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Purpose: To evaluate a knowledge‐based (KB) planning model for RapidPlan, generated using a five‐field intensity‐modulated radiotherapy (IMRT) class solution beam strategy and rigorous dosimetric constraints for accelerated partial breast irradiation (APBI). Materials and methods: The RapidPlan model was configured using 64 APBI treatment plans and validated for 120 APBI patients who were not included in the training dataset. KB plan dosimetry was compared to clinical plan dosimetry, the clinical planning constraints, and the constraints used in phase III APBI trials. Dosimetric differences between clinical and KB plans were evaluated using paired two‐tailed Wilcoxon signed‐rank tests. Results: KB planning was able to produce IMRT‐based APBI plans in a single optimization without manual intervention that are comparable or better than the conventionally optimized, clinical plans. Comparing KB plans to clinical plans, differences in PTV, heart, contralateral breast, and ipsilateral lung dose–volume metrics were not clinically significant. The ipsilateral breast volume receiving at least 50% of the prescription dose was statistically and clinically significantly lower in the KB plans. Conclusion: KB planning for IMRT‐based APBI provides equivalent or better dosimetry compared to conventional inverse planning. This model may be reliably applied in clinical practice and could be used to transfer planning expertise to ensure consistency in APBI plan quality. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the performance of structure‐guided deformable image registration (SG‐DIR) relative to rigid registration and DIR using TG‐132 recommendations. This assessment was performed for image registration of treatment planning computed tomography (CT) and magnetic resonance imaging (MRI) scans with Primovist® contrast agent acquired post stereotactic body radiation therapy (SBRT). SBRT treatment planning CT scans and posttreatment Primovist® MRI scans were obtained for 14 patients. The liver was delineated on both sets of images and matching anatomical landmarks were chosen by a radiation oncologist. Rigid registration, DIR, and two types of SG‐DIR (using liver contours only; and using liver structures along with anatomical landmarks) were performed for each set of scans. TG‐132 recommended metrics were estimated which included Dice Similarity Coefficient (DSC), Mean Distance to Agreement (MDA), Target Registration Error (TRE), and Jacobian determinant. Statistical analysis was performed using Wilcoxon Signed Rank test. The median (range) DSC for rigid registration was 0.88 (0.77–0.89), 0.89 (0.81–0.93) for DIR, and 0.90 (0.86–0.94) for both types of SG‐DIR tested in this study. The median MDA was 4.8 mm (3.7–6.8 mm) for rigid registration, 3.4 mm (2.4–8.7 mm) for DIR, 3.2 mm (2.0–5.2 mm) for SG‐DIR where liver structures were used to guide the registration, and 2.8 mm (2.1–4.2 mm) for the SG‐DIR where liver structures and anatomical landmarks were used to guide the registration. The median TRE for rigid registration was 7.2 mm (0.5–23 mm), 6.8 mm (0.7–30.7 mm) for DIR, 6.1 mm (1.1–20.5 mm) for the SG‐DIR guided by only the liver structures, and 4.1 mm (0.8–19.7 mm) for SG‐DIR guided by liver contours and anatomical landmarks. The SG‐DIR shows higher liver conformality as per TG‐132 metrics and lowest TRE compared to rigid registration and DIR in Velocity AI software for the purpose of registering treatment planning CT and post‐SBRT MRI for the liver region. It was found that TRE decreases when liver contours and corresponding anatomical landmarks guide SG‐DIR. [ABSTRACT FROM AUTHOR]

Objectives: We evaluated the dosimetric and radiobiological impact of abdominal compression (AC) on nearby gastrointestinal critical structures (GI-CS) and reported toxicities of patients treated with non-hepatic abdominal stereotactic body radiotherapy (SBRT). Methods: Two sets of CT scans, planning scans with AC and pre-treatment diagnostic scans without AC (non-AC) were compared for patients treated with a prescription dose to planning target volume (PTV) =25 Gy/5-fractions at a single institution. Target volumes were delineated on both sets of scans and PTV was expanded isotropically by 2 cm (PTV+2) and 4 cm (PTV+4). All GI-CS were summated to create a composite CS (GI-lumen). Rigid registration of AC and non-AC scans was done using Velocity AI (Varian Medical Systems) to obtain dose distribution information. Lymann-Probit and logit models were used for radiobiological calculations. Toxicity scores were obtained from prospectively collected clinical data. Results: A total of 12 patients were included. Mean PTV volumes were 190.3cc and 196.4cc with AC and non-AC (p=0.95). Significant improvement in V30 of GI-lumen was seen with AC (0.11cc vs. 4.97cc, p=0.04). There were no differences in the normal tissue complication probabilities of the individual GI-CS or the summary indices except a notable trend towards better NTCP for small bowel late effects with AC (0.21% vs. 2.45%; p=0.055). Three patients had acute grade-1 anorexia, one patient had acute grade-2 gastritis. There was no grade =3 GI toxicity. At a median follow-up of 2.6 years, total of 8/12 (66.7%) patients developed local recurrence of whom 4 (33.3%) had isolated local recurrence. Conclusion: Use of AC did not result in any dosimetric or radiobiological inferiority for GI-CS. The current cohort completed their treatment with minimal toxicity. [ABSTRACT FROM AUTHOR]