Citations

Introduction Proton dose driven continuous scanning (DDCS) is a form of proton pencil beam scanning (PBS) in which the beam may remain on during transitions between successive spots. Mayo Clinic Florida (MCF) is preparing to commission a synchrotron-based proton therapy system designed for DDCS, incorporating novel irradiation control features. Given the novelty and complexity of this system, a systematic risk-based analysis was performed to inform upcoming commissioning strategies. Methods A prospective risk analysis was conducted using the American Association of Physicists in Medicine (AAPM) Task Group 100 (TG 100) framework. A comprehensive process map of the DDCS irradiation control workflow was developed. Failure modes and effects analysis (FMEA) was performed to identify potential delivery system failure modes and to score each failure mode based on occurrence, severity, and lack of detectability. Targeted mitigation and commissioning strategies were then developed to address the highest-risk items. Results Twenty-nine delivery system failure modes were identified. The highest-risk failure modes were specific to DDCS operation. Targeted commissioning strategies were defined, including scan path measurement and modeling, validation of move and flap dose, dose monitor collection efficiency testing, spot position monitor performance evaluation, and verification of control system intervention behavior. Incorporation of these strategies into the commissioning plan reduced the mean RPN by more than 50%. Discussion This work provides a detailed description of the MCF proton DDCS irradiation control system and uses a TG 100 based approach for identifying system-specific risks. As new systems incorporate technologies for which limited guidance exists, institutions must perform their own risk analyses to determine appropriate quality management strategies.

This study evaluated the effectiveness of using a traditional computed tomography (CT) simulation scan in the Leksell Gamma Knife® Icon™ workflow for stereotactic radiosurgery. We compared two workflows, one involving a traditional CT simulation co-registered with the magnetic resonance imaging (MRI) and cone-beam CT (CBCT) (MRI-CT-CBCT) and another without the CT scan, co-registering the MRI directly with CBCT (MRI-CBCT). The cohort included 50 frame-based (54 targets) and 55 frameless (124 targets) patients treated between August 2020 and December 2022. Target coverage was assessed by the percentage of each target covered by the prescription isodose line. The mean coverage differences for the frame-based and frameless cohorts were −1.20% ± 1.43% and −1.06% ± 1.51%, respectively, with 95% confidence intervals of −1.59, −0.81 and −1.32, −0.79. The MRI-CBCT workflow was deemed noninferior to the MRI-CT-CBCT workflow. Our data indicate that both workflows yield similar results, suggesting that a traditional CT simulation scan is unnecessary.

AbstractPurposeSkin 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.MethodsAttenuation 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.ResultsClinically 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.ConclusionBoth 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.

Abstract 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.

Proton minibeam therapy (PMBT) is a form of spatially fractionated radiotherapy wherein broad beam radiation is replaced with segmented minibeams—either parallel, planar minibeam arrays generated by a multislit collimator or scanned pencil beams that converge laterally at depth to create a uniform dose layer at the tumor. By doing so, the spatial pattern of entrance dose is considerably modified while still maintaining tumor dose and efficacy. Recent studies using computational modeling, phantom experiments, in vitro and in vivo preclinical models, and early clinical feasibility assessments suggest that unique physical and biological attributes of PMBT can be exploited for future clinical benefit. We outline some of the guiding principle of PMBT in this concise overview of this emerging area of preclinical and clinical research inquiry.

147 Background: Prostate cancer patients treated with external beam radiation therapy are instructed to present daily with a full bladder to decrease small bowel and bladder toxicity and to increase reproducibility of treatment. However, older patients may have difficulty presenting with full bladders and variation of bladder volume with treatment is unknown. The objective of this study was to assess bladder filling at the time of radiation treatment (RT) using a bladder ultrasound in patients undergoing treatment for prostate cancer. Methods: Patients with prostate cancer were prospectively enrolled prior to CT simulation from January to August 2017. Bladder volume was recorded during CT simulation and daily immediately prior to RT. Patients were instructed to drink 8-12 ounces of water 30-60 minutes prior to RT. Three bladder volume measurements were recorded daily and averaged at the time of each treatment. Average bladder volume during treatment and the number of treatments with low bladder volumes ( < 50cc, < 60cc, and < 100cc) were reported using descriptive statistics. Results: A total of 13 patients completed a median of 42 days of RT during the study period, resulting in 550 daily bladder volumes. Ten patients were treated definitively and 3 with salvage radiation after prostatectomy. The median age of patients in the study was 72 years. Older patients were statistically more likely to present with low bladder volumes, with percentage of treatments with a bladder volume less than 50cc, 60cc, and 100cc being 29%, 42%, and 66% compared to only 4%, 7%, and 18% in patients aged < 70 (P < 0.01). The average bladder volume at the time of CT simulation was 176cc ± 57cc and the average volume during treatment was 140cc± 93cc, which was not statistically different (P = 0.28). The bladder volume did not significantly change over the course of treatment. Conclusions: Older patients (age 70+) with prostate cancer were more likely to present for RT with low bladder volumes in this prospective study. Our findings suggest that older patients should receive extra counseling about bladder filling and/or may require less bladder filling at the time of CT simulation to provide more accurate bowel dosimetry measurements.