Use of Specific Duodenal Dose Constraints During Treatment Planning Reduces Toxicity After Definitive Paraaortic Radiation Therapy for Cervical Cancer

PurposeThis study aimed to validate the safety of paraaortic nodal (PAN) radiation therapy (RT) for patients with cervical cancer when the duodenal dose is limited to V₅₅ < 15 cm³ and V₆₀ < 2 cm³.Methods and MaterialsA total of 97 patients who were treated with RT for cervical cancer between 2010 and 2018 received at least 56 Gy to grossly involved PANs. Patients were treated with concurrent chemoradiation (n = 88; 91%), with 93% of patients (n = 90) receiving intensity modulated RT to the initial PAN field and 98% (n = 95) receiving intensity modulated RT to a sequential PAN boost. The V₅₅ < 15 cm³ and V₆₀ <2 cm³ criteria were implemented in 2014. Normal tissues were contoured on computed tomography (CT) simulation data sets, and the duodenum was contoured from the gastric outlet to the duodenojejunal flexure. Sixty-six patients (68%) had a resimulation scan after approximately 20 fractions. Composite duodenal doses were calculated using the initial CT scan for 50 patients (52%) and the resimulation CT scan for 47 patients (48%) depending on the anatomic changes throughout treatment.ResultsThe median duodenal V₅₅ was 3.5 cm³ (interquartile range [IQR], 0.2-8.1 cm³) and the median V₆₀ was 0.3 cm³ (IQR, 0.0-1.8). Constraints were exceeded in 18 patients, of whom 16 patients (89%) had been treated before 2014. Treatment for the 2 patients treated after 2014 was complicated by significant weight loss and reduced anterior-posterior diameter, which likely overestimated the true dose on the composite plan. Only 1 patient experienced grade 3 duodenal toxicity (stricture requiring endoscopic balloon dilation 3 months after treatment); however, the stricture was outside of the high-dose boost volume, and the patient had a history of gastritis. Six patients (6%) had a first recurrence within the PAN region.ConclusionsLimiting the duodenal dose to V₅₅ < 15 cm³ and V₆₀ < 2 cm³ for patients with cervical cancer and PAN involvement is feasible, and minimizes duodenal toxicity while maintaining acceptable local control rates.     

Clinical Experience in Prostate Ultrahypofractionated Radiation Therapy With an Online Adaptive Method

PurposeThis study aimed to describe the feasibility of the online adaptive radiation therapy (oART) method developed at the Hospital Quirónsalud Barcelona for prostate cancer, using a standard C-arm linear accelerator (linac) and without the support of artificial intelligence.Methods and MaterialsThe first 18 patients treated at the Hospital Quirónsalud Barcelona with the developed oART method were included. An ultrahypofractionated radiation therapy scheme consisting of 7 × 6.1 Gy was used. Patients were treated on 2 conventional Varian C-arm linacs. For each patient, a reference plan based on a planning computed tomography (pCT) scan was generated using the Eclipse system. On each treatment session, the pCT scan was rigidly registered with the daily cone beam computed tomography (CT) scan. The pCT-based target (prostate) and organs at risk were mapped onto the cone beam CT images and manually adapted to take into account the anatomy of the day. The reference plan was then copied to the cone beam CT scan, and a full reoptimization was done for the current anatomy (adapted plan). For each treatment session, the unaltered reference plan was recomputed on the daily cone beam CT scan by mimicking the soft-tissue alignment performed per our standard procedure (nonadapted plan). Over the 126 adapted sessions from the 18 patients, a dosimetric comparison of adapted against nonadapted plans was done.ResultsA significant difference in the target coverage was found between the adapted and nonadapted plans (97.1 vs 90.4; P < .001) in favor of adapting. Without online adaptation, the optimal coverage of the prostate was not attained in 35% of fractions. Adapting allows for the improvement of the target coverage with compliance of all organ-at-risk dose constraints in all treatment fractions.ConclusionsThe oART technique described in this study is technically feasible with a C-arm linac. To our knowledge, this is the first clinical experience with oART for prostate cancer including full replanning and delivered with a C-arm linac without artificial intelligence capability.     

Technical Report: Development and Implementation of an Open Source Template Interpretation Class Library for Automated Treatment Planning

PurposeWidespread implementation of automated treatment planning in radiation therapy remains elusive owing to variability in clinic and physician preferences, making it difficult to ensure consistent plan parameters. We have developed an open-source class library with the aim to improve efficiency and consistency for automated treatment planning in radiation therapy.Methods and MaterialsAn open-source class library has been developed that interprets clinical templates within a commercial treatment planning system into a treatment plan for automated planning. This code was leveraged for the automated planning of 39 patients and retrospectively compared with the 78 clinically approved manual plans.ResultsFrom the initial 39 patients, 74 of 78 plans were successfully generated without manual intervention. The target dose was more homogeneous for automated plans, with an average homogeneity index of 3.30 for manual plans versus 3.11 for automated plans (P = .107). The generalized equivalent uniform dose (gEUD) was decreased in the femurs and rectum for automated plans, with a mean gEUD of 3746 cGy versus 3338 cGy (P ≤ 0.001) and 5761 cGy versus 5634 cGy (P ≤ 0.001) for the femurs and rectum, respectively. Dose metrics for the bladder and rectum (V6500 cGy and V4000 cGy) showed recognizable but insignificant improvements. All automated plans delivered for quality assurance passed a gamma analysis (>95%), with an average composite pass rate of 99.3% for pelvis plans and 98.8% for prostate plans. Deliverability parameters such as total monitor units and aperture complexity indicated deliverable plans.ConclusionsProstate cancer and pelvic node radiation therapy can be automated using volumetric modulated arc therapy planning and clinical templates based on a standardized clinical workflow. The class library developed in this study conveniently interfaced between the plan template and the treatment planning system to automatically generate high-quality plans on customizable templates.     

Measurements with alanine and film dosimeters for industrial 10 MeV electron reference dosimetry

Alanine and radiochromic film dosimeters were irradiated with absorbed doses from 3 to 10 kGy at a 10 MeV electron accelerator under typical radiation processing conditions. The nominal doses were measured by graphite calorimeters and the dosimeters were irradiated in graphite phantoms. The dosimeters were calibrated by irradiation with ⁶⁰Co photons.The ratios of calorimeter to film and alanine dosimeter readings were generally within 0.99 ± 0.01 for 10 mm phantoms, but larger differences were observed for 20 mm phantoms. The discrepancies may be due to uncertainties in irradiation geometry, or in the stopping power ratios applied.