Yinxiangzi Sheng

This study evaluates the dosimetric feasibility of carbon-ion radiation therapy (CIRT) for ocular melanoma (OM) using a local effect model-I–based treatment planning system (TPS) combined with pencil beam scanning delivery. Cube-shaped targets were designed based on the experience of CIRT for OM at the National Institutes for Quantum Science and Technology (QST). Treatment plans used the local effect model-I–based TPS (Syngo® V13C, SIEMENS, Germany) prescribing an absorbed dose consistent with values reported in the literature. A conversion factor (CF) was established to convert the QST dose to LEM based relative biological effectiveness (RBE)–weighted dose. The physical doses were verified by an in-house Monte Carlo program and measurement. The CF for the LEM, equivalent to the QST RBE-prescribed dose of 70 Gy (RBE) over 5 fractions, was established as 0.65. The 3D gamma passing rate between TPS and MC was ≥94% using 3%–3 mm criteria. Mean dose deviations between the TPS and measurement were ≤±1.61% for all targets sizes except the smallest one (7 mm). Mean distance-to-agreement was <1 mm for all plans except one with a range shifter (distance-to-agreement = 2.92 mm). Phantom cases showed a lateral penumbra of 5.4–6.2 mm, and distal dose fall-off measures 3.6 and 5.6 mm. The results underscore the need for RBE-weighted dose conversion when applying QST’s CIRT experience to OM treatment.

Introduction: Lung particle therapy using pencil beam scanning achieves high dose conformity but remains vulnerable to geometric uncertainties from suboptimal initial setup. Surface-guided radiotherapy (SGRT) improves setup reproducibility in photon workflows, yet evidence in lung particle therapy remains limited. This study evaluates the clinical value of SGRT in improving six degrees of freedom (6-DOF) setup reproducibility in lung cancer particle therapy. Methods: This retrospective cohort study analyzed 63 lung cancer patients receiving 1277 treatment fractions at our center from February 2023 to January 2024. Comparisons were made between conventional laser-based positioning, which included 983 fractions, and SGRT workflows, which included 294 fractions. Following patient positioning, therapists manually registered orthogonal kilovoltage (kV) x-ray images with planning digitally reconstructed radiographs (DRRs) to calculate 6-DOF correction parameters, including translational (lateral, longitudinal, vertical) and rotational (pitch, roll, yaw) components, and to quantify the pre-correction setup error . Absolute 6-DOF displacements and three-dimensional vector magnitudes (MAG) were measured. The analysis included 36 supine patients with 739 treatment fractions and 27 prone patients with 538 fractions. Results: The SGRT group exhibited statistically significant reductions in median shifts for lateral (0.25 cm to 0.21 cm, p = 0.021), longitudinal (0.25 cm to 0.21 cm, p = 0.014), pitch (1.0° to 0.8°, p = 0.001), and MAG (0.59 cm to 0.53 cm, p = 0.002) compared to conventional methods. These improvements in median values were more pronounced in supine-positioned patients, while no significant differences were observed in prone-positioned patients. Furthermore, substantial reductions were achieved in ninth decile deviations (1.09 cm to 1.03 cm), and the third quartile deviations (0.83 cm to 0.74 cm) in the overall cohort. Conclusion: SGRT enhances setup precision for proton and carbon ion lung cancer radiotherapy, reduces pre-correction setup error, and provides clinical support for patient setup reproducibility.

Objective. To validate a Monte Carlo (MC)-based offline positron emission tomography (PET) range verification framework and quantitatively evaluate range uncertainties associated with material assignment strategies, specifically focusing on the clinical practice of overriding silicone implants as adipose tissue in breast proton therapy. Approach. A FLUKA-based MC model was developed. Validation followed a stepwise program using (1) a PMMA phantom, (2) a homogeneous silicone block, and (3) a composite prosthesis-PMMA setup to verify intrinsic precision and material-specific accuracy. Additionally, a cohort of eight breast cancer patients (three with implants) was included for clinical demonstration. Range deviations were quantified by measuring the depth difference at the 50% distal activity falloff ( Δ R 50 ) between simulated and measured PET images. For silicone scenarios, material assignment impact was analyzed by overriding the implant as silicone, adipose tissue, or applying no override. Main results. The MC model demonstrated intrinsic millimeter-level accuracy. In homogeneous silicone phantom experiments, defining the material as silicone yielded the highest agreement with measurements ( Δ R 50 : −0.05–0.88 mm). Reassigning silicone as adipose tissue introduced a systematic deviation but remained within acceptable limits (−1.24–−0.83 mm), whereas applying no override resulted in the largest errors (−3.25–−2.48 mm). Composite phantom results followed a similar trend. In clinical cases, the method successfully verified range delivery, although positioning uncertainties contributed to larger inter-field variability. Significance. This study validates an MC-based PET verification framework with 2 mm intrinsic accuracy, establishing it as a reliable tool for silicone-implanted breast cancer patients. The results quantitatively confirm that overriding silicone as adipose tissue keeps range uncertainty within 2 mm despite distinct elemental compositions, whereas failing to override the material leads to errors exceeding 3 mm.

Carbon-ion radiotherapy (CIRT) for head and neck tumors is typically delivered in the supine posture using fixed beam lines, which limits beam angle select

Spot size is a crucial parameter in the clinical operation of light-ion beam therapy delivery systems. This study aims to quantify the influence of spot size variations on dose distribution in proton pencil beam radiotherapy. Three cubic targets with modulation widths (M) of 3 cm, 6 cm, and 9 cm were positioned at center depths (CD) of 5 cm, 15 cm, and 25 cm within a water phantom. Dosimetric evaluations including 3D γ passing rate (γ-PR), 2D point-to-point dose, lateral penumbra, and flatness, were performed using a Monte Carlo tool. Furthermore, an additional analysis was performed using 3D γ-PR to evaluate the spot size variations of three patients with varying tumor sites and volumes. With a tolerance of 2 % and 2 mm, the dose distribution changes slightly for a 10 % increase in spot size (3D γ-PR>95 %). Decreasing the spot size by 10 %, the 3D γ-PR values were no <90 %. Furthermore, as depth increases, the 3D γ-PR values tend to increase. The 2D point-to-point dose deviations remained below 3 % for spot size variations of ±10 %. Additionally, as depth increases, the 2D point-to-point dose deviations decrease. Increasing the spot size by 10 % led to a maximum change in lateral penumbra of 1.53 mm, while decreasing the spot size by 10 % resulted in lateral penumbra deviations consistently below 1 mm for all cube targets. Additionally, as depth increases, the absolute value of lateral penumbra deviations tends to decrease. With both a 10 % decrease and increase in spot size, the deviations of flatness were always lower than 3 %. And the deviations of flatness decrease as depth increases. The decreasing and increasing spot size had different effects in terms of disturbing the target dose. The dosimetric impact of spot size variations was strongly correlated with target depth. Higher-energy beams showed less sensitivity to the perturbation. Thus, a higher spot size tolerance could be expected.

Background: Carbon‐ion rotating gantries use is limited by its large size, weight, and high cost. Gantry‐free modality enables the reduction of the overall size, weight, and cost. Among them, upright treatment, which utilizes fixed ion beamlines, in combination with a treatment chair capable of 360° rotation and adjustable pitch angle (enabling non‐coplanar beam delivery), provides a wider range of beam entry angles compared to conventional couch‐based setups and has already been applied in particle radiotherapy for head and neck cancer patients. Purpose: In this study, we analyzed clinical data from the Shanghai Proton and Heavy Ion Center (SPHIC) to quantify residual setup errors across various regions of interest (ROIs) for both upright and supine treatments. Methods: A total of 402 treatment fractions from 28 patients (median 5 fractions, range: 5–16 fractions per posture per patient) were enrolled in this study. All these patients were immobilized and scanned in supine posture and received both supine and upright radiotherapy. Three rectangular‐shaped ROIs were delineated based on bone structures, encompassing the mandible, orbit, and neck vertebrae C1–C3. Box‐based registration, focusing solely on the anatomical structures within the specific ROIs was performed to subtract the correction vector used in treatment, thereby obtaining the residual setup error for each ROI. Margins for each ROIs were calculated. Results: For both postures, the median values of residual setup error for all translational directions were less than 1 mm. The median values did not exceed 0.2 degrees for rotational errors. More than 78% of the fractions for upright treatment fell within the 1 mm/° threshold, while 94% were within the 2 mm/° threshold. In contrast, for supine treatment, over 61% fell within the 1 mm/° threshold, while 86% were within the 2 mm/° threshold. The maximum margin was 3.3 mm in the AP direction of the C1–C3 region for the supine posture. Conclusions: Upright treatments demonstrated comparable residual setup errors to supine treatments, with most errors falling within clinically acceptable thresholds. This study provides valuable clinical evidence for the continued development and implementation of upright radiotherapy.