Comparing different boost concepts and beam configurations for proton therapy of pancreatic cancer.

Background and Purpose: Interfractional geometrical and anatomical variations impact the accuracy of proton therapy for pancreatic cancer. This study investigated field-in-field (FIF) and simultaneous integrated boost (SIB) concepts for scanned proton therapy treatment with different beam configurations. Materials and Methods: Robustly optimized treatment plans for fifteen patients were generated using FIF and SIB techniques with two, three, and four beams. The prescribed dose in 20 fractions was 60 Gy(RBE) for the internal gross tumor volume (IGTV) and 46 Gy(RBE) for the internal clinical target volume. Verification computed tomography (vCT) scans was performed on treatment days 1, 7, and 16. Initial treatment plans were recalculated on the rigidly registered vCTs. V100% and D95% for targets and D2cm3 for the stomach and duodenum were evaluated. Robustness evaluations (range uncertainty of 3.5 %) were performed to evaluate the stomach and duodenum dose-volume parameters. Results: For all techniques, IGTV V100% and D95% decreased significantly when recalculating the dose on vCTs (p < 0.001). The median IGTV V100% and D95% over all vCTs ranged from 74.2 % to 90.2 % and 58.8 Gy(RBE) to 59.4 Gy(RBE), respectively. The FIF with two and three beams, and SIB with two beams maintained the highest IGTV V100% and D95%. In robustness evaluations, the ΔD2cm3 of stomach was highest in two beams plans, while the ΔD2cm3 of duodenum was highest in four beams plans, for both concepts. Conclusion: Target coverage decreased when recalculating on CTs at different time for both concepts. The FIF with three beams maintained the highest IGTV coverage while sparing normal organs the most.

Acute genitourinary toxicity of pencil beam scanning proton therapy for localized prostate cancer: utility of the transition zone index and average urinary flow rate in predicting acute urinary retention.

BACKGROUND: The purpose of this study was to evaluate the incidence of acute genitourinary toxicities in patients undergoing pencil beam scanning proton therapy for prostate cancer and investigate predictive factors associated with acute urinary retention. METHODS: A total of 227 patients treated between 2018 and 2021 were divided into the normo-fractionated proton therapy group (n = 107) and the moderately hypo-fractionated proton therapy group (n = 120), with prescribed doses of 76-78 Gy relative biological effectiveness in 38-39 fractions and 60-63 Gy relative biological effectiveness in 20-21 fractions, respectively. Uroflowmetry parameters and the transition zone index were prospectively evaluated. RESULTS: Forty-five patients (42%) in the normo-fractionated proton therapy and 33 (28%) in the moderately hypo-fractionated proton therapy developed acute grade 2 genitourinary toxicities (P = 0.02). The most common acute genitourinary toxicity was acute urinary retention. Thirty-nine patients (36%) treated with normo-fractionated proton therapy and 27 (23%) treated with moderately hypo-fractionated proton therapy developed grade 2 acute urinary retention (P = 0.02). No patients developed grade ≥ 3 toxicity. Univariate analysis showed the transition zone index, prostate volume, international prostate symptom score, voided volume, maximum flow rate and average flow rate were associated with grade 2 acute urinary retention. Multivariate analysis in both groups revealed the transition zone index (P = 0.025 and 0.029) and average flow rate (P = 0.039 and 0.044) were predictors of grade 2 acute urinary retention. CONCLUSIONS: The incidence of acute genitourinary toxicities was lower in the moderately hypo-fractionated proton therapy compared with the normo-fractionated proton therapy. Lower pretreatment average flow rate and a higher transition zone index were useful predictors of grade 2 acute urinary retention.

Normal liver tissue change after proton beam therapy.

PURPOSE: Normal liver tissue changes after proton beam therapy (PBT) were investigated in patients at 1 and 2 years after the therapy. MATERIALS AND METHODS: Changes in normal liver tissue volume were examined. The dose distribution of the normal liver tissue was also simulated on the follow-up CTs. RESULTS: The normal liver tissue volume was 1149 ± 215 cm3 before treatment, 1089 ± 188 cm3 at 1 year, and 1080 ± 236 cm3 at 2 years after treatment. The normal liver tissue volume was increased in 10 and decreased in 20 patients at 2 years and was smaller than that before the treatment in total (P = 0.03). The simulated volume that received more than 30 Gray equivalent [V30 (cm3)] at 1 year was 258 ± 187 cm3 and that at 2 years (244 ± 171 cm3) was smaller than that before treatment (297 ± 140 cm3) (P = 0.03). CONCLUSIONS: The changes in the shape and volume of normal liver tissue are not constant, which cause a large dose distribution discrepancy in the normal liver for 2 years. Therefore, careful consideration of the dose distribution of normal liver tissue is required when planning re-irradiation.