- Email: [email protected]
Ultrasonic treatment of tumors—II
Ultra.sound in Med. &Biol. Vol.6.pp. 341 to 344.
0301-5629~80.[201-0341.$02.0(r0
© PergamonPressLtd 1980.Printedin Great Britain
ULTRASONIC
TREATMENT
OF
TUMORS--II
MODERATE HYPERTHERMIA S. Z. CHILD, B. VlVES, C. W. FRIDD, J. D. HARE, C. A. LINKE, H. T. DAVIS and E. L. CARSTENSEN Departments of Electrical Engineering, Surgery (Urology), Microbiology and Biostatistics, University of Rochester, Rochester, NY 14627, U.S.A. (First received 27 August 1979; and in final form 18 March 1980)
Abstract--Ultrasonically induced hyperthermia (44~,5°C for 10 min) and surgical excision were used in the treatment of hamster fibrosarcomas. Both pulsed and continuous wave 3 MHz radiation was used. Rates of metastasis and effectiveness in eliminating the primary tumor were approximately equal with the two methods of treatment. Key words: Ultrasound, Acoustics, Hyperthermia, Ultrasonic damage, Ultrasonic therapy, Primary
tumors, Metastatic tumors, Surgical excision, Sarcoma, Hamster.
Because of its unique advantages for localized deep heating, ultrasound is now being used to achieve hyperthermia in the treatment of malignant tumors (Marmor et al., 1978ab, 1979). As a part of the background on bioeffects for this potentially beneficial therapy, it is important to assess the risk of an increase in the rate of metastasis as the result of exposure of tumors to ultrasound. There are two different approaches to hyperthermia. In the first, the tissue is held at a high temperature (60-75°C) for a sufficient time to kill all cells. The heat is localized in the tumor and the surrounding normal tissue is protected from heat damage. In the second and more commonly used approach, moderate temperatures (e.g. 42~5°C) are used in the hope that tumor cells will be selectively destroyed by heat. Localization is not as critical with this approach and in some cases whole region or whole body heating is used. Our earlier study, which used marked hyperthermia, found no evidence of increased metastases (Smachlo et al., 1979). In that treatment, it is unlikely that tumor cells survived the first few minutes of irradiation and hence the likelihood of living cells being dispersed was small. In the second method, only partial, immediate killing is achieved. We report here our comparison of both the rate of metastasis and the eradication of a hamster fibrosarcoma. METHODS
et al., 1979). The specified acoustic powers were measured with a radiation force balance which had an absorbing target. Spatial average intensity was taken to be the total power divided by the effective area of the source. Briefly, HTC-3049-91TC fibrosarcoma cells were implanted subcutaneously in the left lower quadrant of the abdomen of female, Syrian hamsters. The treatment procedures were undertaken when the tumor reached a diameter of 0.5-1.0 cm. Before exposures to ultrasound, an acoustic reflector was inserted surgically below the tumor and above the abdominal muscle to protect the viscera and dorsal skeleton of the animal. With this arrangement, sound passes through the tumor and a wave, attenuated by 20-30~o, is returned from the reflector. The progression continues until the acoustic energy is converted into heat, largely in the tumor tissue. Movement of the transducer ensures that near field and standing wave hot spots are minimized and heating of the tumor is uniform. The treatment procedures differed in two respects from earlier experiments: The source frequency was 3 MHz rather than 5 MHz, and before each treatment, a 50 micrometer, buttwelded, copper-constantan thermocouple was threaded through the center of the tumor to monitor temperatures during irradiation. The sound was coupled to the tumor through water and a layer of coupling gel approximately 0.5 cm thick. Before exposure, tumor temperatures ranged from 25 to 28°C. The treatment consisted of a rapid heating period of 3 4 min which brought the temperature of the tissue to
The tumor and details of the experimental methods have been described earlier (Smachlo 341
342
S.Z. CHILD et al.
the desired 44.5°C. The sound power was then reduced to hold the temperature at 44.5 4- I°C for the remainder of the 10min treatment period. Two ultrasonic exposure patterns were followed. In the continuous wave exposures, the initial acoustic power was approximately 5 Watts (spatial average intensity approximately 4W/cm2). After reaching 44.5°C, acoustic power, between 1 and 2 W was required to hold the temperature for the remainder of the period. In another group of animals, the ultrasound was pulsed--50 msec on and 200 msec off--with initial, temporal peak power of approximately 25 W and about 5 W peak acoustic power to maintain the 44.5°C. Sham treated animals went through the same procedure except that the sound was not turned on and thus the tumor temperatures remained in the range 25 28°C for the "exposure." Following treatment, the acoustic reflector was removed and the incision in the abdominal skin was closed with 4-0 silk. After 7 days, tumors which appeared to contain growing tissues were excised. This included all of the controls and approximately 40~o of the ultrasonically treated tumors (see Table 1). The ultrasonic treatment alone eliminated the remaining tumors. The animals were observed periodically for the next 16 weeks. In a few cases, the original excision was not successful in eliminating the primary tumor. Tumors which recurred were removed surgically in those cases. When metastases became obvious from inspection of the animals, they were sacri-
riced. A complete pathological examination was carried out and suspected metastatic tumors were biopsied for histological confirmation (Smachlo et al., 1979). At the end of the 16 week period, all survivors were sacrified and thoroughly examined for signs of metastases.
RESULTS
In contrast with our first study (Smachlo et al., 1979), the placement of the acoustic reflector between the tumor and muscle wall in these experiments preserved the abdominal muscle intact and the hamsters tolerated the procedure well. Metastatic nodules were easily distinguished from normal tissue by color and texture. They were found most frequently in the lungs, kidneys and peritoneal surfaces, but occasionally in axillary lymph nodes. Two experiments were completed, one involving a total of 49 animals and the second 48. The results are summarized in Tables ! and 2. Either excision or ultrasonic treatment decreased the numbers of tumors which matured. Specifically, we can say with p < 0.05 that in the worst case the maturation rate was less than 90~o. A chi-square test showed that there was not a significant difference (p > 0.10) among the success ratios for the different methods of treatment. There was not a significantly different (p > 0.10) rate of metastasis between excision and ultrasonically treated tumors.
Table 1. Rates of successful elimination of primary, HTC-3049-91TC, fibrosarcoma tumors in hamsters by excision and by irradiation with ultrasound. The numerator gives the number of animals without recurrence of the primary tumor after the first treatment (either excision or ultrasound) out of the total number of animals in the group, the denominator. (c.w. = continuous wave). The bottom line gives success ratios within 95~o confidence limits for the two experiments lumped together Excision
Experiment No. 1 Experiment No. 2 Summary
Ultrasound
0 Days
7 Days
6/11 (0.5) (0.5 4- 0.3)
9/16 (0.6) 10/13 (0.8) (0.7 4- 0.2)
c.w.
Pulsed
9/17 (0.5) 8/11 (0.7) (0.6 4- 0.2)
5/16 (0.3) 8/13 (0.6) (0.5 4- 0.2)
Table 2. Rates of metastasis in hamsters with HTC-3049-91TC fibrosarcoma tumors treated by excision or by irradiation with ultrasound. The numerator in the fraction is the number of animals with at least one distant metastasis (as opposed to a regrowth of the primary tumor) out of the total number of animals in the experimental group, the denominator. The bottom line gives the metastasis rates within 95~o confidence limits for the two experiments lumped together. Excision
Experiment No. 1 Experiment No. 2 Summary
Ultrasound
0 Days
7 Days
2/11 (0.2) (0.2 4- 0.2)
8/16 (0.5) 4/13 (0.3) (0.4 4- 0.2)
c.w.
3/17 (0.2) 2/i I (0.2) (0.2 4- 0.1)
Pulsed
5/16 (0.3) 2/11 (0.2) (0.2 _+ 0.2)
Ultrasonic treatment of t u m o r s - - I I
In the first experiment, the sham operated controls were treated exactly the same as the two ultrasound groups. However, from the standpoint of metastasis, this may not have given a proper control. The ultrasound either killed the tumor quickly or retarded its growth. On the other hand, the sham irradiated tumors had an additional 7 days of essentially uninterrupted growth. Instead, an appropriate control might be a group of animals in which the tumors were removed by excision immediately following sham irradiation. The second experiment, therefore, included two control groups: one in which the tumors were sham irradiated and then excised, and a second group in which the tumors were sham irradiated and held 7 days before being excised. A proper control for the metastasis experiment probably lies somewhere between these two groups. In order to monitor tumor temperature in these experiments, it was necessary to place a thermocouple in the tissue. This invasion of the tumor was a new aspect of our procedure. To determine whether metastasis was affected by the temperature monitoring process itself, we carried out an exploratory experiment with a total of 33 hamsters. When the tumors reached 0.5-1.0 cm diameter, all animals were depilated and divided into four groups: In Group 1, the tumors were immediately excised; in Group 2, a thermocouple was threaded into the tumor, held this way for 10 min, the thermocouple removed and the tumor excised; in Group 3, the animals were held for an additional seven days at which time the tumor was excised; in Group 4, a thermocouple was threaded through the tumor, held this way for 10 min, the thermocouple removed, then the animals were maintained for another 7 days at which time the tumor was excised. In this way, we hoped to test the effects of thermocouples under conditions comparable to both control groups in experiment No. 2 above. As in the ultrasound experiments, all animals were
Table 3. Test for the effects of thermocouple insertion on the rate of metastasis for HTC-3049-91TC hamster fibrosarcoma. The n u m e r a t o r in the fraction gives the n u m b e r of animals with metastases out of the total in the group (denominator). The metastasis rates within 9 5 ~ confidence limits are given in parentheses. Excision time Immediate 7 Days Control Thermocouple
2/7 (0.3 + 0.3) 3/8 (0.4 + 0.3)
7/9 (0.8 + 0.3) 7/9 (0.8 + 0.3)
343
observed over a period of approximately 6 weeks. The results are summarized in Table 3. There is a strong suggestion that the rate of metastasis increased from day 0 to day 7 (p < 0.05) but the presence of the thermocouple did not appear to influence the rates
(p > o.lo). DISCUSSION
This study employed the same tumor cell line which had been used in Part I of the investigation of the metastasis question. In the earlier work, only one animal out of a total of 92 in that investigation developed a metastasis. In the present study, at least 20~o of the animals in every group developed one or more distant metastases. The limited test summarized in Table 3 gives no evidence that the insertion of a thermocouple in the tumor affects the rate of metastasis. This leads us to believe that the difference must have arisen in the tumorhost system rather than as a result of the changes in experimental procedure. Whatever the cause of the change, it strengthens the results of the current work. We are clearly dealing with a tumor which will metastasize either spontaneously or with minor mechanical manipulation. We, therefore, ask with our experiments whether ultrasound can modify a finite rate of metastasis. This should reveal more subtle effects than if we were dealing with a tumor which metastasized either 100~o of the time or not at all. Experiment No. 1 alone might lead to the conclusion that ultrasound actually reduces the incidence of metastases. Experiment No. 2 together with the data in Table 3 show that the additional seven days after the initial manipulation of the tumors are very important for the generation of metastatic lesions. When compared with a proper control, however, it appears that ultrasound as used in these studies has no effect on the formation of metastases. This statement applies both for c.w. exposures, in which maximum spatial intensities were of the order of 4W/cm 2, and to pulsed exposures in which the peak intensities were approximately five times greater. Since the tumor-host system appears to have changed between Parts I and II of these studies, it is not proper to make a direct comparison between the results of the two investigations. It should be noted, however, that the mild hyperthermia (44.5°C) used here was somewhat less effective in eliminating the
344
S.Z. CHILD et al.
primary tumor than the higher temperatures (6(~70°C) used before. Even so, the mild hyperthermia produced by ultrasound, c.w. or pulsed, was approximately as effective as excision in treatment of the tumors. Acknowledgements The authors are indebted to Jolynn Jarboe and Lynn Emilson for technical assistance in this program. This study was supported in part by USPHS Grant No. GM09933.
REFERENCES
Hare, J. D. (1967) Location and characteristics of the phenylalanine transport mechanism in normal and
polyomatransformed hamster cells. Cancer Res. 27, 2357 2363. Marmor, J. B., Pounds, D., Hahn, N. and Hahn, G. M. (1978a) Treating spontaneous tumors in dogs and cats by ultrasound induced hyperthermia. Int. J. Radiat. Oncol. Biol. Phys. 4, 967 973. Marmor, J. B. and Hahn, G. M. (1978b) Ultrasound heating in previously irradiated sites. Int. J. Radiat. Oncol. Biol. Phys. 4, 1029 1032. Marmot, J. B., Pounds, D., Postic, T. B. and Hahn, G. M. (1979) Treatment of superficial human neoplasms by local hyperthermia induced by ultrasound. Cancer 43, 188-197. Smachlo, K., Fridd, C. W., Child, S. Z., Hare, J. D., Linke, C. A. and Carstensen, E. L. (1979) Ultrasonic treatment of tumors: I. Absence of metastases following treatment of a hamster fibrosarcoma. Ultrasound in Med. Biol. 5, 45 49.
0301-5629~80.[201-0341.$02.0(r0
© PergamonPressLtd 1980.Printedin Great Britain
ULTRASONIC
TREATMENT
OF
TUMORS--II
MODERATE HYPERTHERMIA S. Z. CHILD, B. VlVES, C. W. FRIDD, J. D. HARE, C. A. LINKE, H. T. DAVIS and E. L. CARSTENSEN Departments of Electrical Engineering, Surgery (Urology), Microbiology and Biostatistics, University of Rochester, Rochester, NY 14627, U.S.A. (First received 27 August 1979; and in final form 18 March 1980)
Abstract--Ultrasonically induced hyperthermia (44~,5°C for 10 min) and surgical excision were used in the treatment of hamster fibrosarcomas. Both pulsed and continuous wave 3 MHz radiation was used. Rates of metastasis and effectiveness in eliminating the primary tumor were approximately equal with the two methods of treatment. Key words: Ultrasound, Acoustics, Hyperthermia, Ultrasonic damage, Ultrasonic therapy, Primary
tumors, Metastatic tumors, Surgical excision, Sarcoma, Hamster.
Because of its unique advantages for localized deep heating, ultrasound is now being used to achieve hyperthermia in the treatment of malignant tumors (Marmor et al., 1978ab, 1979). As a part of the background on bioeffects for this potentially beneficial therapy, it is important to assess the risk of an increase in the rate of metastasis as the result of exposure of tumors to ultrasound. There are two different approaches to hyperthermia. In the first, the tissue is held at a high temperature (60-75°C) for a sufficient time to kill all cells. The heat is localized in the tumor and the surrounding normal tissue is protected from heat damage. In the second and more commonly used approach, moderate temperatures (e.g. 42~5°C) are used in the hope that tumor cells will be selectively destroyed by heat. Localization is not as critical with this approach and in some cases whole region or whole body heating is used. Our earlier study, which used marked hyperthermia, found no evidence of increased metastases (Smachlo et al., 1979). In that treatment, it is unlikely that tumor cells survived the first few minutes of irradiation and hence the likelihood of living cells being dispersed was small. In the second method, only partial, immediate killing is achieved. We report here our comparison of both the rate of metastasis and the eradication of a hamster fibrosarcoma. METHODS
et al., 1979). The specified acoustic powers were measured with a radiation force balance which had an absorbing target. Spatial average intensity was taken to be the total power divided by the effective area of the source. Briefly, HTC-3049-91TC fibrosarcoma cells were implanted subcutaneously in the left lower quadrant of the abdomen of female, Syrian hamsters. The treatment procedures were undertaken when the tumor reached a diameter of 0.5-1.0 cm. Before exposures to ultrasound, an acoustic reflector was inserted surgically below the tumor and above the abdominal muscle to protect the viscera and dorsal skeleton of the animal. With this arrangement, sound passes through the tumor and a wave, attenuated by 20-30~o, is returned from the reflector. The progression continues until the acoustic energy is converted into heat, largely in the tumor tissue. Movement of the transducer ensures that near field and standing wave hot spots are minimized and heating of the tumor is uniform. The treatment procedures differed in two respects from earlier experiments: The source frequency was 3 MHz rather than 5 MHz, and before each treatment, a 50 micrometer, buttwelded, copper-constantan thermocouple was threaded through the center of the tumor to monitor temperatures during irradiation. The sound was coupled to the tumor through water and a layer of coupling gel approximately 0.5 cm thick. Before exposure, tumor temperatures ranged from 25 to 28°C. The treatment consisted of a rapid heating period of 3 4 min which brought the temperature of the tissue to
The tumor and details of the experimental methods have been described earlier (Smachlo 341
342
S.Z. CHILD et al.
the desired 44.5°C. The sound power was then reduced to hold the temperature at 44.5 4- I°C for the remainder of the 10min treatment period. Two ultrasonic exposure patterns were followed. In the continuous wave exposures, the initial acoustic power was approximately 5 Watts (spatial average intensity approximately 4W/cm2). After reaching 44.5°C, acoustic power, between 1 and 2 W was required to hold the temperature for the remainder of the period. In another group of animals, the ultrasound was pulsed--50 msec on and 200 msec off--with initial, temporal peak power of approximately 25 W and about 5 W peak acoustic power to maintain the 44.5°C. Sham treated animals went through the same procedure except that the sound was not turned on and thus the tumor temperatures remained in the range 25 28°C for the "exposure." Following treatment, the acoustic reflector was removed and the incision in the abdominal skin was closed with 4-0 silk. After 7 days, tumors which appeared to contain growing tissues were excised. This included all of the controls and approximately 40~o of the ultrasonically treated tumors (see Table 1). The ultrasonic treatment alone eliminated the remaining tumors. The animals were observed periodically for the next 16 weeks. In a few cases, the original excision was not successful in eliminating the primary tumor. Tumors which recurred were removed surgically in those cases. When metastases became obvious from inspection of the animals, they were sacri-
riced. A complete pathological examination was carried out and suspected metastatic tumors were biopsied for histological confirmation (Smachlo et al., 1979). At the end of the 16 week period, all survivors were sacrified and thoroughly examined for signs of metastases.
RESULTS
In contrast with our first study (Smachlo et al., 1979), the placement of the acoustic reflector between the tumor and muscle wall in these experiments preserved the abdominal muscle intact and the hamsters tolerated the procedure well. Metastatic nodules were easily distinguished from normal tissue by color and texture. They were found most frequently in the lungs, kidneys and peritoneal surfaces, but occasionally in axillary lymph nodes. Two experiments were completed, one involving a total of 49 animals and the second 48. The results are summarized in Tables ! and 2. Either excision or ultrasonic treatment decreased the numbers of tumors which matured. Specifically, we can say with p < 0.05 that in the worst case the maturation rate was less than 90~o. A chi-square test showed that there was not a significant difference (p > 0.10) among the success ratios for the different methods of treatment. There was not a significantly different (p > 0.10) rate of metastasis between excision and ultrasonically treated tumors.
Table 1. Rates of successful elimination of primary, HTC-3049-91TC, fibrosarcoma tumors in hamsters by excision and by irradiation with ultrasound. The numerator gives the number of animals without recurrence of the primary tumor after the first treatment (either excision or ultrasound) out of the total number of animals in the group, the denominator. (c.w. = continuous wave). The bottom line gives success ratios within 95~o confidence limits for the two experiments lumped together Excision
Experiment No. 1 Experiment No. 2 Summary
Ultrasound
0 Days
7 Days
6/11 (0.5) (0.5 4- 0.3)
9/16 (0.6) 10/13 (0.8) (0.7 4- 0.2)
c.w.
Pulsed
9/17 (0.5) 8/11 (0.7) (0.6 4- 0.2)
5/16 (0.3) 8/13 (0.6) (0.5 4- 0.2)
Table 2. Rates of metastasis in hamsters with HTC-3049-91TC fibrosarcoma tumors treated by excision or by irradiation with ultrasound. The numerator in the fraction is the number of animals with at least one distant metastasis (as opposed to a regrowth of the primary tumor) out of the total number of animals in the experimental group, the denominator. The bottom line gives the metastasis rates within 95~o confidence limits for the two experiments lumped together. Excision
Experiment No. 1 Experiment No. 2 Summary
Ultrasound
0 Days
7 Days
2/11 (0.2) (0.2 4- 0.2)
8/16 (0.5) 4/13 (0.3) (0.4 4- 0.2)
c.w.
3/17 (0.2) 2/i I (0.2) (0.2 4- 0.1)
Pulsed
5/16 (0.3) 2/11 (0.2) (0.2 _+ 0.2)
Ultrasonic treatment of t u m o r s - - I I
In the first experiment, the sham operated controls were treated exactly the same as the two ultrasound groups. However, from the standpoint of metastasis, this may not have given a proper control. The ultrasound either killed the tumor quickly or retarded its growth. On the other hand, the sham irradiated tumors had an additional 7 days of essentially uninterrupted growth. Instead, an appropriate control might be a group of animals in which the tumors were removed by excision immediately following sham irradiation. The second experiment, therefore, included two control groups: one in which the tumors were sham irradiated and then excised, and a second group in which the tumors were sham irradiated and held 7 days before being excised. A proper control for the metastasis experiment probably lies somewhere between these two groups. In order to monitor tumor temperature in these experiments, it was necessary to place a thermocouple in the tissue. This invasion of the tumor was a new aspect of our procedure. To determine whether metastasis was affected by the temperature monitoring process itself, we carried out an exploratory experiment with a total of 33 hamsters. When the tumors reached 0.5-1.0 cm diameter, all animals were depilated and divided into four groups: In Group 1, the tumors were immediately excised; in Group 2, a thermocouple was threaded into the tumor, held this way for 10 min, the thermocouple removed and the tumor excised; in Group 3, the animals were held for an additional seven days at which time the tumor was excised; in Group 4, a thermocouple was threaded through the tumor, held this way for 10 min, the thermocouple removed, then the animals were maintained for another 7 days at which time the tumor was excised. In this way, we hoped to test the effects of thermocouples under conditions comparable to both control groups in experiment No. 2 above. As in the ultrasound experiments, all animals were
Table 3. Test for the effects of thermocouple insertion on the rate of metastasis for HTC-3049-91TC hamster fibrosarcoma. The n u m e r a t o r in the fraction gives the n u m b e r of animals with metastases out of the total in the group (denominator). The metastasis rates within 9 5 ~ confidence limits are given in parentheses. Excision time Immediate 7 Days Control Thermocouple
2/7 (0.3 + 0.3) 3/8 (0.4 + 0.3)
7/9 (0.8 + 0.3) 7/9 (0.8 + 0.3)
343
observed over a period of approximately 6 weeks. The results are summarized in Table 3. There is a strong suggestion that the rate of metastasis increased from day 0 to day 7 (p < 0.05) but the presence of the thermocouple did not appear to influence the rates
(p > o.lo). DISCUSSION
This study employed the same tumor cell line which had been used in Part I of the investigation of the metastasis question. In the earlier work, only one animal out of a total of 92 in that investigation developed a metastasis. In the present study, at least 20~o of the animals in every group developed one or more distant metastases. The limited test summarized in Table 3 gives no evidence that the insertion of a thermocouple in the tumor affects the rate of metastasis. This leads us to believe that the difference must have arisen in the tumorhost system rather than as a result of the changes in experimental procedure. Whatever the cause of the change, it strengthens the results of the current work. We are clearly dealing with a tumor which will metastasize either spontaneously or with minor mechanical manipulation. We, therefore, ask with our experiments whether ultrasound can modify a finite rate of metastasis. This should reveal more subtle effects than if we were dealing with a tumor which metastasized either 100~o of the time or not at all. Experiment No. 1 alone might lead to the conclusion that ultrasound actually reduces the incidence of metastases. Experiment No. 2 together with the data in Table 3 show that the additional seven days after the initial manipulation of the tumors are very important for the generation of metastatic lesions. When compared with a proper control, however, it appears that ultrasound as used in these studies has no effect on the formation of metastases. This statement applies both for c.w. exposures, in which maximum spatial intensities were of the order of 4W/cm 2, and to pulsed exposures in which the peak intensities were approximately five times greater. Since the tumor-host system appears to have changed between Parts I and II of these studies, it is not proper to make a direct comparison between the results of the two investigations. It should be noted, however, that the mild hyperthermia (44.5°C) used here was somewhat less effective in eliminating the
344
S.Z. CHILD et al.
primary tumor than the higher temperatures (6(~70°C) used before. Even so, the mild hyperthermia produced by ultrasound, c.w. or pulsed, was approximately as effective as excision in treatment of the tumors. Acknowledgements The authors are indebted to Jolynn Jarboe and Lynn Emilson for technical assistance in this program. This study was supported in part by USPHS Grant No. GM09933.
REFERENCES
Hare, J. D. (1967) Location and characteristics of the phenylalanine transport mechanism in normal and
polyomatransformed hamster cells. Cancer Res. 27, 2357 2363. Marmor, J. B., Pounds, D., Hahn, N. and Hahn, G. M. (1978a) Treating spontaneous tumors in dogs and cats by ultrasound induced hyperthermia. Int. J. Radiat. Oncol. Biol. Phys. 4, 967 973. Marmor, J. B. and Hahn, G. M. (1978b) Ultrasound heating in previously irradiated sites. Int. J. Radiat. Oncol. Biol. Phys. 4, 1029 1032. Marmot, J. B., Pounds, D., Postic, T. B. and Hahn, G. M. (1979) Treatment of superficial human neoplasms by local hyperthermia induced by ultrasound. Cancer 43, 188-197. Smachlo, K., Fridd, C. W., Child, S. Z., Hare, J. D., Linke, C. A. and Carstensen, E. L. (1979) Ultrasonic treatment of tumors: I. Absence of metastases following treatment of a hamster fibrosarcoma. Ultrasound in Med. Biol. 5, 45 49.