Journal of Medical Physics
LETTER TO EDITOR
Year
: 2013  |  Volume : 38  |  Issue : 4  |  Page : 210--211

Total body irradiation (TBI): Preliminary experience on clinical implementation


Ramamoorthy Ravichandran1, Johnson Pichy Binukumar1, Cheriyathmanjiyial Antony Davis1, Zakia Al Rahbi1, Rajan Balakrishnan2, Zahid Al Mandhari2,  
1 Medical Physics Unit, Royal Hospital, Muscat, Oman
2 Department of Radiation Oncology, Royal Hospital, Muscat, Oman

Correspondence Address:
Ramamoorthy Ravichandran
Medical Physics Unit, National Oncology Centre, Royal Hospital, PBox 1331, PC 111, Muscat
Oman




How to cite this article:
Ravichandran R, Binukumar JP, Davis CA, Al Rahbi Z, Balakrishnan R, Al Mandhari Z. Total body irradiation (TBI): Preliminary experience on clinical implementation.J Med Phys 2013;38:210-211


How to cite this URL:
Ravichandran R, Binukumar JP, Davis CA, Al Rahbi Z, Balakrishnan R, Al Mandhari Z. Total body irradiation (TBI): Preliminary experience on clinical implementation. J Med Phys [serial online] 2013 [cited 2023 Feb 8 ];38:210-211
Available from: https://www.jmp.org.in/text.asp?2013/38/4/210/121200


Full Text

Sir,

A recent publication [1] enumerated a dose analysis in the treatments with total body irradiation (TBI) through in-vivo dosimetry. In our hospital we started TBI last year, based on a protocol developed using the beam configuration and methods reported earlier. [2],[3] TBI is used as a conditioning regimen prior to bone marrow transplantation (BMT) for the management of various types of leukemia, malignant lymphoma, and aplastic anemia. TBI is also used in the treatment of systemic malignant spread and bone pain due to metastases. Before engraftment of donor bone marrow, pre-transplant conditioning is applied to eradicate the tumor cells or cells with genetic disorders. [4] Most common form of pre-transplant conditioning is a combination of high dose chemotherapy and TBI. TBI helps to prevent the failure of the graft by resulting in immune-suppression. Most of the radiotherapy clinics use 6 MV x-rays for these treatments with a prescribed total dose of 12 Gy in six fractions, at two fractions per day (separated by a minimum of 6 h) over 3 days. [4] A homogeneous dose within ±10% and treatment delivery to include skin to 100% dose are some of the other criteria. Dose delivered per min (dose rate) is a factor that influences biological effects of TBI, and the accepted practice is to keep the dose rate between 0.05 and 0.10 Gy/min (<10 cGy/min). [5]

Dosimetric aspects of magna field irradiations and use of entrance and exit detectors for clinical dosimetry are well discussed in literature. [6],[7],[8],[9] The effect of TBI dose fractionation on pulmonary complications was found insignificant with 12 Gy whole body dose delivered in six fractions in 3 days or in four fractions in 2 days. [10] A review of reports published on TBI from established centers [11] has shown biological effective dose to kidneys (BED kidney ) ranging from 14.0 to 28.0 Gy. Using regression analysis they indicated that there may be need for shielding kidneys at an equivalent dose of 16 Gy BED kidney .

TBI is carried out in our clinic using Clinac 600 CD linear accelerator at 4.0 m focus skin distance, along with a locally fabricated acrylic beam spoiler of dimensions 2.0 M × 0.7 M × 0.015 M. As reported earlier, a near perfect flat beam of specifications 100 ± 0.4% is achieved using an added flatness filter [2] at the exit portal of the linac. A pulse repetition rate of 100 MU/min setting, corresponded to a dose rate of 6.7 cGy/min at 4.0 m focus skin distance. At this treatment distance a diamond shaped magna field is achieved which has diverged enough to cover a patient total height of more than 2 m. The objective of the beam spoiler is to degrade the original quality of the 6 MV photon beam which has dose build up occurring at 15 mm. With the present treatment configuration, an entrance dose pattern 100, 99.4, 98.7, 96.8, and 94.7%, respectively at skin, 3, 5, 10, and 15 mm depths is achieved. For dose delivery calculations, 1.5 cm depth normalized percentage depth doses for the magna field are 100, 91.6, 78.6, 66.3, 55.1, and 45.7% at 1.5, 5, 10,15, 20, 25 cm depths, respectively. Attenuation factors for beam spoiler F BS (0.970) and beam flattening filter F FF (0.962) are to be applied on the measured dose/MU (6.84 cGy/100 MU) for treatment planning.

Treatment planning is carried out with computed tomography (CT) scan of the whole body, with 5 mm slices, with patients in supine position. The dose prescription is at the plane of umbilicus. Using radiological thickness estimates at skull, neck, shoulder, chest, umbilicus, knee and ankle levels, midplane doses at other levels are compensated to achieve dose uniformity, using 30 × 30 size acrylic plates. We standardized earlier a method for lung shielding for lateral recumbent positioning of the patients. [3] However, we found that for patient lying supine is more comfortable, and it can also facilitate for eye shielding, if necessary. Further, position of arm along the side can compensate for excess transmission of lung, due to its lower density. (Taking one-third tissue density equivalence for lung, our manual calculations showed that the extra thickness of hands at the lateral side compensated well for the effective radiological thickness of lung included in the path of the beam).

Three patients referred from Sultan Qaboos University Hospital received TBI treatments since 2012. A dedicated treatment table operated by direct current (DC) motor is used for patient set up. The monitor units required for 100 cGy at midplane were 2,412; 2,256; and 1,824 MU; respectively for each field in these three patients. One of the three patients had eye shielding during all six fractions. Direct patient dosimetry (DPD) was carried out using semiconductor detectors (Multi-dos, Scanditronix) in the first two fractions, to confirm efficacy of used acrylic plate compensator thickness and making fine adjustments. For clinical dosimetry, in vivo thermoluminescent detectors (TLD) were kept in the entry-exit locations at four planes representing skull, chest, umbilicus, and knee levels to estimate the delivered dose in TBI in all the six fractions, using method described in an earlier work. [12]

Our DPD dose estimates (represented by 2 nd fraction measurement) for the three patients showed good uniformity in doses delivered to the whole body. The midline dose estimates achieved for the three patients were 2.036 (±4.4%), 1.964 (±0.8%), and 2.006 (±0.02%) Gy, respectively for a planned dose of 2 Gy. The whole body TLD dose estimates (mean of all six fractions) were 2.05 (±7.0%), 2.00 (±3.4%), and 2.05 (±1.8%) Gy for three patients. It could be observed that our data on TBI dose delivery showed good uniformity as per clinical requirements. A published 'Medline search' [11] found the biological effective dose to kidneys (BED kidney ) in the range of 14.0-28.0 Gy for various TBI regimens. By a regression analysis fit, a recommendation was made indicating the need for kidney shielding at an equivalent dose of 16 Gy BED kidney . Our planned dose of 12 Gy in six fractions/3 days has an equivalent BED kidney 20.2 Gy in comparison to the recently published cohort of patients (12 Gy in eight fractions/4 days with BED dose of 19.25 Gy). [1] This is due to same dose of 12 Gy delivered in larger number of fractions in 4 days. From the experience in positioning first two taller patients for treatment, we felt the need for increasing the diagonal field size of 180√2 = 254 cm by using source to skin distance (SSD) 4.5 M. The MU/min may also be changed to 200 MU/min which will give 9.87 cGy/min at 4.5 M, which is still within the accepted dose rate for TBI (<10 cGy/min). [5] This brief communication highlights the salient features of TBI technique implemented at our hospital which conformed to our clinical specifications.

 Acknowledgement



Authors thank Sultan Qaboos University Hospital for patients referral and Director General, Royal Hospital for kind permission obtained for the study and for publishing the initial experience.

References

1Ganapathy K, Kurup PG, Murali V, Muthukumaran M, Bhuvaneshwari N, Velmurugan J. Patient dose analysis in total body irradiation through in vivo dosimetry. J Med Phy 2012;37:214-8.
2Ravichandran R, Binukumar JP, Davis CA, Sivakumar SS, Krishnamurthy K, Mandhari ZA, et al. Beam configuration and physical parameters of clinical high energy photon beam for total body irradiation (TBI). Physica Medica 2011;27:163-8.
3Ravichandran R, Binukumar JP, Davis CA, Zahid AM, Rajan B. Simple technique for fabrication of shielding blocks for total body irradiation at extended treatment distances. J Med Phys 2009;34:223-5.
4Lin H, Drzymala RE. In: Perez CA, Brady LW editors. Principles and practice of radiation oncology. 3 rd ed. Philadelphia: Lippincot-Raven Pubs; 1997. p. 333-41.
5Appelbaum FR. The influence of total dose, fractionation, dose rate and distribution of total body irradiation on bone marrow transplantation. Semin Oncol 1993;20(4 Suppl 4):3-10.
6Podgorsak EB, Pla C, Evans MD, Pla M. The influence of phantom size on output peak scatter factor, and percentage depth dose in large-field photon irradiation. Med Phys 1985:12:639-45.
7Podgorsak EB, Podgorsak MB. Special procedures and techniques in radiotherapy. Total body irradiation. In: Radiation Oncology Physics: A Handbook for Teachers and Students. Vienna: IAEA Pubs; 2005. p. 516-22.
8Van Dyk J, Galvin JM, Glasgow GP and Podgorsak EB. The physical aspects of total and half body photon irradiation. A report of Task group 29. AAPM 1986.
9Khan. FM. Total body irradiation. In: The Physics of Radiation Therapy. 3 rd ed. Philadephia: Lippincott Williams and Wilkins; 2003. p. 455-63.
10Izawa H, Hirowatari H, Yahata Y, Hamano Y, Ito K, Saito AI, et al. Effect of dose fractionation on pulmonary complications during total body irradiation. J Radiat Res 2011;52:502-8.
11Kal HB, van Kempen-Harteveld ML. Renal dysfunction after total body irradiation: Dose-effect relationship. Int J Radiat Oncol Biol Phys 2006;65:1228-32.
12Bloemen-van Gurp EJ, Mijnheer BJ, Verschueren TA, Lambin P. Total body irradiation, toward optimal individual delivery: Dose evaluation with metal oxide field effect transistors, thermoluminescence detectors and a treatment planning system. Int J Radiat Oncol Biol Phys 2007;69:1297-304.