Volumetric modulated arc therapy for total body irradiation: A feasibility study using Pinnacle3 treatment planning system and Elekta Agility™ linac

Treatment robustness of total body irradiation with volumetric modulated arc therapy

This study evaluated the robustness of multi-isocenter Volumetric Modulated Arc Therapy Total Body Irradiation dose distribution in the overlapping region between the head-first and feet-first computed tomography scans, considering the longitudinal isocenter shifts recorded during treatment delivery. For 15 out of 22 patients, the dose distribution in the overlapping region fulfilled all three the robustness criteria. The overlapping region dose distribution of the remaining 7 cases fulfilled two robustness criteria. The dose distribution was found to be robust against daily recorded longitudinal isocenter shifts, as a consequence of the patient position verification procedure, of up to 16 mm.

Feasibility study of total marrow lymphoid irradiation with volumetric modulated arc therapy: clinical implementation in a tertiary care center

PURPOSE

Total marrow lymphoid irradiation (TMLI) with volumetric modulated arc therapy (VMAT) is challenging due to large treatment fields with multiple isocenters, field matching at junctions, and targets being surrounded by many organs at risk. This study aimed to describe our methodology for safe dose escalation and accurate dose delivery of TMLI treatment with the VMAT technique based on early experience at our center.

MATERIALS AND METHODS

Computed tomography (CT) scans were acquired in head-first supine and feet-first supine orientations for each patient with an overlap at mid-thigh. VMAT plans were generated for 20 patients on the head-first CT images with either three or four isocenters in the Eclipse treatment planning system (Varian Medical Systems Inc., Palo Alto, CA) and the treatment was delivered in a Clinac 2100 C/D linear accelerator (Varian Medical Systems Inc., Palo Alto, CA).

RESULTS

Five patients were treated with a prescription dose of 13.5 Gy in 9 fractions and 15 patients were treated with an escalated dose of 15 Gy in 10 fractions. The mean doses to 95% of the clinical target volume (CTV) and planning target volume (PTV) were 14.3 ± 0.3 Gy and 13.6 ± 0.7 Gy for the prescription doses of 15 Gy, and 13 ± 0.2 Gy and 12.3 ± 0.3 Gy for the prescription doses of 13.5 Gy, respectively. Mean dose to the lung in both schedules was 8.7 ± 0.6 Gy. The overall time taken to execute the treatment plans was approximately 2 h for the first fraction and 1.5 h for subsequent fractions. The average in-room time of 15.5 h per patient over 5 days leads to potential changes in the regular treatment schedules for other patients.

CONCLUSION

This feasibility study highlights the methodology adopted for safe implementation of TMLI with the VMAT technique at our institution. Escalation of dose to the target with adequate coverage and sparing of critical structures was achieved with the adopted treatment technique. Clinical implementation of this methodology at our center could serve as a practical guide to start the VMAT-based TMLI program safely by others who are keen to start this service.

Advanced automated treatment planning for total body irradiation: Implementation and effects on standardization

PURPOSE

This work describes the automation of our volumetric modulated arc therapy (VMAT) total body irradiation (TBI) treatment planning. It also aims to determine if plan standardization is impacted by automation.

METHODS

We introduced automated beam placement for TBI in March 2021. For manual beam placement pre-2021, Python-modified DICOM files were imported to pre-set cumulative meterset weights, with other parameters selected by dosimetrists. Our automated planning script automates these processes and sets gantry stop angles and isocentre placement. To determine the impact of automation on plan standardization, we performed a retrospective review of a matched cohort of 168 patients. Plan parameters were compared with an external standard, and passing rates compared between patient cohorts. The dosimetric impact was investigated by comparing a Body-5 mm homogeneity index (HI = D2%/D98%) and mean lung dose (MLD) between cohorts.

RESULTS

Results are listed for manual and automated groups respectively. Median (range) passing rates were 97.7% (96.1-100) and 99.2% (98.3-100). Automated plans had a significantly higher passing rate (p ≪ 0.05) and smaller variance (p = 0.001). Most failures were attributed to human error. Automated plans also had more consistent parameter identifiers. After considering dimensional outliers, median (range) Body-5 mm HI were 1.18 (1.14-1.23) and 1.18 (1.15-1.26), and mean ± standard deviation MLD were 103.8 ± 1.3% and 104.1 ± 0.9%. Variances were not significantly different between Body-5 mm HI (p = 0.092) but were for MLD (p = 0.013).

CONCLUSIONS

Implementation of automated planning in TBI resulted in significantly improved plan standardization. The decrease in variance of the MLD for the automated planning group points towards a potential dosimetric benefit of automation.

Planning and dosimetric evaluation of three total body irradiation techniques: Standard SSD VMAT, Extended SSD VMAT and Extended SSD Field-in-Field

The aim of this study was to dosimetrically compare three total body irradiation (TBI) techniques which can be delivered by a standard linear accelerator, and to deduce which one is preferable. Specifically, Extended Source to Surface Distance (SSD) Field-in-Field (FiF), Extended SSD Volumetric Modulated Arc Therapy (VMAT), and Standard SSD VMAT TBI techniques were dosimetrically evaluated. Percent depth dose and dose profile measurements were made under treatment conditions for each specified technique. After having generated treatment plans with a treatment planning system (TPS), dose homogeneity and critical organ doses were investigated on a Rando phantom using radiochromic films and optically stimulated luminescence dosimeters (OSLDs). TBI dose of 12 Gy in six fractions was prescribed for each technique. The gamma index (5%/5 mm) was used for the analysis of radiochromic films. Passing rates for Extended SSD FiF, Extended SSD VMAT and Standard SSD VMAT techniques were found to be 90%, 87% and 94%, respectively. OSLD measurements were within ± 5% agreement with TPS calculations for the first two techniques whereas the agreement was found to be within ± 3% for the Standard SSD VMAT technique. TPS calculations demonstrated that mean lung doses in the first two techniques were around 8.5 Gy while it was kept around 7 Gy in Standard SSD VMAT. It is concluded that Standard SSD VMAT is superior in sparing the lung tissue while all three TBI techniques are feasible in clinical practice with acceptable dose homogeneity. In the absence of VMAT-based treatment planning, Extended SSD FiF would be a reasonable choice compared to other conventional techniques.

A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques

Objective

The aim of this study is to implement a new treatment technique in total body irradiation (TBI) using the manual field-in-field-TBI (MFIF-TBI) technique and dosimetrically verifying its results with respect to compensator-based TBI (CB-TBI) and open field TBI technique.

Materials and Methods

A rice flour phantom (RFP) was placed on TBI couch with knee bent position at 385 cm source to surface distance. Midplane depth (MPD) was calculated for skull, umbilicus, and calf regions by measuring separations. Three subfields were opened manually for different regions using the multi-leaf collimator and jaws. The treatment Monitor unit (MU) was calculated based on each subfield size. In the CB-TBI technique, Perspex was used as a compensator. Treatment MU was calculated using MPD of umbilicus region and the required compensator thickness was calculated. For open field TBI, treatment MU was calculated using MPD of umbilicus region, and the treatment was executed without placing compensator. The diodes were placed on the surface of RFP to measure the delivered dose and the results were compared.

Results

The MFIF-TBI results showed that the deviation was within ± 3.0% for the different regions, except for the neck for which the deviation was 8.72%. In the CB-TBI delivery, the dose deviation was ± 3.0% for different regions in the RFP. The open field TBI results showed that the dose deviation was not within the limit ± 10.0%.

Conclusion

The MFIF-TBI technique can be implemented for TBI treatment as no TPS is required, and laborious process of making a compensator can be avoided while ensuring that the dose uniformity in all the regions within the tolerance limit.

ESTRO ACROP and SIOPE recommendations for myeloablative Total Body Irradiation in children

BACKGROUND AND PURPOSE

Myeloablative Total Body Irradiation (TBI) is an important modality in conditioning for allogeneic hematopoietic stem cell transplantation (HSCT), especially in children with high-risk acute lymphoblastic leukemia (ALL). TBI practices are heterogeneous and institution-specific. Since TBI is associated with multiple late adverse effects, recommendations may help to standardize practices and improve the outcome versus toxicity ratio for children.

MATERIAL AND METHODS

The European Society for Paediatric Oncology (SIOPE) Radiotherapy TBI Working Group together with ESTRO experts conducted a literature search and evaluation regarding myeloablative TBI techniques and toxicities in children. Findings were discussed in bimonthly virtual meetings and consensus recommendations were established.

RESULTS

Myeloablative TBI in HSCT conditioning is mostly performed for high-risk ALL patients or patients with recurring hematologic malignancies. TBI is discouraged in children <3-4 years old because of increased toxicity risk. Publications regarding TBI are mostly retrospective studies with level III-IV evidence. Preferential TBI dose in children is 12-14.4 Gy in 1.6-2 Gy fractions b.i.d. Dose reduction should be considered for the lungs to <8 Gy, for the kidneys to ≤10 Gy, and for the lenses to <12 Gy, for dose rates ≥6 cGy/min. Highly conformal techniques i.e. TomoTherapy and VMAT TBI or Total Marrow (and/or Lymphoid) Irradiation as implemented in several centers, improve dose homogeneity and organ sparing, and should be evaluated in studies.

CONCLUSIONS

These ESTRO ACROP SIOPE recommendations provide expert consensus for conventional and highly conformal myeloablative TBI in children, as well as a supporting literature overview of TBI techniques and toxicities.

Three-dimensional printers applied for the production of beam blocks in total body irradiation treatment

Purpose

Total body irradiation (TBI) in extended source surface distance (SSD) is a common treatment technique before hematopoietic stem cell transplant. The lungs are organs at risk, which often are treated with a lower dose than the whole body.

Methods

This can be achieved by the application of blocks. Three‐dimensional (3D) printers are a modern tool to be used in the production process of these blocks.

Results

We demonstrate the applicability of a specific printer and printing material, describe the process, and evaluate the accuracy of the product.

Conclusion

The blocks and apertures were found to be applicable in clinical routine.

Optimized Conformal Total Body Irradiation methods with Helical TomoTherapy and Elekta VMAT: Implementation, Imaging, Planning and Dose Delivery for Pediatric Patients

Optimized conformal total body irradiation (OC-TBI) is a highly conformal image guided method for irradiating the whole human body while sparing the selected organs at risk (OARs) (lungs, kidneys, lens). This study investigated the safety and feasibility of pediatric OC-TBI with the helical TomoTherapy (TomoTherapy) and volumetric modulated arc (VMAT) modalities and their implementation in routine clinical practice. This is the first study comparing the TomoTherapy and VMAT modalities in terms of treatment planning, dose delivery accuracy, and toxicity for OC-TBI in a single-center setting. The OC-TBI method with standardized dosimetric criteria was developed and implemented with TomoTherapy. The same OC-TBI approach was applied for VMAT. Standardized treatment steps, namely, positioning and immobilization, contouring, treatment planning strategy, plan evaluation, quality assurance, visualization and treatment delivery procedure were implemented for 157 patients treated with TomoTherapy and 52 patients treated with VMAT. Both modalities showed acceptable quality of the planned target volume dose coverage with simultaneous OARs sparing. The homogeneity of target irradiation was superior for TomoTherapy. Overall assessment of the OC-TBI dose delivery was performed for 30 patients treated with VMAT and 30 patients treated with TomoTherapy. The planned and delivered (sum of doses for all fractions) doses were compared for the two modalities in groups of patients with different heights. The near maximum dose values of the lungs and kidneys showed the most significant variation between the planned and delivered doses for both modalities. Differences in the patient size did not result in statistically significant differences for most of the investigated parameters in either the TomoTherapy or VMAT modality. TomoTherapy-based OC-TBI showed lower variations between planned and delivered doses, was less time-consuming and was easier to implement in routine practice than VMAT. We did not observe significant differences in acute and subacute toxicity between TomoTherapy and VMAT groups. The late toxicity from kidneys and lungs was not found during the 2.3 years follow up period. The study demonstrates that both modalities are feasible, safe and show acceptable toxicity. The standardized approaches allowed us to implement pediatric OC-TBI in routine clinical practice.

Feasibility study of volumetric modulated arc therapy with Halcyon™ linac for total body irradiation

Background

The use of total body irradiation (TBI) with linac-based volumetric modulated arc therapy (VMAT) has been steadily increasing. Helical tomotherapy has been applied in TBI and total marrow irradiation to reduce the dose to critical organs, especially the lungs. However, the methodology of TBI with Halcyon™ linac remains unclear. This study aimed to evaluate whether VMAT with Halcyon™ linac can be clinically used for TBI.

Methods

VMAT planning with Halcyon™ linac was conducted using a whole-body computed tomography data set. The planning target volume (PTV) included the body cropped 3 mm from the source. A dose of 12 Gy in six fractions was prescribed for 50% of the PTV. The organs at risk (OARs) included the lens, lungs, kidneys, and testes.

Results

The PTV D_98%, D_95%, D_50%, and D_2% were 8.9 (74.2%), 10.1 (84.2%), 12.6 (105%), and 14.2 Gy (118%), respectively. The homogeneity index was 0.42. For OARs, the D_mean of the lungs, kidneys, lens, and testes were 9.6, 8.5, 8.9, and 4.4 Gy, respectively. The V_12Gy of the lungs and kidneys were 4.5% and 0%, respectively. The D_max of the testes was 5.8 Gy. Contouring took 1–2 h. Dose calculation and optimization was performed for 3–4 h. Quality assurance (QA) took 2–3 h. The treatment duration was 23 min.

Conclusions

A planning study of TBI with Halcyon™ to set up VMAT-TBI, dosimetric evaluation, and pretreatment QA, was established.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-021-01959-3.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

Image-guided volumetric-modulated arc therapy of total body irradiation: An efficient workflow from simulation to delivery

Introduction

Using multi‐isocenter volumetric‐modulated arc therapy (VMAT) for total body irradiation (TBI) may improve dose uniformity and vulnerable tissue protection compared with classical whole‐body field technique. Two drawbacks limit its application: (1) VMAT‐TBI planning is time consuming; (2) VMAT‐TBI plans are sensitive to patient positioning uncertainties due to beam matching. This study presents a robust planning technique with image‐guided delivery to improve dose delivery accuracy. In addition, a streamlined sim‐to‐treat workflow with automatic scripts is proposed to reduce planning time.

Materials

Twenty‐five patients were included in this study. Patients were scanned in supine head‐first and feet‐first directions. An automatic workflow was used to (1) create a whole‐body CT by registering two CT scans, (2) contour lungs, kidneys, and planning target volume (PTV), (3) divide PTV into multiple sub‐targets for planning, and (4) place isocenters. Treatment planning included feathered AP/PA beams for legs/feet and VMAT for the body. VMAT‐TBI was evaluated for plan quality, planning/delivery time, and setup accuracy using image guidance.

Results

VMAT‐TBI planning time can be reduced to a day with automatic scripts. Treatment time took around an hour per fraction. VMAT‐TBI improved dose coverage (PTV V100 increased from 76.8 ± 10.5 to 88.5 ± 2.6; p < 0.001) and reduced lung dose (lung mean dose reduced from 10.8 ± 0.7 Gy to 9.4 ± 0.8 Gy, p < 0.001) compared with classic AP/PA technique.

Conclusion

A VMAT‐TBI sim‐to‐treat workflow with robust planning and image‐guided delivery was proposed. VMAT‐TBI improved the plan quality compared with classical whole‐body field techniques.

Evaluation of volumetric modulated arc therapy (VMAT) - based total body irradiation (TBI) in pediatric patients

Background

The dosimetric characterization of volumetric modulated arc therapy (VMAT)-based total-body irradiation (TBI) in pediatric patients is evaluated.

Materials and methods

Twenty-two patients between the ages of 2 and 12 years were enrolled for VMAT-based TBI from 2018 to 2020. Three isocenters were irradiated over three overlapping arcs. While prescribing 90% of the TBI dose to the planning treatment volume (PTV), two fractions (2 Gy each) were delivered each day; hence 12 Gy was delivered in six fractions. During treatment optimization, the mean lung and kidney doses were set not to exceed 7 Gy and 7.5 Gy, respectively. The maximum lens dose was also set to less than 4 Gy. Patient quality assurance was carried out by comparing treatment planning system doses to the 3-dimensional measured doses by the ArcCHECK^® detector. The electronic portal imaging device (EPID) gamma indices were also obtained.

Results

The average mean lung dose was 7.75 ± 0.18 Gy, mean kidney dose 7.63 ± 0.26 Gy, maximum lens dose 4.41 ± 0.39 Gy, and the mean PTV dose 12.69 ± 0.16 Gy. The average PTV heterogeneity index was 1.15 ± 0.03. Average differences in mean kidney dose, mean lung dose, and mean target dose were 2.79% ± 0.88, 0.84% ± 0.45 and 0.93% ± 0.47, respectively; when comparing planned and ArcCHECK^® measured doses. Only grade 1-2 radiation toxicities were recorded, based on CTCAE v5.0 scoring criteria.

Conclusions

VMAT-TBI was characterized with good PTV coverage, homogeneous dose distribution, planned and measured dose agreement, and low toxicity.

Safety and efficacy of a nonmyeloablative pretransplant conditioning regimen using total lymphoid irradiation with volumetric modulated arc therapy in healthy dogs: A pilot study

Allogeneic hematopoietic cell transplantation (HCT) has been an effective treatment for human patients with haematological malignancies (Baron & Storb, 2006; Bair et al., 2020; Copelan et al., 2019). However, the optimal pretransplant conditioning treatment is unclear in canine allogeneic HCT. This pilot study aimed to evaluate the safety and efficacy of total lymphoid irradiation (TLI) with volumetric modulated arc therapy (VMAT) for a nonmyeloablative HCT conditioning. Six healthy dogs were treated with 8 or 12 Gy TLI using VMAT. Haematological and physical changes were recorded over 8 weeks. To assess the effect of peripheral lymphocyte condition, lymphocyte subset and proliferative ability were examined. At the end of the experiment, necropsy was performed. All dogs showed mild‐to‐moderate neutropenia and thrombocytopenia, and these haematological changes resolved spontaneously. One dog treated with 8 Gy TLI developed transient cutaneous infection. No major complication was seen in the other seven dogs. Myelocytes and erythroblast cytopenia of bone marrow were detected in two dogs treated with 12 Gy TLI. This study is the first report of TLI using VMAT in dogs, and results suggest that this regimen is a feasible nonmyeloablative treatment.

Automatic treatment planning for VMAT-based total body irradiation using Eclipse scripting

The purpose of this work is to establish an automated approach for a multiple isocenter volumetric arc therapy (VMAT)‐based TBI treatment planning approach. Five anonymized full‐body CT imaging sets were used. A script was developed to automate and standardize the treatment planning process using the Varian Eclipse v15.6 Scripting API. The script generates two treatment plans: a head‐first VMAT‐based plan for upper body coverage using four isocenters and a total of eight full arcs; and a feet‐first AP/PA plan with three isocenters that covers the lower extremities of the patient. PTV was the entire body cropped 5 mm from the patient surface and extended 3 mm into the lungs and kidneys. Two plans were generated for each case: one to a total dose of 1200 cGy in 8 fractions and a second one to a total dose of 1320 cGy in 8 fractions. Plans were calculated using the AAA algorithm and 6 MV photon energy. One plan was created and delivered to an anthropomorphic phantom containing 12 OSLDs for in‐vivo dose verification. For the plans prescribed to 1200 cGy total dose the following dosimetric results were achieved: median PTV V100% = 94.5%; median PTV D98% = 89.9%; median lungs Dmean = 763 cGy; median left kidney Dmean = 1058 cGy; and median right kidney Dmean = 1051 cGy. For the plans prescribed to 1320 cGy total dose the following dosimetric results were achieved: median PTV V100% = 95.0%; median PTV D98% = 88.7%; median lungs Dmean = 798 cGy; median left kidney Dmean = 1059 cGy; and median right kidney Dmean = 1064 cGy. Maximum dose objective was met for all cases. The dose deviation between the treatment planning dose and the dose measured by the OSLDs was within ±4%. In summary, we have demonstrated that scripting can produce high‐quality plans based on predefined dose objectives and can decrease planning time by automatic target and optimization contours generation, plan creation, field and isocenter placement, and optimization objectives setup.

Early clinical experience with a total body irradiation technique using field-in-field beams and on-line image guidance

Background and purpose

Total body irradiation (TBI) is a treatment used in the conditioning of patients prior to hematopoietic stem cell transplantation. We developed an extended-distance TBI technique using a conventional linac with multi-leaf collimator to deliver a homogeneous dose, and spare critical organs.

Materials and methods

Patients were treated either in lateral recumbent or in supine position depending on the dose level. A conventional linac was used with the patient midline at 350 cm from the beam source. A series of beams was prepared manually using a 3D treatment planning system (TPS) aiming to improve dose homogeneity, spare the organs at risk and facilitate accurate patient positioning. An optimized dose calculation model for extended-distance treatments was developed using phantom measurements. During treatment, in-vivo dosimetry was performed using electronic dosimeters, and accurate positioning was verified using a mobile megavoltage imager. We analyzed dose volume histogram parameters for 19 patients, and in-vivo measurements for 46 delivered treatment fractions.

Results

Optimization of the dose calculation model for TBI improved dose calculation by 2.1% at the beam axis, and 17% at the field edge. Treatment planning dose objectives and constraints were met for 16 of 19 patients. Results of in-vivo dosimetry were within the set limitations (±10%) with mean deviations of 3.7% posterior of the lungs and 0.6% for the abdomen.

Conclusions

We developed a TBI treatment technique using a conventional linac and TPS that can reliably be used in the conditioning regimen of patients prior to stem cell transplantation.

A dosimetric evaluation of a novel technique using abutted radiation fields for myeloablative total body irradiation

Background:

The present study reports myeloablative total body irradiation (TBI) on an isocentrically mounted linac by laying the patient on the floor and management of abutting radiation fields and partial shielding of lungs. Dosimetrical efficacy of this novel technique was evaluated.

Materials and methods:

In this retrospective study, dosimetrical parameters from TBI plans on whole-body CT scans of 46 patients were analysed. The prescribed dose to TBI was 12 Gy in six fractions delivered over a period of 3 days for myeloablative conditioning. TrueBeam STx platform Linac (Varian Medical Systems Inc., Palo Alto, CA, USA) was used to deliver opposing fields. Radiation fields were abutted to form a single large field using an arithmetic formula at source-to-skin-distance of 210 cm.

Results:

Discrepancies in dose calculated by treatment planning system were within 1·6% accuracy, and dose profile at the junction of abutting radiation fields was reproduced within 3·0% accuracy. The real treatment time for each patient was ~30 minutes/fraction. Monitor unit was weighted for multiple sub-fields to achieve dose homogeneity within 5·0% throughout the whole body, and the mean dose to lung was ≤10 Gy.

Conclusion:

Our abutting radiation field technique for myeloablative TBI is feasible in any existing linac bunker. ‘Island-blocking’ is feasible in this technique using multi-leaf collimator. This technique is cost-effective as it does not require any costly equipment than the readily available equipment in any radiotherapy facility. In general, TBI requires laborious planning procedures and spacious linac bunkers; this novel technique has the potential to change previously held notions.

Evaluation of three VMAT-TMI planning methods to find an appropriate balance between plan complexity and the resulting dose distribution

PURPOSE

Evaluation of different planning methods of treatment plan preparation for volumetric modulated arc therapy during total marrow irradiation (VMAT-TMI).

METHOD

Three different planning methods were evaluated to establish the most appropriate VMAT-TMI technique, based on organ at risk (OAR) dose reduction, conformity and plan simplicity. The methods were: (M1) the sub-plan method, (M2) use of eight arcs optimised simultaneously and (M3) M2 with monitor unit reduction. Friedman ANOVA comparison, with Nemenyi's procedures, was used in the statistical analysis of the results.

RESULTS

The dosimetric results obtained for the planning target volume and for most OARs do not differ statistically between methods. The M3 method was characterized by the lowest numbers of monitor units (3259 MU vs. 4450 MU for M1 and 4216 MU for M2) and, in general, the lowest complexity. The variability of the monitor units from control points was almost half for M3 than M1 and M2 (i.e. 0.33 MU vs. 0.61 MU for M1 and 0.58 for M2). Analysing the relationship between the dose distributions obtained for the plans and their complexity, the best result was observed for the M3 method.

CONCLUSION

The use of eight simultaneously optimised arcs with MU reduction allows to obtain VMAT-TMI plans that are characterized by the lowest complexity, with dose distributions comparable to the plans generated by other methods.

Development of an Immobilization Device for Total Marrow Irradiation

PURPOSE

A body frame dedicated to total marrow (lymph node) irradiation (TMI/TMLI) could minimize patient motion during the potentially extended beam-on time with this technique. We present the development of a dedicated immobilization system for TMI/TMLI using volumetric modulated arc therapy.

METHODS AND MATERIALS

Since 2010, 59 adult patients were treated with TMI/TMLI using a multi-isocenter volumetric modulated arc therapy technique. Two computed tomographies (CTs) were required (1 head-first supine and 1 feet-first supine) to cover the whole volume. For the first 10 patients, 2 standard commercial frames with personalized masks (with/without personalized vacuum cushion for the lower extremities) were used without specific interfixation (frame A). For the next 49 patients a homemade 3-frame immobilization system was adopted (frame B), where each frame was interlocked with the next one and thermoplastic masks used to fix the patient. The effectiveness of the 2 immobilization systems was assessed by offline/online matching between daily cone beam CT of each isocenter and the simulation CTs.

RESULTS

Mean offline shifts for frame A were 3 to 12 mm in anterior-posterior, 2 to 5 mm in cranilal-caudal, and 2 to 6 mm in left-right directions. Larger shifts were found for feet-first supine series (shifts up to 23 mm). In frame B, mean offline shifts were 1 to 4 mm in anterior-posterior, 1 to 4 mm in cranial-caudal, and 1 to 4 mm in left-right directions. Mean online adjustments were -1 ± 4 mm in anterior-posterior, 0 ± 2 mm in cranial-caudal, and 0 ± 4 mm in left-right directions.

CONCLUSIONS

The patient positioning shifts for TMI/TMLI irradiation were mitigated by a homemade immobilization system and the use of individualized masks.

Novel rotatable tabletop for total-body irradiation using a linac-based VMAT technique

BACKGROUND

Volumetric Modulated Arc Therapy (VMAT) techniques have recently been implemented in clinical practice for total-body irradiation (TBI). To date, most techniques still use special couches, translational tables, or other self-made immobilization devices for dose delivery. Aim of the present study was to report the first results of a newly developed rotatable tabletop designed for VMAT-TBI.

METHODS

The VMAT-TBI technique theoretically allows the use of any standard positioning device at the linear accelerator. Nevertheless, the main problem is that patients taller than 120 cm cannot be treated in one position due to the limited cranial-caudal couch shift capacities of the linac. Therefore, patients are usually turned from a head-first supine position (HFS) to a feet-first supine position (FFS) to overcome this limitation. The newly developed rotatable tabletop consists completely of carbon fiber, including the ball bearing within the base plate of the rotation unit. The patient can be turned 180° from a HFS to a FFS position within a few seconds, without the need of repositioning.

RESULTS

The first 20 patients had a median age of 47 years, and received TBI before bone marrow transplantation for acute myeloid leukemia. Most patients (13/20) received a TBI dose of 4 Gy in 2 fractions, twice daily. The mean number of applied monitor units (MU) was 6476 MU using a multi-arcs and multi-isocenter VMAT-TBI technique. The tabletop has been successfully used in daily clinical practice and helped to keep the treatment times at an acceptable level. During the first treatment fraction, the mean overall treatment time (OTT) was 57 min. Since no additional image guidance was used in fraction 2 of the same day, the OTT was reduced to mean 38 min.

CONCLUSIONS

The easy and reproducible rotation of the patient on the treatment couch using the rotatable tabletop, is time-efficient and overcomes the need of repositioning the patient after turning from a HFS to a FFS position during VMAT TBI. Furthermore, it prevents couch-gantry collisions, incorrect isocenter shifts and beam mix-up due to predicted absolute table coordinates, which are recorded to the R + V system with the corresponding beams.

Clinical implementation of low-dose total body irradiation using topotherapy technique

BACKGROUND AND PURPOSE

The topotherapy technique was recently suggested as a robust alternative to helical radiation delivery for total body irradiation (TBI). It allows to deliver a discrete number of beams with fixed gantry. A Topotherapy-based low-dose TBI technique was optimized and clinically implemented.

MATERIALS AND METHODS

TBI delivery was split in two parts: the first treating from the head to half thigh and the second the remaining legs. An in-silico investigation aimed to optimize plan parameters was first carried out on four patients. For the upper plan, field width and pitch were fixed to 5 cm and 0.5: the combined impact of five modulation factor (MF) values and different field configurations (6/8/12 fields) was investigated. For the lower plan, two anterior/posterior beams (field width: 5 cm; pitch: 0.5; MF:1.5) were used. After assessing the optimal technique, set-up/quality assurance/image-guidance procedures were defined and the technique clinically implemented: 23 patients were treated up to now.

RESULTS

The best compromise between treatment time and planning target volume (PTV) coverage/homogeneity was found for MF = 1.5 and 8 fields. All clinical plans were automatically optimized using an "ad-hoc" plan template: excellent PTV coverage (PTV95%>98.5%) and homogeneity (median SD:4%) were found with a median beam-on time of 17/9 min for the upper/lower plan. All patients were successfully treated and transplanted.

CONCLUSIONS

TBI delivered with the topotherapy approach robustly guarantees adequate coverage and dose homogeneity. Semi-automatic clinical plans can be quickly generated and efficiently delivered.

Total marrow irradiation for hematopoietic malignancies using volumetric modulated arc therapy: A review of treatment planning studies

Total Marrow Irradiation (TMI) has been introduced in the management of hematopoietic malignancies with the aim of reducing toxicities induced by total body irradiation. TMI is one of the most challenging planning and delivery techniques of radiotherapy, as the whole skeleton should be irradiated, while sparing nearby organs at risk (OARs). Target volumes of 7–10 k cm³ and healthy tissue volumes of 50–90 k cm³ should be considered and inverse treatment planning is needed. This review focused on aspects of TMI delivery using volumetric modulated arc therapy (VMAT). In particular, multiple arcs from isocenters with different positions are required for VMAT-TMI as the cranial-caudal lengths of patients are much larger than the jaw aperture. Therefore, many field junctions between arcs with different isocenters should be managed. This review covered, in particular, feasibility studies for managing multiple isocenters, optimization of plan parameters, plan optimization of the lower extremities, robustness of field junctions and dosimetric plan verification of VMAT-TMI. This review demonstrated the possibility of VMAT in delivering TMI with multi-arcs and multi-isocenters. Care should be paid in the patient repositioning, with particular attention to the cranial-caudal direction.