Technical recommendations for implementation of Volumetric Modulated Arc Therapy and Helical Tomotherapy Total Body Irradiation.

As a component of myeloablative conditioning before allogeneic hematopoietic stem cell transplantation (HSCT), Total Body Irradiation (TBI) is employed in radiotherapy centers all over the world. In recent and coming years, many centers are changing their technical setup from a conventional TBI technique to multi-isocenter conformal arc therapy techniques such as Volumetric Modulated Arc Therapy (VMAT) or Helical Tomotherapy (HT). These techniques allow better homogeneity and control of the target prescription dose, and provide more freedom for individualized organ-at-risk sparing. The technical design of multi-isocenter/multi-plan conformal TBI is complex and should be developed carefully. A group of early adopters with conformal TBI experience using different treatment machines and treatment planning systems came together to develop technical recommendations and share experiences, in order to assist departments wishing to implement conformal TBI, and to provide ideas for standardization of practices.

Organ sparing total marrow irradiation compared to total body irradiation prior to allogeneic stem cell transplantation.

OBJECTIVES: Total body irradiation (TBI) is commonly used prior to hematopoietic stem cell transplantation (HSCT) in myeloablative conditioning regimens. However, TBI may be replaced by total marrow irradiation (TMI) at centres with access to Helical TomoTherapy, a modality that has the advantage of delivering intensity-modulated radiotherapy to long targets such as the entire bone marrow compartment. Toxicity after organ sparing TMI prior to HSCT has not previously been reported compared to TBI or with regard to engraftment data. METHODS: We conducted a prospective observational study on 37 patients that received organ sparing TMI prior to HSCT and compared this cohort to retrospective data on 33 patients that received TBI prior to HSCT. RESULTS: The 1-year graft-versus-host disease-free, relapse-free survival (GRFS) was 67.5% for all patients treated with TMI and 80.5% for patients with matched unrelated donor and treated with TMI, which was a significant difference from historical data on TBI patients with a hazard ratio of 0.45 (P = .03) and 0.24 (P < .01). Engraftment with a platelet count over 20 [K/µL] and 50 [K/µL] was significantly shorter for the TMI group, and neutrophil recovery was satisfactory in both treatment cohorts. There was generally a low occurrence of other treatment-related toxicities. CONCLUSIONS: Despite small cohorts, some significant differences were found; TMI as part of the myeloablative conditioning yields a high 1-year GRFS, fast and robust engraftment, and low occurrence of acute toxicity.

Surface-guided tomotherapy improves positioning and reduces treatment time: A retrospective analysis of 16 835 treatment fractions.

PURPOSE: In this study, we have quantified the setup deviation and time gain when using fast surface scanning for daily setup/positioning with weekly megavoltage computed tomography (MVCT) and compared it to daily MVCT. METHODS: A total of 16 835 treatment fractions were analyzed, treated, and positioned using our TomoTherapy HD (Accuray Inc., Madison, USA) installed with a Sentinel optical surface scanning system (C-RAD Positioning AB, Uppsala, Sweden). Patients were positioned using in-room lasers, surface scanning and MVCT for the first three fractions. For the remaining fractions, in-room laser was used for setup followed by daily surface scanning with MVCT once weekly. The three-dimensional (3D) setup correction for surface scanning was evaluated from the registration between MVCT and the planning CT. The setup correction vector for the in-room lasers was assessed from the surface scanning and the MVCT to planning CT registration. The imaging time was evaluated as the time from imaging start to beam-on. RESULTS: We analyzed 894 TomoTherapy treatment plans from 2012 to 2018. Of all the treatment fractions performed with surface scanning, 90 % of the residual errors were within 2.3 mm for CNS (N = 284), 2.9 mm for H&N (N = 254), 8.7 mm for thorax (N = 144) and 10.9 for abdomen (N = 134) patients. The difference in residual error between surface scanning and positioning with in-room lasers was significant (P < 0.005) for all sites. The imaging time was assessed as total imaging time per treatment plan, modality, and treatment site and found that surface scanning significantly reduced patient on-couch time compared to MVCT for all treatment sites (P < 0.005). CONCLUSIONS: The results indicate that daily surface scanning with weekly MVCT can be used with the current target margins for H&N, CNS, and thorax, with reduced imaging time.

A Helical tomotherapy as a robust low-dose treatment alternative for total skin irradiation.

Mycosis fungoides is a disease with manifestation of the skin that has traditionally been treated with electron therapy. In this paper, we present a method of treating the entire skin with megavoltage photons using helical tomotherapy (HT), verified through a phantom study and clinical dosimetric data from our first two treated patients. A whole body phantom was fitted with a wetsuit as bolus, and scanned with computer tomography. We accounted for variations in daily setup using virtual bolus in the treatment plan optimization. Positioning robustness was tested by moving the phantom, and recalculating the dose at different positions. Patient treatments were verified with in vivo film dosimetry and dose reconstruction from daily imaging. Reconstruction of the actual delivered dose to the patients showed similar target dose as the robustness test of the phantom shifted 10 mm in all directions, indicating an appropriate approximation of the anticipated setup variation. In vivo film measurements agreed well with the calculated dose confirming the choice of both virtual and physical bolus parameters. Despite the complexity of the treatment, HT was shown to be a robust and feasible technique for total skin irradiation. We believe that this technique can provide a viable option for Tomotherapy centers without electron beam capability.

Implementing safe and robust Total Marrow Irradiation using Helical Tomotherapy - A practical guide.

Total Marrow Irradiation (TMI) with Helical Tomotherapy is a radiotherapy treatment technique that targets bone marrow and sanctuary sites prior to stem cell or bone marrow transplantation (SCT/BMT). TMI is a complex procedure that involves several critical steps that all need to be carefully addressed for a successful implementation, such as dose homogeneity in field junctions, choice of target margins, integrity of treatment and back-up planning. In this work we present our solution for a robust and reproducible workflow throughout the treatment chain and data for twenty-three patients treated to date. MATERIAL & METHODS: Patients were immobilized in a whole body vacuum cushion and thermoplastic mask. CT-scanning and treatment were performed in two parts with field matching at the upper thigh. Target consisted of marrow containing bone and sanctuary sites. Lungs, kidneys, bowel, heart and liver were defined as organs at risk (OAR). A fast surface scanning system was used to position parts of the body not covered by the imaging system (MVCT) as well as to reduce treatment time. RESULTS: All patients completed their treatment and could proceed with SCT/BMT. Doses to OARs were significantly reduced and target dose homogeneity was improved compared to TBI. Robustness tests performed on field matching and patient positioning support that the field junction technique is adequate. Replacing MVCT with optical surface scanning reduced the treatment time by 25 min per fraction. CONCLUSION: The methodology presented here has shown to provide a safe, robust and reproducible treatment for Total Marrow Irradiation using Tomotherapy.

The feasibility of using Pareto fronts for comparison of treatment planning systems and delivery techniques.

Pareto optimality is a concept that formalises the trade-off between a given set of mutually contradicting objectives. A solution is said to be Pareto optimal when it is not possible to improve one objective without deteriorating at least one of the other. A set of Pareto optimal solutions constitute the Pareto front. The Pareto concept applies well to the inverse planning process, which involves inherently contradictory objectives, high and uniform target dose on one hand, and sparing of surrounding tissue and nearby organs at risk (OAR) on the other. Due to the specific characteristics of a treatment planning system (TPS), treatment strategy or delivery technique, Pareto fronts for a given case are likely to differ. The aim of this study was to investigate the feasibility of using Pareto fronts as a comparative tool for TPSs, treatment strategies and delivery techniques. In order to sample Pareto fronts, multiple treatment plans with varying target conformity and dose sparing of OAR were created for a number of prostate and head & neck IMRT cases. The DVHs of each plan were evaluated with respect to target coverage and dose to relevant OAR. Pareto fronts were successfully created for all studied cases. The results did indeed follow the definition of the Pareto concept, i.e. dose sparing of the OAR could not be improved without target coverage being impaired or vice versa. Furthermore, various treatment techniques resulted in distinguished and well separated Pareto fronts. Pareto fronts may be used to evaluate a number of parameters within radiotherapy. Examples are TPS optimization algorithms, the variation between accelerators or delivery techniques and the degradation of a plan during the treatment planning process. The issue of designing a model for unbiased comparison of parameters with such large inherent discrepancies, e.g. different TPSs, is problematic and should be carefully considered.

In vivo dose verification of IMRT treated head and neck cancer patients.

An independent in vivo dose verification procedure for IMRT treatments of head and neck cancers was developed. Results of 177 intracavitary TLD measurements from 10 patients are presented. The study includes data from 10 patients with cancer of the rhinopharynx or the thyroid treated with dynamic IMRT. Dose verification was performed by insertion of a flexible naso-oesophageal tube containing TLD rods and markers for EPID and simulator image detection. Part of the study focussed on investigating the accuracy of the TPS calculations in the presence of inhomogeneities. Phantom measurements and Monte Carlo simulations were performed for a number of geometries involving lateral electronic disequilibrium and steep density shifts. The in vivo TLD measurements correlated well with the predictions of the treatment planning system with a measured/calculated dose ratio of 1.002+/-0.051 (1 SD, N=177). The measurements were easily performed and well tolerated by the patients. We conclude that in vivo intracavitary dosimetry with TLD is suitable and accurate for dose determination in intensity-modulated beams.