Problems and Solutions in Achieving Uniform Dose Distribution in Superficial Total Body Electron Therapy P. P. Kumar, MD, U. K. Henschke, MD, PhD, and J. Rao Nibhanupudy, MS Washington, D.C.
In treating mycosis fungoides (MF) and Sezary syndrome patients with electron beam, the entire thickness and the area of the skin from crown to sole should be irradiated uniformly. To achieve irradiation of the entire thickness of the skin, electron beams of 3 4 MeV energy with 80 percent depth dose at 6 mm is sufficient. This unique property of limited penetration of electron beam does not cause any systemic toxicity during or after total body electron therapy. However, this property of limited penetration of electrons poses the problem of self-shielding in the curvaceous human body. The optic lens, which is within the range of penetrability of electron beam energy used for total body electron therapy, is to be shielded artificially. The purpose of this paper is to discuss the problems of self and artificial shielding in the superficial total body electron therapy for MF and Sezary syndrome. The advantages of limited penetrability of electron beam were explored by Trump, Van de Graaff, and Cloud and, in 1953, Trump and associates at MIT successfully used electron beam from a low megavoltage Van de Graaf accelerator for total body electron therapy of mycosis fungoides patients.' At the time, the fixed Van de Graaff machine could only produce electron beams in a downward direction with a limited distance between the machine and the floor. Because of these limitations, the patients were moved through a fixed narrow downward beam to achieve total body irradiation. After the development of movable machines, total body electron beam therapy is given in Dr. P. P. Kumar is Associate Professor, Dr. U. K. Henschke is Professor and Chairman, and J. Rao Nibhanupudy a Physicist in the Department of Radiotherapy, Howard University Hospital. Requests for reprints should be addressed to Dr. P. P. Kumar, Department of Radiotherapy, Howard University Hospital, 2041 Georgia Avenus NW, Washington, D.C. 20060.
a standing position. To achieve uniform dose distribution over the entire body surface, various techniques were used, with different fields on patients in different positions.2-7 Phantom studies done by Bjarngard et a18 and our studies on patients9 showed that the multiple-field technique is superior to the two-field technique in achieving better dose distribution. Clinical experience shows that this is not possible in the human body for two good reasons. First, the patient is not a phantom and cannot remain motionless over long periods of time during electron beam therapy and, second, the human body, though beautiful, is very irregular with ups and downs and folds and creases.
Materials and Methods To overcome the problem of uneven dose distribution due to overlapping of fields in the four-field technique8 and inability of the patient
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9, 1977
to remain motionless for long periods of time, we adopted the patient rotation technique. In this technique, the patient stands on a platform which rotates at the rate of 5 rpm (Figure 1). Dual fields are used to enable us to cover the entire length of the body at 3.5 meters focus skin distance (FSD). However, this technique does not solve the problem of self-shielding. Thermal luminescent dosimentry (TLD) dose distribution studies and, more important, the clinical observation of patients receiving total body electron therapy showed that there are five major areas of underdosage due to self-shielding. These are the vertex, the undersurface of the breasts, the perineum, the ventral surface of the penis, and the soles of the feet. Figure 2 shows clinical evidence of underdosage to the vertex from selfshielding by the presence of hair over the vertex, and total loss along the periphery. Figure 3 shows the recurrence of disease in this area when no additional boosting is given. This area therefore needs additional boosting. During upper body electron beam therapy, the upper extremities are kept in an abducted position. In female patients, this position pulls up the breasts, exposing the undersurface. However, in female patients with pendulous breasts, the undersurface of the breast will not be exposed completely and therefore is underdosed (Figure 4). This will be a potential site for recurrence and should be boosted. During lower body electron beam therapy, the patient stands on the rotating platform with the lower extremities apart. This position, however, does not expose the perineum and upper medial aspect of the thighs. 645
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0O4
. ~ ~~~
0
Ak,~ ~~~I
Figure 2. Hair over the periphery of the head is lost but not over the vertex due to underdose from self-shielding when receiving total body electron therapy. Figure 1. Patient standing on the rotation platformn with the upper extremities above the head. The platform rotates at the speed of 5 rpm.
Figure 5 shows recurrent disease in this underdosed area. The perineal area, being the site of friction, does not tolerate the boosting well and shows an early moist reaction leading to discomfort. In male patients, the ventral surface of the penis also is underdosed from self-shielding and is a potential site of recurrence unless boosted. The soles of the feet are totally shielded throughout the treatment and are potential sites for recurrence of the disease, unless boosted (Figure 6). Being weight-bearing areas, the soles of the feet do not tolerate radiation well. Our clinical experience shows that radiation reaction in this area is much earlier and severe in intensity, causing increased morbidity. Even though there are no systemic and thvee fromnisn total artenwithincauthe ealiens toxicities body electron therapy because of limited pene- the optic thisod rangites structureselectronbemIti two trability,ofro
essential to shield the lens to avoid the 646
Figure 3. Shows recurrence of disease over the underdosed vertex when this area is not boosted.
complication of cataract formation. Lead shields of 1.5 mm thickness are sufficient to shield the optic lens totally from the electron beam. However, shields should be placed behind the eyelids instead of in front to avoid recurrence of disease in the eyelids from artificial shielding (Figure 7). Nails can be shielded with 1.5 mm thickness of lead shields whenever there is no evidence of disease in the
Figure 4. In female patients with pendulous breasts, the undersurface of the breasts is not exposed even if the upper extremities are fully abducted.
skin close to the nails. However, this is not of major importance since new nails will grow following radiation without nail shields with no major discomfort to the patient.
Discussion It is absolutely important to irradiate the entire skin uniformly from crown to sole to achieve good results
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9, 1977
z
Figure 6. Soles of the feet showing recurrent disease due to underdosing from self-shielding when the patient is treated in a standing position.
Figure 5. The perineal and the upper medial part of the disease due to underdosing from self-shielding.
in treating cutaneous T cell lymphomas. Even though it looks possible to do this by using multiple fields in phantom studies,8 it is practically impossible in actual patients. The five areas mentioned above are underdosed from self-shielding and should be boosted to avoid recurrence. The artificial lead shields should be tucked under the eyelids to protect the optic lens, and the nail shields should be avoided whenever possible in order to avoid recurrence from artificial shielding in these two areas. We also noted that the perineum and the soles of the feet are more radiosensitive because of friction in the former and weightbearing in the latter. In these, the boost dose should be reduced or protracted. In the rotation technique (Figure 1) two areas of overdose are observed along the ulnar border of the little finger and hand on both sides. This is due to proximity to the focal point. To avoid this, if the upper extremities are fully abducted above the head, the arms will shield the lateral aspect of the neck and face leading to underdosage and recurrence in this area. Therefore, depending on the severity of the reaction, the ulnar surfaces of the little fingers and hands should be artificially shielded. During and after treatmeRt, pqtients develop epiphora and dryness of the skin associated with mild edema of the lower
thighs showing
recurrent
41
:
i
Figure 7. Eye lids showing massive recurrent disease due to artificial eye shields are kept outside the lids to protect the optic lens.
extremities. We feel this is due to obstruction of the lacrimal, sebaceous, and sweat gland passages from initial Iadiation edema. Literature Cited 1. Trump JG, Wright KA, Evans WW, et al: High energy electrons for the treatment of extensive superficial malignant lesions. Am J Roentgenol Radium Ther Nuci Med 69:623-629, 1953 2. Szur L, Silvester JA, Bewley D K: Treatment of the whole body surface with electrons. Lancet 1:1373-1377, 1962 3. Smedal MI, Johnston DO, Salzman FA, et al: Ten year experience with low megavolt electron therapy. Am J Roentgenol Radium Ther NucI Med 88:215-228, 1962 4. Kitagawa T: 10 MeV betatron electron beam therapy adapted to a case of
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9,1977
shiedipg when the
mycosis fungoides. Am J Roentgenol Radium Ther Nucl Med 88:229-234, 1962 5. Grollman JH Jr: Total skin electron therapy of lymphoma cutis and generalized psoriasis: Clinical experience and adverse reactions. Radiology 87:908-915, 1966 6. Bagshaw MA, Eltringham JR: Observations on the electron beam therapy of mycosis fungoides. Front Rad Ther Oncol 2:163, 1968 7. Fuks Z, Bagshaw MA: Total skin electron treatment of mycosis fungoides. Radiology 100:145-150, 1971 8. Bjarngard BE, 'Chen GTY, Piontek RW, et al: Analysis of dose distribution in whole body superficial electron therapy. Intra J Rad Oncology, Biology and Physics 2:319-324, 1977 9. Kumar PP, Henschke UK, Mandal KP, et al: Early experience in using an 18 MeV linear accelerator for mycosis fungoides at Howard University Hospital. J Natl Med Assoc 69:223-226, 1977
647
In treating mycosis fungoides (MF) and Sezary syndrome patients with electron beam, the entire thickness and the area of the skin from crown to sole should be irradiated uniformly. To achieve irradiation of the entire thickness of the skin, electron beams of 3 4 MeV energy with 80 percent depth dose at 6 mm is sufficient. This unique property of limited penetration of electron beam does not cause any systemic toxicity during or after total body electron therapy. However, this property of limited penetration of electrons poses the problem of self-shielding in the curvaceous human body. The optic lens, which is within the range of penetrability of electron beam energy used for total body electron therapy, is to be shielded artificially. The purpose of this paper is to discuss the problems of self and artificial shielding in the superficial total body electron therapy for MF and Sezary syndrome. The advantages of limited penetrability of electron beam were explored by Trump, Van de Graaff, and Cloud and, in 1953, Trump and associates at MIT successfully used electron beam from a low megavoltage Van de Graaf accelerator for total body electron therapy of mycosis fungoides patients.' At the time, the fixed Van de Graaff machine could only produce electron beams in a downward direction with a limited distance between the machine and the floor. Because of these limitations, the patients were moved through a fixed narrow downward beam to achieve total body irradiation. After the development of movable machines, total body electron beam therapy is given in Dr. P. P. Kumar is Associate Professor, Dr. U. K. Henschke is Professor and Chairman, and J. Rao Nibhanupudy a Physicist in the Department of Radiotherapy, Howard University Hospital. Requests for reprints should be addressed to Dr. P. P. Kumar, Department of Radiotherapy, Howard University Hospital, 2041 Georgia Avenus NW, Washington, D.C. 20060.
a standing position. To achieve uniform dose distribution over the entire body surface, various techniques were used, with different fields on patients in different positions.2-7 Phantom studies done by Bjarngard et a18 and our studies on patients9 showed that the multiple-field technique is superior to the two-field technique in achieving better dose distribution. Clinical experience shows that this is not possible in the human body for two good reasons. First, the patient is not a phantom and cannot remain motionless over long periods of time during electron beam therapy and, second, the human body, though beautiful, is very irregular with ups and downs and folds and creases.
Materials and Methods To overcome the problem of uneven dose distribution due to overlapping of fields in the four-field technique8 and inability of the patient
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9, 1977
to remain motionless for long periods of time, we adopted the patient rotation technique. In this technique, the patient stands on a platform which rotates at the rate of 5 rpm (Figure 1). Dual fields are used to enable us to cover the entire length of the body at 3.5 meters focus skin distance (FSD). However, this technique does not solve the problem of self-shielding. Thermal luminescent dosimentry (TLD) dose distribution studies and, more important, the clinical observation of patients receiving total body electron therapy showed that there are five major areas of underdosage due to self-shielding. These are the vertex, the undersurface of the breasts, the perineum, the ventral surface of the penis, and the soles of the feet. Figure 2 shows clinical evidence of underdosage to the vertex from selfshielding by the presence of hair over the vertex, and total loss along the periphery. Figure 3 shows the recurrence of disease in this area when no additional boosting is given. This area therefore needs additional boosting. During upper body electron beam therapy, the upper extremities are kept in an abducted position. In female patients, this position pulls up the breasts, exposing the undersurface. However, in female patients with pendulous breasts, the undersurface of the breast will not be exposed completely and therefore is underdosed (Figure 4). This will be a potential site for recurrence and should be boosted. During lower body electron beam therapy, the patient stands on the rotating platform with the lower extremities apart. This position, however, does not expose the perineum and upper medial aspect of the thighs. 645
0*
0O4
. ~ ~~~
0
Ak,~ ~~~I
Figure 2. Hair over the periphery of the head is lost but not over the vertex due to underdose from self-shielding when receiving total body electron therapy. Figure 1. Patient standing on the rotation platformn with the upper extremities above the head. The platform rotates at the speed of 5 rpm.
Figure 5 shows recurrent disease in this underdosed area. The perineal area, being the site of friction, does not tolerate the boosting well and shows an early moist reaction leading to discomfort. In male patients, the ventral surface of the penis also is underdosed from self-shielding and is a potential site of recurrence unless boosted. The soles of the feet are totally shielded throughout the treatment and are potential sites for recurrence of the disease, unless boosted (Figure 6). Being weight-bearing areas, the soles of the feet do not tolerate radiation well. Our clinical experience shows that radiation reaction in this area is much earlier and severe in intensity, causing increased morbidity. Even though there are no systemic and thvee fromnisn total artenwithincauthe ealiens toxicities body electron therapy because of limited pene- the optic thisod rangites structureselectronbemIti two trability,ofro
essential to shield the lens to avoid the 646
Figure 3. Shows recurrence of disease over the underdosed vertex when this area is not boosted.
complication of cataract formation. Lead shields of 1.5 mm thickness are sufficient to shield the optic lens totally from the electron beam. However, shields should be placed behind the eyelids instead of in front to avoid recurrence of disease in the eyelids from artificial shielding (Figure 7). Nails can be shielded with 1.5 mm thickness of lead shields whenever there is no evidence of disease in the
Figure 4. In female patients with pendulous breasts, the undersurface of the breasts is not exposed even if the upper extremities are fully abducted.
skin close to the nails. However, this is not of major importance since new nails will grow following radiation without nail shields with no major discomfort to the patient.
Discussion It is absolutely important to irradiate the entire skin uniformly from crown to sole to achieve good results
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9, 1977
z
Figure 6. Soles of the feet showing recurrent disease due to underdosing from self-shielding when the patient is treated in a standing position.
Figure 5. The perineal and the upper medial part of the disease due to underdosing from self-shielding.
in treating cutaneous T cell lymphomas. Even though it looks possible to do this by using multiple fields in phantom studies,8 it is practically impossible in actual patients. The five areas mentioned above are underdosed from self-shielding and should be boosted to avoid recurrence. The artificial lead shields should be tucked under the eyelids to protect the optic lens, and the nail shields should be avoided whenever possible in order to avoid recurrence from artificial shielding in these two areas. We also noted that the perineum and the soles of the feet are more radiosensitive because of friction in the former and weightbearing in the latter. In these, the boost dose should be reduced or protracted. In the rotation technique (Figure 1) two areas of overdose are observed along the ulnar border of the little finger and hand on both sides. This is due to proximity to the focal point. To avoid this, if the upper extremities are fully abducted above the head, the arms will shield the lateral aspect of the neck and face leading to underdosage and recurrence in this area. Therefore, depending on the severity of the reaction, the ulnar surfaces of the little fingers and hands should be artificially shielded. During and after treatmeRt, pqtients develop epiphora and dryness of the skin associated with mild edema of the lower
thighs showing
recurrent
41
:
i
Figure 7. Eye lids showing massive recurrent disease due to artificial eye shields are kept outside the lids to protect the optic lens.
extremities. We feel this is due to obstruction of the lacrimal, sebaceous, and sweat gland passages from initial Iadiation edema. Literature Cited 1. Trump JG, Wright KA, Evans WW, et al: High energy electrons for the treatment of extensive superficial malignant lesions. Am J Roentgenol Radium Ther Nuci Med 69:623-629, 1953 2. Szur L, Silvester JA, Bewley D K: Treatment of the whole body surface with electrons. Lancet 1:1373-1377, 1962 3. Smedal MI, Johnston DO, Salzman FA, et al: Ten year experience with low megavolt electron therapy. Am J Roentgenol Radium Ther NucI Med 88:215-228, 1962 4. Kitagawa T: 10 MeV betatron electron beam therapy adapted to a case of
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 69, NO. 9,1977
shiedipg when the
mycosis fungoides. Am J Roentgenol Radium Ther Nucl Med 88:229-234, 1962 5. Grollman JH Jr: Total skin electron therapy of lymphoma cutis and generalized psoriasis: Clinical experience and adverse reactions. Radiology 87:908-915, 1966 6. Bagshaw MA, Eltringham JR: Observations on the electron beam therapy of mycosis fungoides. Front Rad Ther Oncol 2:163, 1968 7. Fuks Z, Bagshaw MA: Total skin electron treatment of mycosis fungoides. Radiology 100:145-150, 1971 8. Bjarngard BE, 'Chen GTY, Piontek RW, et al: Analysis of dose distribution in whole body superficial electron therapy. Intra J Rad Oncology, Biology and Physics 2:319-324, 1977 9. Kumar PP, Henschke UK, Mandal KP, et al: Early experience in using an 18 MeV linear accelerator for mycosis fungoides at Howard University Hospital. J Natl Med Assoc 69:223-226, 1977
647
