guided brachytherapy procedure for a feasibility rate of 93%. A software malfunction resulted in switching one patient from TTI-guided to standard brachytherapy. An average of 2.7 foci per patient was demonstrated and treated with an escalated dose. Dosimetric goals on preplan were achieved. One patient expired from unrelated causes 65 days after brachytherapy. Toxicity was at least as low as standard brachytherapy. Two-year prostate biopsies were obtained from six men; five (83%) were definitively negative, one showed evidence of disease with treatment effect, and none were positive. No patients experienced biochemical recurrence after a median followup of 31.5 (24-52) months. CONCLUSIONS: We have demonstrated that TTI-guided dose-painting prostate brachytherapy is technically feasible and results in clinical outcomes that are encouraging in terms of low toxicity and successful biochemical disease control.

Prostate localization using transabdominal ultrasound imaging.

PURPOSE: Adding margin around a target is done in an attempt to ensure complete coverage of the target. The B-mode acquisition and targeting (BAT) system allows ultrasound imaging of the prostate in patients with a full bladder. This provides a setup tool for patients with localized prostate cancer that takes into account real-time prostate position and may make it possible to decrease tumor margins. Prostate localization using the conventional setup verification method and daily isocenter shifts recommended by the ultrasound imaging system (BAT) were compared and analyzed. METHODS AND MATERIALS: Daily treatment isocenter shifts for patients with localized adenocarcinoma of the prostate, obtained from two different imaging modalities, electronic portal imaging (EPI) and BAT, were calculated. We studied the difference in patient setup error calculated using BAT contour alignment and measured from EPI; the reproducibility of BAT contour alignment; intrafraction prostate motion; and how the BAT imaging procedure itself affected the prostate position. Prostate motion relative to its position during simulation was calculated by subtracting the EPI-measured isocenter shifts from the corresponding BAT-defined isocenter shifts. BAT reproducibility was measured by taking a verification BAT image after the patient was moved according to the initial BAT-defined isocenter shifts. Intrafraction prostate motion was measured by repeating BAT imaging at the end of a treatment fraction. The BAT imaging effect on prostate position was studied by examining the effect of suprapubic pressure on seed position in patients after a seed implant. RESULTS: The mean BAT isocenter shifts for prostate motion were 0.32 +/- 0.46 cm in the lateral, 0.31 +/- 0.73 cm in the superoinferior, and 0.32 +/- 0.56 cm in the AP directions. Isocenter shifts obtained from EPI measurements were significantly smaller, with a mean of 0.05 +/- 0.24 cm in the lateral, 0.01 +/- 0.11 cm in the superoinferior and -0.11 +/- 0.29 cm in the AP directions. This larger shift seen by BAT was due to prostate motion. For BAT reproducibility, the results showed that for BAT verification images, 90% of the lateral shifts were <0.2 cm, 93% of the superoinferior shifts were <0.3 cm, and 83% of the AP shifts were <0.2 cm. The mean isocenter shift (intrafraction localization error) during patient treatment fraction was 0.02 +/- 0.28 cm in the lateral, 0.04 +/- 0.48 cm in the superoinferior, and 0.0 +/- 0.32 cm in the AP direction. The BAT procedure itself induced an average motion of 1 mm in the AP and superoinferior directions. CONCLUSIONS: Prostate patient setup verification on the basis of bony anatomy position does not reflect the actual prostate position. BAT ultrasound target alignment provides a real-time prostate localization system that may make it possible to measure prostate position variations and reduce margins.

Assessment of nodal target definition and dosimetry using three different techniques: implications for re-defining the optimal pelvic field in endometrial cancer.

PURPOSES: 1. To determine the optimal pelvic nodal clinical target volume for post-operative treatment of endometrial cancer. 2. To compare the DVH of different treatment planning techniques applied to this new CTV and the surrounding tissues. METHODS AND MATERIALS: Based on the literature, we selected a methodology to delineate nodal target volume to define a NEW-CTV and NEW-PTV. Conventional 2D fields, 3D fields based on anatomic guidelines per RTOG 0418, 3D fields based on our guidelines, and IMRT based on our guidelines were assessed for coverage of NEW-CTV, NEW-PTV, and surrounding structures. CT scans of 10 patients with gynecologic malignancies after TAH/BSO were used. DVHs were compared. RESULTS: For NEW-PTV, mean V45Gy were 50% and 69% for 2D and RTOG 0418-3DCRT vs. 98% and 97% for NEW-3DCRT and NEW-IMRT (p < 0.0009). Mean V45Gy small bowel were 24% and 20% for 2D and RTOG 0418-3DCRT, increased to 32% with NEW-3DCRT, and decreased to 14% with IMRT (p = 0.005, 0.138, 0.002). Mean V45Gy rectum were 26%, 35%, and 52% for 2D, RTOG 0418-3DCRT, and NEW-3DCRT, and decreased to 26% with NEW-IMRT (p < 0.05). Mean V45Gy bladder were 83%, 51%, and 73% for 2D, RTOG 0418-3DCRT, and NEW-3DCRT, and decreased to 30% with NEW-IMRT (p < 0.002). CONCLUSIONS: Conventional 2D and RTOG 0418-based 3DCRT plans cover only a fraction of our comprehensive PTV. A 3DCRT plan covers this PTV with high doses to normal tissues, whereas IMRT covers the PTV while delivering lower normal tissue doses. Re-consideration of what specifically the pelvic target encompasses is warranted.