A technique for delivery of total body irradiation for bone marrow transplantation in adults and adolescents

An Evidence-Based Review of Total Body Irradiation

The purpose of this literature review is to investigate clinical treatment methods of total body irradiation within the context of a clinical department adopting a paediatric cohort with no existing technique. An extensive review of the literature was conducted using PubMed, Science Direct, Google Scholar, and Clinicians Knowledge Network. Articles were limited to nonhelical tomotherapy, nonparticle therapies, and those using hyperfractionated regimes. Total marrow irradiation was excluded because of national treatment and trial limitations. Of the numerous patient positioning methods present within the literature, the most comfortable and reproducible positioning methods for total body irradiation include both supine and the supine and/or prone combination. These positions increased stability and patient comfort during treatment, while also facilitating computed tomography data acquisition at the simulation stage. Ideally, dose calculations should be performed using a three-dimensional treatment planning system and quality assurance procedures that include in vivo dosimetry measurements. The available literature also suggests inhomogeneity correction factors and intensity modulation are superior to conventional open field techniques and should be implemented within developing protocols. Dynamic machine dose modulation is suggested to reduce department impact, removing the need for tissue compensators and accessory shielding devices, while providing significant improvements to treatment time and dose accuracy. Further long-term survival and intensity modulation studies are warranted, including direct comparisons of both dose modulation and treatment efficiency.

Total body irradiation with step translation and dynamic field matching

The purpose of this study is to develop a total body irradiation technique that does not require additional devices or sophisticated processes to overcome the space limitation of a small treatment room. The technique aims to deliver a uniform dose to the entire body while keeping the lung dose within the tolerance level. The technique treats the patient lying on the floor anteriorly and posteriorly. For each AP/PA treatment, two complementary fields with dynamic field edges are matched over an overlapped region defined by the marks on the body surface. A compensator, a spoiler, and lung shielding blocks were used during the treatment. Moreover, electron beams were used to further boost the chest wall around the lungs. The technique was validated in a RANDO phantom using GAFCHROMIC films. Dose ratios at different body sites along the midline ranged from 0.945 to 1.076. The dose variation in the AP direction ranged from 96.0% to 104.6%. The dose distribution in the overlapped region ranged from 98.5% to 102.8%. Lateral dose profiles at abdomen and head revealed 109.8% and 111.7% high doses, respectively, at the body edges. The results confirmed that the technique is capable of delivering a uniform dose distribution to the midline of the body in a small treatment room while keeping the lung dose within the tolerance level.

Dosimetric aspects of inverse-planned modulated-arc total-body irradiation

PURPOSE

To develop optimal beam parameters and to verify the dosimetric aspects of the recently developed modulated-arc total-body irradiation (MATBI) technique, which delivers an inverse-planned dose to the entire body using gantry rotation.

METHODS

The patient is positioned prone and supine underneath the gantry at about 2 m source-to-surface distance (SSD). Then, up to 28 beams irradiate the patient from different gantry angles. Based on full-body computed-tomography (CT) images of the patient, the weight of each beam is optimized, using inverse planning, to create a uniform body dose. This study investigates how to best simulate patients and the ideal beam setup parameters, such as field size, number of beams, and beam geometry, for treatment time and dose homogeneity. In addition, three anthropomorphic water phantoms were constructed and utilized to verify the accuracy of dose delivery, with both diode array and ion chamber measurements. Furthermore, to improve the accuracy of the new technique, a beam model is created specifically for the extended-SSD positioning for MATBI.

RESULTS

Low dose CT scans can be utilized for dose calculations without affecting the accuracy. The largest field size of 40 × 40 cm(2) was found to deliver the most uniform dose in the least amount of time. Moreover, a higher number of beams improves dose homogeneity. The average dose discrepancy between ion chamber measurements and extended-SSD beam model calculations was 1.2%, with the largest discrepancy being 3.2%. This average dose discrepancy was 1.4% with the standard beam model for delivery at isocenter.

CONCLUSIONS

The optimum beam setup parameters, regarding dose uniformity and treatment duration, are laid out for modulated-arc TBI. In addition, the presented dose measurements show that these treatments can be delivered accurately. These measurements also indicated that a new beam model did not significantly improve the accuracy of dose calculations. The optimum beam setup parameters along with the measurements performed to ensure accurate dose delivery serve as a useful guide for the clinical implementation of MATBI.

Dose compensation of the total body irradiation therapy

The aim of the study is to improve dose uniformity in the body by the compensator-rice and to decrease the dose to the lung by the partial lung block. Rando phantom supine was set up to treat bilateral fields with a 15 MV linear accelerator at 415cm treatment distance. The experimental procedure included three parts. The first part was the bilateral irradiation without rice compensator, and the second part was with rice compensator. In the third part, rice compensator and partial lung block were both used. The results of thermoluminescent dosimeters measurements indicated that without rice compensator the dose was non-uniform. Contrarily, the average dose homogeneity with rice compensator was measured within +/- 5%, except for the thorax region. Partial lung block can reduce the dose which the lung received. This is a simple method to improve the dose homogeneity and to reduce the lung dose received. The compensator-rice is cheap, and acrylic boxes are easy to obtain. Therefore, this technique is suitable for more studies.

TLD dose measurement: a simplified accurate technique for the dose range from 0.5 cGy to 1000 cGy

A simplified TLD technique characterized by high precision and reproducibility of dose measurement is presented. One hundred eighty LiF TLD rods 1 mm diam x 3 mm length as obtained from the manufacturer were annealed for 1 h at 400 degrees C followed immediately by 2 h at 105 degrees C. After exposure to a dose of 1 Gy of 4 MV x rays, TLDs were annealed for 15 min at 105 degrees C, then read out. TLDs were then sorted into five groups, ranging from 26 to 50 rods each with approximately equal sensitivity after correcting for the drift in the sensitivity of the TLD reader during the readout session. Maintaining group identity, the TLDs were again annealed, irradiated and read out. Fewer than 10% of the TLDs were removed from each group because the corrected readings differed from the respective group mean by more than 3.5%. The standard deviation of the readout was approximately 1.5% within each group. The planchet heater was not flushed with nitrogen gas. Various tests were performed to assess the stability of the group sorting technique and the linearity of TLD dose response. After reannealing, five TLDs were randomly drawn from one of the presorted groups, and subjected to various dose of 4 MV radiation over the range from 0.5 to 1000 cGy. This resulted in an average readout standard deviation of 1.2%. Response per unit dose was almost flat over the range from 0.5 cGy to 100 cGy, and increased by 15% over the range from 100 cGy to 1000 cGy. TLD sensitivity was affected by the duration of the anneal, but was virtually independent of the various time delays between irradiation, prereadout anneal, and readout. The group annealing and sorting (GAS) procedure provides a simple, reliable, precise, convenient, and accurate method for TLD measurements.

[Total body irradiation: techniques, dosimetry, and complications]

Total-body irradiation (TBI) has an established role in many preparative regimens used before bone marrow transplantation (BMT) in the treatment of hematological malignancies in children and adults. Better choice in TBI techniques and dosimetry have permitted better homogeneity of dose, and therefore a significant sparing of critical tissues. Advances in treatments over the past 20 years have greatly improved survival; therefore, the evaluation of early and late complications, with a sufficient follow-up, according to different conditioning regimens is important. In this article, we review and compare different TBI techniques and dosimetry, and their influence on the distribution and homogeneity of dose, and the possible relationship to the risk of complications. We also describe the acute and late effects of TBI in children and adults appearing in the first month post-BMT as veno-occlusive disease, interstitial pneumonitis, or after 3 months, i.e., endocrinal late effects and growth in children, cataracts, neurological and bone or other complications, secondary tumors and alteration in the quality of life. The responsibility of TBI in the increased rate of certain complications is difficult to assess from chemotherapy or allograft side effects (chronic graft vs. host disease) or from other associated medical treatments, such as long term steroid therapy.

Can a total body irradiation technique be fast and reproducible?

PURPOSE

Total body irradiation (TBI) is frequently a complex and time-consuming technique that significantly overloads Radiation Oncology departments. In an attempt to shorten TBI setup and treatment time we aimed to develop a system where the lung blocks are fixed with optimal precision to the build-up booster lucite screen while the patient is immobilized in a reproducible upright position.

METHODS AND MATERIALS

Fifteen patients diagnosed with leukemia were conditioned before bone marrow transplant since March 1992. Patients were immobilized in a semistanding position in a special stand with arm bars and hand grips. Treatment was delivered with a 6 MV x-ray horizontal beam. Six fractions of 2.25 Gy (mean instantaneous dose rate of 13.8 +/- 3.8 cGy/min) were delivered twice a day over 3 days (total dose: 13.5 Gy). Each fraction was given in alternating AP (facing the beam) and PA (turning the back) projections. Customized lung blocks (35% transmission) were used to assure a maximum lung dose of 10 +/- 0.5 Gy. The blocks were taped to a 1 cm thick lucite screen interposed between the source and the patient. Lung shields were checked by port films before each fraction. The reproducibility of the patient's positioning (and lung shielding) was evaluated by measuring the horizontal and vertical deviations of the infero-external corners of the lung blocks in the port films in relation to the same point in the simulation films. In vivo dosimetry (thermoluminescence and diodes) was performed by placing dosimeters and probes in the central axis and in several off-axis sites.

RESULTS

The mean horizontal and vertical deviations were 3.5 +/- 4.1 mm and 7.5 +/- 5.9 mm for the anterior fields, and 4.1 +/- 4.1 mm and 6.9 +/- 6.4 mm for the posterior fields. An acceptable position of the blocks was considered when deviations were < 5 mm horizontally and/or < 10 mm vertically. The mean time per fraction (i.e., interval between the patient's entering and leaving the treatment room) was 35 +/- 5 min.

CONCLUSIONS

A satisfactory level of reproducibility can be reached with this technique. The reasonably short treatment time contributes to reproducibility and patient comfort.

Total-body irradiation before bone marrow transplantation. Results of two randomized instantaneous dose rates in 157 patients

One hundred fifty-seven patients referred to the Department of Radiation Oncology of the Hôpital Tenon, Paris, France, between December 10, 1986 and December 31, 1989 for total-body irradiation (TBI) were treated according to the following two techniques: (1) either in one fraction (1000 cGy administered to the midplane at L4 and 800 cGy to the lungs) or (2) in six fractions (1200 cGy on 3 consecutive days to the midplane at L4 and 900 cGy to the lungs). The patients were randomized according to two instantaneous dose rates, called LOW and HIGH, in single-dose (6 versus 15 cGy/min) and hexafractionated (3 versus 6 cGy/min) TBI groups. There were 77 patients in the LOW group and 80 in the HIGH group, with 57 patients receiving single-dose TBI (28 LOW and 29 HIGH) and 100 patients receiving fractionated-dose TBI (49 LOW and 51 HIGH). In March 1991, the 4-year relapse-free and overall survival rates were 58.4% and 52.1%, respectively. The 4-year relapse-free survival and survival rates were 54.9% and 50.7% in the LOW group; 61.9% and 53.5% in the HIGH group (P = 0.69 and 0.82, respectively); 60.3% and 50.4% in the single-dose group; and 57.9% and 53.3% in the fractionated group (P = 0.65 and 0.78, respectively). There was no difference in the incidence of graft versus host disease, interstitial pneumonitis, or venoocclusive disease either between the LOW and the HIGH groups or between the single-dose and fractionated-dose TBI groups. The 4-year estimated cataract incidence was significantly higher in the single-dose HIGH instantaneous dose rate group than in the LOW instantaneous dose rate TBI group (P = 0.049). Multivariate analyses showed that instantaneous dose rate and fractionation do not influence the relapse-free and overall survival rates or the incidence of interstitial pneumonitis.