- Email: [email protected]
A modified 60C teletherapy unit for total body irradiation
Int. J. Radiation
Oncology
Biol.
Phys., Vol. 33. No. 4. pp. 951-957, 1995 Copyright 0 1995 Elsevier Science Inc. Printed in the USA. All rights reserved
036cL3016/95
$9.50 + .oo
0360~3016( 95) 00208-t
A MODIFIED
@C TELETHERAPY
CLAUDE DOMINIQUE, KATIA KEIUUDY, MAHMUT OZSAHEN,
UNIT
FOR TOTAL
BODY
IRRADIATION
H. SCHWARTZ, M.D., JACQUES LESCRAINIER, PH .D, PH .D., YAZID BELKACEMI, M.D., JE~~oEL~o~QU~,~ .D., M.D., DIMITRIOS LEFKOPOULOS, PH.D. AND FRANCOISE PENE, M.D. PH II.,
LAURENT
Department of Radiation Oncology, HBpital Tenon, 75970 Paris Cedex 20, France Puruose: A modified teletherauv unit to achieve total bodv irradiation with a vertical beam in a conventional iZSiii&t room. Methods and Materials: A standard @C teletherapy unit has been mod&d to achieve total body irradiation with a vertical beam in a inventions t~a~ent room. Patients are treated in ~r0ne and supine PositiOns. Removal of the adjustabie eollhnator assembiy of this standard machine p&ides a circular fieid of 1% cm in diameter at 167 cm from the source. Second, the maetine has been elevated by about 50 cm on a metallic baseto enlarge irradiation field to obtain 248 cm in diameter at 210 cm from the source, and to encompasstall patients under better conditions. A speciallead conical beam flattening filter, lo-mm thick at the center, was designedto compensatethe spatial Homogeneity of the beam. An instantaneousdose rate of 6.10Y2Gy/min is attained at the L4 level (midplane) in an average 20-cm thick patient with a source activity of 5099 RKM (air kerma rate of 44.8 Gy - h-’ - m*). Between February 2,19&l and December27, 1990, 244 total body irradiations were performed either by single dose-(R = 69, 10 Gy were given to ~dpl~ at L4 level in about 6 to 8 h, 8 Gy to the lungs), or by f~~~ona~ dose(n = 17512 Gy were given in 6 fractions over 3 consecutivedays to midplane at LA Ievel, 9 Gy to the lungs). Results: The dosedistribution is similar than the onesobtained by a linear accelerator with patients lying atheir sides. Conclusion: Patients were treated in a comfortable and highly reproductible position. Organ shieldingwas easily achievable. This could be a lessexpensiveand reasonablealternative to linear accelerator. _”
Total body irradiation, Dosimetry, @CUnit, Build-up characteristics.
therapy unit2 has been modified to treat patients in prone and supine position using a single vertical beam. There were three distinct periods of use of the teletherapy unit for total body irradiation: Before 1985: This teletherapy unit was, mostly, used for conventional treatments and modified only during total body irradiation. M~i~ca~ons for use in one or another confi~ation needed less than half an hour. A check of the coincidence of the light field with the radiation field and of the collimator rotation axis was necessary before conventional treatment. From 1985 to 1993: The % teletherapy unit was ‘ ‘dedicated” for total body irradiation only. Since January 1994; The modified teletherapy unit has
Bone-marrow transplantation is a widely accepted form of treatment for acute and chronic leukemias. Favorable results have also been obtained in lymphomas (9) and myelomas (5). Total body irradiation plays an important role in the conditioning treatment of these malignancies. At Tenon Hospital in Paris more than 700 total body irradiations have been performed since 1979. One hundred and ninety-one of them were realized using 6-MV photons from a linear accelerator ’ using a horizontal beam (gantry at 90”). The patient was laid on his or her side on a special bed. The source-skin distance (SSD) was 360 cm. Because of increased patient load, the %Z tele-
Presentedin part at the First Biennial ESTRO Meeting on Physics in Clinical Radiotherapy,Budapest,Hungary, 14-17 October 1991. Reprint requests to: Claude Dominique, Ph.D., H6pital Tenon, Servicesde Canckologie-OncologicA et B desPrs M. Schliengeret A. Laugier,4 rue de la Chine,75970ParisCedex 20, France.
Acknowledgements-The authors thank Ms. G. Marinello, Ph.D. for her help in reviewing the manuscript. Accepted for publication 20 April 1995. ’ Neptune6 MV; GE-CGR MeV, But, France. ’ Alcyon; GE-CGR MeV, But, France.
951
952
1. J. Radiation
Oncology
* Biology
l
Volume
Physics
33.
Number
0
4, 1995
cm
Fig. 1. The modified Alcyon telecobalt unit: (a) beam flattening filter; (b) Lipwitz’alloy plastic trolley; (c) portal film.
block placed on the
-
Without
flattening
With flattening
-200
-150
-100
-50 Dietance
0 from axis of the beam
50
100
filter filter
150
(cm)
Fig. 2. Depth-dose profile of ‘YZ with and without beam flattening filter at 210 cm from the source and at lomm depth.
200
@% Teletherapy unit
0 C. DOMINIQUE
953
et al.
-
CobaMO
0,600 0 3
0,500
c
0,400 0,300
0,2001 0,100 t 0,000
A-----04
5,O
A
--
/ 10,o
15,o Depth
20,o
250
30,o
(cm)
Fie. 3. Tissue-~imum ratio curves at 210 cm sourcedetectordistancefor 60Cgammarays and at 360 cm source-detectordistance for 6-MV photons.
been elevated by 50 cm on a metallic base to enlarge the field size. METHODS
AND MATERIALS
The Alcyon Teletherapy Unit The Alcyon 6oC Teletherapy Unit had been originally designed to treat at 80-cm source-axis distance (SAD). The field size ranged from 3.5 x 3.5 cm2 to 32 X 32 cm’ at 80 cm from the source, and the source-floor distance is 200 cm. The air kerma rate for a source activity of 5099 RHM (air kerma rate of 44.8 Gy*h-’ am’) was 1.178 Gy/min at 80 cm from the source for a 10 X 10 cm* field ( 1, 2). To treat the whole body, a large field was needed to encompass the patient. Tbis was achieved by removal of the adjustable collimator (Fig. 1). This was feasible because the Alcyon teletherapy unit was specially designed to meet the international radiation protection requirement for cobalt source transport without its adjustable collimator (4). The collimator weighs about 250 kg. After positioning the gantry upward, the adjustable collimator is easily removed by lifting it out of the treatment head using a lifting jig. The gantry is then rotated 180” to a downward position for treatment of total body irradiation patients. In this case, the field size is a circle of 196 cm in diameter at 167 cm from the source. The patient lies on a low bed, in prone or supine position, where he or she can comfortably rest.
’ PTW 0.3 ml or Markus chambersandDL4-D14,FTW, Germany. NE type 2.581and FMER 2570, Nuclear Enterprise, England.
To get a better dose homogeneity, a 2-mm thick aluminium plate carrying a beam-flattening filter is mounted in place of the adjustable collimator at 45 cm from the source. This conical filter is constructed by juxtaposition of concentric discs of lead, with a maximum thickness of 10 mm in its center. The filter was specially designed to obtain a u~fo~ ( + 10% ‘ ‘in air’ ’ ) circular beam for total body irradiations, to encompass a patient 5190 cm in height, at 167 cm SSD. The transmission is 34% on the central beam axis. To treat tall patients under better conditions, the Alcyon has been elevated by about 50 cm on a metallic base. The source-floor distance is 250.8 cm. The useful circular field at 210 cm from the source is now 248 cm in diameter with a + 10% uniform beam. We show in Fig. 2 the depthdose profile in a longi~~n~ axis at 210 cm from the source and at 1 cm depth, with and without flattening filter. Irradiation technique The patients are treated alternatively in prone and supine position on a lightweight treatment bed situated 24 cm above the floor. The long axis of the treatment table is perpendicular to the axis of Gus-station angle. Organ shielding (lungs and event~ly heart, liver, brain) is achieved using Lipwitz’s alloy custom-made shield blocks (transmission < 5%) on a plastic trolley mounted on the treatment table 60 cm above the bed. The right positioning of the blocks is always checked by portal films.
4WP700, Welihafer, Germany.
1. J. RadiationOncology 0 Biology l Physics
954
Volume 33, Number 4, 1995
-- .._.__~
(4
Cdx3&60*
-
1Ocm
RX6MV-10cm
distance to the center (cm) CoMt430-2Ocm
i 0.98 0,98 J/
I*
0.94 -8
-8
-4
-2
-a% \
-0
2
4
8
8
10
distance to the center (cm)
(4
g
* c-4
5
tn N
distance to the center (cm)
Fig. 4. Dose distribution for two oppositefieds in total body irradiation conditionsfor lo-cm (a), 20-cm (b), and 25cm (c) thick patients. Dosimetty Beam and depth-daseprofiles. Multiple measurements have been performed to evaluate the sui~bility of this teletherapy unit in the treatment position. Ionization
chambers with their electrometers,’ were used with water phantom4 and polystyrene plates (40 x 40 x 0.1 to 5 cm”) stacked in three rows (total length 120 cm) to simulate an average patient body. The percentage-depth dose (PDD), the tissue-maximum ratio (TMR), and the beam profiles at different
depths were studied and the beam uniformity obtained by the beam-flat~~ng device was checked. Tissue-maximum ratio (Fig. 3) and ~rcentage-dep~ dose measurements revealed that maximum dose was situated at the surface and not at 5 mm as for a standard teletherapy unit. The 100% isodose at the surface is explained by the secondary electron contamination due to the interaction of the beam with aluminium plate and the beam flattener. A comparative dose distribution on the beam axis for two opposite fields in total body irradiation conditions using
*‘C Teletherapy
unit l C.
955
,
Head
/
i-
-100
et al.
~)MINI~U~
1.15
+
0,85
-
1
Feet A
no --+----I
-60
-60
-40
-20 distance
0 from
I
20
40
60
80
100
axis of the beam (cm)
Fig. 5. Depth-dose profiles of ‘j°C at 167 cm SSD on surface, at lo-cm and 20-cm depths. 6oC gamma rays and 6-MV photons at 210 cm and 360 cm from the source, respectively, and at three depths ( 10, 20, and 25 cm) is shown in Fig. 4. The m~imum thickness of patients lying in prone and supine position is at the level of their media&turn, and it is not usually greater than 25 cm. Up to 20 cm thickness, 6oC permits superior uniform dose distribution on the thickness, particularly in the first millimeters. When considering thickness larger than 25 cm (Fig. 3) the dose uniformity is better with linear accelerators. Indeed, with the teletherapy WC unit, there is 12% averdose at the surface (at 12.5 cm from the midplane) with -7% variation during the first 3 mm. Using the specially designed fla~e~ng device, beam profiles were measured 167 cm from the source using polystyrene phantom ( 120 X 30 X 30 cm’), PTW 0.3 cm’, and Markus ionization chambers, at the surface, at 10 cm and at 20 cm depth (Fig. 5). At this distance, a useful circular beam 196 cm in diameter is obtained with t 10% dose uniformity from its center, which is set to be “lOO%.” However, the dose uniformity at 277 cm from the center of the beam is 25% with an elevation of 10% of the dose between 77 and 98 cm from the center. Thus, there is a slightly higher dose at the head and the
’ Model 1, Automatic TLD Reader 5500 HARSHAW, cren, USA.
Bi-
feet as compared to the center of the patient at the level of L4, but this variation of relative dose is com~nsat~ by a rather smaller thickness of these volumes. With the elevated Alcyon teletherapy unit, the useful circular beam is 191 cm in diameter with 25% dose uniformity, and 248 cm with 210%. Therefore, uniformity of the relative dose distribution is better in all cases. In Vivo dosimetry. During treatment, dosimetry was performed (3, 9) by thermoluminescence5 and semiconductors.’ Lithium fluoride capsules (3 X 3 X 1 mm”) and semiconductors were calibrated at total body irradiation conditions using an ionization chamber in a solid phantom, the day before each total body irradiation. During t~a~ent, se~condu~tor diodes and lithium fluoride capsules were positioned by pairs, directly on the front and the back of the patient, at five main areas (head, lungs, mediastinum, calves, and level of L4). The mean absorbed dose in different body volumes (head, lungs, mediastinum, and abdomen), using different total body irradiation techniques in 435 patients refered to our department, are shown in Table 1. The absorbed dose at the mid-depth of each measured volume is calculated by: Dmid-depth
=
[(all + ~o",v2l*Fc,
’ DPD510 with 10 EDE diodes, SCANDlTRONIX,
Sweden.
1. J. Radiation Oncology l Biology l Physics
956
Volume 33, Number 4, 1995
Table 1. Dosimetricmeas~ementsin contact with the headof the modified “C teletherapyunit without its adjustablecollimator (air kermarate of the source:44.8 Gy -h-l - m2 0”
45”
90”
135”
I 80”
280
120
100
14
24
Angle from the centerof the head Dose rate (pGy *h-‘)
with Fc = 2*TMR<,,,,/[(a/b)’
+ TMR,,*(alc)‘],
where (Fig. 6) Fc = correction factor; 4, = entrance dose (Gy); L>,,, = exit dose (Gy ) ; a = source to middepth distance (cm) ; e = width (cm) ; b = a - (e/2) ; and c = a + (e/2). Fc is calculated with a classical estimation of the dose at middepth in function of entrance (Oi”) and exit (D,,,) dose: Dmid-depth= Din* [TMR~,,~,/l.OOO]* Dmid-depth= Doat*
[b/al21
[ThQb,,~TMR
~~i~t~on protection The Alcyon is a specially designed teletherapy machine to meet the requirements for cobalt source transport. When a source exchange is needed, the whole head of the machine is replaced. With this technique, there is no radioactive source handling in the hospital. Because of this design, our total body irradiation-related machine modification did not cause any radiation protection problem. The dosimetric measurements in contact with the head of the modified teletherapy machine, without its adjustable collimator, are shown in Table 1. At 1 m distance, all the measurements meet the ICRP recommendations (4). Patient population Two hundred forty-four patients have been treated between February 2, 1984 and December 27, 1990 using Source
c
,
4 e/2
midplane-
--
_ e/2 ~
t
t‘
*D out
Fig. 6. Determinationof correction factor Fe.
225” 3.4
270” 5
325” 18
this technique. Sixty-nine patients were treated by singledose total body irradiation ( 10 Gy delivered in about 6 to 8 h to the midplane at the level of L4, and 8 Gy to the lungs by partial s~elding) . One hundred seventy-five were treated by f~~~onated total body irradiation ( 12 Gy delivered in 6 fractions over 3 consecutive days to the midplane at the level of LA, and 9 Gy to the lungs by partial shielding). The type of fractionation protocol depends on several parameters, such as clinical status, age, or bone marrow team wish. The mean instantaneous and average dose rate was 5.28 lo-’ Gy/min and 2.58 10m2 Gy/min, respectively, in single-dose total body irradiation; 4.38 lo-* Gy/min and 2.40 lo-’ Gy/min in fractionated total body irradiation (Table 2). Clinical results have been published elsewhere ( 11) . DISCUSSION This technique is simple, practical, reproducible, and comfortable. It is easily performed by means of a vertically downward beam in a standard treatment room while the patient lies comfortably in prone and supine position. An instantaneous dose rate of 6 lo-’ Gy/min at middepth (level of LA) of the patient can be used, and if necessary, lower dose rates can be achieved by means of a beam attenuator. The dosimetry is similar to other total body irradiation techniques using @‘Cunits (6,7,8,12). The dose homoge~i~ is adequate as reported by Quast ( 13) and Van Dyke and Leung ( 15), and there is no need for tissue compensators, in contrast to total body irradiation techniques using horizontal beam laterally (patient prone and supine) (14). Lung shielding is easy, and due to the patient position, the setup and organ shielding is quickly and easily performed. It is more reproducible, especially in fractionated regimens, than techniques where the patients are not comfortable and may be unstable because they are lying on their sides. Patients may have a generalized skin erythema during the first few days following the total body ration. It has little effect on the patient’s general status. No long-term skin side effects have been noticed ( 11) . Our results, comparing patients irradiated either by 6-w photons or by teletherapy machine, showed no major differences between the two techniques ( 10). In our randomized study of 157 patients, according to the type of fractionation and instantaneous dose rate no significant diffenznces were observed in terms of early complications. In terms of interstitial pneumonitis and venoclusive disease, there was no influence of the total body irradiation parameters. However, the analyses showed higher incidence of cataractogenesis in patients treated with high insect dose rate than low i~~~~ dose rate (p = 0.006) (11).
“‘C Teletherapy
unit 0 C. DOMINIQUE
et al.
957
Table 2. Mean absorbed dose in different anatomic regions according to the instantaneous and average dose rate in different TBI techniques for a serial of 435 patients y*
Mean absorbed dose (Gy) L4 (minimum-maximum) Lung (minimum-maximum) Mediastinum (minimum-maximum) Head (minimum-maximum) Average dose rate at mid-plane (lo-’ Gy.min-‘) Instantaneous dose rate at midplane (lo-* Gym mini’)
6MV photons+
Single dose (n = 69)
Six fractions (n = 175)
Single dose (n = 191)
10.01 (9.76- 10.60) 7.92 (7.40-8.70) 9.69 (8.80- 10.40) 10.26 (9.18-11.80) 2.58 (1.68-3.36) 5.28 (3.42-6.24)
12.01 (11.23-12.90) 8.96 (7.71- 10.48) 11.32 (10.30-12.52) 11.75 (9.00-13.40) 2.40 (1.74-3.60) 4.38 (2.64-6.60)
10.03 (9.05-10.83) 7.93 (7.40-8.70) 9.34 (8.80- 10.40) 9.53 (7.23-11.20) 2.94 (2.16-4.08) 7.86 (5.27-17.40)
* Alcyon, GE-CGR MeV, But, France. ’ Neptune, GE-CGR MeV, But, France. Finally, this method is not limited to use with the Alcyon teletherapy unit. It may be used with other teletherapy units ( 12), provided radiation protections can be met when removing the collimator assembly. One can perform total body irradiation using a simple
“C head, fixed to the ceiling of a standard treatment room. This would be a reasonable alternative for a cancer center where many total-body irradiations are performed. This could be a less expensive and reasonable alternative to a linear accelerator.
REFERENCES 1. Andreo, P.; Cunningham, J. R.; Hohlfeld, K.; Svensson, H. Absorbed dose determination in photon and electron beams. An international code of practice. Vienna: International Atomic Energy Agency; 1987. 2. CFMRI. Recommandations pour la mesure de la dose absorbee en radiotherapie dans les faisceaux de photons et d’electrons d’energie comprise entre 1 MeV et 50 MeV. Paris: Collection des monographies, Bureau National de Metrologie, Volume 2; 1986. 3. Dutreix, A.; Bridier, A. Total body irradiation techniques and dosimetry. Pathol. Biol. 27:373-378; 1979. 4. ICRP Publication 60. 1990 Recommendations of the International Commission on Radiological Protection. Ann. ICRP 21:1-3; 1990. 5. Gahrton, G.; Tura, S.; Ljungman, P.; Belanger, C.; Brandt, L.; Cavo, M.; Facon, T.; Granena, A.; Gore, M.; Gratwhol, A.; Lowenberg, B.; Nikoskelainen, J.; Reiffers, J. J.; Samson, D.; Verdonck, L.; Volin, L. Allogeneic bone marrow transplantation in multiple myeloma. N. Engl. J. Med. 325:1267-1273; 1991. 6. Glasgow, G. P.; Mill, W. B. Cobalt-60 total-body irradiation dosimetry at 220 cm source-axis distance. Int. J. Radiat. Oncol. Biol. Phys. 6:773-777; 1980. 7. Jablonski, 0.; Motta-Veyssiere, J.; Chenal, C.; Guerin, R. A. Irradiations corporelles totales: techniques d’irradiation fractionnee par t&&cobalt. J. Radiol. 60:339-342; 1979. 8. Lam, W. C.; Order, S. E.; Thomas, E. D. Uniformity and standardization of single and opposing cobalt-60 sources for total body irradiation. Int. J. Radiat. Oncol. Biol. Phys. 6:245-250: 1980.
9. Mascret, B.; Maraninchi, D.; Gastaut, J. A.; Tubiana, N.; Sebahoun, G.; Horschowski, N.; Sainty, D.; Camerlo, J.; Lejeune, C.; Novakovitch, G.; Carcassone, Y. Treatment of malignant lymphoma with high dose of chemo or chemoradiotherapy and bone marrow transplantation. Eur. J. Cancer. Clin. Oncol. 22:461-471; 1986. 10. Ozsahin, M.; Belkacemi, Y.; P&e, F.; Dominique, C.; Schwartz, L. H.; Uzal, C.; Lef kopoulos, D.; Gindrey-Vie, B.; Vitu-Loas, L.; Touboul, E.; Schlienger, M.; Laugier, A. Total-body irradiation and cataract incidence: A randomized comparison of two instantaneous dose rates. Int. J. Radiat. Oncol. Biol. Phys. 28:343-347; 1994. 11. Ozsahin, M.; P&e, F.; Touboul, E.; Gindrey-Vie, B.; Dominique, C.; Lef kopoulos, D.; Krzisch, C.; Balosso, J.; Vitu, L.; Schwartz, L. H.; Rio, B.; Gorin, N. C.; Leblond, V.; Schlienger, M.; Laugier, A. Total-body irradiation before bone marrow transplantation: Results of two randomized instantaneous dose rates in 157 patients. Cancer 69:28532865; 1992. 12. Peters, V. G.; Herer, A. S. Modification of a standard cobalt-60 unit for total body irradiation at 150 cm SSD. Int. J. Radiat. Oncol. Biol. Phys. 10~927-932; 1984. 13. Quast, U. Physical problems of total body irradiation. Strahlenther. Onkol. 162:233-236; 1986. 14. Svensson, G. K.; Larsen, R. D.; Chen, T. S. The use of a 4 MV linear accelerator for whole body irradiation. Int. J. Radiat. Oncol. Biol. Phys. 6:761-765; 1980. 15. Van Dyke, J.; Leung, P. M. K.; Cunningham, J. R. Dosimetric considerations of very large cobalt-60 fields. Int. J. Radiat. Oncol. Biol. Phys. 6:753-759; 1980.
Oncology
Biol.
Phys., Vol. 33. No. 4. pp. 951-957, 1995 Copyright 0 1995 Elsevier Science Inc. Printed in the USA. All rights reserved
036cL3016/95
$9.50 + .oo
0360~3016( 95) 00208-t
A MODIFIED
@C TELETHERAPY
CLAUDE DOMINIQUE, KATIA KEIUUDY, MAHMUT OZSAHEN,
UNIT
FOR TOTAL
BODY
IRRADIATION
H. SCHWARTZ, M.D., JACQUES LESCRAINIER, PH .D, PH .D., YAZID BELKACEMI, M.D., JE~~oEL~o~QU~,~ .D., M.D., DIMITRIOS LEFKOPOULOS, PH.D. AND FRANCOISE PENE, M.D. PH II.,
LAURENT
Department of Radiation Oncology, HBpital Tenon, 75970 Paris Cedex 20, France Puruose: A modified teletherauv unit to achieve total bodv irradiation with a vertical beam in a conventional iZSiii&t room. Methods and Materials: A standard @C teletherapy unit has been mod&d to achieve total body irradiation with a vertical beam in a inventions t~a~ent room. Patients are treated in ~r0ne and supine PositiOns. Removal of the adjustabie eollhnator assembiy of this standard machine p&ides a circular fieid of 1% cm in diameter at 167 cm from the source. Second, the maetine has been elevated by about 50 cm on a metallic baseto enlarge irradiation field to obtain 248 cm in diameter at 210 cm from the source, and to encompasstall patients under better conditions. A speciallead conical beam flattening filter, lo-mm thick at the center, was designedto compensatethe spatial Homogeneity of the beam. An instantaneousdose rate of 6.10Y2Gy/min is attained at the L4 level (midplane) in an average 20-cm thick patient with a source activity of 5099 RKM (air kerma rate of 44.8 Gy - h-’ - m*). Between February 2,19&l and December27, 1990, 244 total body irradiations were performed either by single dose-(R = 69, 10 Gy were given to ~dpl~ at L4 level in about 6 to 8 h, 8 Gy to the lungs), or by f~~~ona~ dose(n = 17512 Gy were given in 6 fractions over 3 consecutivedays to midplane at LA Ievel, 9 Gy to the lungs). Results: The dosedistribution is similar than the onesobtained by a linear accelerator with patients lying atheir sides. Conclusion: Patients were treated in a comfortable and highly reproductible position. Organ shieldingwas easily achievable. This could be a lessexpensiveand reasonablealternative to linear accelerator. _”
Total body irradiation, Dosimetry, @CUnit, Build-up characteristics.
therapy unit2 has been modified to treat patients in prone and supine position using a single vertical beam. There were three distinct periods of use of the teletherapy unit for total body irradiation: Before 1985: This teletherapy unit was, mostly, used for conventional treatments and modified only during total body irradiation. M~i~ca~ons for use in one or another confi~ation needed less than half an hour. A check of the coincidence of the light field with the radiation field and of the collimator rotation axis was necessary before conventional treatment. From 1985 to 1993: The % teletherapy unit was ‘ ‘dedicated” for total body irradiation only. Since January 1994; The modified teletherapy unit has
Bone-marrow transplantation is a widely accepted form of treatment for acute and chronic leukemias. Favorable results have also been obtained in lymphomas (9) and myelomas (5). Total body irradiation plays an important role in the conditioning treatment of these malignancies. At Tenon Hospital in Paris more than 700 total body irradiations have been performed since 1979. One hundred and ninety-one of them were realized using 6-MV photons from a linear accelerator ’ using a horizontal beam (gantry at 90”). The patient was laid on his or her side on a special bed. The source-skin distance (SSD) was 360 cm. Because of increased patient load, the %Z tele-
Presentedin part at the First Biennial ESTRO Meeting on Physics in Clinical Radiotherapy,Budapest,Hungary, 14-17 October 1991. Reprint requests to: Claude Dominique, Ph.D., H6pital Tenon, Servicesde Canckologie-OncologicA et B desPrs M. Schliengeret A. Laugier,4 rue de la Chine,75970ParisCedex 20, France.
Acknowledgements-The authors thank Ms. G. Marinello, Ph.D. for her help in reviewing the manuscript. Accepted for publication 20 April 1995. ’ Neptune6 MV; GE-CGR MeV, But, France. ’ Alcyon; GE-CGR MeV, But, France.
951
952
1. J. Radiation
Oncology
* Biology
l
Volume
Physics
33.
Number
0
4, 1995
cm
Fig. 1. The modified Alcyon telecobalt unit: (a) beam flattening filter; (b) Lipwitz’alloy plastic trolley; (c) portal film.
block placed on the
-
Without
flattening
With flattening
-200
-150
-100
-50 Dietance
0 from axis of the beam
50
100
filter filter
150
(cm)
Fig. 2. Depth-dose profile of ‘YZ with and without beam flattening filter at 210 cm from the source and at lomm depth.
200
@% Teletherapy unit
0 C. DOMINIQUE
953
et al.
-
CobaMO
0,600 0 3
0,500
c
0,400 0,300
0,2001 0,100 t 0,000
A-----04
5,O
A
--
/ 10,o
15,o Depth
20,o
250
30,o
(cm)
Fie. 3. Tissue-~imum ratio curves at 210 cm sourcedetectordistancefor 60Cgammarays and at 360 cm source-detectordistance for 6-MV photons.
been elevated by 50 cm on a metallic base to enlarge the field size. METHODS
AND MATERIALS
The Alcyon Teletherapy Unit The Alcyon 6oC Teletherapy Unit had been originally designed to treat at 80-cm source-axis distance (SAD). The field size ranged from 3.5 x 3.5 cm2 to 32 X 32 cm’ at 80 cm from the source, and the source-floor distance is 200 cm. The air kerma rate for a source activity of 5099 RHM (air kerma rate of 44.8 Gy*h-’ am’) was 1.178 Gy/min at 80 cm from the source for a 10 X 10 cm* field ( 1, 2). To treat the whole body, a large field was needed to encompass the patient. Tbis was achieved by removal of the adjustable collimator (Fig. 1). This was feasible because the Alcyon teletherapy unit was specially designed to meet the international radiation protection requirement for cobalt source transport without its adjustable collimator (4). The collimator weighs about 250 kg. After positioning the gantry upward, the adjustable collimator is easily removed by lifting it out of the treatment head using a lifting jig. The gantry is then rotated 180” to a downward position for treatment of total body irradiation patients. In this case, the field size is a circle of 196 cm in diameter at 167 cm from the source. The patient lies on a low bed, in prone or supine position, where he or she can comfortably rest.
’ PTW 0.3 ml or Markus chambersandDL4-D14,FTW, Germany. NE type 2.581and FMER 2570, Nuclear Enterprise, England.
To get a better dose homogeneity, a 2-mm thick aluminium plate carrying a beam-flattening filter is mounted in place of the adjustable collimator at 45 cm from the source. This conical filter is constructed by juxtaposition of concentric discs of lead, with a maximum thickness of 10 mm in its center. The filter was specially designed to obtain a u~fo~ ( + 10% ‘ ‘in air’ ’ ) circular beam for total body irradiations, to encompass a patient 5190 cm in height, at 167 cm SSD. The transmission is 34% on the central beam axis. To treat tall patients under better conditions, the Alcyon has been elevated by about 50 cm on a metallic base. The source-floor distance is 250.8 cm. The useful circular field at 210 cm from the source is now 248 cm in diameter with a + 10% uniform beam. We show in Fig. 2 the depthdose profile in a longi~~n~ axis at 210 cm from the source and at 1 cm depth, with and without flattening filter. Irradiation technique The patients are treated alternatively in prone and supine position on a lightweight treatment bed situated 24 cm above the floor. The long axis of the treatment table is perpendicular to the axis of Gus-station angle. Organ shielding (lungs and event~ly heart, liver, brain) is achieved using Lipwitz’s alloy custom-made shield blocks (transmission < 5%) on a plastic trolley mounted on the treatment table 60 cm above the bed. The right positioning of the blocks is always checked by portal films.
4WP700, Welihafer, Germany.
1. J. RadiationOncology 0 Biology l Physics
954
Volume 33, Number 4, 1995
-- .._.__~
(4
Cdx3&60*
-
1Ocm
RX6MV-10cm
distance to the center (cm) CoMt430-2Ocm
i 0.98 0,98 J/
I*
0.94 -8
-8
-4
-2
-a% \
-0
2
4
8
8
10
distance to the center (cm)
(4
g
* c-4
5
tn N
distance to the center (cm)
Fig. 4. Dose distribution for two oppositefieds in total body irradiation conditionsfor lo-cm (a), 20-cm (b), and 25cm (c) thick patients. Dosimetty Beam and depth-daseprofiles. Multiple measurements have been performed to evaluate the sui~bility of this teletherapy unit in the treatment position. Ionization
chambers with their electrometers,’ were used with water phantom4 and polystyrene plates (40 x 40 x 0.1 to 5 cm”) stacked in three rows (total length 120 cm) to simulate an average patient body. The percentage-depth dose (PDD), the tissue-maximum ratio (TMR), and the beam profiles at different
depths were studied and the beam uniformity obtained by the beam-flat~~ng device was checked. Tissue-maximum ratio (Fig. 3) and ~rcentage-dep~ dose measurements revealed that maximum dose was situated at the surface and not at 5 mm as for a standard teletherapy unit. The 100% isodose at the surface is explained by the secondary electron contamination due to the interaction of the beam with aluminium plate and the beam flattener. A comparative dose distribution on the beam axis for two opposite fields in total body irradiation conditions using
*‘C Teletherapy
unit l C.
955
,
Head
/
i-
-100
et al.
~)MINI~U~
1.15
+
0,85
-
1
Feet A
no --+----I
-60
-60
-40
-20 distance
0 from
I
20
40
60
80
100
axis of the beam (cm)
Fig. 5. Depth-dose profiles of ‘j°C at 167 cm SSD on surface, at lo-cm and 20-cm depths. 6oC gamma rays and 6-MV photons at 210 cm and 360 cm from the source, respectively, and at three depths ( 10, 20, and 25 cm) is shown in Fig. 4. The m~imum thickness of patients lying in prone and supine position is at the level of their media&turn, and it is not usually greater than 25 cm. Up to 20 cm thickness, 6oC permits superior uniform dose distribution on the thickness, particularly in the first millimeters. When considering thickness larger than 25 cm (Fig. 3) the dose uniformity is better with linear accelerators. Indeed, with the teletherapy WC unit, there is 12% averdose at the surface (at 12.5 cm from the midplane) with -7% variation during the first 3 mm. Using the specially designed fla~e~ng device, beam profiles were measured 167 cm from the source using polystyrene phantom ( 120 X 30 X 30 cm’), PTW 0.3 cm’, and Markus ionization chambers, at the surface, at 10 cm and at 20 cm depth (Fig. 5). At this distance, a useful circular beam 196 cm in diameter is obtained with t 10% dose uniformity from its center, which is set to be “lOO%.” However, the dose uniformity at 277 cm from the center of the beam is 25% with an elevation of 10% of the dose between 77 and 98 cm from the center. Thus, there is a slightly higher dose at the head and the
’ Model 1, Automatic TLD Reader 5500 HARSHAW, cren, USA.
Bi-
feet as compared to the center of the patient at the level of L4, but this variation of relative dose is com~nsat~ by a rather smaller thickness of these volumes. With the elevated Alcyon teletherapy unit, the useful circular beam is 191 cm in diameter with 25% dose uniformity, and 248 cm with 210%. Therefore, uniformity of the relative dose distribution is better in all cases. In Vivo dosimetry. During treatment, dosimetry was performed (3, 9) by thermoluminescence5 and semiconductors.’ Lithium fluoride capsules (3 X 3 X 1 mm”) and semiconductors were calibrated at total body irradiation conditions using an ionization chamber in a solid phantom, the day before each total body irradiation. During t~a~ent, se~condu~tor diodes and lithium fluoride capsules were positioned by pairs, directly on the front and the back of the patient, at five main areas (head, lungs, mediastinum, calves, and level of L4). The mean absorbed dose in different body volumes (head, lungs, mediastinum, and abdomen), using different total body irradiation techniques in 435 patients refered to our department, are shown in Table 1. The absorbed dose at the mid-depth of each measured volume is calculated by: Dmid-depth
=
[(all + ~o",v2l*Fc,
’ DPD510 with 10 EDE diodes, SCANDlTRONIX,
Sweden.
1. J. Radiation Oncology l Biology l Physics
956
Volume 33, Number 4, 1995
Table 1. Dosimetricmeas~ementsin contact with the headof the modified “C teletherapyunit without its adjustablecollimator (air kermarate of the source:44.8 Gy -h-l - m2 0”
45”
90”
135”
I 80”
280
120
100
14
24
Angle from the centerof the head Dose rate (pGy *h-‘)
with Fc = 2*TMR<,,,,/[(a/b)’
+ TMR,,*(alc)‘],
where (Fig. 6) Fc = correction factor; 4, = entrance dose (Gy); L>,,, = exit dose (Gy ) ; a = source to middepth distance (cm) ; e = width (cm) ; b = a - (e/2) ; and c = a + (e/2). Fc is calculated with a classical estimation of the dose at middepth in function of entrance (Oi”) and exit (D,,,) dose: Dmid-depth= Din* [TMR~,,~,/l.OOO]* Dmid-depth= Doat*
[b/al21
[ThQb,,~TMR
~~i~t~on protection The Alcyon is a specially designed teletherapy machine to meet the requirements for cobalt source transport. When a source exchange is needed, the whole head of the machine is replaced. With this technique, there is no radioactive source handling in the hospital. Because of this design, our total body irradiation-related machine modification did not cause any radiation protection problem. The dosimetric measurements in contact with the head of the modified teletherapy machine, without its adjustable collimator, are shown in Table 1. At 1 m distance, all the measurements meet the ICRP recommendations (4). Patient population Two hundred forty-four patients have been treated between February 2, 1984 and December 27, 1990 using Source
c
,
4 e/2
midplane-
--
_ e/2 ~
t
t‘
*D out
Fig. 6. Determinationof correction factor Fe.
225” 3.4
270” 5
325” 18
this technique. Sixty-nine patients were treated by singledose total body irradiation ( 10 Gy delivered in about 6 to 8 h to the midplane at the level of L4, and 8 Gy to the lungs by partial s~elding) . One hundred seventy-five were treated by f~~~onated total body irradiation ( 12 Gy delivered in 6 fractions over 3 consecutive days to the midplane at the level of LA, and 9 Gy to the lungs by partial shielding). The type of fractionation protocol depends on several parameters, such as clinical status, age, or bone marrow team wish. The mean instantaneous and average dose rate was 5.28 lo-’ Gy/min and 2.58 10m2 Gy/min, respectively, in single-dose total body irradiation; 4.38 lo-* Gy/min and 2.40 lo-’ Gy/min in fractionated total body irradiation (Table 2). Clinical results have been published elsewhere ( 11) . DISCUSSION This technique is simple, practical, reproducible, and comfortable. It is easily performed by means of a vertically downward beam in a standard treatment room while the patient lies comfortably in prone and supine position. An instantaneous dose rate of 6 lo-’ Gy/min at middepth (level of LA) of the patient can be used, and if necessary, lower dose rates can be achieved by means of a beam attenuator. The dosimetry is similar to other total body irradiation techniques using @‘Cunits (6,7,8,12). The dose homoge~i~ is adequate as reported by Quast ( 13) and Van Dyke and Leung ( 15), and there is no need for tissue compensators, in contrast to total body irradiation techniques using horizontal beam laterally (patient prone and supine) (14). Lung shielding is easy, and due to the patient position, the setup and organ shielding is quickly and easily performed. It is more reproducible, especially in fractionated regimens, than techniques where the patients are not comfortable and may be unstable because they are lying on their sides. Patients may have a generalized skin erythema during the first few days following the total body ration. It has little effect on the patient’s general status. No long-term skin side effects have been noticed ( 11) . Our results, comparing patients irradiated either by 6-w photons or by teletherapy machine, showed no major differences between the two techniques ( 10). In our randomized study of 157 patients, according to the type of fractionation and instantaneous dose rate no significant diffenznces were observed in terms of early complications. In terms of interstitial pneumonitis and venoclusive disease, there was no influence of the total body irradiation parameters. However, the analyses showed higher incidence of cataractogenesis in patients treated with high insect dose rate than low i~~~~ dose rate (p = 0.006) (11).
“‘C Teletherapy
unit 0 C. DOMINIQUE
et al.
957
Table 2. Mean absorbed dose in different anatomic regions according to the instantaneous and average dose rate in different TBI techniques for a serial of 435 patients y*
Mean absorbed dose (Gy) L4 (minimum-maximum) Lung (minimum-maximum) Mediastinum (minimum-maximum) Head (minimum-maximum) Average dose rate at mid-plane (lo-’ Gy.min-‘) Instantaneous dose rate at midplane (lo-* Gym mini’)
6MV photons+
Single dose (n = 69)
Six fractions (n = 175)
Single dose (n = 191)
10.01 (9.76- 10.60) 7.92 (7.40-8.70) 9.69 (8.80- 10.40) 10.26 (9.18-11.80) 2.58 (1.68-3.36) 5.28 (3.42-6.24)
12.01 (11.23-12.90) 8.96 (7.71- 10.48) 11.32 (10.30-12.52) 11.75 (9.00-13.40) 2.40 (1.74-3.60) 4.38 (2.64-6.60)
10.03 (9.05-10.83) 7.93 (7.40-8.70) 9.34 (8.80- 10.40) 9.53 (7.23-11.20) 2.94 (2.16-4.08) 7.86 (5.27-17.40)
* Alcyon, GE-CGR MeV, But, France. ’ Neptune, GE-CGR MeV, But, France. Finally, this method is not limited to use with the Alcyon teletherapy unit. It may be used with other teletherapy units ( 12), provided radiation protections can be met when removing the collimator assembly. One can perform total body irradiation using a simple
“C head, fixed to the ceiling of a standard treatment room. This would be a reasonable alternative for a cancer center where many total-body irradiations are performed. This could be a less expensive and reasonable alternative to a linear accelerator.
REFERENCES 1. Andreo, P.; Cunningham, J. R.; Hohlfeld, K.; Svensson, H. Absorbed dose determination in photon and electron beams. An international code of practice. Vienna: International Atomic Energy Agency; 1987. 2. CFMRI. Recommandations pour la mesure de la dose absorbee en radiotherapie dans les faisceaux de photons et d’electrons d’energie comprise entre 1 MeV et 50 MeV. Paris: Collection des monographies, Bureau National de Metrologie, Volume 2; 1986. 3. Dutreix, A.; Bridier, A. Total body irradiation techniques and dosimetry. Pathol. Biol. 27:373-378; 1979. 4. ICRP Publication 60. 1990 Recommendations of the International Commission on Radiological Protection. Ann. ICRP 21:1-3; 1990. 5. Gahrton, G.; Tura, S.; Ljungman, P.; Belanger, C.; Brandt, L.; Cavo, M.; Facon, T.; Granena, A.; Gore, M.; Gratwhol, A.; Lowenberg, B.; Nikoskelainen, J.; Reiffers, J. J.; Samson, D.; Verdonck, L.; Volin, L. Allogeneic bone marrow transplantation in multiple myeloma. N. Engl. J. Med. 325:1267-1273; 1991. 6. Glasgow, G. P.; Mill, W. B. Cobalt-60 total-body irradiation dosimetry at 220 cm source-axis distance. Int. J. Radiat. Oncol. Biol. Phys. 6:773-777; 1980. 7. Jablonski, 0.; Motta-Veyssiere, J.; Chenal, C.; Guerin, R. A. Irradiations corporelles totales: techniques d’irradiation fractionnee par t&&cobalt. J. Radiol. 60:339-342; 1979. 8. Lam, W. C.; Order, S. E.; Thomas, E. D. Uniformity and standardization of single and opposing cobalt-60 sources for total body irradiation. Int. J. Radiat. Oncol. Biol. Phys. 6:245-250: 1980.
9. Mascret, B.; Maraninchi, D.; Gastaut, J. A.; Tubiana, N.; Sebahoun, G.; Horschowski, N.; Sainty, D.; Camerlo, J.; Lejeune, C.; Novakovitch, G.; Carcassone, Y. Treatment of malignant lymphoma with high dose of chemo or chemoradiotherapy and bone marrow transplantation. Eur. J. Cancer. Clin. Oncol. 22:461-471; 1986. 10. Ozsahin, M.; Belkacemi, Y.; P&e, F.; Dominique, C.; Schwartz, L. H.; Uzal, C.; Lef kopoulos, D.; Gindrey-Vie, B.; Vitu-Loas, L.; Touboul, E.; Schlienger, M.; Laugier, A. Total-body irradiation and cataract incidence: A randomized comparison of two instantaneous dose rates. Int. J. Radiat. Oncol. Biol. Phys. 28:343-347; 1994. 11. Ozsahin, M.; P&e, F.; Touboul, E.; Gindrey-Vie, B.; Dominique, C.; Lef kopoulos, D.; Krzisch, C.; Balosso, J.; Vitu, L.; Schwartz, L. H.; Rio, B.; Gorin, N. C.; Leblond, V.; Schlienger, M.; Laugier, A. Total-body irradiation before bone marrow transplantation: Results of two randomized instantaneous dose rates in 157 patients. Cancer 69:28532865; 1992. 12. Peters, V. G.; Herer, A. S. Modification of a standard cobalt-60 unit for total body irradiation at 150 cm SSD. Int. J. Radiat. Oncol. Biol. Phys. 10~927-932; 1984. 13. Quast, U. Physical problems of total body irradiation. Strahlenther. Onkol. 162:233-236; 1986. 14. Svensson, G. K.; Larsen, R. D.; Chen, T. S. The use of a 4 MV linear accelerator for whole body irradiation. Int. J. Radiat. Oncol. Biol. Phys. 6:761-765; 1980. 15. Van Dyke, J.; Leung, P. M. K.; Cunningham, J. R. Dosimetric considerations of very large cobalt-60 fields. Int. J. Radiat. Oncol. Biol. Phys. 6:753-759; 1980.