Eye Plaque Brachytherapy for Choroidal Malignant Melanoma: A Case Report on the Use of Innovative Technology to Expand Access, Improve Practice, and Enhance Outcomes.

Our institute established an eye plaque interstitial brachytherapy (EPIBT) program in 2007 using the Collaborative Ocular Melanoma Study (COMS) eye plaque. In this case report, we demonstrated an eye plaque treatment planned and executed using Eye Physics Plaque (Los Alamitos, CA) for a 72-year-old male patient with an extra-large tumor with a maximum width of 18.6 mm and height of 13.7 mm. The use of a customized eye plaque, manufactured through three-dimensional (3D) printing, has empowered us to plan and administer treatment for this patient with uveal melanoma. Without this option, enucleation, an option declined by the patient, or proton beam therapy (PBT), which the patient was unwilling to pursue in another state, would have been the alternative course of action. We were able to use more than one activity of the I-125 seeds, which enabled us to shape and reduce the dose to normal surrounding structures at risk within the orbit and in the vicinity of the orbital cavity. Using the dose evaluation tools available with the modern treatment planning system, we reduced the prescription dose from 85 to 70 Gy, with D90 of 140 Gy, thereby providing effective treatment and limiting risk organ doses. In summary, we were able to dose-deescalate without compromising the chances of controlling retinal/scleral tumors. The patient is doing well from a recent follow-up visit 12 months after the eye plaque brachytherapy treatment. The tumor was 4.80 mm high, 1/3 of the original height, and vision is back to 20/60, demonstrating a successful treatment.

Model development of dose and volume predictors for esophagitis induced during chemoradiotherapy for lung cancer as a step towards radiobiological treatment planning.

BACKGROUND: Currently, radiation therapy treatment planning system intends biological optimization that relies heavily upon plan metrics from tumor control probability (TCP) and normal tissue complication probability (NTCP) modeling. Implementation and expansion of TCP and NTCP models with alternative data is an important step towards reliable radiobiological treatment planning. In this retrospective single institution study, the treatment charts of 139 lung cancer patients treated with chemo-radiotherapy were reviewed and correlated dosimetric predictors with the incidence of esophagitis and established NTCP model of esophagitis grade 1 and 2 for lung cancer patients. METHODS: Esophagus is an organ at risk (OAR) in lung cancer radiotherapy (RT). Esophagitis is a common toxicity induced by RT. In this study, dose volume parameters Vx (Vx: percentage esophageal volume receiving ≥ x Gy) and mean esophagus dose (MED) as quantitative dose-volume metrics, the esophagitis grade 1 and 2 as endpoints, were reviewed and derived from the treatment planning system and the electronic medical record system. Statistical analysis of binary logistic regression and probit were performed to have correlated the probability of grade 1 and 2 esophagitis to MED and Vx. IBM SPSS software version 24 at 5% significant level (α = 0.05) was used in the statistical analysis. RESULTS: The probabilities of incidence of grade 1 and 2 esophagitis proportionally increased with increasing the values of Vx and MED. V20, V30, V40, V50 and MED are statistically significant good dosimetric predictors of esophagitis grade 1. 50% incidence probability (TD50) of MED for grade 1 and 2 esophagitis were determined. Lyman Kutcher Burman model parameters, such as, n, m and TD50, were fitted and compared with other published findings. Furthermore, the sigmoid shaped dose responding curve between probability of esophagitis grade 1 and MED were generated respecting to races, gender, age and smoking status. CONCLUSIONS: V20, V30, V40 and V50 were added onto Quantitative Analysis of Normal Tissue Effects in the clinic, or QUANTEC group's dose constrains of V35, V50, V70 and MED. Our findings may be useful as both validation of 3-Dimensional planning era models and also additional clinical guidelines in treatment planning and plan evaluation using radiobiology optimization.

Real World and Public Health Perspectives of Intraoperative Radiotherapy in Early-Stage Breast Cancer: A Multidisciplinary Analysis Beyond the Statistical Facts.

Breast conservation therapy (BCT) (usually a lumpectomy plus radiotherapy (RT)) has become a standard alternative to radical mastectomy in early-stage breast cancers with equal, if not higher, survival rates. The established standard of the RT component of the BCT had been about six weeks of Monday through Friday external beam RT to the whole breast (WBRT). Recent clinical trials have shown that partial breast radiation therapy (PBRT) to the region surrounding the lumpectomy cavity with shorter courses can result in equal local control, survival, and slightly improved cosmetic outcomes. Intraoperative RT (IORT) wherein RT is administered at the time of operation for BCT to the lumpectomy cavity as a single-fraction RT is also considered PBRT. The advantage of IORT is that weeks of RT are avoided. However, the role of IORT as part of BCT has been controversial. The extreme views go from "I will not recommend to anyone" to "I can recommend to all early-stage favorable patients." These divergent views are due to difficulty in interpreting the clinical trial results. There are two modalities of delivering IORT, namely, the use of low-energy 50 kV beams or electron beams. There are several retrospective, prospective, and two randomized clinical trials comparing IORT versus WBRT. Yet, the opinions are divided. In this paper, we try to bring clarity and consensus from a highly broad-based multidisciplinary team approach. The multidisciplinary team included breast surgeons, radiation oncologists, medical physicists, biostatisticians, public health experts, nurse practitioners, and medical oncologists. We show that there is a need to more carefully interpret and differentiate the data based on electron versus low-dose X-ray modalities; the randomized study results have to be extremely carefully dissected from biostatistical points of view; the importance of the involvement of patients and families in the decision making in a very transparent and informed manner needs to be emphasized; and the compromise some women may be willing to accept between 2-4% potential increase in local recurrence (as interpreted by some of the investigators in IORT randomized studies) versus mastectomy. We conclude that, ultimately, the choice should be that of women with detailed facts of the pros and cons of all options being presented to them from the angle of patient/family-focused care. Although the guidelines of various professional societies can be helpful, they are only guidelines. The participation of women in IORT clinical trials is still needed, and as genome-based and omics-based fine-tuning of prognostic fingerprints evolve, the current guidelines need to be revisited. Finally, the use of IORT can help rural, socioeconomically, and infrastructure-deprived populations and geographic regions as the convenience of single-fraction RT and the possibility of breast preservation are likely to encourage more women to choose BCT than mastectomy. This option can also likely lead to more women choosing to get screened for breast cancer, thus enabling the diagnosis of breast cancer at an earlier stage and improving the survival outcomes.

The Influence of Patient and System Factors on the Radiotherapy Treatment Time in the Treatment of Non-metastatic Cervical Cancer Patients in a Rural and Resource-Lean State's Safety-Net Hospital: Benefits of Strategic Planning.

Objective To decrease radiotherapy treatment time (RTT), measured from the day of initiation of radiotherapy to the day of its completion, specific strategies were initiated in early 2020 in the only academic safety-net medical center in a rural, resource-lean state. The factors that can succeed and those that need further improvements were analyzed in this initial assessment phase of our efforts to shorten the RTT. Methods This is an analysis of 28 cervix cancer patients treated with magnetic resonance imaging (MRI)-guided brachytherapy (February 2020-November 2021). The relationship between independent and dependent variable were analyzed by simple linear regression, and p-values ≤ 0.05 were considered statistically significant. SPSS software version 28.0 (IBM, Armonk, NY, USA) was used for statistical analysis. Results Two RTT groups (≤ 60 (32.1%) vs. > 60 days {67.9%}) with median RTT of 68 days (range, 51 to 106 days) were analyzed. Caucasians represented 66.7% of the RTT ≤ 60 days group. Four 'issues' were identified that increased the RTT: non-compliance, learning curve (early days of implementation of MRI-guided brachytherapy in the department), stage IV comorbidities, and with more than one issue mentioned; 77.8% with no issues had ≤ 60 days RTT vs. 26.3% for the > 60 days group. The breakdown of the no-issues factor by calendar year showed the RTT of ≤ 60 days was achieved higher in 2021 (85.7% vs. 20.0%; p=0.023) compared to 2020. For this entire cohort, the RTT of ≤ 60 days was achieved higher in 2021 (50.0% vs. 8.3%; p=0.019) compared to 2020. Data also showed improvement in RTT of ≤ 60 days for every sequential six months. 'Non-compliance' and 'learning curve' were the most important factors among patients having the longest RTTs. Conclusion The RTT can be further decreased. As a result of this preliminary analysis of the our strategic planning approach of 'circular' "See it," "Own it," "Solve it," and "Do it" and go back to the first step again, we plan to implement the following strategies in the immediate future to shorten the RTTs further and, in turn, improve our overall outcomes (local/regional control, disease-free survival, and overall survival): (a) Interdigitate MRI-guided brachytherapy during external beam radiotherapy (EBRT); patients who can not get the interdigitated brachytherapy procedures performed during the course of EBRT for any reason will receive two brachytherapy procedures per week; (c) attempt to add a cervix cancer care navigator to our staff to help patients having social issues, thus leading to compliance problems; (d) finally, in a year or two after these new strategic implementations, the RTT data will be reanalyzed.

Strategic Reduction of Package Time in Head and Neck Cancer.

Purpose: Total package time, or the time from diagnosis to completion of definitive treatment, has been associated with outcomes for a variety of tumor sites, but especially to head and neck (HN) cancer. Patients with HN cancer often undergo a complex diagnosis and treatment process involving multiple disciplines both within and outside of oncology. This complexity can lead to longer package times, and each involved discipline has the responsibility to maintain an efficient and effective process. Strategic intervention to improve package time must involve not only new technology or tools, but also "soft" components such as accountability, motivation, and leadership. This combination is necessary to truly optimize radiation therapy for HN cancer, leading to shorter total package times for these patients. Methods and Materials: Two interventions were strategically executed to improve radiation therapy workflow: upgrade of the treatment planning system and implementation of an automated patient management and accountability system. The radiation therapy-related timelines of 112 patients with HN cancer treated over 2 years were reviewed, and the average time differences were compared between the patient populations before and after the strategic interventions. Results: Purely upgrading the treatment planning system did not show significant improvements, but when combined with the patient management system, significant improvement in radiation-related package time can be noted for every time point. The overall reduction of radiation-related package time was statistically significant at 22.85 days (P = .002). Conclusions: On face value, the patient management system could be credited as responsible for the improvement, but on qualitative analysis, it is noted that the new system is only a tool that can be ignored or underused. Owing to the addition of important "soft" components such as accountability, motivation, and leadership, the patient management system was optimized and implemented in such a manner as to have the desired effect.

Ramifications of Setup Margin Use During Frameless Stereotactic Radiosurgery/Therapy With Gamma Knife Icon Cone-Beam Computed Tomography (CBCT): A Dosimetric Study.

Objective The objective is to explore the possibility of optimal/rational application of setup margin during treatment planning for frameless stereotactic Gamma Knife radiosurgery/therapy. Methods Uncertainty measurements for frameless Gamma Knife Icon treatment were used to calculate the necessary setup margin via four different published recipes and these margins were subsequently applied to treatment plans of 30 previously treated patients and replans were generated meeting comparable plan quality metrics. All plans were then analyzed based on the ability to maintain normal tissue dose tolerances and the relative increase in target dose coverage probability using a pass/fail scoring system based on published normal tissue dose constraints and an in-house developed optimal scoring method. Results Gross tumor volume/planning target volume (GTV/PTV) size strongly correlated with both meeting normal tissue tolerances and optimal scores for single fraction plans corroborating published clinical outcomes. The Van Herk Margin Formula (VHMF) and Parker margin formulae were indicated as good candidates for high probabilities of both meeting normal tissue goals and high optimal scores which generally translated to just over 1 mm in GTV to PTV margin. Conclusion For single fraction treatment, GTV size is highly significant in predicting failure to meet normal tissue goals whereas whether setup margin was used was not a significant predictor. Setup margin can rationally be applied when fraction number is dictated by clinically indicated metrics regarding GTV size of greater or less than 4 cc. 1 mm is a reasonable practical application of margin added to GTV to ensure physical prescription dose target coverage for most cases when clinically desired based on disease type and intended outcome.

Predictors of Significant Patient Movement During Frameless Radiosurgery with the Gamma Knife® Icon™ Cone-Beam CT.

Objective The objective of the study is to discern any factors that may be predictive of patient-specific uncertainty related to residual error after cone-beam CT (CBCT) correction and motion measured by the high-definition motion management (HDMM) system. Methods HDMM treatment logs were parsed via a Python 3 script and then analyzed for 30 patients. Additionally, CBCT registration and correction data was also collected and analyzed for the same 30 patients. Correlation analysis was then performed against various patient- and treatment-related factors to discern any potentially predictive factors. Results BMI was the only statistically significant predictor identified in this study with an r value of 0.393, p=0.032. Despite being identified as a predictor in other studies, treatment time, when treated as a continuous variable, did not show up as significant in this work. Conclusion BMI may be predictive of patients who might require extra tactics to mitigate motion during frameless Gamma Knife® treatment.

Total workflow uncertainty of frameless radiosurgery with the Gamma Knife Icon cone-beam computed tomography.

OBJECTIVE: Frameless treatment with the Gamma Knife Icon is still relatively new as a treatment option. As a result, additional confidence/knowledge about the uncertainty that exists within each portion of the treatment workflow could be gained especially regarding steps that have not been previously studied in the literature. METHODS: The Icon base delivery device (Perfexion) uncertainty is quantified and validated. The novel portions of the Icon such as mask immobilization, cone-beam computed tomography image guidance, and the intrafraction motion management methods are studied specifically and to a greater extent to determine a total workflow uncertainty of frameless treatment with the Icon. RESULTS: The uncertainty of each treatment workflow step has been identified with the total workflow uncertainty being identified in this work as 1.3 mm with a standard deviation of 0.51 mm. CONCLUSION: The total uncertainty of frameless treatment with the Icon has been evaluated and this data may indicate the need for setup margin in this setting with data that could be used by other institutions to calculate needed setup margin per their preferred recipe after validation of this data in their context.

Changing Role of PET/CT in Cancer Care With a Focus on Radiotherapy.

Positron emission tomography (PET) integrated with computed tomography (CT) has brought revolutionary changes in improving cancer care (CC) for patients. These include improved detection of previously unrecognizable disease, ability to identify oligometastatic status enabling more aggressive treatment strategies when the disease burden is lower, its use in better defining treatment targets in radiotherapy (RT), ability to monitor treatment responses early and thus improve the ability for early interventions of non-responding tumors, and as a prognosticating tool as well as outcome predicting tool. PET/CT has enabled the emergence of new concepts such as radiobiotherapy (RBT), radioimmunotherapy, theranostics, and pharmaco-radiotherapy. This is a rapidly evolving field, and this primer is to help summarize the current status and to give an impetus to developing new ideas, clinical trials, and CC outcome improvements.

Single Institution Experience of Stereotactic Body Radiation Therapy in Non-small Cell Lung Cancer: Comparison of Two Dose Regimes and a Perspective on Ideal Dose Regimens.

Introduction Stereotactic body radiation therapy (SBRT) is an effective treatment for early-stage non-small cell lung cancer (NSCLC) patients who are either medically inoperable or who decline surgery. SBRT improves tumor control and overall survival (OS) in medically inoperable, early-stage, NSCLC patients. In this study, we investigated the effectiveness of two different SBRT doses commonly used and present our institutional experience. Purpose To determine the clinical outcomes between two treatment regiments (50 Gray [Gy] vs. 55 Gy in five fractions) among Stage I NSCLC patients treated with SBRT at a state academic medical center. Methods We performed a retrospective analysis of 114 patients with Stage I (T1-2 N0 M0) NSCLC treated at a state academic medical center between October 2009 and April 2019. Survival analyses with treatment regimens of 50 Gy and 55 Gy in five fractions were conducted to detect any improvement in outcomes associated with the higher dose. The primary endpoints of this study included OS, local control (LC), and disease-free survival (DFS). Log-rank test and the Kaplan-Meier method were used to analyze the survival curves of the two treatment doses. The SPSS v.24.0 (IBM Corp., Armonk, NY, USA) was used for statistical analyses. Results The 114 early-stage NSCLC patients (median age, 68 years; range 12 to 87 years) had a median follow-up of 25 months (range two to 86 months). The number of males (n = 72; 63.2 %) exceeded the number of females (n = 42; 36.8 %). The majority of patients in this study were Caucasians (n = 68; 59.6 %) and 46 patients were African Americans (40.4 %). Two-thirds of the patients (n = 76; 66.7 %) were treated with 50 Gy in five fractions, and 38 patients (33.3 %) with 55 Gy in five fractions. The one-, two-, and three-year OS and DFS rates were improved in the patients treated with 55 Gy [OS, 81.7 % vs. 72.8 %; 81.7 % vs. 58.9 %; 81.7 % vs. 46.7 % (p = 0.049)], [DFS, 69.7 % vs. 69.7 %; 61.9 % vs. 55.7 %; 61.9 % vs. 52.0 % (p = 0.842)], compared to those treated with 50 Gy. Adenocarcinoma was the most common histology in both groups (51.3 % and 68.4 %). Failure rates were elevated for the 50 Gy regimen [39 (34.2 %) vs. 12 (8.5 %)]. Three year control rates were (66.3 % vs. 96.6 %; p = 0.002) local control; (63.3 % vs. 94.4 %; p = 0.000) regional control; and (65.7 % vs. 97.1 %; p = 0.000) distant control, compared to those treated with 55 Gy. Conclusion Early-stage NSCLC patients treated with SBRT 55 Gy in five fractions did better in terms of local control, overall survival, and disease-free survival rates compared to the 50 Gy in five fractions group.

Considering inhomogeneities in Gamma Knife treatment planning: Factors affecting the loss of prescription dose coverage†.

OBJECT: To compare the consistency of the agreement between the Convolution and TMR10 algorithms using a homogeneous phantom and to identify target characteristics that lead to large changes in target isodose coverage when the Convolution algorithm is used in GammaPlan as opposed to the TMR10 algorithm. METHODS: The IROC phantom end-to-end test was performed and RTDose for both the TMR10 and Convolution algorithm were submitted for comparison to the measurement. Treatment plans for 16 patients and 26 different targets were retrospectively re-calculated with the Convolution algorithm when originally planned with the TMR10 algorithm. Multivariate regression was used to find statistically significant predictors of loss in target prescription isodose coverage. RESULTS: Both algorithms agreed well with the IROC TLD measurement (within 1 %) and slightly better agreement was seen in the film analysis for the Convolution algorithm. After multivariate regression, small target volumes, < 1cm from air cavity, and minimum dose to target were potential predictors of large percentage loss of prescription isodose coverage (p = 0.049, 0.026, and 0.002, respectively). CONCLUSION: Convolution and TMR10 appear to be equivalent in homogeneous situations. Some target characteristics have been identified that might be indications for use of the Convolution algorithm in clinical practice.

Evaluating the accuracy of geometrical distortion correction of magnetic resonance images for use in intracranial brain tumor radiotherapy.

AIM: Determine the 1) effectiveness of correction for gradient-non-linearity and susceptibility effects on both QUASAR GRID3D and CIRS phantoms; and 2) the magnitude and location of regions of residual distortion before and after correction. BACKGROUND: Using magnetic resonance imaging (MRI) as a primary dataset for radiotherapy planning requires correction for geometrical distortion and non-uniform intensity. MATERIALS AND METHODS: Phantom Study: MRI, computed tomography (CT) and cone beam CT images of QUASAR GRID3D and CIRS head phantoms were acquired. Patient Study: Ten patients were MRI-scanned for stereotactic radiosurgery treatment. Correction algorithm: Two magnitude and one phase difference image were acquired to create a field map. A MATLAB program was used to calculate geometrical distortion in the frequency encoding direction, and 3D interpolation was applied to resize it to match 3D T1-weighted magnetization-prepared rapid gradient-echo (MPRAGE) images. MPRAGE images were warped according to the interpolated field map in the frequency encoding direction. The corrected and uncorrected MRI images were fused, deformable registered, and a difference distortion map generated. RESULTS: Maximum deviation improvements: GRID3D , 0.27 mm y-direction, 0.07 mm z-direction, 0.23 mm x-direction. CIRS, 0.34 mm, 0.1 mm and 0.09 mm at 20-, 40- and 60-mm diameters from the isocenter. Patient data show corrections from 0.2 to 1.2 mm, based on location. The most-distorted areas are around air cavities, e.g. sinuses. CONCLUSIONS: The phantom data show the validity of our fast distortion correction algorithm. Patient-specific data are acquired in <2 min and analyzed and available for planning in less than a minute.

Gamma Knife® icon CBCT offers improved localization workflow for frame-based treatment.

OBJECT: The purpose of this study was to compare two methods of stereotactic localization in Gamma Knife treatment planning: cone beam computed tomography (CBCT) or fiducial. While the fiducial method is the traditional method of localization, CBCT is now available for use with the Gamma Knife Icon. This study seeks to determine whether a difference exists between the two methods and then whether one is better than the other regarding accuracy and workflow optimization. METHODS: Cone beam computed tomography was used to define stereotactic space around the Elekta Film Pinprick phantom and then treated with film in place. The same phantom was offset known amounts from center and then imaged with CBCT and registered with the reference CBCT image to determine if measured offsets matched those known. Ten frameless and 10 frame-based magnetic resonance imaging (MRI) to CBCT patient fusions were retrospectively evaluated using the TG-132 TRE method. The stereotactic coordinates defined by CBCT and traditional fiducials were compared on the Elekta 8 cm Ball phantom, an anthropomorphic phantom, and actual patient data. Offsets were introduced to the anthropomorphic phantom in the stereotactic frame and CBCT's ability to detect those offsets was determined. RESULTS: Cone beam computed tomography defines stereotactic space well within the established limits of the mechanical alignment system. The CBCT to CBCT registration can detect offsets accurately to within 0.1 mm and 0.5°. In all cases, some disagreement existed between fiducial localization and that of CBCT which in some cases was small, but also was as high as 0.43 mm in the phantom domain and as much as 1.54 mm in actual patients. CONCLUSION: Cone beam computed tomography demonstrates consistent accuracy in defining stereotactic space. Since both localization methods do not agree with each other consistently, the more reliable method must be identified. Cone beam computed tomography can accurately determine offsets occurring within stereotactic space that would be nondiscernible utilizing the fiducial method and seems to be more reliable. Using CBCT localization offers the opportunity to streamline workflow both from a patient and clinic perspective and also shows patient position immediately prior to treatment.

Evaluation of the Geometric and Dosimetric Accuracy of Synthetic Computed Tomography Images for Magnetic Resonance Imaging-only Stereotactic Radiosurgery.

Introduction Stereotactic radiosurgery (SRS) plans created using synthetic computed tomography (CT) images derived from magnetic resonance imaging (MRI) data may offer the advantage of inhomogeneity correction by convolution algorithms, as is done for CT-based plans. We sought to determine and validate the clinical significance and accuracy of synthetic CT images for inhomogeneity correction in MRI-only stereotactic radiosurgery plans for treatment of brain tumors. Methods In this retrospective study, data from two patients with brain metastases and one with meningioma who underwent imaging with multiple modalities and received frameless SRS treatment were analyzed. The SRS plans were generated using a convolution algorithm to account for brain inhomogeneity using CT and synthetic CT images and compared with the original clinical TMR10 plans created using MRI images. Results Synthetic CT-derived SRS plans are comparable with CT-based plans using convolution algorithm, and for some targets, based on location, they provided better coverage and a lower maximum dose. Conclusions The results suggest similar dose delivery results for CT and synthetic CT-based treatment plans. Synthetic CT plans offered a noticeable improvement in target dose coverage and a more gradual dose fall-off relative to TMR10 MRI-based plans. The major disadvantage is a slightly increased dose (by 0.37%) to nearby healthy tissue (brainstem) for synthetic CT-based plans relative to those created using clinical MRI images, which may be a problem for patients undergoing high-dose treatment.

Optimizing MRI sequences and images for MRI-based stereotactic radiosurgery treatment planning.

AIM: Development of MRI sequences and processing methods for the production of images appropriate for direct use in stereotactic radiosurgery (SRS) treatment planning. BACKGROUND: MRI is useful in SRS treatment planning, especially for patients with brain lesions or anatomical targets that are poorly distinguished by CT, but its use requires further refinement. This methodology seeks to optimize MRI sequences to generate distortion-free and clinically relevant MR images for MRI-only SRS treatment planning. MATERIALS AND METHODS: We used commercially available SRS MRI-guided radiotherapy phantoms and eight patients to optimize sequences for patient imaging. Workflow involved the choice of correct MRI sequence(s), optimization of the sequence parameters, evaluation of image quality (artifact free and clinically relevant), measurement of geometrical distortion, and evaluation of the accuracy of our offline correction algorithm. RESULTS: CT images showed a maximum deviation of 1.3 mm and minimum deviation of 0.4 mm from true fiducial position for SRS coordinate definition. Interestingly, uncorrected MR images showed maximum deviation of 1.2 mm and minimum of 0.4 mm, comparable to CT images used for SRS coordinate definition. After geometrical correction, we observed a maximum deviation of 1.1 mm and minimum deviation of only 0.3 mm. CONCLUSION: Our optimized MRI pulse sequences and image correction technique show promising results; MR images produced under these conditions are appropriate for direct use in SRS treatment planning.

Machine-Specific Magnetic Resonance Imaging Quality Control Procedures for Stereotactic Radiosurgery Treatment Planning.

Purpose Magnetic resonance (MR) images are necessary for accurate contouring of intracranial targets, determination of gross target volume and evaluation of organs at risk during stereotactic radiosurgery (SRS) treatment planning procedures. Many centers use magnetic resonance imaging (MRI) simulators or regular diagnostic MRI machines for SRS treatment planning; while both types of machine require two stages of quality control (QC), both machine- and patient-specific, before use for SRS, no accepted guidelines for such QC currently exist. This article describes appropriate machine-specific QC procedures for SRS applications. Methods and materials We describe the adaptation of American College of Radiology (ACR)-recommended QC tests using an ACR MRI phantom for SRS treatment planning. In addition, commercial Quasar MRID3D and Quasar GRID3D phantoms were used to evaluate the effects of static magnetic field (B0) inhomogeneity, gradient nonlinearity, and a Leksell G frame (SRS frame) and its accessories on geometrical distortion in MR images. Results QC procedures found in-plane distortions (Maximum = 3.5 mm, Mean = 0.91 mm, Standard deviation = 0.67 mm, >2.5 mm (%) = 2) in X-direction (Maximum = 2.51 mm, Mean = 0.52 mm, Standard deviation = 0.39 mm, > 2.5 mm (%) = 0) and in Y-direction (Maximum = 13. 1 mm , Mean = 2.38 mm, Standard deviation = 2.45 mm, > 2.5 mm (%) = 34) in Z-direction and < 1 mm distortion at a head-sized region of interest. MR images acquired using a Leksell G frame and localization devices showed a mean absolute deviation of 2.3 mm from isocenter. The results of modified ACR tests were all within recommended limits, and baseline measurements have been defined for regular weekly QC tests. Conclusions With appropriate QC procedures in place, it is possible to routinely obtain clinically useful MR images suitable for SRS treatment planning purposes. MRI examination for SRS planning can benefit from the improved localization and planning possible with the superior image quality and soft tissue contrast achieved under optimal conditions.

Dosimetric comparison of brachytherapy sources for high-dose-rate treatment of endometrial cancer: (192)Ir, (60)Co and an electronic brachytherapy source.

OBJECTIVE: To compare high-dose-rate (HDR) brachytherapy systems with (192)Ir, (60)Co and electronic brachytherapy source (EBS) for treatment of endometrial cancers. METHODS: Two additional plans were generated per patient fraction using a (60)Co source and Xoft-EBS on 10 selected patients, previously treated with a vaginal cylinder applicator using a (192)Ir source. Dose coverage of "PTV_CYLD", a 5-mm shell surrounding the cylinder, was evaluated. Doses to the following organs at risk (OARs) the rectum, bladder and sigmoid were evaluated in terms of V35% and V50%, the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D2cm(3), the highest dose to a 2-cm(3) volume of an OAR. RESULTS: Xoft-EBS reduces doses to all OARs in the lower dose range, but it does not always provide better sparing of the rectum in higher dose range as does evaluation using D2cm3. V150% and V200% for PTV_CYLD was up to four times greater for Xoft-EBS plans than for plans generated with (192)Ir or (60)Co. Surface mucosal (vaginal cylinder surface) doses were also 23% higher for Xoft-EBS than for (192)Ir or (60)Co plans. CONCLUSION: Xoft-EBS is a suitable HDR source for vaginal applicator treatment with advantages of reducing radiation exposure to OARs in the lower dose range, while simultaneously increasing the vaginal mucosal dose. ADVANCES IN KNOWLEDGE: This work presents newer knowledge in dosimetric comparison between (192)Ir or (60)Co and Xoft-EBS sources for endometrial vaginal cylinder HDR planning.

Modeling treatment couches in the Pinnacle treatment planning system: Especially important for arc therapy.

This study is to demonstrate the importance and a method of properly modeling the treatment couch for dose calculation in patient treatment using arc therapy. The 2 treatment couch tops-Aktina AK550 and Elekta iBEAM evo-of Elekta LINACs were scanned using Philips Brilliance Big Bore CT Simulator. Various parts of the couch tops were contoured, and their densities were measured and recorded on the Pinnacle treatment planning system (TPS) using the established computed tomography density table. These contours were saved as organ models to be placed beneath the patient during planning. Relative attenuation measurements were performed following procedures outlined by TG-176 as well as absolute dose comparison of static fields of 10 × 10 cm(2) that were delivered through the couch tops with that calculated in the TPS with the couch models. A total of 10 random arc therapy treatment plans (5 volumetric-modulated arc therapy [VMAT] and 5 stereotactic body radiation therapy [SBRT]), using 24 beams, were selected for this study. All selected plans were calculated with and without couch modeling. Each beam was evaluated using the Delta(4) dosimetry system (Delta(4)). The Student t-test was used to determine statistical significance. Independent reviews were exploited as per the Imaging and Radiation Oncology Core head and neck credentialing phantom. The selected plans were calculated on the actual patient anatomies with and without couch modeling to determine potential clinical effects. Large relative beam attenuations were noted dependent on which part of the couch top beams were passing through. Substantial improvements were also noted for static fields both calculated with the TPS and delivered physically when the couch models were included in the calculation. A statistically significant increase in agreement was noted for dose difference, distance to agreement, and γ-analysis with the Delta(4) on VMAT and SBRT plans. A credentialing review showed improvement in treatment delivery after couch modeling with both thermoluminescent dosimeter doses and film analysis. Furthermore, analysis of treatment plans with and without using the couch model showed a statistically significant reduction in planning target volume coverage and increase in skin dose. In conclusion, ignoring the treatment couch, a common practice when generating a patient treatment plan, can overestimate the dose delivered especially for arc therapy. This work shows that explicitly modeling the couch during planning can meaningfully improve the agreement between calculated and measured dose distributions. Because of this project, we have implemented the couch models clinically across all treatment plans.

Radiation safety consideration during intraoperative radiation therapy.

Using in-house-designed phantoms, the authors evaluated radiation exposure rates in the vicinity of a newly acquired intraoperative radiation therapy (IORT) system: Axxent Electronic Brachytherapy System. The authors also investigated the perimeter radiation levels during three different clinical intraoperative treatments (breast, floor of the mouth and bilateral neck cancer patients). Radiation surveys during treatment delivery indicated that IORT using the surface applicator and IORT using balloons inserted into patient body give rise to exposure rates of 200 mR h(-1), 30 cm from a treated area. To reduce the exposure levels, movable lead shields should be used as they reduce the exposure rates by >95%. The authors' measurements suggest that intraoperative treatment using the 50-kVp X-ray source can be administered in any regular operating room without the need for radiation shielding modification as long as the operators utilise lead aprons and/or stand behind lead shields.

Medical Physics Residency Consortium: collaborative endeavors to meet the ABR 2014 certification requirements.

In 2009, Mary Bird Perkins Cancer Center (MBPCC) established a Radiation Oncology Physics Residency Program to provide opportunities for medical physics residency training to MS and PhD graduates of the CAMPEP-accredited Louisiana State University (LSU)-MBPCC Medical Physics Graduate Program. The LSU-MBPCC Program graduates approximately six students yearly, which equates to a need for up to twelve residency positions in a two-year program. To address this need for residency positions, MBPCC has expanded its Program by developing a Consortium consisting of partnerships with medical physics groups located at other nearby clinical institutions. The consortium model offers the residents exposure to a broader range of procedures, technology, and faculty than available at the individual institutions. The Consortium institutions have shown a great deal of support from their medical physics groups and administrations in developing these partnerships. Details of these partnerships are specified within affiliation agreements between MBPCC and each participating institution. All partner sites began resident training in 2011. The Consortium is a network of for-profit, nonprofit, academic, community, and private entities. We feel that these types of collaborative endeavors will be required nationally to reach the number of residency positions needed to meet the 2014 ABR certification requirements and to maintain graduate medical physics training programs.