Technical feasibility of online adaptive stereotactic treatments in the abdomen on a robotic radiosurgery system

BACKGROUND AND PURPOSE: Stereotactic body radiotherapy (SBRT) has been proven to be beneficial for several disease sites in the (lower) abdomen. However, the quality of the treatment plan, based on a single planning computed tomography (CT), can be compromised due to large inter-fraction motion of the target and organs at risk (OARs) in this anatomical region. The aim of this study was to investigate the feasibility of online adaptive SBRT treatments on a robotic radiosurgery system and to record estimated total treatment times. MATERIALS AND METHODS: For two disease sites, locally advanced pancreatic cancer (LAPC) and oligometastatic lymph nodes, four patients with repeat CTs were included in the feasibility study. Quick treatment plan templates were generated based on the planning CT and validated by running them on the plan and fraction CTs. For two cases a dummy run was performed and the individual steps were timed. Dose delivery was the largest contributor to the total treatment time, followed by contour adaptation. RESULTS: Running the quick plan templates resulted in plans similar to unrestricted plans, obeying the OAR constraints. The dummy runs showed that online adaptive treatments were completed in 64 to 83 min respectively for oligometastases and LAPC, comparable to other clinically available solutions. CONCLUSIONS: This study showed the feasibility of online re-planning for two challenging disease sites within a clinically acceptable time frame on a robotic radiosurgery system, making use of commercially available elements that are not integrated by the vendor

Cochlea-sparing acoustic neuroma treatment with 4π radiation therapy.

PurposeThis study investigates whether 4π noncoplanar radiation therapy can spare the cochleae and consequently potentially improve hearing preservation in patients with acoustic neuroma who are treated with radiation therapy.Methods and materialsClinical radiation therapy plans for 30 patients with acoustic neuroma were included (14 stereotactic radiation surgery [SRS], 6 stereotactic radiation therapy [SRT], and 10 intensity modulated radiation therapy [IMRT]). The 4π plans were created for each patient with 20 optimal beams selected using a greedy column generation method and subsequently recalculated in Eclipse for comparison. Organ-at-risk (OAR) doses, homogeneity index, conformity, and tumor control probability (TCP) were compared. Normal tissue complication probability (NTCP) was calculated for sensorineural hearing loss (SNHL) at 3 and 5 years posttreatment. The dose for each plan was then escalated to achieve 99.5% TCP.Results4π significantly reduced the mean dose to both cochleae by 2.0 Gy (32%) for SRS, 3.2 Gy (29%) for SRT, and 10.0 Gy (32%) for IMRT. The maximum dose to both cochleae was also reduced with 4π by 1.6 Gy (20%), 2.2 Gy (15%), and 7.1 Gy (18%) for SRS, SRT, and IMRT plans, respectively. The reductions in mean/maximum brainstem dose with 4π were also statistically significant. Mean doses to other OARs were reduced by 19% to 56% on average. 4π plans had a similar CN and TCP, with a significantly higher average homogeneity index (0.93 vs 0.92) and significantly lower average NTCP for SNHL at both 3 years (30.8% vs 40.8%) and 5 years (43.3% vs 61.7%). An average dose escalation of approximately 116% of the prescription dose achieved 99.5% TCP, which resulted in 32.6% and 43.4% NTCP for SNHL at 3 years and 46.4% and 64.7% at 5 years for 4π and clinical plans, respectively.ConclusionsCompared with clinical planning methods, optimized 4π radiation therapy enables statistically significant sparing of the cochleae in acoustic neuroma treatment as well as lowering of other OAR doses, potentially reducing the risk of hearing loss

Complementing Prostate SBRT VMAT With a Two-Beam Non-Coplanar IMRT Class Solution to Enhance Rectum and Bladder Sparing With Minimum Increase in Treatment Time

Purpose Enhance rectum and bladder sparing in prostate SBRT with minimum increase in treatment time by complementing dual-arc coplanar VMAT with a two-beam non-coplanar IMRT class solution (CS). Methods For twenty patients, an optimizer for automated multi-criterial planning with integrated beam angle optimization (BAO) was used to generate dual-arc VMAT plans, supplemented with five non-coplanar IMRT beams with individually optimized orientations (VMAT+5). In all plan generations, reduction of high rectum dose had the highest priority after obtaining adequate PTV coverage. A CS with two most preferred directions in VMAT+5 and largest rectum dose reductions compared to dual-arc VMAT was then selected to define VMAT+CS. VMAT+CS was compared with automatically generated i) dual-arc coplanar VMAT plans (VMAT), ii) VMAT+5 plans, and iii) IMRT plans with 30 patient-specific non-coplanar beam orientations (30-NCP). Plans were generated for a 4 x 9.5 Gy fractionation scheme. Differences in PTV doses, healthy tissue sparing, and computation and treatment delivery times were quantified. Results For equal PTV coverage, VMAT+CS, consisting of dual-arc VMAT supplemented with two fixed, non-coplanar IMRT beams with fixed Gantry/Couch angles of 65 degrees/30 degrees and 295 degrees/-30 degrees, significantly reduced OAR doses and the dose bath, compared to dual-arc VMAT. Mean relative differences in rectum D-mean, D-1cc, V-40GyEq and V-60GyEq were 19.4 +/- 10.6%, 4.2 +/- 2.7%, 34.9 +/- 20.3%, and 39.7 +/- 23.2%, respectively (all p Conclusions The proposed two-beam non-coplanar class solution to complement coplanar dual-arc VMAT resulted in substantial plan quality improvements for OARs (especially rectum) and reduced irradiated patient volumes with minor increases in treatment delivery times

Computer- and robot-assisted Medical Intervention

Medical robotics includes assistive devices used by the physician in order to make his/her diagnostic or therapeutic practices easier and more efficient. This chapter focuses on such systems. It introduces the general field of Computer-Assisted Medical Interventions, its aims, its different components and describes the place of robots in that context. The evolutions in terms of general design and control paradigms in the development of medical robots are presented and issues specific to that application domain are discussed. A view of existing systems, on-going developments and future trends is given. A case-study is detailed. Other types of robotic help in the medical environment (such as for assisting a handicapped person, for rehabilitation of a patient or for replacement of some damaged/suppressed limbs or organs) are out of the scope of this chapter.Comment: Handbook of Automation, Shimon Nof (Ed.) (2009) 000-00

Towards real-time MRI-guided 3D localization of deforming targets for non-invasive cardiac radiosurgery.

Radiosurgery to the pulmonary vein antrum in the left atrium (LA) has recently been proposed for non-invasive treatment of atrial fibrillation (AF). Precise real-time target localization during treatment is necessary due to complex respiratory and cardiac motion and high radiation doses. To determine the 3D position of the LA for motion compensation during radiosurgery, a tracking method based on orthogonal real-time MRI planes was developed for AF treatments with an MRI-guided radiotherapy system. Four healthy volunteers underwent cardiac MRI of the LA. Contractile motion was quantified on 3D LA models derived from 4D scans with 10 phases acquired in end-exhalation. Three localization strategies were developed and tested retrospectively on 2D real-time scans (sagittal, temporal resolution 100 ms, free breathing). The best-performing method was then used to measure 3D target positions in 2D-2D orthogonal planes (sagittal-coronal, temporal resolution 200-252 ms, free breathing) in 20 configurations of a digital phantom and in the volunteer data. The 3D target localization accuracy was quantified in the phantom and qualitatively assessed in the real data. Mean cardiac contraction was  ⩽  3.9 mm between maximum dilation and contraction but anisotropic. A template matching approach with two distinct template phases and ECG-based selection yielded the highest 2D accuracy of 1.2 mm. 3D target localization showed a mean error of 3.2 mm in the customized digital phantoms. Our algorithms were successfully applied to the 2D-2D volunteer data in which we measured a mean 3D LA motion extent of 16.5 mm (SI), 5.8 mm (AP) and 3.1 mm (LR). Real-time target localization on orthogonal MRI planes was successfully implemented for highly deformable targets treated in cardiac radiosurgery. The developed method measures target shifts caused by respiration and cardiac contraction. If the detected motion can be compensated accordingly, an MRI-guided radiotherapy system could potentially enable completely non-invasive treatment of AF

Treatment planning and dosimetric verification of cyberknife prostate SBRT (stereotactic body radiation therapy) on an MR-based 3D prostate model imaging insert in a pelvis phantom

Purpose of this study was to validate a novel CyberKnife stereotactic body radiotherapy (SBRT) treatment planning on an MRI-based 3D prostate model insert in an anthropomorphic pelvis phantom using Gafchromic EBT3 films to perform dosimetric measurements. The methodology of this study is based on a pelvis phantom and a physical printed 3D model of the prostate with dominant intra-prostatic-lesion and surrounding organs at risk segmented from a patient MR images. Cyberknife prostate treatment planning was performed to have at least 95% the planning target volumes (PTV: prostate expanded with margins of 5 mm in all directions except 3 mm posteriorly) covered by 3625 cGy (725x5) and a simultaneous dose escalation to 4750 cGy on the dominant intra-prostatic-lesion. Plan dosimetry verification was performed using Gafchromic EBT3 films on a Stereotactic Dose Verification Phantom. First, film calibration was done on Gafchromic EBT3 films exposed to various doses of 0-2500 cGy based on a LINAC (Trilogy) and CyberKnife monthly quality assurance (QA) for machine output calibration. Second, absolute dose measurements were taken by using films within the dose range 0-2250 cGy. Third, Gafchromic EBT3 films were placed in coronal and sagittal planes on the standard “blue phantom” or Stereotactic Dose Verification Phantom (SDVP) on which one fraction of the treatment plan is delivered for verification measurements. Then, on the prostate-pelvis phantom, a dosimetry inserts were used with films through the DIL region. After the calibration, the accuracy of absolute dose measurements with EBT3 was verified to be ≤ 1% in the dose range of interest (500-1500 cGy). On the SDVP phantom, comparison of films vs. plan for the coronal plane yielded ≥ 99.7% passing rates while for sagittal plane yielded ≥ 95.3% passing rates under the gamma criteria of ≤ 2% in dose and ≤ 2mm in distance to agreement (DTA). This study demonstrated that it is feasible to plan and deliver a SBRT treatment to prostate with a simultaneous dose escalation to the dominant intra-prostatic lesion

Clinical Validation of an Optical Surface Detection System for Stereotactic Radiosurgery with Frameless Immobilization Device in CNS Tumors

Tese de mestrado integrado, Engenharia Biomédica e Biofísica (Radiações em Diagnóstico e Terapia), 2022Stereotactic Radiosurgery (SRS) has been consolidated in recent years as the treatment of choice in selected central nervous system (CNS) tumors. With the introduction of stereotactic approach in clinical practice, accurate immobilization and motion control during treatment becomes fundamental. During SRS treatments, the common practice is to immobilize CNS patients in a cushion molded head support, with specific open-face thermoplastic masks. To verify and correct internal isocenter uncertainties before and during treatment, X-Ray volumetric imaging (XVI) is performed - image guided radiation therapy (IGRT). An alternative to mid‐treatment imaging is optical surface detection (OSD) imaging – a non‐invasive, non‐radiographic form of image guidance – to monitor patient intra-fraction motion. This imaging technique has shown to properly position, accurately monitor, and quantify patient movements throughout the entirety of the treatment – surface guided radiation therapy (SGRT). The aim of this investigation is to test the viability of the implementation of a maskless immobilization approach, using only a vacuum mouthpiece suction system for head fixation in patients with CNS tumors who will undergo SRS treatment under the guidance of an OSD system coupled with 6-Degree of Freedom (6-DOF) robotic couch for submillimeter position correction. This master thesis addresses the five technical performance tests conducted on the Linear Accelerator components – XVI, HexaPOD couch and OSD system in the Radiotherapy Department of Hospital CUF Descobertas. The results obtained lecture the best acquisition orientation to perform image verification; if the HexaPOD couch is correctly calibrated to the XVI radiation isocenter to assure submillimeter corrections; OSD system performance regarding phantom surface detection since some immobilization components can block the signal reading; which coplanar and non-coplanar angles occur most signal inconsistencies due to camera pod occlusion; what is the overall OSD system accuracy and what is the best non-coplanar angle arrangement to perform an SRS treatment with OSD system monitoring