Total Body Irradiation Conditions Research Articles

Commissioning of 6 and 10 MV Beams for Total Body Irradiation (TBI)

The objective of the TBI treatment is the ablation of the bone marrow and the destruction of the circulating leukemia cells, once they are widely distributed throughout the body. Using beam parameters acquired under conventional SSD in TBI treatments may add non-negligible uncertainties in the monitor units calculation or in the beam profiles. The study, aims to commission the 6 and 10 MV photon beams, of the Varian accelerator CX model. A slab phantom and dosimetric assembly were used under TBI conditions. The accuracy of the TPS was evaluated against the experimental data. A set of data were acquired, highlighting the TPR table and methodology for calculating MU has been implemented. The TPS has presented a statistical uncertainty of ± 2.7 % compared to the experimental data for monitor unit calculation. The use of an acrylic spoiler has been shown to be clinically advantageous where, for a 6 MV beam, the entrance PDD was 75 % without a spoiler and 99.5 % with a spoiler. For a 10 MV beam, it was verified that without a spoiler, the entrance PDD was about 55 %, but with a spoiler, it was about 93 %. For medium Heterogeneous the TPS underestimated dose values by up to - 3.5 % with a mean deviation of – 2.9 %, for 6 MV and for 10 MV, the TPS overestimated the dose values by up to 1.1 %, with an average deviation of 1.0 % using the acrylic thorax phantom. The data obtained can be used clinically.

Quantitative Evaluation of the Reduced Capacity of Skeletal Muscle Hypertrophy after Total Body Irradiation in Relation to Stem/Progenitor Cells.

The effects of total body irradiation (TBI) to the capacity of skeletal muscle hypertrophy were quantified using the compensatory muscle hypertrophy model. We additionally assessed the responses of stem and/or progenitor cells in the muscles. A single TBI of 9.0, 5.0 and 2.5 Gy was delivered to C57BL/6 mice. Bone marrow stromal cells were obtained from GFP-Tg mice, and were injected into the tail vein of the recipient mice (1 × 106 cells/mouse), for bone marrow transplantation (BMT). Five weeks after TBI, the mean GFP-chimerism in the blood was 96 ± 0.8% in the 9 Gy, 83 ± 3.9% in the 5 Gy, and 8.4 ± 3.4% in the 2.5 Gy groups. This implied that the impact of 2.5 Gy is quite low and unavailable as the BMT treatment. Six weeks after the TBI/BMT procedure, muscle hypertrophy was induced in the right plantaris muscle by surgical ablation (SA) of the synergist muscles (gastrocnemius and soleus), and the contralateral left side was preserved as a control. The muscle hypertrophy capacity significantly decreased by 95% in the 9 Gy, 48% in the 5 Gy, and 36% in the 2.5 Gy groups. Furthermore, stem/progenitor cells in the muscle were enzymatically isolated and fractionated into non-sorted bulk cells, CD45-/34-/29+ (Sk-DN), and CD45-/34+ (Sk-34) cells, and myogenic capacity was confirmed by the presence of Pax7+ and MyoD+ cells in culture. Myogenic capacity also declined significantly in the Bulk and Sk-DN cell groups in all three TBI conditions, possibly implying that skeletal muscles are more susceptible to TBI than bone marrow. However, interstitial Sk-34 cells were insusceptible to TBI, retaining their myogenic/proliferative capacity.

Evaluation of sodium orthovanadate as a radioprotective agent under total-body irradiation and partial-body irradiation conditions in mice

Purpose Our previous study indicated that sodium orthovanadate (vanadate), a strong inhibitor of p53, effectively suppressed the lethality from the hematopoietic (HP) and gastrointestinal (GI) syndromes after 12 Gy total-body irradiation (TBI) in mice. This conclusion, however, was inconsistent with the fact that p53 plays a radioprotective role in the intestinal epithelium. The death after TBI of around 12 Gy was attributed to a combined effect of HP and GI syndromes. To verify the effect from prophylactic administration of p53 inhibitor on protection of HP and GI syndromes, in this study, the radioprotective effects from vanadate were investigated in TBI and lower half-body irradiation (partial-body irradiation: PBI) mouse models. Methods Female ICR mice were given a single injection of vanadate or vehicle, followed by a lethal dose of TBI or PBI. Radioprotective effects of vanadate against the irradiations were evaluated by analyzing survival rate, body weight, hematopoietic parameters, and histological changes in the bone marrow and intestinal epithelium. Results TBI-induced HP syndrome was effectively suppressed by vanadate treatment. After TBI, the vanadate-treated mice retained better bone marrow cellularity and showed markedly higher survival rate compared to the vehicle-treated animals. In contrast, vanadate did not relieve loss of intestinal crypts and failed to rescue mice from GI death after PBI. Conclusion Vanadate is a p53 inhibitor that has been shown to be beneficial as a radiation protective agent against HP but was not effective in protecting against acute GI radiation injury.

Comparison of calculated and measured basic dosimetric parameters for total body irradiation with 6- and 18-MV photon beams

AbstractPurpose:Total body irradiation (TBI) is an external beam radiation therapy in which large field size and extended source skin distances (SSDs) are applied to deliver a therapeutic dose to the whole body. As measurements in such situations are not common and have more uncertainties in comparison to standard dosimetry situations, it is more precise if calculated beam data can be used instead of measurements taken under TBI situations. The purpose of this study is to compare calculated beam data [percentage depth dose (PDD) and dose rate] with those obtained from simulated treatment measurements.Materials and methods:PDD and dose rates were measured for the 6- and 18-MV photon beams under TBI and standard conditions using 9,000 cm3 water phantom and ion chambers (Markus and Farmer). The results were then compared with the calculated PDD and dose rate data. The beam flatness was also measured under TBI and standard conditions for both 6- and 18-MV photon beams, and the results were then compared.Results:A comparison of the measurement and calculated beam data shows that the difference between calculated and measured PDD values is −6·97 and −4·14% for the 6- and 18-MV photon beams, respectively. The ratio of calculated to measured dose rate was 1·09 and 1·02 for the 6- and 18-MV photon beams, respectively. The beam flatness under TBI conditions was 4·59% for 6-MV and 5·37% for 18-MV photon beam, whereas under standard conditions, these values were 1·50 and 1·98% for 6- and 18-MV radiation beams, respectively.Findings:According to the results, due to a high error level in dose rate and PDD calculations, these parameters must be directly measured under TBI conditions; however, regarding the obtained results, direct measurement is not necessary for the 18-MV photon beam.

Comparison of dose distributions for 6MV and 15MV energy for Total Body Irradiation (TBI).

Introduction Contemporary radiotherapy uses a number of highly specialized irradiation techniques dedicated to well-defined clinical diagnoses. Among these methods are techniques to irradiate the skin (TSEI), bone marrow (TMI) or the whole body of the patient (TBI). TBI has over the last century been used in the treatment of a variety of conditions, both benign and malignant. However, its importance has increased with the development of knowledge about the impact of ionizing radiation on the human body and the development of clinical dosimetry techniques. At present, however, this method is primarily used in the treatment of hyperplasia.
 Aim The general aim of the study is to compare dose distributions at selected points of the anthropomorphic phantom under full body radiation conditions for X: 6MV and 15MV radiation. Specific objectives are defined: comparison of percent depth and function of photon emission profiles: 6MV and 15MV measured with radiofrequency hydrophobic films; measurement of doses in selected cross sections of the anthropomorphic phantom.
 Material and method
 A number of measuring devices and materials used in daily work by staff of the Medical Physics Department of the Greater Poland Cancer Centre were used to carry out the study part, but Alderson's anthropomorphic phantom and the radiochromic films in the form of point detectors were essential. In addition to each step of the research part, a special measuring system was prepared to reproduce the conditions prevailing during the TBI session as closely as possible. The research was carried out in three stages: Calibration of radiochromic films; PDD and OCR measurement for: 6MV and 15MV photon beam under TBI conditions; Measurement of dose distribution in selected anthropomorphic phantom's cross sections using radiochromic films in the form of point detectors.
 
 Results For the lateral field irradiated with 6MV photon beam, the maximum compliance (less than 2%) was obtained for the elbows at the entrance and in the center of the phantom; abdomen for the detector positioned in the center of the phantom, the lungs at the entrance and the arms in the middle, and the neck at the position of the film at the entrance. In the case of the lateral field X 15MV, the highest correspondence occurred for the points: the head and the PC in the position of the film in the center of the phantom and the entrance neck. In the case of AP/PA fields for 6MV energy, the highest compatibility was obtained for the mediastinum in all positions of the film. A small difference was also obtained for the points: head in the middle and at the output of the beam; as well as PC on the output. For AP/PA X 15MV fields, the highest dose compliance not exceeding 1% was obtained for the location of the neck - at the beam entrance, and the lung and mediastinum at the detector position at the center of the phantom.
 Conclusions On the basis of measurements of dose distribution at selected points of the patient's body for radiation X: 6MV and 15MV in the TBI procedure, the following conclusions can be made: Gafchromic EBT (radiochromic type film) can be successfully used for dosimetric measurements, among others. Due to their properties, such as the ability to cut from the sheet of film spot detectors of any shape and size, flexibility, low sensitivity to daylight, resistance to humidity, etc.; Their main drawback is the high cost of buying films and the long time required to prepare the detectors and then read the measured doses. Because of the low popularity of point-based EBTs in point dosing, further research is needed to improve their response to ionizing radiation. There is a noticeable increase in the difference between the dose calculated and measured as the distance between the position of individual detectors increases from the center point. The difference between the dose measured and planned in any of the cases examined does not exceed 9%. The measurements show that the method used is fast, accurate, and can be successfully used as a validation tool not only for the TBI procedure but also for other methods of cancer radiotherapy.

17. Evaluation of the EDD-53G diodes for their utilization in vivo dosimetry control during total body irradiation

Introduction During total body irradiation (TBI), the control of the dose received by the patient during each fraction of the treatment is necessary. The aim of this study was to verify that the EDD-53G diodes could be used in the TBI conditions and afterward to set up a measurement protocol for in vivo dosimetry during the fractions of treatment. Methods The diodes used were IBA’s EDD-53G (black) diodes with an OmniPro-InViDos supports DPD-12 electrometer. All measurements were made with the patient’s treatment conditions for a TBI: gantry at 270°, collimator at 45°, irradiation fields size 40 cm by 40 cm and source-skin distance (SSD) of 303 cm, 333 cm, 373 cm or 403 cm (clinically used SSD). Diode calibration was carried out with diodes placed at the input and the output of a phantom of 20 cm composed of RW3 polystyrene plaque with a FARMER ionization chamber (IBA FC65-P) positioned at mid-thickness. During the evaluation phase of the diodes, repeatability and reproducibility studies were carried out. The diodes angulation influence on the irradiation incidence and the diodes influence on each other were evaluated. A verification of the diode’s dose linearity was also carried out. Secondly, thickness correction factors (from 4 cm to 30 cm) were established at the four SSD, taking the patient’s different thicknesses compared to the reference conditions into account. Results In the study of the diodes angulation influence, an anisotropy of the diodes according to their rotation axis was established: relative mean deviation σ average = 1.2% (max deviation of 4%) σ average = 0.3% if the diode is always placed in accordance with the same axis. Therefore, the repeatability and reproducibility studies were carried out taking into account this effect and positioning the diode always at the same angle of incidence with the beam. These two studies yielded the following results: σ average = 0.08% for repeatability (σmax = 1.55%) and σ average = 0.88% for reproducibility (σmax = 0.11%). The diode presence in the vicinity of another did not show influence on the measurement (σ average = 0.09%). The response linearity of the diodes according to the delivered dose has been demonstrated (slope coefficient = 1.000 ± 0.001). For each SSD, a correction factor curve to be applied as a function of the thickness of the phantom was performed. Conclusions The first results obtained with these diodes were satisfying. Subsequently, an anthropomorphic phantom test is considered to verify the in vivo dosimetry measurement protocol with the diodes.

SU‐E‐T‐522: Investigation of Underdosage of Total Body Irradiation with Bilateral Irradiation Scheme

Purpose:Patient in‐vivo measurements report lower readings than those predicted from TMR‐based treatment planning on TBI patient knees and ankles where rice was placed to fill the gap between patient's legs. This study is to understand and correct the under dosage of Total Body Irradiation(TBI) with rice tissue equivalent bolus placement at TBI treatment patient setup.Methods:Bilateral TBI scheme was investigated with rice bags bolus placing between patient's two legs acting as missing tissue. In‐house TMR based treatment planning system was commissioned with measurements under TBI condition at 10MV, i.e. source‐to‐reference distance 383.4cm with 40×40cm field size with 1cm thickness Lucite. Predictions of patient specific dose points are reported at different sites with 200cGy prescription at patient umbilicus point. Solid water and rice bag phantoms are used at TBI conditions for the attenuation factor verification and CT scanned to verify the CT number and electron density.Results:We found that the rice bag bolus overall density is 11% lower than the water; however, the attenuation factor of rice bags could become 15% lower than that of water at TBI condition. This overestimate of rice bag electron density could cause the lack of lateral scatter and the lack of backscatter. This could Result in an overestimate of dose at in‐vivo dosimeter measurement points with TMR‐based treatment planning systems. Observations of patient specific optically stimulated luminescent dosimeters(OSLDs) were used to confirm this overestimation. Measurements of setups with increasing the rice bag filled patient leg separation were performed to demonstrate eliminating the overdose issue.Conclusion:Rice bolus has a lower electron density than water does(11%) but results in 15% lower in attenuation factor at TBI condition. This effect was observed in patient delivery with OSLD measurements and can be corrected by increasing the filling rice bolus thickness with 15% longer of separation.

SU‐E‐T‐485: In Vivo Dosimetry with EBT3 Radiochromic Films for TBI Treatments

Purpose:Total body irradiation (TBI) is a technique that requires special equipment to control “in vivo” the dose to the patient because it is a complex technique performed in extraordinary conditions. There are several devices to perform this task (diodes, TLDs, ionization chambers, MOSFET). In this paper we study the possibility of performing these measurements with radiochromic films EBT3 properly calibrated. This method has been compared to the PTW diodes system for TBI.Methods:Once made the TC to the patients, we measured different thicknesses of the relevant areas of the body (head, neck, chest with or without arms, umbilicus area, knees and ankles); for each of these thicknesses we measured dose rate (cGy / UM) in RW3 phantom, in TBI conditions, with ionization chamber in the center; in turn, the input diode and the output of each configuration is placed to assign dose to each set of diodes. Movie calibration is performed according to manufacturer's recommendations but TBI conditions. The dose at the center of each thickness compared to a linear interpolation of the dose at the entrance and exit, resulting in an adequate approximation. Finally in each session for each patient put a piece of film (2×2 cm2) at the entrance and another at the exit in each area, obtaining these readings and interpolating the estimated center dose, as with the diodes.Results:These results show a greater homogeneity in the distribution for use with film and validate the use of the same for this task and, if necessary, to avoid purchasing diode group if they have not.Conclusion:By using radiochromic films for this technique gives us a proper calculation of the dose received by the patient in the absence of other methods, or gives us a second additional track that already used normally.

SU-E-T-85: Total Body Irradiation (TBI) Optically Stimulated Luminescence In Vivo Dosimetry

Purpose: To adequately monitor the doses for Total Body Irradiation (TBI) patients using opposed fields, we carry out both active and passive in vivo dosimetry, with the passive dosimeter being Optically Stimulated Luminescence (OSL) detectors. The OSLs are embedded in hemispherical brass buildup caps with the OSL/flat surface placed against patient skin. The in vivo dosimetry devices are not repositioned when the patient is rotated, so both entrance and exit dosimetry are carried out, which arguably gives a better midline dose estimate, and improves marrow graft acceptance by minimizing treatment time. The OSLs were calibrated using a 100cm SAD entrance method with brass buildup caps. The buildup caps have a maximum density thickness of 6.6g/cm2; dmax for our 18MV beam is 3.4g/cm2. This method results in an overestimation of exit dose due to the density thickness differences, requiring a correction factor for exit measured doses. Methods: To determine the exit dosimetry correction factor, OSLs were placed on the entrance and exit sides of solid water phantoms under TBI conditions having thicknesses of 10, 30, and 49.2cm. Combinations of OSLs included entrance-only, exit-only and combined entrance and exit measured doses. The entrance and exit dose to the dosimeter position was calculated. Results: The exit dose correction factor calculated from the ratio of calculated to measured values was larger than anticipated (∼17%). The correction factor was applied to the exit dose calculations and compared to the combined measurement for verification. Results were within 1.2% (Table 1).The method was tested on ten patients, giving agreement within 1.1±4% (Table 2). Acceptable TBI tolerance is ±10%. Conclusion: While this is acceptable, we will consider using non-brass buildup caps to obtain smaller correction factors.

Total Body Irradiation Using a Modified Standing Technique: In Vivo Dosimetry with Semiconductor Diodes

The aim of this study was to establish a fast and simple online dosimetric verification method for total body irradiation (TBI) using semiconductor diodes. Twenty one patients were treated with fractionated TBI (12 Gy, 2 Gy BID) using a modified standing technique between February 2010 and March 2012. The prescribed dose was administered to the patient’s mid-plane at the level of the umbilicus. The lungs were shielded to allow only the absorption of an 8 Gy dose. To verify the dose administered during TBI, 12 semiconductor diodes were attached to the patient’s skin to measure the entrance and exit doses at six anatomical reference points (umbilicus, lungs, neck, forehead, hand, and knee). An adapted version of the arithmetic method which uses a correction factor was used to calculate the mid-plane doses from the entrance and exit dose measurements. The mid-plane doses were then compared with the expected doses. The results of in vivo dosimetry showed that the mid-plane dose calculations conducted using the adapted arithmetic method were consistent with the expectations of the treatment plan. The average percentage dose differences and standard deviations were -0.5 ± 5.3 % for the neck, -2.1 ± 3.7 % for the umbilicus, 2.8 ± 5.2 % for the forehead, and -5.9 ± 11.1 % for the lungs. The extremity doses (hand and knee) were not calculated in the treatment planning program; however they were measured for documentary purposes. In vivo dose verification under TBI conditions was efficiently conducted through the use of semiconductor diodes. The measurement results were consistent with treatment plan dose calculations. The modified standing technique provides a practical method for TBI treatments. The observed heterogeneity is acceptable, the technique does not require additional shields or bolus material, the dosimetric verification is simple and fast, the set-up of the patient is easily reproducible, and the treatment time is within the acceptable limits for a non-dedicated treatment machine.

SU-E-T-169: Initial Investigation into the Use of Optically Stimulated Luminescent Dosimeters (OSLDs) for In-Vivo Dosimetry of TBI Patients.

To report on an initial investigation into the use of optically stimulated luminescent dosimeters (OSLDs) for in-vivo dosimetry for total body irradiation (TBI) treatments. Specifically, we report on the determination of angular dependence, sensitivity correction factors and the dose calibration factors. The OSLD investigated in our work was InLight/OSL nanoDot dosimeters (Landauer Inc.). Nanodots are 5 mm diameter, 0.2 mm thick disk-shaped Carbon-doped Al2O3, and were read using a Landauer InLight microstar reader and associated software.OSLDs were irradiated under two setup conditions: a) typical clinical reference conditions (95cm SSD, 5cm depth in solid water, 10×10 cm field size), and b) TBI conditions (520cm SSD, 5cm depth in solid water, 40×40 cm field size,). The angular dependence was checked for angles ranging ±60 degree from normal incidence. In order to directly compare the sensitivity correction factors, a common dose was delivered to the OSLDs for the two setups. Pre- and post-irradiation readings were acquired. OSLDs were optically annealed under various techniques (1) by keeping over a film view box, (2) Using multiple scan on a flat bed optical scanner and (3) Using natural room light. Under reference conditions, the calculated sensitivity correction factors of the OSLDs had a SD of 2.2% and a range of 5%. Under TBI conditions, the SD increased to 3.4% and the range to 6.0%. The variation in sensitivity correction factors between individual OSLDs across the two measurement conditions was up to 10.3%. Angular dependence of less than 1% is observed. The best bleaching method we found is to keep OSLDs for more than 3 hours on a film viewer which will reduce normalized response to less than 1%. In order to obtain the most accurate results when using OSLDs for in-vivo dosimetry for TBI treatments, sensitivity correction factors and dose calibration factors should all be determined under clinical TBI conditions.

SU-E-T-239: In Vivo Dosimetry with Surface Diodes during Total Body Irradiation: A Patient Thickness Factor to Correct Midline Dose.

In vivo dosimetry (IVD) assessment of treatment dose is important when delivering total body irradiation (TBI). One method is to average AP and PA surface diode measurements and compare them to prescribed midline doses. We designed phantom studies to examine the impact of patient thickness on surface IVD measurements under TBI conditions. Phantom studies were designed to assess the effects of patient thickness on diode IVD. Sun Nuclear QED diodes with inherent buildup were placed on anterior and posterior surfaces of a solid water phantom. Phantom thickness was varied between 20 and 40 cm. A PTW farmer chamber was inserted in the center of the phantom at 425 SSD to reflect prescribed midline dose, and 50 cGy was delivered to midline with 18 MV photons. Averaged entrance and exit diode doses were then compared to farmer chamber measurements of phantom midline dose. A trend of increased deviation with increasing umbilicus thickness was observed between averaged surface diodes and midline farmer chamber measurements. Averaged surface diode dose ranged from 49.6 cGy (20 cm thickness) to 52.1 cGy (40 cm thickness). Interpolation of diode measurements to midline resulted in linear overestimation of delivered dose relative to farmer chamber measurements at midline, up to 6.8% at 40 cm umbilicus thickness. Accurate in vivo dosimetry at time of patient TBI is important to allow individual correction of MU exposure and tissue compensation. Without patient thickness correction, overresponse of surface diodes may lead to unnecessary clinical intervention to treatment MU or compensation and insufficient midline dose. Additionally, SAD setup is preferable to SSD setup to minimize thickness non-linearity. In conclusion, thickness correction factors should be used to generate expected diode readings for patients with thickness greater than 30 cm.

Étude de la dosimétrie in vivo par semi-conducteurs EPD-20 dans les conditions de l’irradiation corporelle totale

Purpose The objective of this work was the study of in vivo dosimetry performed in a series of 54 patients receiving total body irradiation (TBI) at the Salah-Azaiz Institute of Tunis since 2004. In vivo dosimetry measurements were compared to analytically calculated doses from monitor units delivered. Patients and method The irradiation was conducted by a linear accelerator (Clinac ® 1800, Varian, Palo Alto, USA) using nominal X-rays energies of 6 MV and 18 MV, depending on the thickness of the patient at the abdomen. The dose was measured by semi-conductors p-type EPD-20. These diodes were calibrated in advance with an ionization chamber “PTW Farmer” type of 0.6 cm 3 and were placed on the surface of plexiglas phantom in the same TBI conditions. A study of dosimetric characteristics of semi-conductors EPD-20 was carried out as a function of beam direction and temperature. Afterwards, we conducted a comparative analysis of doses measured using these detectors during irradiation to those calculated retrospectively from monitor units delivered to each patient conditioned by TBI. Results Experience showed that semi-conductors are sensitive to the angle of beam radiation (0–90°) and the temperature (22–40 °C). The maximum variation is respectively 5 and 7%, but in our irradiation conditions these correction factors are less than 1%. The analysis of the results of the in vivo dosimetry had shown that the ratio of the average measured doses and analytically calculated doses at the abdomen, mediastina, right lung and head are 1.005, 1.007, 1.0135 and 1.008 with a standard deviation “type A” respectively of 3.04, 2.37, 7.09 et 4.15%. Conclusion In vivo dosimetry by semi-conductors is in perfect agreement with dosimetry by calculation. However, in vivo dosimetry using semiconductors is the only technique that can reflect the dose actually received instantly by the patient during TBI given the many factors that calculation can not take into account: patient and organs motions and the heterogeneity of the targets.

Poster - Thurs Eve-39: Full 3D dose calculation for total body irradiation: A comparison study between treatment planning systems in homogeneous and heterogeneous conditions.

To perform full 3D heterogeneous dose calculations for total body irradiation (TBI) cases and compare different treatment planning softwares (TPS). A retrospective study was performed on 7 patients. Dose distributions obtained with Pinnacle3 v.7.9u (Philips Medical Systems) were compared with the ones calculated using our actual TBI planning system Theraplan Plus (TPP) by MDS Nordion/Nucletron. Two different Pinnacle3 models were studied: standard beam commissioning (std_Pinnacle3 ) and TBI commissioning (TBI_Pinnacle3 ). For the later case, commissioning was adapted for the special TBI conditions (extended SSD of 190cm, large field, acrylic beam spoiler, and out of field dose (OFD)). Significant differences are found between the TPP, std_Pinnacle3 and TBI_Pinnacle3 dose distributions. For the relative mid-line doses, differences up to 12% were observed. Systematic overestimations of 5% were found in patients extremities between TPP and TBI_Pinnacle3 . Average dose underestimation of 3% was observed between std_Pinnacle3 and TBI_Pinnacle3 . Differences in patient extremities are attributed to the OFD contribution which is not correctly computed in TPP and std_Pinnacle3 . Dose comparison outside the patient's mid-line showed greater differences (up to 20%) between models. Accurate 3D heterogeneous dose calculations with TBI_Pinnacle3 model show major differences (homogeneous versus heterogeneous) in high and low density regions. Dose overestimation of 5% was observed in bony regions and dose underestimation of 5% to 10% was observed in lung regions. Those results are of major interest since they show a strong dependence of the dose calculation outcome on both TPS and commissioning used, potentially leading to significant dose misevaluation.

Effect of total body irradiation on peri-implant tissue reaction: an experimental study.

The aim of the present study was to evaluate the osseointegration process under total body irradiation conditions (LD 50/30). Twenty Wistar rats (mean body weight: 90 g) were used. Under ethyl urethane intraperitoneal anesthesia (1 g/kg body weight), the animals were irradiated with a single 700 cGy dose (linear accelerator 6 Mev photons). Four days post irradiation, a titanium laminar implant was placed in the left tibia of each rat. Antibiotic therapy (ceftriaxone) was administered daily post implantation, to prevent infection by radiation. Fourteen days post implantation, the animals were killed by ether overdose. The tibiae were resected, radiographed and processed for embedding in methyl methacrylate. The results showed impaired osteogenesis and absence of osseointegration in experimental tibiae. This could be due to a direct action of total body irradiation on osteogenesis precursor cells. This effect would impair bone formation involved in peri-implant osseointegration processes in this experimental model.

Polarity effects of ionization chambers used in TBI dosimetry due to cable irradiation

This paper presents the results of an investigation on polarity effects in total-body irradiation (TBI) dosimetry. Thimble (NE2571, 0.6 cc) and plane-parallel (Markus NE2534 0.055 cc) chambers were investigated in a 30 × 30 × 30-cm 3 acrylic phantom in TBI conditions (6-MV x-rays). The thimble chamber was positioned at the midline and at the entrance and exit D max (1.5 cm from the phantom surface) levels. The Markus chamber, which is generally used for skin dose estimations, was positioned at various depths from the entrance surface of the phantom (from 0- to 2-cm depth). The polarity factor (P pol) was defined as (Q + + Q −)/2Q −, where Q + and Q − were the collected charges at positive and negative bias voltage, respectively. The variations of P pol with many parameters (absorbed dose, dose rate, the presence or absence of a 1-cm acrylic spoiler, irradiated cable length) were investigated. Results show that P pol is quite small (within 1.002 for on-axis measurements and 1.005 for off-axis measurements) for the NE2571 chamber when the beam spoiler is placed. P pol was significantly higher without the beam spoiler (within 1.008 for on-axis measurements, up to 1.02 for off-axis measurements). Concerning the Markus chamber, for on-axis skin dose measurements, P pol was found to be less than unity (around 0.988) or more than unity (around 1.0035), respectively, with and without the beam spoiler. Possible “directional effects” of the currents generated in the cable were investigated for both chambers and found to be insignificant. This shows that the application of P pol correction has to be considered a reliable procedure in minimizing these effects. When the beam spoiler is placed, the cable has to be drawn to minimize the portion of cable just outside the beam; if this is not the case, P pol may significantly vary (for the NE2571 chamber values up to 1.0035 were found for on-axis measurements).

Total body irradiation before bone marrow transplantation. Technique and acute toxicity.

To evaluate the total body irradiation methods in the National Institute of Oncology between January 1984 and February 1998. One hundred and twenty-four patients underwent total body irradiation prior to bone marrow transplantation in the last 15 years. A special cobalt unit has been used, the dose rate was 6 to 8 cGy/min in the midline of the abdomen. The source-midline distance (SMD) was 340 cm and the field size was 80 x 200 cm. The dose calculation was done on the basis of a tissue-phantom ratio curve measured in total body irradiation conditions and effective tissue thickness (ETT). Between 1984 and 1992 the beam direction was horizontal, the patients laid in lateral position. In 11 cases the total dose to the abdominal midline was 10 Gy in 1 fraction. From 1986 the fractionation changed to 4 x 3 Gy in 4 days. Within individual lung shielding the average lung dose was 8.5 Gy. In 44/124 cases the order of conditioning treatment was chemo-radiotherapy. Since 1992 vertical beams were used, and the patients (80/124) laid in prone/supine position. The fractionation remained the same but radio-chemotherapy regime has been used. The irradiation in prone position proved to be safer than lateral because of smaller patient motion and it resulted in a more accurate positioning of lung shielding too. In all cases, the acute side effects (headache, nausea, vomiting) were moderate. Using radio-chemotherapy the acute side effects during the total body irradiation were uncommon and well tolerable. Our technique with the large source-midline distance, vertical beam direction and the supine/prone position is stable, convenient and safe to produce homogeneous dose distribution and ensures accurate and reproducible lung shielding.

Calibration of a MOSFET Detection System for 6-MV In Vivo Dosimetry

Purpose: Metal oxide semiconductor field-effect transistor (MOSFET) detectors were calibrated to perform in vivo dosimetry during 6-MV treatments, both in normal setup and total body irradiation (TBI) conditions. Methods and Materials: MOSFET water-equivalent depth, dependence of the calibration factors (CFs) on the field sizes, MOSFET orientation, bias supply, accumulated dose, incidence angle, temperature, and spoiler-skin distance in TBI setup were investigated. MOSFET reproducibility was verified. The correlation between the water-equivalent midplane depth and the ratio of the exit MOSFET readout divided by the entrance MOSFET readout was studied. MOSFET midplane dosimetry in TBI setup was compared with thermoluminescent dosimetry in an anthropomorphic phantom. By using ionization chamber measurements, the TBI midplane dosimetry was also verified in the presence of cork as a lung substitute. Results: The water-equivalent depth of the MOSFET is about 0.8 mm or 1.8 mm, depending on which sensor side faces the beam. The field size also affects this quantity; Monte Carlo simulations allow driving this behavior by changes in the contaminating electron mean energy. The CFs vary linearly as a function of the square field side, for fields ranging from 5 × 5 to 30 × 30 cm 2. In TBI setup, varying the spoiler-skin distance between 5 mm and 10 cm affects the CFs within 5%. The MOSFET reproducibility is about 3% (2 SD) for the doses normally delivered to the patients. The effect of the accumulated dose on the sensor response is negligible. For beam incidence ranging from 0° to 90°, the MOSFET response varies within 7%. No monotonic correlation between the sensor response and the temperature is apparent. Good correlation between the water-equivalent midplane depth and the ratio of the exit MOSFET readout divided by the entrance MOSFET readout was found (the correlation coefficient is about 1). The MOSFET midplane dosimetry relevant to the anthropomorphic phantom irradiation is in agreement with TLD dosimetry within 5%. Ionization chamber and MOSFET midplane dosimetry in inhomogeneous phantoms are in agreement within 2%. Conclusion: MOSFET characteristics are suitable for the in vivo dosimetry relevant to 6-MV treatments, both in normal and TBI setup. The TBI midplane dosimetry using MOSFETs is valid also in the presence of the lung, which is the most critical organ, and allows verifying that calculation of the lung attenuator thicknesses based only on the density is not correct. Our MOSFET dosimetry system can be used also to determine the surface dose by using the water-equivalent depth and extrapolation methods. This procedure depends on the field size used.

Physical aspects of total-body irradiation at the Middlesex Hospital (UCL group of hospitals), London 1988 - 1993: I. Phantom measurements and planning methods

This paper, which is divided into parts I and II, describes the physical aspects of work on total-body irradiation (TBI) at the Middlesex Hospital, London, from 1988 to 1993. Irradiation is fractionated and bi-lateral with horizontal accelerator photon beams of 8 MV (1988 - 1992) at a source - surface distance (SSD) of 3.36 m and 10 MV (1992 - 1993) at an SSD of 4.62 m. The main aims were maximum patient comfort, a simple, accurate set-up with overall times per fraction of 30 min or less, dose homogeneity throughout the body within to , pre-irradiation treatment planning on nine CT slices using our commercial IGE RTplan (1988 - 1992) and Target 2 (1992 - 1993) treatment planning systems and, most important, verification of the plans by in vivo dosimetry to within . Verification of the planned lung doses, which are distributed over five CT slices, was given special attention. In part I of this paper we describe the preliminary work, most of which was done prior to patient treatment. This consisted of standard dosimetric measurements (central axis depth doses, beam profiles at several depths, build-up and build-down curves, beam output calibrations, effect of body compensators, etc), in evaluating silicon diode dosimeters for in vivo dosimetry and of adapting and verifying the methods of treatment planning for TBI conditions. The results obtained with phantoms, including a Rando body phantom, showed that, in principle, our aims could be achieved. The final proof depended, however, on an analysis of the results of the in vivo work and this forms the subject of part II of this paper.

Eye shielding for patients treated with total body irradiation

The incidence of cataracts in patients who have received total body irradiation (TBI) is about 20% and increases to 40% if the patient is treated for graft-versus-host disease. At our institution, all TBI patients are treated with two lateral opposed 24 MV photon fields. No attempt is usually made to shield the eyes during the TBI treatment because of the amount of lead required to adequately attenuate megavoltage photon beams, the difficulty in properly positioning an eye shield and the possibility of compromising the effectiveness of the treatment. However, we were asked to treat a TBI patient who is a professional pilot, and thus his livelihood is contingent upon maintaining perfect vision. A custom eye shield was constructed out of lead and ionization chamber and film measurements were performed under TBI conditions to determine the thickness and location of the eye block to optimize the competing effects of increased scatter and attenuation from the lead. Phantom data were also obtained for 6 MV irradiation for comparison with 24 MV. In-vivo patient and phantom measurements with thermoluminescent dosimeters showed that with visual positioning of the eye block the dose was reduced from 16 to 20% across the orbits of both eyes.