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Matching intraoperative electron beam fields: Dosimetric and clinical considerations
Radiation
90
Oncology
Biology
??
Physics
??
RESIDENT MATCHING
INTRAOPERATIVE
E. G. Shaw, M.D., Mayo Clinic
ELECTRON
BEAM FIELDS:
C. R. Blackwell,
and Graduate
School
M.S.,
November
ESSAYS
DOSIMETRIC
E. C. McCullough,
of Medicine,
Rochester,
1986, Volume 12, Sup. 1
AND CLINICAL Ph.D.
CONSIDERATIONS
and L. L. Gunderson,
M.D.
MN 55905
Adjacent intraoperative electron beam fields present special dosimetric problems due to the surface In the intraoperative setting, where large, narrowing of electron isodose curves relative to those at depth. single fraction doses are delivered, the low and high dose areas which result from gaps or overlaps between the isodose curves of matched electron fields may translate into decreased local control or excessive normal In this talk, the dosimetry of gapped, adjacent and overlapped 8x9 cm* rectangular tissue toxicity. An "ideal" method of matching intraoperative intraoperative cones for 9-18 MeV electrons are detailed. electron fields is presented. Dose in the mid-separation reqion was examined over a ranqe of field separations between two cones, from a 1.0 cm gap to a cgapped+ 1.5 cm overlap in 2 to 5 mm increments. The mid-separation 175 reqion dose (at d=dmax. relative to a central axis dmax for a c single field) ranges from 60% for a 5 mm gap between fields, to 150.135% for adjacent fields, to 180% for a 5 mm overlap between fields (see Fiqure 1). This sensitivitv of dose in the match region, i.e . a-120% change in dose over-a 10 mm change in field separation, is independent of energy for 9, 12, 15 and 18 MeV The plot of mid-separation dose versus field separaelectrons. tion shows that electron fields will be ideally matched at d=dmax when there is a 2 mm gap between fields, independent of electron However, this gap results in a energy over the 9-18 MeV range. low dose area of up to 50% within the gap region to a depth of nearly 1.0 cm. When 0.5 to 1.0 cm of tissue equivalent bolus material is placed so that it covers the fields including the gap region, the isodose curves shift toward the surface, effectively eliminating the low dose area and creating the "ideal" match between the rectangular electron fields. When intraoperative electron fields must be intentionally overlapped, due to irregular tumor volumes which cannot be adequately covered by a single cone, a lead cut-out should be placed exactly equal in size and shape to the overlap region, with sufficient thickness to attenuate the electron dose by 90%. This results in full dose at the surface, with negligible high dose areas at depth within the match region. The clinical application of these field matching guidelines in an intraoperative setting will be presented. The Effect Of Temperature On The Tumor Fibrosarcoma Tumor In C3Hf/Sed Mice
a! {
125..
F '2
100..
2 =
75-m 50--
Field Separation
(mm)
Figure 1: Percent dose in the midseparation region (at d=dmax, relative to a central axis dmax for a single field) between two gapped,'adjacent or overlapped 8x9 cm* rectangular cones
Blood Flow And On The Size Of Hypoxic
Cell Fraction
Christopher G. Willett,l M.D., Munelasu Urano,l M.D., Ph.D., Herman D. Suit,I M.D. Ph.D., William Strauss,* M.D., Julia Kahn, B.S. and Paul Okunieff,l M.D.
In A Murine H.
Edwin L. Steele Laboratory of Radiation Biology, Department of Radiation Medicine,1 Department of Nuclear Medicine,* Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114 The effect of various hypothermic, or hypo to hyperthermic temperatures on the tumor blood flow and the hypoxic cell fractions was studied in a murine fibrosarcoma transplanted in the hind leg of anesthetized mice. The blood flow to the tumor was assessed by the determination of the uptake of Thallium-201; the hypoxic cell fraction was estimated from cell survival curves derived from data based At room temperature, the intratumor temperature of 8 mn fibrosarcoma in an on lung colony assay. anesthesized mouse was 27.7" C. Over a temperature range of 18' to 46'C, the maximal blood flow occurred at 35°C which was approximately 2 times greater than that at room temperature (24" to 27' C) or at 39' C. The hypoxic cell fraction at 35°C was 12%, and was significantly less than that at room temperature or at These 39" c. The hypoxic cell fractions at room temperature and at 39'C were 45% and 32%, respectively. results suggest that the optimal radiation sensitivity of peripherally located tumors can be obtained by warming the tumors to temperatures where maximal blood flow and minimal hypoxic cell fraction occur.
90
Oncology
Biology
??
Physics
??
RESIDENT MATCHING
INTRAOPERATIVE
E. G. Shaw, M.D., Mayo Clinic
ELECTRON
BEAM FIELDS:
C. R. Blackwell,
and Graduate
School
M.S.,
November
ESSAYS
DOSIMETRIC
E. C. McCullough,
of Medicine,
Rochester,
1986, Volume 12, Sup. 1
AND CLINICAL Ph.D.
CONSIDERATIONS
and L. L. Gunderson,
M.D.
MN 55905
Adjacent intraoperative electron beam fields present special dosimetric problems due to the surface In the intraoperative setting, where large, narrowing of electron isodose curves relative to those at depth. single fraction doses are delivered, the low and high dose areas which result from gaps or overlaps between the isodose curves of matched electron fields may translate into decreased local control or excessive normal In this talk, the dosimetry of gapped, adjacent and overlapped 8x9 cm* rectangular tissue toxicity. An "ideal" method of matching intraoperative intraoperative cones for 9-18 MeV electrons are detailed. electron fields is presented. Dose in the mid-separation reqion was examined over a ranqe of field separations between two cones, from a 1.0 cm gap to a cgapped+ 1.5 cm overlap in 2 to 5 mm increments. The mid-separation 175 reqion dose (at d=dmax. relative to a central axis dmax for a c single field) ranges from 60% for a 5 mm gap between fields, to 150.135% for adjacent fields, to 180% for a 5 mm overlap between fields (see Fiqure 1). This sensitivitv of dose in the match region, i.e . a-120% change in dose over-a 10 mm change in field separation, is independent of energy for 9, 12, 15 and 18 MeV The plot of mid-separation dose versus field separaelectrons. tion shows that electron fields will be ideally matched at d=dmax when there is a 2 mm gap between fields, independent of electron However, this gap results in a energy over the 9-18 MeV range. low dose area of up to 50% within the gap region to a depth of nearly 1.0 cm. When 0.5 to 1.0 cm of tissue equivalent bolus material is placed so that it covers the fields including the gap region, the isodose curves shift toward the surface, effectively eliminating the low dose area and creating the "ideal" match between the rectangular electron fields. When intraoperative electron fields must be intentionally overlapped, due to irregular tumor volumes which cannot be adequately covered by a single cone, a lead cut-out should be placed exactly equal in size and shape to the overlap region, with sufficient thickness to attenuate the electron dose by 90%. This results in full dose at the surface, with negligible high dose areas at depth within the match region. The clinical application of these field matching guidelines in an intraoperative setting will be presented. The Effect Of Temperature On The Tumor Fibrosarcoma Tumor In C3Hf/Sed Mice
a! {
125..
F '2
100..
2 =
75-m 50--
Field Separation
(mm)
Figure 1: Percent dose in the midseparation region (at d=dmax, relative to a central axis dmax for a single field) between two gapped,'adjacent or overlapped 8x9 cm* rectangular cones
Blood Flow And On The Size Of Hypoxic
Cell Fraction
Christopher G. Willett,l M.D., Munelasu Urano,l M.D., Ph.D., Herman D. Suit,I M.D. Ph.D., William Strauss,* M.D., Julia Kahn, B.S. and Paul Okunieff,l M.D.
In A Murine H.
Edwin L. Steele Laboratory of Radiation Biology, Department of Radiation Medicine,1 Department of Nuclear Medicine,* Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114 The effect of various hypothermic, or hypo to hyperthermic temperatures on the tumor blood flow and the hypoxic cell fractions was studied in a murine fibrosarcoma transplanted in the hind leg of anesthetized mice. The blood flow to the tumor was assessed by the determination of the uptake of Thallium-201; the hypoxic cell fraction was estimated from cell survival curves derived from data based At room temperature, the intratumor temperature of 8 mn fibrosarcoma in an on lung colony assay. anesthesized mouse was 27.7" C. Over a temperature range of 18' to 46'C, the maximal blood flow occurred at 35°C which was approximately 2 times greater than that at room temperature (24" to 27' C) or at 39' C. The hypoxic cell fraction at 35°C was 12%, and was significantly less than that at room temperature or at These 39" c. The hypoxic cell fractions at room temperature and at 39'C were 45% and 32%, respectively. results suggest that the optimal radiation sensitivity of peripherally located tumors can be obtained by warming the tumors to temperatures where maximal blood flow and minimal hypoxic cell fraction occur.