BACKGROUND:Head and neck (H&N) patients frequently undergo anatomical changes such as weight loss and tumour shrinkage during treatment, requiring repeat imaging and replanning to maintain accurate dose delivery. On-board cone-beam CT (CBCT) systems could support these workflows, however they have historically been limited by reduced Hounsfield unit accuracy, inferior image quality, and susceptibility to metal artifacts from dental hardware, all of which are critical for effective radiotherapy treatment planning and dose delivery. HyperSight CBCT offers improved image quality comparable to FBCT along with metal artifact reduction techniques, but its dosimetric performance in H&N patients, particularly in the presence of dental metal implants, has not yet been evaluated. PURPOSE:This work evaluates the dosimetric accuracy of the HyperSight CBCT system (Varian Medical Systems), including the impact of metal artifact reduction, to determine its reliability for H&N treatment planning. METHODS:Images of 25 H&N cancer patients were acquired on a conventional fan-beam CT (FBCT. GE Healthcare) and on two CBCT systems: an Ethos radiotherapy system equipped with HyperSight CBCT, which provides advanced iterative reconstruction (HS-Acuros) and metal artifact reduction reconstruction (HS-MAR) options, and a TrueBeam linear accelerator system with conventional CBCT, which uses filtered back projection reconstruction (Varian Medical Systems). For each patient, the CBCTs were rigidly registered to the FBCT, and the clinically accepted reference plans were forward calculated on all images. Gamma evaluations (3%/3 mm, 2%/2 mm, 1%/1 mm) for all CBCT modes were performed relative to FBCT on slices both unaffected and affected by metal artifacts, with the latter also analyzed as a function of the metal artifact index (AI). DVH metrics were assessed for the planning target volume (PTV), mandible, oral cavity, and parotid glands. RESULTS:For all gamma criteria, HS-Acuros images demonstrated significantly higher pass rates than both HS-MAR and TrueBeam CBCTs in the artifact-free slices (p ≤ 0.033). In artifact-affected slices, HS-MAR reconstructions performed the best in slices affected by metal artifacts (p ≤ 0.001), exhibiting the least reduction in gamma pass rates with increasing artifact index (AI). Conventional TrueBeam CBCT consistently yielded the lowest gamma pass rates in artifact-prone regions (p ≤ 0.005). Across all slices, the median 3D 3%/3 mm gamma passing rates were above 99.2%, 98.7% and 97.7% for HS-Acuros, HS-MAR and TrueBeam, respectively. Across all CBCT images, the median DVH-metric deviations relative to CTsim FBCT were within 2% for all structures and metrics except for PTV Dmax. CONCLUSIONS:HyperSight provides imaging suitable for direct dose calculation in H&N adaptive radiotherapy with iCBCT MAR improving accuracy in the presence of dental metal artifacts; however, iCBCT Acuros may be preferred when artifact reduction is not critical. This work highlights a significant advancement towards CBCT-based direct-dose calculation for adaptive radiotherapy.

Noncoplanar arc optimization has been shown to reduce OAR doses in SRS/SRT and has the potential to reduce doses to OARs in SBRT. Extracranial targets have additional considerations, including large OARs and, in the case of the liver, volume constraints on the healthy liver. Considering pathlengths through OARs that encompass target volumes may lead to specific dose reductions as in the encompassing healthy liver tissue. These optimizations must also leverage delivery efficiency and trajectory sampling to ensure ease of clinical translation. The purpose of this research is to generate optimized static-couch arcs that separately consider serial and parallel OARs and arc delivery efficiency, with a trajectory sampling metric, towards the aim of reducing dose to OARs and the surrounding healthy liver tissue. Separate BEV cost maps were created for parallel, and serial OARs by means of a fast ray-triangle intersection algorithm. An additional BEV cost map was created for the liver which, by definition, encompasses the liver tumors. The individual costs of these maps were summed and combined with the sampling metric for 100 000 random combinations of arc trajectories. A search algorithm was applied to find an arc trajectory solution that satisfied BEV cost and sampling optimization, while also ensuring an efficient delivery was possible with a low number of arcs. This method of arc selection was evaluated for 16 liver SBRT patients characterized by small and large target volumes. Comparisons were made with a clinical arc template of coplanar arcs. Dosimetric plan quality was evaluated using published guidelines and metrics from RTOG1112. Four of five plan quality metrics for the liver were significantly reduced when planned with optimized noncoplanar arcs. Median (range) reductions of the volumes receiving 10, 18, and 21 Gy were found of 140.4 (295.8) cc (p = 0.001), 28.2 (230.6) cc (p = 0.002) and 18.5 (155.5) cc (p = 0.04). A significant increase in median (range) dose to the right kidney of 0.2 +/- 0.9 Gy (p = 0.03) was also found using optimized noncoplanar arcs, which was below the tolerance of 10 Gy for all cases. The average number of arcs chosen was 4 +/- 1. Optimizing serial and parallel OARs separately during static couch noncoplanar arc selection significantly reduced the dose to the liver during SBRT using a moderate number of arcs.

The incidence of malignancies seen after solid organ transplant is increasing, and oncologists are seeing more patients with transplanted organs. In this case report, we present how pelvic radiotherapy can be safely administered in a patient with a transplanted kidney by conducting a comprehensive chart review and analyzing the dosimetry in the radiotherapy planning software Eclipse. A 52-year-old female patient received a kidney transplant in 2002 and was diagnosed 11 years later with a cT3 N0 M0 squamous cell carcinoma of the anal canal. She was offered radical radiation therapy with 45 Gy in 25 fractions using a volumetric modulated arc therapy plan to the pelvic lymph nodes and tumor followed by a 9-Gy boost to the anal tumor alone using a three-dimensional conformal radiation therapy plan with concurrent 5-fluorouracil/mitomycin chemotherapy for a total dose of 54 Gy. The right external iliac and inguinal lymph nodes coverage was compromised to decrease the solitary pelvic kidney dose in addition to creating a 1-cm planning risk volume around the kidney and using half-beam blocks. Her pelvic kidney only received a mean dose of 6.68 Gy. Eight years later, the patient continues to be cancer-free, as evident with a recent sigmoidoscopy in 2021 and a physical examination in 2022. Her creatinine started to rise one year post-treatment, but age of the transplanted kidney is likely the cause of kidney failure.

PurposeTo develop a novel system for patient‐specific combined optimization of couch, collimator, and gantry angles for use in volumetric modulated arc therapy (VMAT) treatment planning. The system was designed to produce highly compact dose distributions by extensively sampling the 4π space. Automated fixed couch trajectory planning was used to reduce normal tissue doses by avoiding beams‐eye‐view (BEV) overlap with organs‐at‐risk (OARs) and improve monitor unit (MU) efficiency through collimator angle optimization.MethodsBy merging distinct BEV objective functions used to optimize the couch rotation angle and collimator angle, a three‐dimensional (3D) cost space (the CODA cube) was constructed with axes of gantry, couch, and collimator rotation angles. At each voxel in this CODA cube, the cost of implementing this combination of axes positions in fixed couch trajectories was quantified. The CODA cube was sampled and explored using a modified constrained Bellman‐Ford algorithm to suggest low‐cost fixed candidate arcs on each plane of the space, from which 10‐arcs are chosen throughout the 3D space using a k‐means clustering algorithm. These fixed couch trajectories were then imported into the Eclipse treatment planning system (v.11) and inverse‐optimized according to clinical standards. Eight artificial cranial targets were contoured in a test‐patient anatomy, and seven treatment plans were generated from combinations of three and four targets. The CODA cube optimized plans were compared to standard 4‐arc VMAT plans for cranial stereotactic radiotherapy/surgery that were optimized for the same sets of targets; maximum dose to each OAR, V12Gy to normal brain, conformity, and total MUs were compared. Both planning methods were inverse‐optimized with identical dosimetric objectives.ResultsCODA plans resulted in a reduction in maximum dose to OARs of 20.6% (P < 0.01), with maximum brainstem dose decreased by 2.63 Gy (P = 0.031) on average when compared to the standard arc arrangement. The mean reduction in total MU was 8.6% (P = 0.156), the mean increase in the inverse of the van’t Riet conformation number was 0.1%, (P = 0.67) and the mean decrease in normal brain tissue receiving 12 Gy or higher was 3.9% (P = 0.16), when compared to the standard VMAT arc configuration (n = 7).ConclusionsThe optimization of couch, collimator, and gantry angles simultaneously using a 3D optimization space achieved improvement on multiple clinical metrics when compared to the standard VMAT arc configuration. A statistically significant sparing to OAR maximum doses was seen. Combining these optimizations may yield superior results to independent optimization.

PURPOSE:To design and implement a novel treatment planning algorithm based on a modification of dynamic conformal arc (DCA) therapy for the treatment of multiple cranial metastases with variable prescription doses.METHODS:A workflow was developed in which separate dose matrices were calculated for each target at each control point (i.e., the multileaf collimator (MLC) was fit conformally to that single target). A cost function was used to quantify the relative contributions of each dose matrix in the plan to the overall plan objectives. Simulated annealing was used to allow for the inclusion or exclusion of individual dose matrices at each control point. The exclusion of individual targets at a given control point is termed intra-arc binary collimation (iABC) in this work and is accomplished by closing the MLCs over the target for a duration specified by simulated annealing optimization. Dynamic collimator motions were employed to minimize the variation between the idealized dose matrices (i.e., perfectly collimated targets) and actual dose matrices (i.e., MLC apertures that include quantities of nontarget tissue due to the relative orientations of targets in the field). An additional simulated annealing optimization was performed to weight the relative contributions of dose at each control point [referred to as the monitor unit distribution (MUD)] to improve compliance with plan objectives. The algorithm was tested on seven previously treated multiple metastases patients and plans were compared to the clinically treated VMAT plans.RESULTS:Treatment plans generated with iABC used an average of 2716 (34%) fewer MU in the total plan than VMAT (P = 0.01). All normal tissue metrics for all plans and all patients were clinically acceptable. There were no statistically significant differences in any normal tissue dose metrics. Normalized prescription target coverage accuracy for all targets was 3% better on average for VMAT plans when compared to iABC (P = 0.07), and 14% better on average for iABC when compared to optimized DCA (P = 0.03).CONCLUSION:A novel method of aperture and dose distribution design has been developed to significantly increase the MU efficiency of single isocenter treatment of multiple metastases with variable prescription doses when compared to VMAT, and which improves target coverage accuracy significantly when compared to optimized DCA. By applying a DCA approach to subsets of targets across control points, a hybrid method of treatment delivery has been developed that combines the efficiency of dynamic conformal treatments and the dosimetric flexibility of VMAT.

Malignant glioma is a devastating primary tumour located in the brain with a median survival less than two years. Standard of care for gliomas is maximal surgical resection followed by radiation therapy and chemotherapy. The standard dose used is 60 Gy in 30 fractions to the post-operative bed with 3D conformal radiation therapy (3DCRT). This technique has been shown to have a definitive impact on patient survival. These tumours are often nearby or abutting dose limiting OARs such as the brainstem or optical structures. With the development of new technologies such as IMRT and VMAT there is an increased potential for dose escalation because of the improved ability to spare such OARs while covering the target with full radiation dose. Several studies have compared 3DCRT with IMRT to assess tumour volume coverage and OAR sparing; however, despite the increasing use of VMAT, there has been minimal comparison of 3DCRT with VMAT or even VMAT with IMRT for treatment of malignant gliomas. This study will compare and contrast VMAT and 3DCRT treatment plans to determine whether the use of VMAT significantly improves treatment plans over 3DCRT. Standard 3DCRT 4 non-coplanar beam plans and 2 arc VMAT plans will be generated for 20 anonymized patient datasets. The plans will be assessed by reviewing the coverage of the PTV using mean, maximum and minimum doses while the OAR doses will be compared using the maximal doses for each, as set out in the QUANTEC dose limits. The use of VMAT for the treatment of malignant gliomas has the potential to increase dose to the PTV while sparing OARs optimally. As VMAT has become the current practice within our cancer centre it is necessary to verify that our current practice is indeed the best possible option for radiation therapy for this patient population. The VMAT plans show better sparing of the OARs where the PTV wraps around or abuts it than the 3DCRT plans which allow for higher target volume doses to be delivered.