Total Body Irradiation Technique Research Articles

Image Guided Volumetrically Modulated Total Body Irradiation (TBI): Progress on Single Institution Phase 2 Clinical Trial

<h3>Purpose/Objective(s)</h3> TBI is a backbone of many conditioning regimens for hematopoietic stem cell transplants but can lead to both acute and late toxicity including radiation-induced interstitial pneumonitis. The incidence of idiopathic pneumonia syndrome (IPS) after TBI-based myeloablative conditioning regimens ranges from 7% to 35%. The purpose of this study is to implement image guided volumetrically modulated technique (VMAT) for TBI with the goal of lung sparing and improved target coverage. <h3>Materials/Methods</h3> Nine patients have been treated using image-guided VMAT based TBI at our institution as part of a single-arm phase 2 clinical trial for patients undergoing myeloablative conditioning regimens. The trial was approved by our internal review board (IRB) in September 2020 and aims to accrue 15 patients within one year. All patients enrolled in the trial have signed informed consent. The primary endpoints of the study are the following dosimetric constraints: V100% ≥ 90%, D98% ≥ 85% of Rx dose for the planning target volume (PTV), and a mean lung dose < 9 Gy. PTV is defined as the body contour cropped 5 mm from the surface and excluding lungs and kidneys but extended 3 mm into these organs. Additional secondary dosimetric endpoints include mean dose to each individual kidney < 11 Gy, and maximum dose to 2cc of the entire body < 130% of Rx dose. Clinical endpoints include the occurrence of IPS in the first 100 days after transplant, occurrence of acute graft versus host disease (GVHD), transplant related mortality or mortality in the first 100 days following transplant. <h3>Results</h3> Patients were treated to 12 Gy in 8 BID fractions (n = 6) or 13.2 Gy in 8 BID fractions (n = 3) over four consecutive days. All patients were able to complete treatment to the prescribed dose as planned. All patient plans met dosimetric constraints of the study. The median PTV V100% was 93.2% of Rx dose (Max: 95.6%, Min: 92.1%), the median PTV D98% was 90.2% of Rx dose (Max: 94.3%, Min: 88.3%), and the median lung dose mean was 7.63 Gy (Max: 7.94 Gy, Min: 7.29 Gy). In addition, individual kidney mean doses were < 11 Gy, and body maximum dose (D_2cc) was < 130% of Rx dose for all patients. At this time, only one patient (12 Gy treatment) has reached the 100 day post-transplant follow-up with the following findings: no relapse on bone marrow biopsy, no pneumonitis, resolved acute GVHD overall grade 1 (skin: 1, GI: 0, Liver: 0), resolved dermatitis (grade 1), resolved vomiting (grade 2), ongoing diarrhea and nausea (grade 1, previously grade 2). <h3>Conclusion</h3> Our initial results indicate that primary and secondary dosimetric endpoints were achievable for all protocol patients treated thus far. As the trial progresses, secondary clinical endpoints at 100 day follow-up will be analyzed to evaluate occurrence of IPS, survival, and treatment related toxicities.

Improved Organ Sparing with Autoplanned VMAT TBI

To evaluate dosimetric differences between Volumetric Modulated Arc Therapy (VMAT) and conventional 2D AP/PA Total Body Irradiation (TBI) techniques.Ten pediatric patients treated with a VMAT TBI technique on a C-arm Linac from November 2019 to August 2020 were included in this study. The VMAT TBI plans were generated using an in-house developed autoplanning script using a treatment planning system. For each VMAT TBI plan a corresponding 2D plan was created replicating our institution's current conventional AP/PA technique with the patient positioned standing in a booth at extended SSD with custom compensators to account for patient thickness variations in 8 regions on central axis, lung blocks with 50%-transmission and electron chest-wall boosts. The clinically relevant metrics in this study, including plan global Dmax, PTV V110%, lungs, and lungs contracted by 1cm (lungs-1 cm) Dmean were analyzed and compared between the VMAT TBI plans and simulated 2D plans. All dosimetric comparisons between the VMAT and 2D plans were made with the dose expressed as a percentage of the prescription dose (2Gy or 12 Gy) and the volume expressed as a percentage of the PTV volume. Paired t-test was used to compare the dosimetric indices between VMAT and 2D TBI plans.All VMAT TBI plans achieved D90%≥100% of prescription. PTV coverage, D90%, was reduced significantly (-6.2% ± 2.4%, P < 0.001) with the 2D plans, whereas no significant differences were observed between the 2D and VMAT global Dmax (P < 0.226) and PTV V110% (P < 0.444). Compared to 2D plans, VMAT TBI plans produced a significant decrease in the Dmean to the lungs and lungs-1cm volumes of -25.6% ± 11.5% (P < 0.001) and -34.1% ± 10.1% (P < 0.001), respectively. In addition to lungs, VMAT TBI technique enabled sparing of other organs: for 12 Gy prescription, kidneys Dmean of 64.7% ± 3.3% of prescription dose; for 2 Gy prescription, testes/ovaries Dmean of 31.6% ± 10.7%, brain Dmean of 74.8% ± 1.6% and thyroid Dmean of 72.5 ± 3.5% of prescription dose. Kidneys, gonads, brain and thyroid received the full prescription dose with 2D plans.Improved lung sparing with superior target coverage and similar global Dmax were observed with the VMAT plans as compared to 2D plans. In addition, VMAT TBI plans provided dose reduction in gonads, kidneys, brain and thyroid. Furthermore, VMAT TBI treatments were tolerated well by the patients in more comfortable supine position.

Dosimetric comparison of AP/PA and bilateral geometries for total body irradiation treatment.

Total body irradiation (TBI) is an external radiotherapy technique. Its aim is to deliver a therapeutic dose uniformly within ± 10% of the absorbed dose to the prescription point. In the present study, the TBI technique was implemented in anterior/posterior (AP/PA), and bilateral geometry with photons from a 6 [Formula: see text] and 18 [Formula: see text] accelerator. The TBI technique was implemented on an Alderson Rando phantom at 312 [Formula: see text] source surface distance. During bilateral fraction, rice bags were applied as tissue compensators. To reduce the lung's absorbed dose to the acceptance level, in AP/PA geometry lung blocks made of Cerrobend were used. The required monitor unit (MU) for each fraction was calculated regarding depending on the prescribed dose and beam output. Gafchromic EBT3 films were used for dosimetry between the phantom layers in eight selected points. It is demonstrated that dose uniformity for AP/PA geometry with 6 [Formula: see text] and 18 [Formula: see text] photons was within ± 10%. In contrast, for the bilateral geometry the dose uniformity was not acceptable for both studied energies; However, the results for 18 [Formula: see text] were better than those for 6 [Formula: see text]. Dose accuracy for all measurements was within ± 5 of the prescribed dose. The absorbed dose to the lungs was successfully reduced using the lung blocks. By combining different therapeutic geometries and energies over six fractions, the results of uniformity and accuracy of dose delivery could be improved. It is concluded that the introduced TBI method achieved good dose accuracy and acceptable dose uniformity. Lungs absorbed dose was lower than 10 [Formula: see text] using the lungs blocks. Based on these results, the TBI technique can now be implemented in radiotherapy at Tehran's Imam Hospital. The approach developed in the present study can be used and adapted to match with the conditions at other hospitals.

Practice Patterns of Pediatric Total Body Irradiation Techniques: A Children's Oncology Group Survey

The aim of this study was to examine current practice patterns in pediatric total body irradiation (TBI) techniques among COG member institutions. Between November 2019 and February 2020, a questionnaire containing 52 questions related to the technical aspects of TBI was sent to medical physicists at 152 COG 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 COG member radiation oncologists at the same institutions. 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 (69% response rate) responded. The anterior-posterior/posterior-anterior (AP/PA) technique was the most common technique reported (49 institutions [56%]); 44 institutions (50%) used the lateral technique, and 14 (16%) used volumetric modulated arc therapy or tomotherapy. Midplane dose rates of 6 to 15 cGy/min were most commonly used. The most common specification for lung dose was the midlung dose for both AP/PA techniques (71%) and lateral techniques (63%). Almost 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. There was no consistency in the practice patterns, methods for dose measurement, and reporting of TBI doses among COG institutions. The lack of standardization precludes meaningful correlation between TBI doses and clinical outcomes including disease control and normal tissue toxicity. The COG 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 COG centers.

Commissioning of a three-dimensional arc-based technique for total body irradiation.

The purpose of this study is to describe the commissioning of a novel three‐dimensional arc‐based technique for total body irradiation (TBI) treatments. The development and implementation of this technique allowed our institution to transition from a bilateral two‐dimensional (2D) technique to a methodology based on volumetric dose calculation. The methodology described in this work is a derivation from the MATBI technique, with the static fields being replaced by four contiguous arc‐fields for each anterior and posterior incidence. The reduced number of fields we employed makes it possible to reach a satisfactory dose uniformity through manual optimization in a straightforward process. We use the Eclipse anisotropic analytical algorithm (AAA) algorithm, commissioned with preconfigured beam data for a 6 MV photon beam, at standard SSD (100 cm). A thorough evaluation of the accuracy of the AAA algorithm at an extended distance (approximately 200 cm) was carried out. For the evaluation, we compared measured and calculated percentage depth–dose and profiles that included open‐field, penumbra, and out‐of‐field regions. The analysis was performed for both static and arc fields, taking into consideration unshielded fields and also in the presence of lung shielding blocks. End‐to‐end tests were carried out for our institutional template plan by two means: with a 2D ion chamber array detector in solid phantom and using Gafchromic films in an anthropomorphic phantom. The results obtained in this work demonstrate that the Eclipse AAA algorithm commissioned for standard treatments can be safely used with our TBI planning technique. Moreover, this technique proved to be a highly efficient path to replace conventional treatment techniques, providing a homogeneous dose distribution, dosimetric robustness, and shorter treatment times. In addition, as inherited from the MATBI technique, our methodology can be implemented in small treatment rooms, with no need for ancillary equipment.

Determining the incidence of interstitial pneumonitis and chronic kidney disease following full intensity haemopoetic stem cell transplant conditioned using a forward-planned intensity modulated total body irradiation technique

Purpose/ObjectiveTotal body irradiation (TBI) remains a key component of conditioning for allogeneic haemopoietic stem cell transplant (HSCT), with interstitial pneumonitis (IP) and chronic kidney disease (CKD) important late sequelae. We undertook a retrospective service evaluation of TBI patients treated with a forward-planned intensity modulated radiotherapy technique (FP IMRT). Material/Methods74 adult patients were identified; all received step and shoot FP IMRT TBI, 14.4 Gy in 8 fractions over 4 days. Mean doses to the lungs and kidneys were 12–12.5 Gy. Toxicities were defined as per CTCAE v4.0: IP as multilobar infiltrates on CT with symptoms of dyspnoea, and renal dysfunction as an Estimated Glomerular Filtration rate (eGFR) < 60 ml/min/1.73 m2 for > 3 months. Secondary endpoints were overall survival (OS), progression free survival (PFS), cumulative incidence of non-relapse mortality (NRM), relapse risk and of acute and chronic GvHD. ResultsPatients received treatment for the following diagnosis: ALL/LBL (n = 37); AML (n = 33), CML-BC (n = 2) and High grade NHL (n = 2). The rate of IP due to any cause was 30%; positive microbiological evidence in 73% (16 /22). Idiopathic IP was seen in 8%, with only 4% (n = 3) having IP Grade ≥ 3.Two (4%) of 52 long term survivors developed CKD, one with thrombotic microangiopathy.4 year NRM was 16% (CI 11–32%); no treatment related deaths in matched sibling or umbilical cord blood HSCT. ConclusionFP IMRT TBI, reducing dose to the lungs and kidneys, has lower rates of idiopathic IP and CKD compared to the literature. This technique is safe and effective conditioning for full intensity HSCT.

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

PurposeIn 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 MaterialsAs 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. ResultsAs old and more recent studies have shown, clinical protocols for TBI and TSI still vary considerably between institutions. ConclusionsNew radiation therapy technologies have been introduced relatively slowly for TBI purposes.

Comparison of different TBI techniques in terms of dose homogeneity – review study

Total body irradiation (TBI) is a kind of external beam radiotherapy, used in conjunction with chemotherapy with the purpose of immunosuppression. Since the target in TBI is the whole body, so achieving uniform dose distribution throughout the entire body during TBI is necessary. As recommended by AAPM dose variation must be within ±10% of the prescription dose. With the evidences from literature there is limited substantiation to consider a treatment method better than others, but with regard to the size of the treatment room, workload of the radiotherapy department and prevalent technology used within each treatment department it is recommended to make the suitable and optimum method in each department. In this work, a review study was performed on different TBI techniques with the purpose of assessment and comparison of dose distribution homogeneity in these methods.

Total body irradiation using helical tomotherapy: Set-up experience and in-vivo dosimetric evaluation

PurposeHelical Tomotherapy (HT) appears as a valuable technique for total body irradiation (TBI) to create highly homogeneous and conformal dose distributions with more precise repositioning than conventional TBI techniques. The aim of this work is to describe the technique implementation, including treatment preparation, planning and dosimetric monitoring of TBI delivered in our institution from October 2016 to March 2019. Material and methodPrior to patient care, irradiation protocol was set up using physical phantoms. Gafchromic films were used to assess dose distribution homogeneity and evaluate imprecise patient positioning impact. Sixteen patients’ irradiations with a prescribed dose of 12Gy were delivered in 6 fractions of 2Gy over 3 days. Pre-treatment quality assurance (QA) was performed for the verification of dose distributions at selected positions. In addition, in-vivo dosimetry was carried out using optically stimulated luminescence dosimeters (OSLD). ResultsPlanning evaluation, as well as results of pre-treatment verifications, are presented. In-vivo dosimetry showed the strong consistency of OSLD measured doses. OSLD mean relative dose differences between measurement and calculation were respectively +0,96% and −2% for armpit and hands locations, suggesting better reliability for armpit OSLD positioning. Repercussion of both longitudinal and transversal positioning inaccuracies on phantoms is depicted up to 2cm shifts. ConclusionThe full methodology to set up TBI protocol, as well as dosimetric evaluation and pre-treatment QA, were presented. Our investigations reveal strong correspondence between planned and delivered doses shedding light on the dose reliability of OSLD for HT based TBI in-vivo dosimetry.

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

AbstractBackground: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 Body Irradiation Among Recipients of Tcrαβ /CD19- Depleted Grafts in a Cohort of Children with Hematologic Malignances: Single Center Experience

Purpose: to analyze the radiation-induced organ-specific toxicity and survival outcomes in pediatric patients after hematopoietic stem cell transplantation (HSCT) with TCRαβ /CD19- depletion and myeloablative total body irradiation (TBI)-based conditioning regimen. Methods and Materials: We analyzed retrospectively a cohort of 197 patients (pts) with different hematological malignances. ALL - 150 pts: 1st CR - 40 pts; 2nd CR - 77; advanced - 33 pts; AML - 24 pts: active disease - 20 pts, 1st CR - 1 pt; 2nd CR - 3 pts; others (JMML, NHL etc.) - 23 pts. All the patients received allo-HSCT with TCRαβ /CD19- Depletion at Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology between 07/2014 and 04/2020. TBI (1200 cGy given twice daily in 6 fractions or once daily given in 4 fractions) was used as a part of HSCT conditioning regimens. The TBI technique included the irradiation of whole body using IMRT (TomoTherapy Helical System and IMRT Vmat on Elekta Linac) with following organ sparing: lungs, kidneys, lenses. The lung dose was prescribed as V8&amp;lt;40% (i.e the volume of each lung receiving 8 Gy, not to exceed 40%). The mean kidney dose was prescribed at &amp;lt; 8Gy. Forty-four patients received additional simultaneous integrated boost (SIB) up to 15 Gy or consecutive boost up to 18 Gy to different sites (bone marrow, etc.). Age of patients was from 3 to 21 y.o. (median - 10 y.o.). 26 pts were treated under anesthesia. Haploidentical HSCT was performed in 172 pts, allo-HSCT from matched unrelated donor was performed in 14 pts, from matched related donor - in 12 pts. We register acute toxicity (nausea/vomit/diarrhea, headache, veno-occlusive disease (VOD)) - during radiation therapy and 30 days after SCT, subacute toxicity - up to 100th day after SCT and late toxicity - at least 100 days after SCT according RTOG scale. Results: Follow-up period was from 0,3 to 7,2 years (median follow up period - 2 years). OS for all the patients was 66,7%±3,8%; EFS was 63,0%±3,6%; the transplant-related mortality rate was 8,9±2,1%. OS in patients with acute leukemia was 69,9±4,2% in ALL-group and 44,8±11,0% in AML-group (p=0,015). Mean survival time for patients with ALL was 4,3 years. EFS for pts with ALL was 66,7±4,1%; TRM = 8,4±2,3%. EFS for pts with AML was 43,1±10,3%; TRM = 16,3±7,5%. TRM in patients with 1st and 2nd CR was 5,5%±2,9%. TBI-related toxicity not significantly contribute to TRM, as most cases were infection-related. Acute toxicity during radiation therapy was registered among 100% of pts, in 97% of pts acute toxicity didn't exceed grade 1-2 according to RTOG scale. Among 3% of pts - grade 3 acute toxicity (nausea/vomiting/headache/diarrhea) was observed. We also registered VOD in 3 pts (all of them received SIB to bone marrow). Subacute toxicity was registered in 0.5% of patients (n=1) (interstitial pneumonia 3-4 stage according RTOG). Radiation-induced kidney toxicity was not registered. Conclusion: The developed TBI method included in conditioning regimen before allogenic SCT with TCRαβ /CD19-depletion in pediatric pts has tolerable organ-specific toxicity and predictable results of survival outcomes. Disclosures No relevant conflicts of interest to declare.

Towards homogenization of total body irradiation practices in pediatric patients across SIOPE affiliated centers. A survey by the SIOPE radiation oncology working group

Background and purposeTo reduce relapse risk, Total Body Irradiation (TBI) is part of conditioning regimens for hematopoietic stem cell transplantation (HSCT) in pediatric acute leukemia. The study purpose was to evaluate clinical practices regarding TBI, such as fractionation, organ shielding and delivery techniques, among SIOPE affiliated radiotherapy centers. MethodsAn electronic survey was sent out to 233 SIOPE affiliated centers, containing 57 questions about clinical practice of TBI. Surveys could be answered anonymously. ResultsFrom over 25 countries, 82 responses were collected. For TBI-performing centers, 40/48 irradiated ≤10 pediatric patients annually (range: 1–2 to >25). Most indications concerned acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML). Four different fractionation schedules were used, of which 12 Gy in 6 fractions was applied in 91% for ALL and 86% for AML. Dose reduction to the lungs, mostly to a mean dose of 8–10 Gy, was applied by 28/33 centers for ALL and 19/21 centers for AML, in contrast to much less applied dose reduction to the kidneys (7/33 ALL and 7/21 AML), thyroid (2/33 ALL and 2/21 AML), liver (4/33 ALL and 3/21 AML) and lenses (4/33 ALL and 4/21 AML). Conventional TBI techniques were used by 24/29 responding centers, while 5/29 used advanced optimized planning techniques. ConclusionAcross SIOPE, there is a high level of uniformity in fractionation and use of lung shielding. Practices vary regarding other organs-at-risk shielding and implementation of advanced techniques. A SIOPE radiotherapy working group will be established to define international guidelines for pediatric TBI.

A Novel AP/PA Total Body Irradiation Technique Using Abutting IMRT Fields at Extended SSD

A Novel AP/PA Total Body Irradiation Technique Using Abutting IMRT Fields at Extended SSD

Practice Patterns of Pediatric Total Body Irradiation (TBI) Techniques: A Children’s Oncology Group Survey

Practice Patterns of Pediatric Total Body Irradiation (TBI) Techniques: A Children’s Oncology Group Survey

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

Background and purposeTotal 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 methodsPatients 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.ResultsOptimization 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.ConclusionsWe 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.

Use of CT simulation and 3-D radiation therapy treatment planning system to develop and validate a total-body irradiation technique for the New Zealand White rabbit

Purpose Well-controlled ionizing radiation injury animal models for testing medical countermeasure efficacy require robust radiation physics and dosimetry to ensure accuracy of dose-delivery and reproducibility of the radiation dose-response relationship. The objective of this study was to establish a simple, convenient, robust and accurate technique for validating total body irradiation (TBI) exposure of the New Zealand White rabbit. Methods We use radiotherapy techniques such as computed tomography simulation and a 3 D-conformal radiation therapy treatment planning system (TPS) on three animals to comprehensively design and preplan a TBI technique for rabbits. We evaluate the requirement for bolus, treatment geometry, bilateral vs anterior-posterior treatment delivery, the agreement between monitor units calculated using the TPS vs a traditional hand calculation to the mid-plane, and resulting individual organ doses. Results The optimal technique irradiates animals on the left-decubitus position using two isocentric bilateral parallel-opposed 6 MV x-ray beams. Placement of a 5 mm bolus and 8.5 mm beam spoiler was shown to increase the dose to within ≤5 mm of the surface, improving dose homogeneity throughout the body of the rabbit. A simple hand calculation formalism, dependent only on mid-abdominal separation, could be used to calculate the number of monitor units (MUs) required to accurately deliver the prescribed dose to the animal. For the representative animal, the total body volume receiving > 95% of the dose, V95% > 99%, V100% > 95%, and V107% < 20%. The area of the body receiving >107% of the prescribed dose was mainly within the limbs, head, and around the lungs of the animal, where the smaller animal width reduces the x-ray attenuation. Individual organs were contoured by an experienced dosimetrist, and each received doses within 95–107% of the intended dose, with mean values ∼104%. Only the bronchus showed a maximal dose >107% (113%) due to the decreased attenuation of the lungs. To validate the technique, twenty animals were irradiated with four optically-stimulated luminescence dosimeters (OSLDs) placed on the surface of each animal (two on each side in the center of the radiation beam). The average dose over all animals was within <0.1% from intended values, with no animal receiving an average dose more than ±3.1% from prescription. Conclusion The TBI technique developed in this pilot study was successfully used to establish the dose-response relationship for 45-day lethality across the dose-range to induce the hematopoietic-subsyndrome of the acute radiation syndrome (ARS).

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.

Considerations and adaptions to the modulated arc total body irradiation technique: dosimetry description.

Total body irradiation (TBI) is a complex treatment technique, which has been slow to transition to a three‐dimensional (3D) planning approach. There is limited literature available providing a detailed description on methods to plan TBI on a 3D planning system. 3D planning using the modulated arc TBI (MATBI) technique is a complex process involving a significant number of quality assurance processes and scripts, due to more than 40 treatment beams and two patient positions. This article will focus on the workflow and technical planning aspects of our institution’s MATBI technique and identify reasons for modifications made to the developing institution’s original MATBI approach. Included is a description of specific simulation equipment, detailed explanation of the four‐stage computing process including the role of scripting to standardise and streamline what is otherwise a complex number of steps. The information provided is specific to one centre’s approach but shows the fundamental planning process and demonstrates a streamlined method, which can be adapted to other planning systems. Overall, the ability to accurately represent the TBI technique in 3D on a planning system will be shown.

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

Background and PurposeThe 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 methodsTBI 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.ResultsThe 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.ConclusionsTBI delivered with the topotherapy approach robustly guarantees adequate coverage and dose homogeneity. Semi-automatic clinical plans can be quickly generated and efficiently delivered.

TLI in pediatric patients.

Hematopoietic progenitor cell transplantation (HSCT) is a procedure used in different hematological diseases as part of the curative treatment, so the investigators propose a system of conditioning of reduced intensity based on total lymphoid irradiation (TLI) as an alternative to the classic total body irradiation (TBI) followed by haploidentical transplantation in patients compatible with a single HLA haplotype, as an alternative to patients who do not have an HLA compatible donor. A cohort of 25 patients with hematological disease underwent haploidentical HSCT from February 2015 to May 2018, conditioned with TLI from day -10 (2-4days of treatment) followed by thiotepa (5mg/kg/12h) and melphalan (70mg/m2/day) prior to HSCT and prophylaxis with ciclosporin (1.5mg/kg/12h). 2Gy/fraction was administered to complete 8Gy with IMRT and VMAT technique. 12% rejection of the transplant was obtained with acute GVHD < II (48%) and chronic GVHD 12%. No acute toxicity was recorded in irradiated patients and 56% survival of patients at the end of follow-up. Conditioning the haploidentical transplant with TLI, IMRT, and VMAT techniques compared with TBI and RT3D-C techniques is a feasible technique that helps inducing the necessary immunosuppression in patients with a high risk of graft rejection, minimal adverse effects, low incidence of GVHD, and high survival rate.