Total body irradiation with volumetric modulated arc therapy: Dosimetric data and first clinical experience

Dose to organs at risk for total body irradiation: Single-institution data using the modulated arc total body irradiation technique

BACKGROUND

Organs at risk (OAR) dose reporting for total body irradiation (TBI) patients is limited, and standardly reported only as mean doses to the lungs and kidneys. Consequently, dose received and effects on other OAR remain unexplored. To remedy this gap, this study reports dose data on an extensive list of OAR for patients treated at a single institution using the modulated arc total body irradiation (MATBI) technique.

METHOD

An audit was undertaken of all patients treated with MATBI between January 2015 and March 2021 who had completed their course of treatment. OAR were contoured on MATBI patient treatment plans, with 12 Gy in six fraction prescription. OAR dose statistics and dose volume histogram data are reported for the whole body, lungs, kidneys, bones, brain, lens, heart, liver and bowel bag.

RESULTS

The OAR dose data for 29 patients are reported. Mean dose results are body 11.77 Gy, lungs 9.86 Gy, kidneys 11.84 Gy, bones 12.03 Gy, brain 12.12 Gy, right lens 12.31 Gy, left lens 12.64 Gy, heart 11.07 Gy, liver 11.81 Gy and bowel bag 12.06 Gy. Dose statistics at 1-Gy intervals of V6-V13 for lungs and V10-V13 for kidneys are also included.

CONCLUSION

This is the first time an extensive list of OAR data has been reported for any TBI technique. Due to the paucity of reporting, this information could be used by centres implementing the MATBI technique, in addition to aiding comparison between TBI techniques, with the potential for greater understanding of the relationship between dose volume data and toxicity.

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.

Tungsten Filled 3-Dimensional Printed Lung Blocks for Total Body Irradiation

PURPOSE

Lung blocks for total-body irradiation are commonly used to reduce lung dose and prevent radiation pneumonitis. Currently, molten Cerrobend containing toxic materials, specifically lead and cadmium, is poured into molds to construct blocks. We propose a streamlined method to create 3-dimensional (3D)-printed lung block shells and fill them with tungsten ball bearings to remove lead and improve overall accuracy in the block manufacturing workflow.

METHODS AND MATERIALS

3D-printed lung block shells were automatically generated using an inhouse software, printed, and filled with 2 to 3 mm diameter tungsten ball bearings. Clinical Cerrobend blocks were compared with the physician drawn blocks as well as our proposed tungsten filled 3D-printed blocks. Physical and dosimetric comparisons were performed on a linac. Dose transmission through the Cerrobend and 3D-printed blocks were measured using point dosimetry (ion-chamber) and the on-board Electronic-Portal-Imaging-Device (EPID). Dose profiles from the EPID images were used to compute the full-width-half-maximum and to compare with the treatment-planning-system. Additionally, the coefficient-of-variation in the central 80% of full-width-half-maximum was computed and compared between Cerrobend and 3D-printed blocks.

RESULTS

The geometric difference between treatment-planning-system and 3D-printed blocks was significantly lower than Cerrobend blocks (3D: -0.88 ± 2.21 mm, Cerrobend: -2.28 ± 2.40 mm, P = .0002). Dosimetrically, transmission measurements through the 3D-printed and Cerrobend blocks for both ion-chamber and EPID dosimetry were between 42% to 48%, compared with the open field. Additionally, coefficient-of-variation was significantly higher in 3D-printed blocks versus Cerrobend blocks (3D: 4.2% ± 0.6%, Cerrobend: 2.6% ± 0.7%, P < .0001).

CONCLUSIONS

We designed and implemented a tungsten filled 3D-printed workflow for constructing total-body-irradiation lung blocks, which serves as an alternative to the traditional Cerrobend based workflow currently used in clinics. This workflow has the capacity of producing clinically useful lung blocks with minimal effort to facilitate the removal of toxic materials from the clinic.

A novel AP/PA total body irradiation technique using abutting IMRT fields at extended SSD

PURPOSE

To develop a Total Body Irradiation (TBI) technique using IMRT at extended SSD that can be performed in any size Linac room.

METHODS

Patients studied were placed on a platform close to the floor, directly under the gantry with cranial-caudal axis parallel to the gantry rotation plane and at SSD ∼200 cm. Two abutting fields with the same external isocenter at gantry angles of ±21˚, collimator angle of 90˚, and field size of 25 × 40 cm2 are employed for both supine and prone positions. An iterative optimization algorithm was developed to generate a uniform dose at the patient mid-plane with adequate shielding to critical organs such as lungs and kidneys. The technique was validated in both phantom and patient CT images for treatment planning, and dose measurement and QA were performed in phantom.

RESULTS

A uniform dose distribution in the mid-plane within ±5% of the prescription dose was reached after a few iterations. This was confirmed with ion-chamber measurements in phantom. The mean dose to lungs and kidneys can be adjusted according to clinical requirements and can be as low as ∼25% of the prescription dose. For a typical prescription dose of 200 cGy/fraction, the total MU was ∼2400/1200 for the superior/inferior field. The overall treatment time for both supine/prone positions was ∼54 min to meet the maximum absorbed dose rate criteria of 15 cGy/min. IMRT QA with portal dosimetry shows excellent agreement.

CONCLUSIONS

We have developed a promising TBI technique using abutting IMRT fields at extended SSD. The patient is in a comfortable recumbent position with good reproducibility and less motion during treatment. An additional benefit of this technique is that full 3D dose distribution is available from the TPS with a DVH summary for organs of interest. The technique allows precise sparing of lungs and kidneys and can be executed in any linac room.

Non-contact scintillator imaging dosimetry for total body irradiation in radiotherapy

Objective.The goal of this work was to assess the potential use of non-contact scintillator imaging dosimetry for tracking delivery in total body irradiation (TBI).Approach. Studies were conducted to measure the time-gated light signals caused by radiation exposure to scintillators that were placed on tissue. The purpose was to assess efficacy in conditions common for TBI, such as the large source to surface distance (SSD) commonly used, the reduced dose rate, the inclusion of a plexiglass spoiler, angle of incidence and effects of peripheral patient support structures. Dose validation work was performed on phantoms that mimicked human tissue optical properties and body geometry. For this work, 1.5 cm diameter scintillating disks were developed and affixed to phantoms under various conditions. A time-gated camera synchronized to the linac pulses was used for imaging. Scintillation intensity was quantified in post processing and the values verified with simultaneous thermolumiescent dosimeter (TLD) measurements. Mean scintillation values in each region were compared to TLD measurements to produce dose response curves, and scatter effects from the spoiler and patient bed were quantified.Main results.The dose determined by scintillators placed in TBI conditions agreed with TLD dose determinations to within 2.7%, and did so repeatedly within 1.0% standard deviation variance. A linear fit between scintillator signal and TLD dose was achieved with anR2= 0.996 across several body sites. Scatter from the patient bed resulted in a maximum increase of 19% in dose.Significance.This work suggests that non-contact scintillator imaging dosimetry could be used to verify dose in real time to patients undergoing TBI at the prescribed long SSD and low dose rate. It also has shown that patient transport stretchers can significantly influence surface dose by increasing scatter.

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.

Optimized Conformal Total Body Irradiation with VMAT Using a Linear-Accelerator-Based Radiosurgery Treatment System in Comparison to the Golden Standard Helical TomoTherapy

Modern irradiation techniques for optimized conformal TBI can be realized by Helical Tomotherapy (HT) or Volumetric Modulated Arc Therapy (VMAT), depending on the availability of suitable specialized equipment. In this dosimetric planning study, we compared both modalities and addressed the question of whether VMAT with small field sizes is also suitable as a backup in case of HT equipment malfunctions. For this purpose, we retrospectively used planning computed tomography (CT) data from 10 patients treated with HT with a total dose of 8 Gy (n = 5) or 12 Gy (n = 5) for treatment planning for VMAT with a small field size (36 × 22 cm). The target volume coverage, dose homogeneity at target volume, and dose reduction in organs at risk (OAR) (lungs, kidneys, lenses) were analyzed and compared. One patient was irradiated with both modalities due to a device failure of the HT equipment during the study, which facilitated a comparison in a real clinical setting. The findings indicate that in addition to a higher mean dose to the lenses in the 12 Gy group for VMAT and a better dose homogeneity in the target volume for HT, comparably good and adequate target dose coverage and dose reduction in the other OAR could be achieved for both modalities, with significantly longer treatment times for VMAT. In conclusion, after appropriate optimization of the treatment times, VMAT using linear accelerator radiosurgery technology can be used both as a backup in addition to HT and in clinical routines to perform optimized conformal TBI.

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.

Modern Radiation for Hematologic Stem Cell Transplantation: Total Marrow and Lymphoid Irradiation or Intensity-Modulated Radiation Therapy Total Body Irradiation

The development of large-field intensity-modulated radiation therapy (IMRT) has enabled the implementation of total marrow irradiation (TMI), total marrow and lymphoid irradiation (TMLI), and IMRT total body irradiation (TBI). IMRT TBI limits doses to organs at risk, primarily the lungs and in some cases the kidneys and lenses, which may mitigate complications. TMI/TMLI allows for dose escalation above TBI radiation therapy doses to malignant sites while still sparing organs at risk. Although still sparingly used, these techniques have established feasibility and demonstrated promise in reducing the adverse effects of TBI while maintaining and potentially improving survival outcomes.

ACR-ARS Practice Parameter for the Performance of Total Body Irradiation

OBJECTIVES

This practice parameter was revised collaboratively by the American College of Radiology (ACR) and the American Radium Society (ARS). This practice parameter provides updated reference literature regarding both clinical-based conventional total body irradiation and evolving volumetric modulated total body irradiation.

METHODS

This practice parameter was developed according to the process described under the heading The Process for Developing ACR Practice Parameters and Technical Standards on the ACR website ( https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards ) by the Committee on Practice Parameters-Radiation Oncology of the ACR Commission on Radiation Oncology in collaboration with the ARS.

RESULTS

This practice parameter provides a comprehensive update to the reference literature regarding conventional total body irradiation and modulated total body irradiation. Dependence on dose rate remains an active area of ongoing investigation in both the conventional setting (where instantaneous dose rate can be varied) and in more modern rotational techniques, in which average dose rate is the relevant variable. The role of imaging during patient setup and the role of inhomogeneity corrections due to computer-based treatment planning systems are included as evolving areas of clinical interest notably surrounding the overall dose inhomogeneity. There is increasing emphasis on the importance of evaluating mean lung dose as it relates to toxicity during high-dose total body irradiation regimens.

CONCLUSIONS

This practice parameter can be used as an effective tool in designing and evaluating a total body irradiation program that successfully incorporates the close interaction and coordination among the radiation oncologists, medical physicists, dosimetrists, nurses, and radiation therapists.

Optimised conformal total body irradiation: a heterogeneous practice, so where next?

The use of volumetric arc therapy and inverse planning has been in routine use in radiotherapy for two decades. However, use in total body irradiation (TBI) has been more recent and few guidelines exist as to how to plan or verify. This has led to heterogeneous approaches. The goal of this review is to provide an overview of current advanced planning and dosimetry verification protocols used in optimised conformal TBI as a basis for investigating the need for greater standardisation in TBI.

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.

Commissioning and performance evaluation of commercially available mobile imager for image guided total body irradiation

BACKGROUND

The setup of lung shield (LS) in total body irradiation (TBI) with the computed radiography (CR) system is a time-consuming task and has not been quantitatively evaluated. The TBI mobile imager (TBI-MI) can solve this problem through real-time monitoring. Therefore, this study aimed to perform commissioning and performance evaluation of TBI-MI to promote its use in clinical practice.

METHODS

The source-axis distance in TBI treatment, TBI-MI (CNERGY TBI, Cablon Medical B.V.), and the LS position were set to 400, 450, and 358 cm, respectively. The evaluation items were as follows: accuracy of image scaling and measured displacement error of LS, image quality (linearity, signal-to-noise ratio, and modulation transfer function) using an EPID QC phantom, optimal thresholding to detect intra-fractional motion in the alert function, and the scatter radiation dose from TBI-MI.

RESULTS

The accuracy of image scaling and the difference in measured displacement of the LS was <4 mm in any displacements and directions. The image quality of TBI imager was slightly inferior to the CR image but was visually acceptable in clinical practice. The signal-to-noise ratio was improved at high dose rate. The optimal thresholding value to detect a 10-mm body displacement was determined to be approximately 5.0%. The maximum fraction of scattering radiation to irradiated dose was 1.7% at patient surface.

CONCLUSION

MI-TBI can quantitatively evaluate LS displacement with acceptable image quality. Furthermore, real-time monitoring with alert function to detect intrafraction patient displacement can contribute to safe TBI treatment.

Total marrow irradiation (TMI): Addressing an unmet need in hematopoietic cell transplantation - a single institution experience review

Purpose

TMI utilizes IMRT to deliver organ sparing targeted radiotherapy in patients undergoing hematopoietic cell transplantation (HCT). TMI addresses an unmet need, specifically patients with refractory or relapsed (R/R) hematologic malignancies who have poor outcomes with standard HCT regimens and where attempts to improve outcomes by adding or dose escalating TBI are not possible due to increased toxicities. Over 500 patients have received TMI at this center. This review summarizes this experience including planning and delivery, clinical results, and future directions.

Methods

Patients were treated on prospective allogeneic HCT trials using helical tomographic or VMAT IMRT delivery. Target structures included the bone/marrow only (TMI), or the addition of lymph nodes, and spleen (total marrow and lymphoid irradiation, TMLI). Total dose ranged from 12 to 20 Gy at 1.5-2.0 Gy fractions twice daily.

Results

Trials demonstrate engraftment in all patients and a low incidence of radiation related toxicities and extramedullary relapses. In R/R acute leukemia TMLI 20 Gy, etoposide, and cyclophosphamide (Cy) results in a 1-year non-relapse mortality (NRM) rate of 6% and 2-year overall survival (OS) of 48%; TMLI 12 Gy added to fludarabine (flu) and melphalan (mel) in older patients (≥ 60 years old) results in a NRM rate of 33% comparable to flu/mel alone, and 5-year OS of 42%; and TMLI 20 Gy/flu/Cy and post-transplant Cy (PTCy) in haplo-identical HCT results in a 2-year NRM rate of 13% and 1-year OS of 83%. In AML in complete remission, TMLI 20 Gy and PTCy results in 2-year NRM, OS, and GVHD free/relapse-free survival (GRFS) rates of 0%, 86·7%, and 59.3%, respectively.

Conclusion

TMI/TMLI shows significant promise, low NRM rates, the ability to offer myeloablative radiation containing regimens to older patients, the ability to dose escalate, and response and survival rates that compare favorably to published results. Collaboration between radiation oncology and hematology is key to successful implementation. TMI/TMLI represents a paradigm shift from TBI towards novel strategies to integrate a safer and more effective target-specific radiation therapy into HCT conditioning beyond what is possible with TBI and will help expand and redefine the role of radiotherapy in HCT.

Total body irradiation using volumetric modulated arc therapy, experience of a cancer hospital in Pakistan

Introduction:

To report the planning parameters, efficacy and toxicity of total body irradiation using volumetric modulated arc therapy (VMAT).

Methods:

From July 2019 till May 2021, nine patients treated with VMAT-based total body irradiation as a part of the myeloablative regimen for homologous stem cell transplant were evaluated. The CT acquisition, planning parameters, doses to target volume and critical structures were evaluated retrospectively.

Results:

Median age was 24 with median height 172 cm. Average Mean Lung dose was 9·5 Gy, mean dose to kidney was kidney dose 8·4 Gy, planning target volume (PTV) 95% was 98 % and mean heterogeneity index of PTV was 1·2 all patients. Total fraction delivery time including setup was 3·1 h while beam on time was 23 min. Main toxicity observed was mucositis and fatigue, while no Grade 3 or more acute radiation toxicity was observed.

Conclusion:

At our institution, high dose TBI performed with multi-isocentric VMAT is now a standard procedure. Though it is cumbersome and time-consuming process but VMAT offers an advantage of increased dose homogeneity in the target volume with reduction in doses to critical organs especially lungs and kidneys in comparison to standard source to skin distance technique, longer follow-up time is necessary to evaluate our method and long-term toxicity.

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.

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.

The Stanford VMAT TBI Technique

PURPOSE

In this work, we describe the technical aspects of the XXX VMAT TBI technique, compare it to other VMAT TBI techniques, and share our initial experience.

METHODS

From September 2019 to August 2021, 35 patients were treated with VMAT TBI at our institution. Treatment planning was performed using in-house developed automated planning scripts. Organ sparing depended on the regimen: myeloablative (lungs, kidneys, and lenses); non-myeloablative with benign disease (lungs, kidneys, lenses, gonads, brain, and thyroid). Quality assurance was performed using EPID portal dosimetry and Mobius3D. Robustness was evaluated for the first ten patients by performing local and global isocenter shifts of 5 mm. Treatment was delivered using IGRT for every isocenter and every fraction. In-vivo measurements were performed on the matchline between the VMAT and AP/PA fields and on the testes for the first fraction.

RESULTS

The lungs, lungs-1cm, and kidneys D_mean were consistently spared to 57.6±4.4%, 40.7±5.5%, and 70.0±9.9% of the prescription dose, respectively. Gonadal sparing (D_mean=0.69±0.13 Gy) was performed for all patients with benign disease. The average PTV D_1cc was 120.7±6.4% for all patients. The average Gamma passing rate for the VMAT plans was 98.1±1.6% (criteria of 3%/2mm). Minimal differences were observed between Mobius3D- and EclipseAAA-calculated PTV D_mean (0.0±0.3%) and lungs D_mean (-2.5±1.2%). Robustness evaluation showed that the PTV D_max and lungs D_mean are insensitive to small positioning deviations between the VMAT isocenters (1.1±2.4% and 1.2±1.0%, respectively). The average matchline dose measurement indicated patient setup was reproducible (96.1±4.5% relative to prescription dose). Treatment time, including patient setup and beam-on, was 47.5±9.5 min.

CONCLUSIONS

The XXX VMAT TBI technique, from simulation to treatment delivery, was presented and compared to other VMAT TBI techniques. Together with publicly shared autoplanning scripts, our technique may provide the gateway for wider adaptation of this technology and the possibility of multi-institutional studies in the cooperative group setting.

Evaluation of Surface Dose and Commissioning of Compensator-Based Total Body Irradiation

Purpose:

The aim of the current study is to commission compensator-based total body irradiation (TBI) and to compare surface dose using percentage depth dose (PDD) while varying the distance between beam spoiler and phantom surface.

Materials and Methods:

TBI commissioning was performed on Elekta Synergy® Platform linear accelerator for bilateral extended source to surface distance treatment technique. The PDD was measured by varying the distance (10 cm, 20 cm, 30 cm, and 40 cm) between the beam spoiler and the phantom surface. Beam profile and half-value layer (HVL) measurement were carried out using the FC65 ion-chamber. Quality assurance (QA) was performed using an in-house rice-flour phantom (RFP). In-vivo diodes (IVD) were placed on the RFP at various regions to measure the delivered dose, and it was compared to the calculated dose.

Results:

An increase in Dmax and surface dose was observed when beam spoiler was moved away from the phantom surface. The flatness and symmetry of the beam profile were calculated. The HVL of Perspex and aluminum is 17 cm and 8 cm, respectively. The calculated dose of each region was compared to the measured dose on the RFP with IVD, and the findings showed that the variation was <4.7% for both Perspex and Aluminum compensators.

Conclusion:

The commissioning of the compensator-based TBI technique was performed and its QA measurements were carried out. The Mayneord factor corrected PDD and measured PDD values were compared. The results are well within the clinical tolerance limit. This study concludes that 10 cm −20 cm is the optimal distance from the beam spoiler to phantom surface to achieve prescribed dose to the skin.

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.

Two compound techniques for total body irradiation

INTRODUCTION

Total body irradiation (TBI) is an important treatment modality that is used in combination with chemotherapy in many stem cell transplantation protocols. Therefore, the quality of the irradiation is important. Two techniques for planning and delivering TBI are presented and compared.

METHODS AND MATERIALS

The technique named ExIMRT is a combination of manually shaped conventional fields from an extended SSD and isocentric IMRT fields. The technique named ExVMAT is a combination of conventional and IMRT fields from an extended SSD and isocentric VMAT fields. Dosimetric data from 32 patients who were planned and treated according to one of the two techniques were compared.

RESULTS

When comparing the two techniques, it is determined that the ExVMAT technique is able to significantly reduce the mean total volume overdosed by 120% from 408 to 12 cm³. The dose covering 98% of the total lung volume is significantly increased by this technique from a mean of 9.7 Gy to 10.3 Gy. Additionally, the dose covering 2% of the total kidney volume is significantly decreased from a mean of 12.8 to 12.5 Gy. Furthermore, the population-based variance of the median dose to the total lung volume, the heart and the volume of the body prescribed to 12.5 Gy is significantly reduced. The results are obtained without compromising overall treatment quality as treatment time or dose rate to the lungs.

CONCLUSION

Using the ExVMAT technique, a superior dose distribution can be delivered both from a patient and a population perspective compared to the ExIMRT technique.

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.

Volumetric Modulated Arc Therapy Enabled Total Body Irradiation (VMAT-TBI): Six-year Clinical Experience and Treatment Outcomes

Total body irradiation is an important part of the conditioning regimens frequently used to prepare patients for allogeneic hematopoietic stem cell transplantation (SCT). Volumetric-modulated arc therapy enabled total body irradiation (VMAT-TBI), an alternative to conventional TBI (cTBI), is a novel radiotherapy treatment technique that has been implemented and investigated in our institution. The purpose of this study is to (1) report our six-year clinical experience in terms of treatment planning strategy and delivery time and (2) evaluate the clinical outcomes and toxicities in our cohort of patients treated with VMAT-TBI. This is a retrospective single center study. Forty-four patients at our institution received VMAT-TBI and chemotherapy conditioning followed by allogeneic SCT between 2014 and 2020. Thirty-two patients (73%) received standard-dose TBI (12-13.2 Gy in 6-8 fractions twice daily), whereas 12 (27%) received low-dose TBI (2-4 Gy in one fraction). Treatment planning, delivery, and treatment outcome data including overall survival (OS), relapse-free survival (RFS), and toxicities were analyzed. The developed VMAT-TBI planning strategy consistently generated plans satisfying our dose constraints, with planning target volume coverage >90%, mean lung dose ∼50% to 75% of prescription dose, and minimal hotspots in critical organs. Most of the treatment deliveries were <100 minutes (range 33-147, mean 72). The median follow-up was 26 months. At the last follow-up, 34 of 44 (77%) of patients were alive, with 1- and 2-year OS of 90% and 79% and RFS of 88% and 71%, respectively. The most common grade 3+ toxicities observed were mucositis (31 patients [71%]) and nephrotoxicity (6 patients [13%]), both of which were deemed multifactorial in cause. Four patients (9%) in standard-dose cohort developed grade 3+ pneumonitis, with 3 cases in the setting of documented respiratory infection and only 1 (2%) deemed likely related to radiation alone. VMAT-TBI provides a safe alternative to cTBI. The dose modulation capability of VMAT-TBI may lead to new treatment strategies, such as simultaneous boost and further critical organ sparing, for better malignant cell eradication, immune suppression, and lower toxicities.

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.

A customizable aluminum compensator system for total body irradiation

Purpose

To develop a simplified aluminum compensator system for total body irradiation (TBI) that is easy to assemble and modify in a short period of time for customized patient treatments.

Methods

The compensator is composed of a combination of 0.3 cm thick aluminum bars, two aluminum T‐tracks, spacers, and metal bolts. The system is mounted onto a plexiglass block tray. The design consists of 11 fixed sectors spanning from the patient's head to feet. The outermost sectors utilize 7.6 cm wide aluminum bars, while the remaining sectors use 2.5 cm wide aluminum bars. There is a magnification factor of 5 from the compensator to the patient treatment plane. Each bar of aluminum is interconnected at each adjacent sector with a tongue and groove arrangement and fastened to the T‐track using a metal washer, bolt, and nut. Inter‐bar leakage of the compensator was tested using a water tank and diode. End‐to‐end measurements were performed with an ion chamber in a solid water phantom and also with a RANDO phantom using internal and external optically stimulated luminescent detectors (OSLDs). In‐vivo patient measurements from the first 20 patients treated with this aluminum compensator were compared to those from 20 patients treated with our previously used lead compensator system.

Results

The compensator assembly time was reduced to 20–30 min compared to the 2–4 h it would take with the previous lead design. All end‐to‐end measurements were within 10% of that expected. The median absolute in‐vivo error for the aluminum compensator was 3.7%, with 93.8% of measurements being within 10% of that expected. The median error for the lead compensator system was 5.3%, with 85.1% being within 10% of that expected.

Conclusion

This design has become the standard compensator at our clinic. It allows for quick assembly and customization along with meeting the Task Group 29 recommendations for dose uniformity.

Practice patterns of pediatric total body irradiation techniques: A Children's Oncology Group survey

PURPOSE

The aim of this study was to examine current practice patterns in pediatric total body irradiation (TBI) techniques among xxx member institutions.

METHODS AND MATERIALS

Between Nov 2019 and Feb 2020 a questionnaire, containing 52 questions related to the technical aspects of TBI was sent to medical physicists at 152 xxx institutions. The questions were designed to obtain technical information on commonly used TBI treatment techniques. Another set of 9 questions related to the clinical management of patients undergoing TBI was sent to 152 xxx member radiation oncologists at the same institutions.

RESULTS

Twelve institutions were excluded because TBI was not performed in their institutions. A total of 88 physicists from 88 institutions (63% response rate) and 96 radiation oncologists from 96 institutions responded (69% response rate). The AP/PA technique was the most common (49 institutions - 56%); 44 institutions (50%) used the lateral technique and 14 institutions (16%) used volumetric modulated arc therapy (VMAT)/Tomotherapy. Mid-plane dose rates of 6-15 cGy/min were most commonly used. The most common specification for lung dose was the mid lung dose for both AP/PA (71%) and lateral (63%) techniques. All physician responders agreed with the need to refine current TBI techniques and 79% supported the investigation of new TBI techniques to further lower the lung dose.

CONCLUSION

There is no consistency in the practice patterns, methods for dose measurement and reporting of TBI doses among xxx institutions. The lack of a standardization precludes meaningful correlation between TBI doses and clinical outcomes including disease control and normal tissue toxicity. The xxx radiation oncology discipline is currently undertaking several steps to standardize the practice and dose reporting of pediatric TBI using detailed questionnaires and phantom-based credentialing for all xxx centers.

Advances in radiotherapy technology for pediatric cancer patients and roles of medical physicists: COG and SIOP Europe perspectives

Over the last two decades, rapid technological advances have dramatically changed radiation delivery to children with cancer, enabling improved normal-tissue sparing. This article describes recent advances in photon and proton therapy technologies, image-guided patient positioning, motion management, and adaptive therapy that are relevant to pediatric cancer patients. For medical physicists who are at the forefront of realizing the promise of technology, challenges remain with respect to ensuring patient safety as new technologies are implemented with increasing treatment complexity. The contributions of medical physicists to meeting these challenges in daily practice, in the conduct of clinical trials, and in pediatric oncology cooperative groups are highlighted. Representing the perspective of the physics committees of the Children's Oncology Group (COG) and the European Society for Paediatric Oncology (SIOP Europe), this paper provides recommendations regarding the safe delivery of pediatric radiotherapy. Emerging innovations are highlighted to encourage pediatric applications with a view to maximizing the therapeutic ratio.

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.

A Step Toward Making VMAT TBI More Prevalent: Automating the Treatment Planning Process

PURPOSE

Our purpose was to automate the treatment planning process for total body irradiation (TBI) with volumetric modulated arc therapy (VMAT).

METHODS AND MATERIALS

Two scripts were developed to facilitate autoplanning: the binary plug-in script automating the creation of optimization structures, plan generation, beam placement, and setting of the optimization constraints and the stand-alone executable performing successive optimizations. Ten patients previously treated in our clinic with VMAT TBI were used to evaluate the efficacy of the proposed autoplanning process. Paired t tests were used to compare the dosimetric indices of the produced auto plans to the manually generated clinical plans. In addition, 3 physicians were asked to evaluate the manual and autoplans for each patient in a blinded retrospective review.

RESULTS

No significant differences were observed between the manual and autoplan global D_max (P < .893), planning target volume V110% (P < .734), kidneys D_mean (P < .351), and bowel D_max (P < .473). Significant decreases in the D_mean to the lungs and lungs-1cm (ie, lungs with 1-cm inner margin) volumes of 5.4% ± 6.4% (P < .024) and 6.8% ± 7.4% (P < .017), respectively, were obtained with the autoplans compared with the manual plans. The autoplans were selected 77% of the time by the reviewing physicians as equivalent or superior to the manual plans. The required time for treatment planning was estimated to be 2 to 3 days for the manual plans compared with approximately 3 to 5 hours for the autoplans.

CONCLUSIONS

Large reductions in planning time without sacrificing plan quality were obtained using the developed autoplanning process compared with manual planning, thus reducing the required effort of the treatment planning team. Superior lung sparing with the same target coverage and similar global D_max were observed with the autoplans as compared with the manual treatment plans. The developed scripts have been made open-source to improve access to VMAT TBI at other institutions and clinics.

Gonadal-sparing total body irradiation with the use of helical tomotherapy for nonmalignant indications

Background

The aim was to demonstrate the feasibility and technique of gonadal sparing total body irradiation (TBI) with helical tomotherapy. Total body irradiation is a common part of the conditioning regimen prior to allogeneic stem cell transplantation. Shielding or dose-reduction to the gonads is often desired to preserve fertility, particularly in young patients undergoing transplant for non-malignant indications. Helical tomotherapy (HT) has been shown to be superior to traditional TBI delivery for organ at risk (OA R) doses and dose homogeneity.

Materials and methods

We present two representative cases (one male and one female) to illustrate the feasibility of this technique, each of whom received 3Gy in a single fraction prior to allogeneic stem cell transplant for benign indications. The planning target volume (PTV) included the whole body with a subtraction of OA Rs including the lungs, heart, and brain (each contracted by 1cm) as well as the gonads (testicles expanded by 5 cm and ovaries expanded by 0.5 cm).

Results

For the male patient we achieved a homogeneity index of 1.35 with a maximum and median planned dose to the testes of 0.53 Gy and 0.35 Gy, respectively. In-vivo dosimetry demonstrated an actual received dose of 0.48 Gy. For the female patient we achieved a homogeneity index of 1.13 with a maximum and median planned dose to the ovaries of 1.66 Gy and 0.86 Gy, respectively.

Conclusion

Gonadal sparing TBI is feasible and deliverable using HT in patients with non-malignant diseases requiring TBI as part of a pre-stem cell transplant conditioning regimen.

Total Body Irradiation for Hematopoietic Stem Cell Transplantation: What Can We Agree on?

Total body irradiation (TBI), used as part of the conditioning regimen prior to allogeneic and autologous hematopoietic cell transplantation, is the delivery of a relatively homogeneous dose of radiation to the entire body. TBI has a dual role, being cytotoxic and immunosuppressive. This allows it to eliminate disease and create “space” in the marrow while also impairing the immune system from rejecting the foreign donor cells being transplanted. Advantages that TBI may have over chemotherapy alone are that it may achieve greater tumour cytotoxicity and better tissue penetration than chemotherapy as its delivery is independent of vascular supply and physiologic barriers such as renal and hepatic function. Therefore, the so-called “sanctuary” sites such as the central nervous system (CNS), testes, and orbits or other sites with limited blood supply are not off-limits to radiation. Nevertheless, TBI is hampered by challenging logistics of administration, coordination between hematology and radiation oncology departments, increased rates of acute treatment-related morbidity and mortality along with late toxicity to other tissues. Newer technologies and a better understanding of the biology and physics of TBI has allowed the field to develop novel delivery systems which may help to deliver radiation more safely while maintaining its efficacy. However, continued research and collaboration are needed to determine the best approaches for the use of TBI in the future.

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.

Total Body Irradiation and Total Skin Irradiation Techniques in Belgium and the Netherlands: Current Clinical Practice

Purpose

In 2014, a Belgian/Dutch Nederlandse Commissie voor Stralingsdosimetrie (NCS) task group was formed to develop guidelines on the clinical practice of total body irradiation (TBI) and total skin irradiation (TSI).

Methods and Materials

As a basis for these guidelines, a survey conducted among 17 Belgian and Dutch radiation oncology institutions measured the clinical practice of TBI. Four of these institutions also performed TSI. An update was performed in 2019 and 2020 because several institutions innovated their TBI techniques.

Results

As old and more recent studies have shown, clinical protocols for TBI and TSI still vary considerably between institutions.

Conclusions

New radiation therapy technologies have been introduced relatively slowly for TBI purposes.

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.

Total marrow and lymphoid irradiation with helical tomotherapy: a practical implementation report

Purpose

To standardize the technique; evaluate resources requirements and analyze our early experience of total marrow and lymphoid irradiation (TMLI) as part of the conditioning regimen before allogenic bone marrow transplantation using helical tomotherapy.

Materials and Methods

Computed tomography (CT) scanning and treatment were performed in head first supine (HFS) and feet first supine (FFS) orientations with an overlap at mid-thigh. Patients along with the immobilization device were manually rotated by 180° to change the orientation after the delivery of HFS plan. The dose at the junction was contributed by a complementary dose gradient from each of the plans. Plan was to deliver 95% of 12 Gy to 98% of clinical target volume with dose heterogeneity <10% and pre-specified organs-at-risk dose constraints. Megavoltage-CT was used for position verification before each fraction. Patient specific quality assurance and in vivo film dosimetry to verify junction dose were performed in all patients.

Results

Treatment was delivered in two daily fractions of 2 Gy each for 3 days with at least 8-hour gap between each fraction. The target coverage goals were met in all the patients. The average person-hours per patient were 16.5, 21.5, and 25.75 for radiation oncologist, radiation therapist, and medical physicist, respectively. Average in-room time per patient was 9.25 hours with an average beam-on time of 3.32 hours for all the 6 fractions.

Conclusion

This report comprehensively describes technique and resource requirements for TMLI and would serve as a practical guide for departments keen to start this service. Despite being time and labor intensive, it can be implemented safely and robustly.

A Preliminary Report of Gonadal-Sparing TBI Using a VMAT Technique

Reproductive toxicity is common after total body irradiation (TBI) and has major quality of life implications for patients. In that context, this is the first report of gonadal-sparing volumetric-modulated arc therapy (VMAT) TBI, successfully delivered in a boy and a girl with aplastic anemia. Both patients' VMAT TBI plans demonstrated improved gonadal sparing versus simulated conventional 2-dimensional (2D) approach (mean testes dose, 0.45 Gy VMAT vs 0.72 Gy 2D; mean ovary dose, 0.64 Gy VMAT vs 1.47 Gy 2D). Planning target volume coverage was also improved for both cases with the VMAT plan versus conventional 2D plan (2 Gy D90% vs 1.9 Gy D90%, respectively). Given these dosimetric advantages, the present study can serve as a proof-of-concept for further prospective studies evaluating this technique for wider applications in populations receiving TBI.

Standardized flattening filter free volumetric modulated arc therapy plans based on anteroposterior width for total body irradiation

In this work, the feasibility of using flattening filter free (FFF) beams in volumetric modulated arc therapy (VMAT) total body irradiation (TBI) treatment planning to decrease protracted beam‐on times for these treatments was investigated. In addition, a methodology was developed to generate standardized VMAT TBI treatment plans based on patient physical dimensions to eliminate plan optimization time. A planning study cohort of 47 TBI patients previously treated with optimized VMAT ARC 6 MV beams was retrospectively examined. These patients were sorted into six categories depending on height and anteroposterior (AP) width at the umbilicus. Using Varian Eclipse, clinical 40 cm × 10 cm open field arcs were substituted with 6 MV FFF. Mid‐plane lateral dose profiles in conjunction with relative arc output factors (RAOF) yielded how far a given multileaf collimator (MLC) leaf must move in order to achieve a mid‐plane 100% isodose for a specific control point. Linear interpolation gave the dynamic MLC aperture for the entire arc for each patient AP width category, which was subsequently applied through Python scripting. All FFF VMAT TBI plans were then evaluated by two radiation oncologists and deemed clinically acceptable. The FFF and clinical VMAT TBI plans had similar Body–5 mm D98% distributions, but overall the FFF plans had statistically significantly increased or broader Body–5 mm D2% and mean lung dose distributions. These differences are not considered clinically significant. Median beam‐on times for the FFF and clinical VMAT TBI plans were 11.07 and 18.06 min, respectively, and planning time for the FFF VMAT TBI plans was reduced by 34.1 min. In conclusion, use of FFF beams in VMAT TBI treatment planning resulted in dose homogeneity similar to our current VMAT TBI technique. Clinical dosimetric criteria were achieved for a majority of patients while planning and calculated beam‐on times were reduced, offering the possibility of improved patient experience.

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.

Organ sparing of linac-based targeted marrow irradiation over total body irradiation

PURPOSE

Targeted marrow irradiation (TMI) is an alternative conditioning regimen to total body irradiation (TBI) before bone marrow transplantation in hematologic malignancies. Intensity-modulation methods of external beam radiation therapy are intended to permit significant organ sparing while maintaining adequate target coverage, improving the therapeutic ratio. This study directly compares the dose distributions to targets and organs at risk from TMI and TBI, both modalities conducted by general-use medical linacs at our institution.

METHODS

TMI treatments were planned for 10 patients using multi-isocentric feathered volumetric arc therapy (VMAT) plans, delivered by 6 MV photon beams of Elekta Synergy linacs. The computed tomography (CT) datasets used to obtain these plans were also used to generate dose distributions of TBI treatments given in the AP/PA extended-field method. We compared dose distributions normalized to the same prescription for both plan types. The generalized equivalent uniform dose (gEUD) of Niemierko for organs and target volumes was used to quantify effective whole structure dose and dose savings.

RESULTS

For the clinical target volume (CTV), no significant differences were found in mean dose or gEUD, although the radical dose homogeneity index (minimum dose divided by maximum dose) was 31.7% lower (P = 0.002) and the standard deviation of dose was 28.0% greater (P = 0.027) in the TMI plans than in the TBI plans. For the TMI plans, gEUD to the lungs, brain, kidneys, and liver was significantly lower (P < 0.001) by 47.8%, 33.3%, 55.4%, and 51.0%, respectively.

CONCLUSION

TMI is capable of maintaining CTV coverage as compared to that achieved in TBI, while significantly sparing organs at risk. Improvement on sparing organs at risk permits a higher prescribed dose to the target or the maximum number of times marrow conditioning may be delivered to a patient while maintaining similar typical tissue complication rates.

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.

A step and shoot intensity modulated technique for total body irradiation

Introduction

Total body irradiation (TBI) is a part of the conditioning regimen for bone marrow transplant.At the Royal Marsden (Sutton, UK) and Rigshospitalet (Copenhagen, Denmark), we introduced a step and shoot IMRT (SS IMRT) technique for TBI. This technique requires no equipment other than that used to deliver other external beam radiation. In this paper, we describe this technique and report on data from the two clinics.

Materials and methods

The patients were positioned supine, supported by vacuum bag(s). The entire body of the patients were CT scanned with 5 mm slices. Multiple multi-leaf collimator (MLC) defined fields were used.In-vivo dosimetry was performed at the Royal Marsden for 113 patients.Calculated doses for 18 adult and 4 paediatric patients from Rigshospitalet were extracted.

Results

The in-vivo data from the Royal Marsden showed that the mean TLD measured dose difference was -1.9% with a standard deviation of 4.5%.SS IMRT plans for 22 patients from Rigshospitalet resulted in mean doses to the brain, lungs and kidneys all within the range of 11.1-11.8 Gy, while the V(12 Gy) was below 5% for the brain, 2% for the lungs and 0% for the kidneys.

Discussion

SS IMRT is feasible for TBI and can deliver targeted doses to the organs at risk.

Extended SSD VMAT treatment for total body irradiation

In this work, we develop a total body irradiation technique that utilizes arc delivery, a buildup spoiler, and inverse optimized multileaf collimator (MLC) motion to shield organs at risk. The current treatment beam model is verified to confirm its applicability at extended source‐to‐surface distance (SSD). The delivery involves 7–8 volumetric modulated arc therapy arcs delivered to the patient in the supine and prone positions. The patient is positioned at a 90° couch angle on a custom bed with a 1 cm acrylic spoiler to increase surface dose. Single‐step optimization using a patient CT scan provides enhanced dose homogeneity and limits organ at risk dose. Dosimetric data of 109 TBI patients treated with this technique is presented along with the clinical workflow. Treatment planning system (TPS) verification measurements were performed at an extended SSD of 175 cm. Measurements included: a 4‐point absolute depth‐dose curve, profiles at 1.5, 5, and 10 cm depth, absolute point‐dose measurements of an treatment field, 2D Gafchromic^® films at four locations, and measurements of surface dose at multiple locations of a Alderson phantom. The results of the patient DVH parameters were: Body‐5 mm D98 95.3 ± 1.5%, Body‐5 mm D2 114.0 ± 3.6%, MLD 102.8 ± 2.1%. Differences between measured and calculated absolute depth‐dose values were all <2%. Profiles at extended SSD had a maximum point difference of 1.3%. Gamma pass rates of 2D films were greater than 90% at 5%/1 mm. Surface dose measurements with film confirmed surface dose values of >90% of the prescription dose. In conclusion, the inverse optimized delivery method presented in the paper has been used to deliver homogenous dose to over 100 patients. The method provides superior patient comfort utilizing a commercial TPS. In addition, the ability to easily shield organs at risk is available through the use of MLCs.

Single-Dose Daily Fractionation Is Not Inferior to Twice-a-Day Fractionated Total-Body Irradiation Before Allogeneic Stem Cell Transplantation for Acute Leukemia: A Useful Practice Simplification Resulting From the SARASIN Study

PURPOSE

Total-body irradiation (TBI) is a major constituent of myeloablative conditioning regimens. The standard technique consists of 12 Gy in 6 fractions over a period of 3 days. The Standard-fractionation compAred to one-daily fRaction total body irrAdiation prior to tranSplant In LEUkemia patieNts (SARASIN) study aimed to compare standard fractionation with once-daily fractionation before transplant in leukemia.

METHODS AND MATERIALS

We retrospectively compared TBI regimens delivered in 2993 patients from the European Society for Blood and Marrow Transplantation database, who underwent transplantation between 2000 and 2014 for acute lymphoblastic leukemia (ALL, n = 1729) or acute myeloid leukemia (AML, n = 1264). TBI was delivered as either 12 Gy in 6 fractions (group 1, considered the reference group; 1362 ALL and 857 AML patients), 9 to 12 Gy in 2 fractions (group 2, 173 ALL and 256 AML patients), or 12 Gy in 3 to 4 fractions (group 3, 194 ALL and 151 AML patients).

RESULTS

The median follow-up was 60 and 84 months in ALL and AML patients, respectively. At 5 years, the leukemia-free survival rate, overall survival rate, relapse incidence, and nonrelapse mortality rate were 46.6%, 50.4%, 28.8%, and 24.6%, respectively, in ALL patients and 46.6%, 48.9%, 29.7%, and 23.6%, respectively, in AML patients. In multivariate analyses, the outcomes of groups 2 and 3 were not statistically different from those in group 1. The cumulative incidence of secondary malignancies (SMs) was significantly higher in group 2 (7.2%; P < 10^-6 for group 2 vs group 1). However, group 2 was not associated with an increase in SMs when we considered non-T-cell-depleted transplant patients.

CONCLUSIONS

We showed that the 12-Gy fractionated TBI dose delivered either in 2 fractions or in 1 fraction per day over a period of 3 to 4 days resulted in nonsignificant differences in disease control and survival. However, 1-day fractionation may be associated with a higher risk of mucositis and hemorrhagic cystitis. The absence of a significant difference in the SM incidence in the non-T-cell-depleted group should be interpreted with caution in the context of a retrospective study design. Our findings are important to consider for radiation therapy department organization. In-depth analyses of other nonlethal toxicities and late effects are required.