Technical note: A comparison of in-house 3D-printed and commercially available patient-specific skin collimators for use with electron beam therapy.

PURPOSE: Skin collimation is a useful tool in electron beam therapy (EBT) to decrease the penumbra at the field edge and minimize dose to nearby superficial organs at risk (OARs), but manually fabricating these collimation devices in the clinic to conform to the patient's anatomy can be a difficult and time intensive process. This work compares two types of patient-specific skin collimation (in-house 3D printed and vendor-provided machined brass) using clinically relevant metrics. METHODS: Attenuation measurements were performed to determine the thickness of each material needed to adequately shield both 6 and 9 MeV electron beams. Relative and absolute dose planes at various depths were measured using radiochromic film to compare the surface dose, flatness, and penumbra of the different skin collimation materials. RESULTS: Clinically acceptable thicknesses of each material were determined for both 6 and 9 MeV electron beams. Field width, flatness, and penumbra results between the two systems were very similar and significantly improved compared to measurements performed with no surface collimation. CONCLUSION: Both skin collimation methods investigated in this work generate sharp penumbras at the field edge and can minimize dose to superficial OARs compared to treatment fields with no surface collimation. The benefits of skin collimation are greatest for lower energy electron beams, and the benefits decrease as the measurement depth increases. Using bolus with skin collimation is recommended to avoid surface dose enhancement seen with collimators placed on the skin surface. Ultimately, the appropriate choice of material will depend on the desire to create these devices in-house or outsource the fabrication to a vendor.

Multicenter Multivendor Evaluation of Dose Volume Histogram Creation Consistencies for 8 Commercial Radiation Therapy Dosimetric Systems.

PURPOSE: To evaluate dose volume histogram (DVH) construction differences across 8 major commercial treatment planning systems (TPS) and dose reporting systems for clinically treated plans of various anatomic sites and target sizes. METHODS AND MATERIALS: Dose files from 10 selected clinically treated plans with a hypofractionation, stereotactic radiation therapy prescription or sharp dose gradients such as head and neck plans ranging from prescription doses of 18 Gy in 1 fraction to 70 Gy in 35 fractions, each calculated at 0.25 and 0.125 cm grid size, were created and anonymized in Eclipse TPS, and exported to 7 other major TPS (Pinnacle, RayStation, and Elements) and dose reporting systems (MIM, Mobius, ProKnow, and Velocity) systems for comparison. Dose-volume constraint points of clinical importance for each plan were collected from each evaluated system (D0.03 cc [Gy], volume, and the mean dose were used for structures without specified constraints). Each reported constraint type and structure volume was normalized to the value from Eclipse for a pairwise comparison. A Wilcoxon rank-sum test was used for statistical significance and a multivariable regression model was evaluated adjusting for plan, grid size, and distance to target center. RESULTS: For all DVH points relative to Eclipse, all systems reported median values within 1.0% difference of each other; however, they were all different from Eclipse. Considering mean values, Pinnacle, RayStation, and Elements averaged at 1.038, 1.046, and 1.024, respectively, while MIM, Mobius, ProKnow, and Velocity reported 1.026, 1.050, 1.033, and 1.022, respectively relative to Eclipse. Smaller dose grid size improved agreement between the systems marginally without statistical significance. For structure volumes relative to Eclipse, larger differences are seen across all systems with a range in median values up to 3.0% difference and mean up to 10.1% difference. CONCLUSIONS: Large variations were observed between all systems. Eclipse generally reported, at statistically significant levels, lower values than all other evaluated systems. The nonsignificant change resulting from lowering the dose grid resolution indicates that this resolution may be less important than other aspects of calculating DVH curves, such as the 3-dimensional modeling of the structure.

Does bridging radiation therapy affect the pattern of failure after CAR T-cell therapy in non-Hodgkin lymphoma?

PURPOSE: Analyze the pattern of disease failure after anti-CD19-directed chimeric antigen receptor T-cell therapy (CART) for non-Hodgkin lymphoma, assess the local control rate of bridging radiotherapy (bRT) and characterize in-field recurrences. METHODS: We retrospectively reviewed 120 patients with NHL who received CART between 2018 and 2020. Baseline characteristics and treatment outcomes were compared between patients who received bRT and those who did not (noRT). RESULTS: Of the 118 patients included, 14 (12%) received bRT, while 104 (88%) did not. bRT group had more localized and extranodal disease. bRT was delivered with a median dose of 20 Gy (range: 15-36) in 5 fractions (range: 3-24). Pattern of failure analysis revealed that progression involving pre-existing sites was the predominant pattern of failure in both the bRT and noRT groups (86% and 88%, respectively). Median duration of response was 128 days (range: 25-547) for bRT group and 93 days (range: 22-965) for noRT group (p = 0.78). In the bRT group, only 2/15 sites irradiated had infield recurrence and where characterized by bulky disease, SUVmax >20, elevated LDH at the time of CART infusion, and extranodal involvement. The bRT 1-year LC was 86%. Median duration of local response was 257 days (range: 25-630) for radiation-bridged sites. CONCLUSION: Majority of progressions after CART infusion involve pre-existing sites. Bridging RT prior to CART provides excellent in-field local control and durable response. Patients with bulky disease, SUVmax >20, elevated LDH, and extranodal involvement are likely at higher risk of in-field recurrence after bRT and may benefit from higher curative doses of bRT.

Crizotinib-associated renal cyst development may be associated with prolonged progression-free survival in patients with ALK-positive non-small-cell lung cancer: Case report and review of the literature.

Non-small cell lung cancer patients with anaplastic lymphoma kinase or c-ros oncogene 1 mutations who are treated with the tyrosine kinase inhibitor crizotinib rarely develop crizotinib-associated renal cysts (CARCs). Here, we present a case report and review of the literature supporting the hypothesis that CARCs may correlate positively with progression-free survival.

Atlas based segmentation in prone breast cancer radiation therapy.

The evidence supporting atlas based contour generation is growing and includes breast, prostate, central nervous system, gastrointestinal, gynecologic, and head and neck cancer patient populations. We sought to investigate atlas based segmentation (ABS) in patients with early stage breast cancer status post breast conserving surgery treated with adjuvant radiation therapy in the prone position. An initial atlas library was generated by uploading 20 previously treated patients. Subsequently, a group of 20 consecutive patients underwent treatment planning. Heart, right lung, left lung, total lungs, and breast clinical target volume (CTV) targets were manually contoured per our standard workflow. ABS was then incorporated into our radiation planning workflow and differences in contouring time were recorded, including time needed for ABS volume refinement. ABS generated volumes were compared subjectively in the unedited and edited stages by an independent radiation oncologist to reduce bias by incorporating an interobserver quality analysis. Various objective measurements were used to compare target volume quality including mean distance to agreement (MDA), Dice Coefficient (DC), logit transformation of DC (logit(DC)). The contouring physician edited 88.75% of organ at risk (OAR) volumes on average per patient, whereas the independent reviewing physician recommended revision of 27.5% OAR on average volumes per patient. CTV editing was performed in 20/20 (100%) of cases by the contouring physician, whereas CTV revision was recommended by the independent reviewing physician in 4/20 (20%) of cases. Our atlas performed well with DC values of >0.909 and logit(DC) of >2.344 across heart, lung, and breast volumes when compared to manually generated volumes. All objective measurements demonstrated improvement with physician refinement of ABS generated volumes. The largest absolute improvement was seen in the heart and breast CTV targets. There was 100% acceptance of the edited ABS generated volumes by the independent reviewing physician. The average time saved using ABS was 6.27 minutes (56.92%) per patient. This study confirms ABS offers improvements in efficiency without sacrificing contour quality in the early stage breast cancer patient population and demonstrates the functionality of ABS with prone patient positioning.