Comparison of different TBI techniques in terms of dose homogeneity

Introduction: Total body irradiation (TBI) is a form of external beam radiotherapy which is used in conjunction with chemotherapy with the purpose of immunosuppression. Since the target in TBI is the whole body so a uniform dose distribution throughout the entire body during TBI is necessary. As recommended by AAPM dose variation must be within ±۱۰% of prescription dose. A review was undertaken of clinical treatment techniques of TBI with purpose of assessment and comparison of dose distribution homogeneity in these methods.   Materials and Methods: This review article was conducted using PubMed, Science Direct and Google scholar. The articles were limited to megavoltage photon beams. Total marrow irradiation was excluded from the study.   Results: Numerous TBI techniques have been developed with the purpose of dose distribution homogeneity improvement. Some centers use opposed lateral fields and tissue compensators over thinner parts of the body to make homogeneity percent whitin۱۰%. Compensators are usually made of lead, while, some centers use rice bags as compensators to make dose homogeneity within ±۵%. Field-in-field technique is one of the recent methods that has been investigated by some departments. This technique dose not requires patient movement trough the treatment or secondary dose modulation equipment to make a homogeneous dose distribution. Arc therapy in a TBI technique that uses two generic arcs with rectangular segments to deliver TBI treatment dose with less than ۳% dose deviation was also performed. Translational couch (TC) technique is the technique that uses translational couch to administer total body irradiation reproducibly and safely. This system can replace the stationary anterior-posterior technique for providing better dose uniformity within the patient compared to fixed beam techniques. Dynamic field technique is a method that does not require additional devices or complex processes to overcome the space limitations of small treatment rooms. This technique can deliver a uniform dose distribution to the body midline in a small treatment room while keeping the lung dose within the tolerance level. Techniques mentioned above are some of the various methods witch are being used to improve dose distribution homogeneity in total body irradiation.   Conclusion: Although 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 implement the suitable and optimum method in each department. However, when only compare the technique in terms of homogeneity percent the best techniques are FIF and Arc-therapy with almost ±۳% homogeneity percent.