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Purpose: To assess the efficacy of placing a polyethylene glycol (PEG) spacing hydrogel in patients undergoing proton beam radiation therapy for prostate cancer. This study also aims to assess the effect on rectal radiation dose of prostate–rectum separation in various anatomic planes. Methods and Materials: Seventy-two consecutive prostate cancer patients undergoing conventionally fractionated pencil beam scanning proton radiation therapy with and without hydrogel placement were compared. Magnetic resonance images taken after hydrogel placement measured prostate–rectum separation and were correlated to rectal dosing and rectal toxicity. Univariate analysis of clinical variables and radiation dosing was conducted using nonparametric Wilcoxon rank-sum test with continuity correction between groups (hydrogel spacer vs controls). Spearman's rank correlation coefficient assessed relationships between the various anatomic dimensions of perirectal space and rectal radiation dosing. Results: Fifty-one patients had hydrogel placement before therapy and 21 did not. There was a 42.2% reduction in rectal dosing (mL3 rectum) in hydrogel patients (P

Background Mega-voltage fan-beam Computed Tomography (MV-FBCT) holds potential in accurate determination of relative electron density (RED) and proton stopping power ratio (SPR) but is not widely available. Objective To demonstrate the feasibility of MV-FBCT using a medical linear accelerator (LINAC) with a 2.5 MV imaging beam, an electronic portal imaging device (EPID) and multileaf collimators (MLCs). Methods MLCs were used to collimate MV beam along z direction to enable a 1 cm width fan-beam. Projection data were acquired within one gantry rotation and preprocessed with in-house developed artifact correction algorithms before the reconstruction. MV-FBCT data were acquired at two dose levels: 30 and 60 monitor units (MUs). A Catphan 604 phantom was used to evaluate basic image quality. A head-sized CIRS phantom with three configurations of tissue-mimicking inserts was scanned and MV-FBCT Hounsfield unit (HU) to RED calibration was established for each insert configuration using linear regression. The determination coefficient ($${R}^{2}$$ R 2 ) was used to gauge the accuracy of HU-RED calibration. Results were compared with baseline single-energy kilo-voltage treatment planning CT (TP-CT) HU-RED calibration which represented the current standard clinical practice. Results The in-house artifact correction algorithms effectively suppressed ring artifact, cupping artifact, and CT number bias in MV-FBCT. Compared to TP-CT, MV-FBCT was able to improve the prediction accuracy of the HU-RED calibration curve for all three configurations of insert materials, with $${R}^{2}$$ R 2 > 0.9994 and $${R}^{2}$$ R 2 < 0.9990 for MV-FBCT and TP-CT HU-RED calibration curves of soft-tissue inserts, respectively. The measured mean CT numbers of blood-iodine mixture inserts in TP-CT drastically deviated from the fitted values but not in MV-FBCT. Reducing the radiation level from 60 to 30 MU did not decrease the prediction accuracy of the MV-FBCT HU-RED calibration curve. Conclusion We demonstrated the feasibility of MV-FBCT and its potential in providing more accurate RED estimation.

Implementing tighter intensity modulated radiation therapy (IMRT) quality assurance (QA) tolerances initially resulted in high numbers of marginal or failing QA results and motivated a number of improvements to our calculational processes. This work details those improvements and their effect on results. One hundred eighty IMRT plans analyzed previously were collected and new gamma criteria were applied and compared to the original results. The results were used to obtain an estimate for the number of plans that would require additional dose volume histogram (DVH)‐based analysis and therefore predicted workload increase. For 2 months and 133 plans, the established criteria were continued while the new criteria were applied and tracked in parallel. Because the number of marginal or failing plans far exceeded the predicted levels, a number of calculational elements were investigated: IMRT modeling parameters, calculation grid size, and couch top modeling. After improvements to these elements, the new criteria were clinically implemented and the frequency of passing, questionable, and failing plans measured for the subsequent 15 months and 674 plans. The retrospective analysis of selected IMRT QA results demonstrated that 75% of plans should pass, while 19% of IMRT QA plans would need DVH‐based analysis and an additional 6% would fail. However, after applying the tighter criteria for 2 months, the distribution of plans was significantly different from prediction with questionable or failing plans reaching 47%. After investigating and improving several elements of the IMRT calculation processes, the frequency of questionable plans was reduced to 11% and that of failing plans to less than 1%. Tighter IMRT QA tolerances revealed the need to improve several elements of our plan calculations. As a consequence, the accuracy of our plans have improved, and the frequency of finding marginal or failing IMRT QA results, remains within our practical ability to respond.

Purpose Custom-fabricated lead shields are often used for superficial radiation treatments to reduce radiation doses to adjacent healthy tissue. However, the process for fabricating these lead shields is time consuming, labor intensive, and uncomfortable for patients. Alternatively, patient-specific shields can be 3-dimensionally (3D) printed from a high-density bronze-based filament to address these concerns. This study was performed to assess the shielding characteristics of 3D-printed bronze (3DPB) shields, demonstrate their clinical viability, and report the first ever published case of a patient treated with a 3DPB shield. Methods and Materials The transmission of 6 and 9 MeV electron beams through varying thicknesses of 3DPB was first measured. Percent depth doses and beam profiles were measured with flat 3DPB shields and equivalent lead shields to determine surface dose enhancement, output factors, and field widths. Two 3DPB shields were designed and fabricated for an anthropomorphic phantom, and phantom measurements were performed using optically stimulated luminescence dosimeters and film. Finally, 3DPB shields were used during the treatment of 7 patients' skin lesions. Results Ten and 15 mm of 3DPB were sufficient to shield 6 and 9 MeV electrons, respectively, by 95%. The 3DPB and lead shields had nearly identical beam widths (within 1%). Output factors were on average within 0.8% for bronze shields and 1.2% for lead shields relative to an unshielded field. The skin enhancement for bronze was higher than for lead by an average of 6.3%. Phantom measurements using 3DPB shields generally showed less than 3% transmission of the primary beam under the 3DPB shield. The patients' shields fit as designed and were all deemed clinically acceptable by their physicians. Conclusions The 3DPB shields fit better than lead shields, are easier to design and manufacture, and have similar dosimetric properties. 3DPB shields are a viable clinical option for patient-specific superficial shielding.