Implementation of a water compensator for total body irradiation

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 with a compensator fabricated using a 3D optical scanner and a 3D printer

We propose bilateral total body irradiation (TBI) utilizing a 3D printer and a 3D optical scanner. We acquired surface information of an anthropomorphic phantom with the 3D scanner and fabricated the 3D compensator with the 3D printer, which could continuously compensate for the lateral missing tissue of an entire body from the beam's eye view. To test the system's performance, we measured doses with optically stimulated luminescent dosimeters (OSLDs) as well as EBT3 films with the anthropomorphic phantom during TBI without a compensator, conventional bilateral TBI, and TBI with the 3D compensator (3D TBI). The 3D TBI showed the most uniform dose delivery to the phantom. From the OSLD measurements of the 3D TBI, the deviations between the measured doses and the prescription dose ranged from  -6.7% to 2.4% inside the phantom and from  -2.3% to 0.6% on the phantom's surface. From the EBT3 film measurements, the prescription dose could be delivered to the entire body of the phantom within  ±10% accuracy, except for the chest region, where tissue heterogeneity is extreme. The 3D TBI doses were much more uniform than those of the other irradiation techniques, especially in the anterior-to-posterior direction. The 3D TBI was advantageous, owing to its uniform dose delivery as well as its efficient treatment procedure.

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

PURPOSE

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.

METHODS

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.

RESULTS

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%.

CONCLUSIONS

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.

Total body irradiation dose optimization based on radiological depth

We have previously demonstrated the use of Eclipse fluence optimization to define aperture sizes for a novel aperture modulated translating bed total body irradiation (TBI) technique. The purposes of the present study were to identify, characterize, and correct for sources of error inherent in our previous fluence optimization technique, and to develop a clinically viable fluence optimization module for the translating bed TBI technique. Aperture modulated TBI is delivered by translating the patient at constant speed on a custom bed under a modulated radiation beam. The patient is then turned from supine to prone and the process repeated, resulting in an AP‐PA treatment. Radiological depths were calculated along divergent ray lines through individual CT slices of a RANDO phantom. Beam apertures, defined using a dynamic multileaf collimator (DMLC), were generated using calculated radiological depths and calibration factors that relate fluence to aperture size in a dynamic environment. These apertures were defined every 9 mm along the phantom superior‐inferior axis. The calculated beam apertures were further modified to account for scatter within the patient. For dose calculation purposes the individual MLC files were imported into Eclipse. For treatment delivery, dynamic MLC files for both AP and PA beams were generated and delivered dynamically. Dose homogeneity in the head and neck region of the RANDO phantom was within ± 4% of the prescribed dose with this novel technique compared to −5% to +7% with our previous aperture modulated technique based on Eclipse fluence optimization. Fluence optimization and beam aperture calculation using the new technique offers a ten‐fold reduction in planning time and significantly reduces the likelihood of user error during the planning process. In conclusion, a clinically viable aperture modulated translating bed TBI technique that employs dynamically shaped MLC‐defined beam apertures based on radiological depth calculations, has been developed.

PACS numbers: 87.55.‐x, 87.55.D‐

Comparison of total body irradiation before and after chemotherapy in pretreatment for hematopoietic stem cell transplantation

OBJECTIVE

To explore the best time to carry out total body irradiation (TBI) in hematopoietic stem cell transplantation (HSCT) pretreatment.

METHODS

Retrospective analysis was applied in 88 cases of HSCT using TBI as pretreatment from March 2001 to June 2009 in our hospital. Using 8 MV X-ray, all the patients were irradiated by linear accelerator in 2 consecutive days, with a total dose of 7-11 Gy and an instantaneous dose rate ranging between 4.0 and 5.0 cGy/min. Of the 88 cases, 40 cases were given traditional high-dose chemotherapy before TBI (Group CT/TBI), and 48 cases were given TBI before chemotherapy (Group TBI/CT) instead.

RESULTS

Eighty-seven cases of transplantation were successful, with no serious complications, including radiation pneumonia. Compared with Group CT/TBI, Group TBI/CT showed similar incidence of complications (p=0.08), similar recent chemotherapy toxicity (p=0.833), and significantly lower recent radiation toxicity (p=0.000).

CONCLUSIONS

TBI in the pretreatment of HSCT is safe and effective. Using TBI before the high-dose chemotherapy can maintain the same pretreatment effect, effectively reduce apparent immediate reaction/discomfort during TBI, reduce preparation workload of radiotherapy, and lower radiation side-effects. Further research is needed to expand its clinical application.