Total Body Irradiation Technique Research Articles

Total Body Irradiation – Comparison of Outcome after Various Techniques of Irradiation and Shielding: A Polish Lymphoma Research Group (PLRG) Multicenter Study

The aim of the study was to compare the efficiency and side effects of total body irradiation (TBI) performed with various techniques in hematology and radiotherapy centers across the country. Three radiotherapy departments performing TBI and five hematology centers performing hematopoietic stem-cell transplantation (HSCT) responded to invitation to the study. Patients conditioned with TBI before HSCT between 2005 and 2010 irrespective of diagnosis were included. Technique of irradiation, dosage, dose rate and usage of lung and lens shields were recorded and analyzed in the context of occurrence of radiation-induced pneumonitis, lung fibrosis, cataract and localization of the recurrence on relation to shields. Patients in whom follow-up data were not available were excluded from the study leaving 138 subjects for further analysis. Three TBI techniques were analyzed: a pair of AP-PA fields with lung and lens shielding, and two variations of four-field box technique, one with standard lung shielding and electron boosts to supplement the chest dose and the other with lung dose reduction to 11 Gy; both without lens shielding. The total dose was 12 Gy: 4 Gy/fx once daily (lung dose approximately 6 Gy) in the first scheme, in the other two 2 Gy/fx bid with approximate lung dose of 11 and 8.5 Gy, respectively. Pneumonitis within the first 6 months after TBI was reported in 15.2% of patients: in 42% with minimum shielding and in 11.1% with standard shielding (p<0.05), lung fibrosis in 3.6% (2.5 and 10.4%, respectively, ns.). The incidence of pneumonitis did not differ between children and adults. In 12.3% of patients a recurrence within the 1st year after TBI was reported, in two in the brain only, and both had lens shielding. Only one case of cataract was reported in a patient with lens shielding. The purposefulness of lens shields application demands reevaluation as they do not seem to significantly reduce the cataract rate whereas partial shielding of the brain can be associated with isolated CNS recurrence in lymphoma patients. Utilization of TBI techniques with more strict lung sparing is associated with reduced pneumonitis rate and does not jeopardize the outcome.

A step and shoot intensity modulated technique for total body irradiation.

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

Modulated volumetric arc therapy for total marrow irradiation: A feasibility study in the oncology hospital of CMN SXXI from a medical physics approach.

The objective of this study is to explore the use of volumetric arc therapy (VMAT) to perform total marrow irradiation (TMI) and compare its results to the standard TBI technique in the Mexican public health system. The standard total body irradiation (TBI) technique is used with chemotherapy as a method of a pre-transplant conditioning of the bone marrow. In this technique, the whole body of the patient is considered to be PTV and irradiated generating toxicities and raising concerns about possible development of radio-induced tumors. Through the use of simulation tomography of 12 patients previously treated with TBI, twelve different treatment plans were created with the proposed TMI technique and compared with the conventional protocol, the treatment plans were evaluated with a dose volume histogram analysis and quality assurance was evaluated with a portal dosimetry system using the gamma index criteria 3%/3mm. Experimental results show an increasing dose to 99% of PTV of up to 41.1% by using TMI with the VMAT technique. The mean average dose to PTV was increased up to 19.3%. The use of the new TMI technique caused an improvement in the mean average dose to 99% of the PTV as well the homogeneity of the dose distribution prescribed at the PTV while leading to a better reproducibility of the treatment. The Qa of all the plans met the criterion of gamma index 3mm-3%. The results analysis shows that the proposed TMI technique is feasible and applicable in the Mexican public health system.

Higher Reported Lung Dose Received During Total Body Irradiation for Allogeneic Hematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukemia Is Associated With Inferior Survival: A Report from the Children's Oncology Group

To examine the relationship between lung radiation dose and survival outcomes in children undergoing total body irradiation (TBI)-based hematopoietic stem cell transplantation (HSCT) for acute lymphoblastic leukemia on the Children's Oncology Group trial. TBI (1200 or 1320cGy given twice daily in 6 or 8 fractions) was used as part of 3 HSCT preparative regimens, allowing institutional flexibility regarding TBI techniques, including lung shielding. Lung doses as reported by each participating institution were calculated for different patient setups, with and without shielding, with a variety of dose calculation techniques. The association between lung dose and transplant-related mortality, relapse-free survival, and overall survival (OS) was examined using the Cox proportional hazards regression model controlling for the following variables: TBI dose rate, TBI fields, patient position during TBI, donor type, and pre-HSCT minimal residual disease level. Of a total of 143 eligible patients, 127 had lung doses available for this analysis. The TBI techniques were heterogeneous. The mean lung dose was reported as 904.5cGy (standard deviation, ±232.3). Patients treated with lateral fields were more likely to receive lung doses ≥800cGy(P<.001). The influence of lung dose ≥800cGy on transplant-related mortality was not significant (hazard ratio [HR], 1.78; P=.21). On univariate analysis, lung dose ≥800cGy was associated with inferior relapse-free survival (HR, 1.76; P=.04) and OS (HR, 1.85; P=.03). In the multivariate analysis, OS maintained statistical significance (HR, 1.85; P=.04). The variability in TBI techniques resulted in uncertainty with reported lung doses. Lateral fields were associated with higher lung dose, and thus they should be avoided. Patients treated with lung dose <800cGy in this study had better outcomes. This approach is currently being investigated in the Children's Oncology Group AALL1331 study. Additionally, the Imaging and Radiation Oncology Core Group is evaluating effects of TBI techniques on lung doses using a phantom.

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.

Total Body Irradiation Techniques: Patterns of Care with Advanced Technology

Total Body Irradiation Techniques: Patterns of Care with Advanced Technology

Monte-Carlo Based Total-Body Irradiation Using Linac-Based Volumetric Modulated Arc Therapy

To assess the accuracy, feasibility, and reliability of a total-body irradiation (TBI) technique with linac-based volumetric modulated arc therapy (VMAT) in patients with acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL). From 2015-2017, 26 patients (15 men, 11 women) with AML or ALL underwent allogenic stem-cell transplantation following TBI with linac-based VMAT technique, which consisted of three isocenters and three overlapping arcs for head first CT sets. We added one or two more overlapping arcs, depending on the height of the patient for feet first CT sets. Patient age ranged from 6-63 years with a mean and median age of 20.5 and 17.5 years, respectively. TBI dose was prescribed to 90% of the clinical target volume receiving 12 Gy in six fractions, at two fractions per day. Mean lung and kidney doses were restricted less than 10 Gy, and maximum lens dose less than 6 Gy. Dose rate was variable, and mean dose rate was 250 MU/min. Calculation parameters were grid spacing 0.4 cm, minimum segment width 0.5 cm, maximum 180 control points per arc, fluence-smoothing medium, statistical uncertainty 1.0% per calculation, gantry increment of 30°, and calculate dose deposition to medium. Patients were immobilized in supine position using customized thermoplastic masks for head support and a vacuum cushion for body support on an adjustable combined immobilization board. Laser-based optical surface-guided devices were used for patient positioning and intra-fraction motion detection. Quality assurance (QA) comprised the verification of the radiation plans via dose-volume histograms (DVH) based 3D patient QA system. Average mean lung dose was 9.7 ± 0.2 Gy, mean kidney dose 9.6 ± 0.2 Gy, maximum lens dose 4.5 ± 0.4 Gy, mean planning treatment volume (PTV) dose 12.7 ± 0.1 Gy, and heterogenity index of PTV was 1.16 ± 0.02 in all patients. Overall acute toxicity was low with only grade 1 and 2 morbidity: patchy mucositis in 16 (62%), nausea not requiring antiemetics in 12 (46%), headache in 11 (42%), fatigue in 9 (35%), neck pain in 8 (31%), xerostomia in 7 (27%), loss of appetite in 6 (23%), and faint or dull erythema in 4 (15%) patients. Grade 3 and more acute radiation toxicity was not observed. All patients are stil alive. When comparing plan and DVH-based 3D patient QA results, average differences of 3.4% ± 1.3 in mean kidney doses, 1.0% ± 0.7 in mean lung doses, and 0.9% ± 0.4 in mean target doses were observed. Linac-based VMAT simplifies the process of TBI, and is accurate, feasible, and reliable. Partial cone-beam CT and optical surface-guided system assure patient positioning. Moreover, up to 6-mm longitudinal misalignment does not cause an average more than 3.5% mean lung dose enhancement. DVH-based 3D patient dose verification QA was possible with linac-based VMAT showing small differences between planned and delivered doses.

Modification of a modulated arc total body irradiation technique: Implementation and first clinical experience for paediatric patients.

IntroductionTo implement the modulated arc total body irradiation (MATBI) technique within the existing infrastructure of a radiation oncology department. The technique needed to treat paediatric patients of all ages, some of whom would require general anaesthesia (GA).MethodsThe MATBI technique required minor modifications to be incorporated within existing departmental infrastructure. Ancillary equipment essential to the technique were identified and in some cases custom designed to meet health and safety criteria. GA equipment was also considered. To evaluate the effectiveness of the implemented technique, an audit of the cases clinically treated was conducted.ResultsA motorised treatment couch was designed to allow the patient to be positioned in stabilisation equipment at a height, then lowered to the floor to accommodate source‐to‐skin‐distances from 180 cm to 198 cm to treat the fixed 40 cm × 40 cm field size. Treatment couch design also facilitated positioning of the bespoke two‐part spoiler. While organ at risk dose is limited using a beam weight optimisation technique, the dose is further reduced using compensators placed close to the patient's skin on a 3D printed custom‐made support bridge. A digital radiography system is used to verify compensator position. Fifteen patients have been treated to date for various diseases using a variety of dose fractionations ranging from 2 Gy in a single fraction to 12 Gy in 6 fractions. Five patients have required GA due to age or behavioural issues.ConclusionThe modified MATBI technique and the equipment required for treatment delivery has been found to be well tolerated by all patients.

Improved dose homogeneity using electronic compensation technique for total body irradiation.

In total body irradiation (TBI) utilizing large parallel‐opposed fields, the manual placement of lead compensators has conventionally been used to compensate for the varying thickness throughout the body. The goal of this study is to pursue utilizing the modern electronic compensation (E‐comp) technique to more accurately deliver dose to TBI patients. Bilateral parallel‐opposed TBI treatment plans were created using E‐comp for 15 patients for whom CT data had been previously acquired. A desirable fluence pattern was manually painted within each field to yield a uniform dose distribution. The conventional compensation technique was simulated within the treatment planning system (TPS) using a field‐in‐field (FIF) method. This allows for a meaningful evaluation of the E‐comp technique in comparison to the conventional method. Dose–volume histograms (DVH) were computed for all treatment plans. The mean total body dose using E‐comp deviates from the prescribed dose (4 Gy) by an average of 2.4%. The mean total body dose using the conventional compensation deviates from the prescribed dose by an average of 4.5%. In all cases, the mean body dose calculated using E‐comp technique deviates less than 10% from that of conventional compensation. The average reduction in maximum dose using E‐comp compared to that of the conventional method was 30.3% ± 6.6% (standard deviation). In all cases, the s‐index for the E‐comp technique was lower (10.5% ± 0.7%) than that of the conventional method (15.8% ± 4.4%), indicating a more homogenous dose distribution. In conclusion, a large reduction in maximum body dose can be seen using the proposed E‐comp technique while still producing a mean body dose that accurately complies with the prescription dose. Dose homogeneity was quantified using s‐index which demonstrated a reduction in hotspots with E‐comp technique. Electronic compensation technique is capable of more accurately delivering a total body dose compared to conventional methods.

Dose calculation with MCNPX code for Total Body Irradiation technique in sitting and lying postures

Total Body Irradiation (TBI) is a radiotherapy technique used to destroy malignant cells in bone marrow transplant conditioning regimens. The aim of this work was to estimate the equivalent and effective doses in TBI computational scenarios to analyze the changes in these quantities for different sources (cobalt-60 source and 6 MV photon beam), postures of the phantom, irradiation geometries, backscatter factors, and attenuators. The simulations were performed in MCNPX code using hybrid phantoms from the University of Florida. The simulation results showed uniform equivalent doses for the phantoms in the lying posture. It is also observed that when the phantoms are closer to a wall, there is an additional dose contribution of up to 6.55% to organs near to this structure. When the lead attenuators for the lungs are not present in exposure scenarios, the equivalent dose increases by more than 20%. For the effective dose, the values are considerably higher for the left lateral projection due to the greater energy absorption by more radiosensitive organs. The results of the simulations reaffirm the data found in the literature about TBI procedures.

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

A study was undertaken to explore the use of volumetric modulated arc therapy (VMAT) for total body irradiation (TBI). Five patient plans were created in Pinnacle3 using nine 6 MV photon dynamic arcs. A dose of 12 Gy in six fractions was prescribed. The planning target volume (PTV) was split into four subsections for the head, chest, abdomen, and pelvis. The head and chest beams were optimized together, followed by the abdomen and pelvis beams. The last stage of the planning process involved turning all beams on and performing a final optimization to achieve a clinically acceptable plan. Beam isocenters were shifted by 3 or 5 mm in the left–right, anterior–posterior, and superior–inferior directions to simulate the effect of setup errors on the dose distribution. Treatment plan verification consisted of ArcCheck measurements compared to calculated doses using a global 3%/3 mm gamma analysis. All five patient plans achieved the planning aim of delivering 12 Gy to at least 90% of the target. The mean dose in the PTV was 12.7 Gy. Mean lung dose was restricted to 8 Gy, and a dose reduction of up to 40% for organs such as the liver and kidneys proved feasible. The VMAT technique was found to be sensitive to patient setup errors particularly in the superior–inferior direction. The dose predicted by the planning system agreed with measured doses and had an average pass rate of 99.2% for all arcs. VMAT was found to be a viable treatment technique for total body irradiation.

Comparison of Radiation-Induced Secondary Cancer Occurrence Rates for Major Organs Between Total Body Irradiation and Total Marrow Irradiation

We aimed to quantify radiation-induced secondary cancer occurrence risks from conditioning total marrow irradiation (TMI) for patients undergoing bone marrow transplant, and to compare the risks with those using the conventional total body irradiation (TBI) technique. We randomly selected 20 patients who received targeted TMI treatments prior to bone marrow transplant at our institution. Among them, 10 patients (5 male and 5 female) had prescription dose of 12 Gy to the skeletal bones, lymph nodes, and spleen, while the other 10 patients (5 male and 5 female) had escalated prescription dose of 20 Gy to the same targets as well as 12 Gy to the brain and liver. A conventional total body irradiation treatment plan was generated for each patient with prescription dose of 12 Gy, using AP and PA photon beams at extended source-to-surface distance with 50% transmission blocks for lung shielding, and local chest wall boost using electron beams. Secondary cancer risks were estimated using one linear model and two non-linear models (the linear-exponential and plateau models) for fifteen non-target organs. The model parameters were obtained from atomic bomb survivor data as well as historical secondary cancer occurrence data from radiotherapy treatments. At the 12 Gy dose level, all the fifteen organs had significantly lower mean dose in TMI plans compared to those with the TBI plans (average mean dose range: 28.2% - 79.2% relative to 12 Gy); using the linear-exponential model, the total radiation-induced secondary cancer risks for the organs evaluated were 135.7±8.1 for male and 198.6±13.4 for female with TMI plans, compared to 224.4±1.3 for male and 295.3±1.1 for female with TBI plans (unit: cancer occurrence per 10,000 people per year). At the 20 Gy dose level, all the organs except the female breast and skin had significantly lower mean dose in TMI plans than with the TBI plans (average mean dose: 35.3% - 82.3% relative to 12 Gy); the total secondary cancer risks for all the organs were 184.6±8.1 for male and 263.7±9.2 for female with 20-Gy TMI plans, compared to 223.0±2.3 for male and 293.2±1.3 for female with 12-Gy TBI plans (unit: cancer occurrence per 10,000 people per year). All the differences between TMI and TBI plans were statistically significant (p < 0.05 in all the paired t-tests). Similar relative risk reductions were obtained using the other two risk models. At both prescription dose levels, the top five organs with the highest secondary cancer risks were the colon, lung, stomach, bladder, and stomach. Based on existing models, significantly lower overall radiation-induced secondary cancer risks to major organs were expected with TMI treatments compared to conventional TBI treatments, even at escalated prescription dose levels.

Reduced incidence of interstitial pneumonitis after allogeneic hematopoietic stem cell transplantation using a modified technique of total body irradiation.

Allogeneic hematopoietic stem cell transplantation is a curative-intent treatment for patients with high-risk hematologic diseases. However, interstitial pneumonitis (IP) and other toxicities remain major concerns after total body irradiation (TBI). We have proposed using linear accelerators with rice-bag compensators for intensity modulation (IM-TBI), as an alternative to the traditional cobalt-60 teletherapy with lung-shielding technique (Co-TBI). Patients who received a TBI-based myeloablative conditioning regimen between 1995 and 2014 were recruited consecutively. Before March 2007, TBI was delivered using Co-TBI (n = 181); afterward, TBI was administered using IM-TBI (n = 126). Forty-four patients developed IP; of these cases, 19 were idiopathic. The IP-related mortality rate was 50% in the total IP cohort and 63% in the idiopathic subgroup. The 1-year cumulative incidences of IP and idiopathic IP were 16.5% and 7.4%, respectively; both rates were significantly higher in the Co-TBI group than in the IM-TBI group. Multivariate analysis revealed that Co-TBI was an independent prognostic factor for both total and idiopathic IP. In the acute myeloid leukemia subgroup, patients with different TBI techniques had similar outcomes for both overall and relapse-free survival. In conclusion, IM-TBI is an easy and effective TBI technique that could substantially reduce the complication rate of IP without compromising treatment efficacy.

A depth-sensing technique on 3D-printed compensator for total body irradiation patient measurement and treatment planning.

The purpose of total body irradiation (TBI) techniques is to deliver a uniform radiation dose to the entire volume of a patient's body. Due to variations in the thickness of the patient, it is difficult to produce such a uniform dose distribution throughout the body. In many techniques, a compensator is used to adjust the dose delivered to various sections of the patient. The current study aims to develop and validate an innovative method of using depth-sensing cameras and 3D printing techniques for TBI treatment planning and compensator fabrication. A tablet with an integrated depth-sensing camera and motion tracking sensors was used to scan a RANDO™ phantom positioned in a TBI treatment booth to detect and store the 3D surface in a point cloud format. The accuracy of the detected surface was evaluated by comparing extracted body thickness measurements with corresponding measurements from computed tomography (CT) scan images. The thickness, source to surface distance, and off-axis distance of the phantom at different body section were measured for TBI treatment planning. A detailed compensator design was calculated to achieve a uniform dose distribution throughout the phantom. The compensator was fabricated using a 3D printer, silicone molding, and a mixture of wax and tungsten powder. In vivo dosimetry measurements were performed using optically stimulated luminescent detectors. The scan of the phantom took approximately 30 s. The mean error for thickness measurements at each section of phantom relative to CT was 0.48 ± 0.27 cm. The average fabrication error for the 3D-printed compensator was 0.16 ± 0.15 mm. In vivo measurements for an end-to-end test showed that overall dose differences were within 5%. A technique for planning and fabricating a compensator for TBI treatment using a depth camera equipped tablet and a 3D printer was demonstrated to be sufficiently accurate to be considered for further investigation.

Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 10: Results from Canada Wide Survey on Total Body Irradiation Practice

Purpose:Total Body Irradiation (TBI) is delivered to a relatively small number of patients with a variety of techniques; it has been a challenge to develop consensus studies for best practice. This survey was created to assess the current state of TBI in Canada.Methods:The survey was created with questions focusing on the radiation prescription, delivery technique and resources involved. The survey was circulated electronically to the heads of every clinical medical physics department in Canada. Responses were gathered and collated, and centres that were known to deliver TBI were urged to respond.Results:Responses from 20 centres were received, including 12 from centres that perform TBI. Although a variety of TBI dose prescriptions were reported, 12 Gy in 6 fractions was used in 11 centres while 5 centres use unique prescriptions. For dose rate, a range of 9 to 51 cGy/min was reported.Most centres use an extended SSD technique, with the patient standing or lying down against a wall. The rest use either a “sweeping” technique or a more complicated multi‐field technique. All centres but one indicated that they shield the lungs, and only a minority shield other organs.The survey also showed that considerable resources are used for TBI including extra staffing, extended planning and treatment times and the use of locally developed hardware or software.Conclusions:This survey highlights that both similarities and important discrepancies exist between TBI techniques across the country, and is an opportunity to prompt more collaboration between centres.

Total body irradiation-an attachment free sweeping beam technique.

IntroductionA sweeping beam technique for total body irradiation in standard treatment rooms and for standard linear accelerators (linacs) is introduced, which does not require any accessory attached to the linac. Lung shielding is facilitated to reduce the risk of pulmonary toxicity. Additionally, the applicability of a commercial radiotherapy planning system (RTPS) is examined.Material and MethodsThe patient is positioned on a low couch on the floor, the longitudinal axis of the body in the rotational plane of the linac. Eight arc fields and five additional fixed beams are applied to the patient in supine and prone position respectively. The dose distributions were measured in a solid water phantom and in an Alderson phantom. Diode detectors were calibrated for in-vivo dosimetry. The RTPS Oncentra was employed for calculations of the dose distribution.ResultsFor the cranial 120 cm the longitudinal dose profile in a slab phantom measured with ionization chamber varies between 94 and 107 % of the prescription dose. These values were confirmed by film measurements and RTPS calculations. The transmittance of the lung shields has been determined as a function of the thickness of the absorber material. Measurements in an Alderson phantom and in-vivo dosimetry of the first patients match the calculated dose.Discussion and conclusionA treatment technique with clinically good dose distributions has been introduced, which can be applied with each standard linac and in standard treatment rooms. Dose calculations were performed with a commercial RTPS and should enable individual dose optimization.

TH‐EF‐BRB‐11: Volumetric Modulated Arc Therapy for Total Body Irradiation

Purpose:To develop a modern, patient‐comfortable total body irradiation (TBI) technique suitable for standard‐sized linac vaults.Methods:An indexed rotatable immobilization system (IRIS) was developed to make possible total‐body CT imaging and radiation delivery on conventional couches. Treatment consists of multi‐isocentric volumetric modulated arc therapy (VMAT) to the upper body and parallel‐opposed fields to the lower body. Each isocenter is indexed to the couch and includes a 180° IRIS rotation between the upper and lower body fields. VMAT fields are optimized to satisfy lung dose objectives while achieving a uniform therapeutic dose to the torso. End‐to‐end tests with a rando phantom were used to verify dosimetric characteristics. Treatment plan robustness regarding setup uncertainty was assessed by simulating global and regional isocenter setup shifts on patient data sets. Dosimetric comparisons were made with conventional extended distance, standing TBI (cTBI) plans using a Monte Carlo‐based calculation. Treatment efficiency was assessed for eight courses of patient treatment.Results:The IRIS system is level and orthogonal to the scanned CT image plane, with lateral shifts &lt;2mm following rotation. End‐to‐end tests showed surface doses within ±10% of the prescription dose, field junction doses within ±15% of prescription dose. Plan robustness tests showed &lt;15% changes in dose with global setup errors up to 5mm in each direction. Local 5mm relative setup errors in the chest resulted in &lt; 5% dose changes. Local 5mm shift errors in the pelvic and upper leg junction resulted in &lt;10% dose changes while a 10mm shift error causes dose changes up to 25%. Dosimetric comparison with cTBI showed VMAT‐TBI has advantages in preserving chest wall dose with flexibility in leveraging the PTV‐body and PTV‐lung dose.Conclusion:VMAT‐TBI with the IRIS system was shown clinically feasible as a cost‐effective approach to TBI for standard‐sized linac vaults.

The first Russian experience of TomoTherapy for total body irradiation in children

Background. Combination of total body irradiation (TBI) with chemotherapy is widely used technique for conditioning before hematopoietic stem cell transplantation for patient with hematological malignancies worldwide. Best results of patient’s survival were showed in comparison with conditioning regimen included only chemotherapy. Aim – development of TBI technique at children with the help of TomoTherapy equipment and including it to the conditioning protocol before allogenic bone marrow transplantation. Materials and methods. During the period between July 2014 and February 2016 radiation therapy was made for 38 patients. Treatment was performed daily, 2 times per day with single basic dose on extended target (PTV) 2 Gr to total focal dose 12 Gr. Taking into account potential sensitivity of healthy organs and based on literature data, the following risk organs were chosen: lungs, kidneys and anterior eye chamber. Results. All patients successfully passed the planned program of treatment. Follow-up period was from 0 to 21 months (average – 7.2 months). No one of the patients did not showed any toxic episodes from the critical organs (lungs, kidneys, eye lens). Conclusions. TBI on TomoTherapy equipment allows to provide maximal control on irradiation dose distribution in PTV with the decreasing of radiation for critical organs. This allows achieving the decreasing of possibility of serious complications of radiation therapy and high effectiveness of treatment.

Translating bed total body irradiation lung shielding and dose optimization using asymmetric MLC apertures.

A revised translating bed total body irradiation (TBI) technique is developed for shielding organs at risk (lungs) to tolerance dose limits, and optimizing dose distribution in three dimensions (3D) using an asymmetrically‐adjusted, dynamic multileaf collimator. We present a dosimetric comparison of this technique with a previously developed symmetric MLC‐based TBI technique. An anthropomorphic RANDO phantom is CT scanned with 3 mm slice thickness. Radiological depths (RD) are calculated on individual CT slices along the divergent ray lines. Asymmetric MLC apertures are defined every 9 mm over the phantom length in the craniocaudal direction. Individual asymmetric MLC leaf positions are optimized based on RD values of all slices for uniform dose distributions. Dose calculations are performed in the Eclipse treatment planning system over these optimized MLC apertures. Dose uniformity along midline of the RANDO phantom is within the confidence limit (CL) of 2.1% (with a confidence probability p=0.065). The issue of over‐ and underdose at the interfaces that is observed when symmetric MLC apertures are used is reduced from more than ±4% to less than ±1.5% with asymmetric MLC apertures. Lungs are shielded by 20%, 30%, and 40% of the prescribed dose by adjusting the MLC apertures. Dose‐volume histogram analysis confirms that the revised technique provides effective lung shielding, as well as a homogeneous dose coverage to the whole body. The asymmetric technique also reduces hot and cold spots at lung‐tissue interfaces compared to previous symmetric MLC‐based TBI technique. MLC‐based shielding of OARs eliminates the need to fabricate and setup cumbersome patient‐specific physical blocks.PACS number(s): 87.55.‐x, 87.55.de, 87.55.D‐

TBI Technique Improvements for Anesthetized Pediatric Patients Based on Near-Miss Incident Reporting

Purpose: To share our clinical experience of an optimized and comprehensive pediatric TBI technique. Methods and Materials: Through the use of incident learning, safety-critical areas were identified in our procedure for total body irradiation (TBI) for pediatric patients under anesthesia for bone-marrow transplant. The previous procedure lacked flexibility to accommodate various requests from the anesthesia team due to the wide range of patient sizes. To address this issue and to improve the process overall, we updated our procedure for TBI simulation, dosimetry planning, patient setup during treatment, and in vivo dosimetry. A simulation form was redesigned with additional detailed instructions and documentation requirements. The dose calculation procedure was reformulated to remove dependence on setup variations. Tissue compensation determination and therefore dose uniformity were improved by introducing rigorous calculation methods. Calculations were performed on 28 previously-treated patients to compare the dose uniformity using the new versus previous methods. Results: The new procedures improve interdepartmental communication, simplify the workflow, decrease the risk of treating patients in a setup that differs from that used during the simulation, and reduce dose heterogeneity. The new compensator design significantly improved patient dose uniformity: 0.8% ± 0.4% (new method) vs. 4.2% ± 2.3% (previous method) (p Conclusion: A near-miss incident reporting system was used to improve the safety and quality of pediatric TBI procedures under anesthesia.