Therapeutic Gain Factors for Fractionated Radiation Treatment of Spontaneous Murine Tumors Using Fast Neutrons, Photons Plus ${\rm O}_{2}1$ or 3 ATA, or Photons Plus Misonidazole

• Published in: Radiation research Vol. 116; no. 3; pp. 482 - 502
• Main Authors: Suit, Herman D., Sedlacek, Robert, Silver, Geoffrey, Hsieh, Chung-Cheng, Epp, Edward R., Frank Q. H. Ngo, Roberts, William K., Verhey, Lynn
• Format: Journal Article
• Language: English
• Published: Academic Press, Inc 01-12-1988
• Subjects: Dose fractionation; Fast neutrons; Irradiation; Medical treatment; Mice; Neutrons; Oxygen; Photons; Radiotherapy; Tumors
• ISSN: 0033-7587; 1938-5404

Therapeutic gain factors (TGFs) have been determined for three spontaneous tumors of the C3H mouse treated by photons + normobaric oxygen (${\rm O}_{2}1$ ATA), photons + hyperbaric oxygen ( O2 3 ATA), photons + misonidazole, or fast neutrons. The tumors were early generation isotransplants of spontaneous tumors: MCaIV, a mammary carcinoma; FSaII, a fibrosarcoma; and SCCVII, a squamous cell carcinoma. The tumors, transplanted to the right leg, were 6 mm at start of treatment. Normal tissue responses studied were acute reaction of normal skin (all treatment modalities) and LD50 following irradiation of the upper abdomen (in test of photons + O2 at 1 or 3 ATA). Thus both the tumor and normal tissues would be classified as "acute responding." All subject tissues were at ≃34.5-35°C at irradiation. Treatments were based on d(25)Be or p(43)Be fast neutron beams, 60 Co and 137 Cs photon beams. Treatments were given in 5 or 15 equal doses in 5 days. For photon treatments, TGFs ($\text{air}/{\rm O}_{2}$ 3 ATA) were substantially and significantly larger than 1 for all three tumor systems treated at small or large doses per fraction when related to skin or abdominal tissue responses. The TGFs ($\text{air}/{\rm O}_{2}$ 1 ATA) were > 1 at small doses per fraction for MCaIV and FSaII for skin as the normal tissue; the TGFs for all three tumors and at all doses per fraction would be > 1 when related to upper abdominal tissues. TGFs ( O2 1 ${\rm ATA}/{\rm O}_{2}$ 3 ATA) for photon irradiation > 1 were found only for SCCVII and that obtained for both large and small doses per fraction. Misonidazole achieved impressive TGFs (air/air + miso or $\text{air}/{\rm O}_{2}$ 1 ATA + miso); the drug was tested only at 10-12 Gy/fraction and relative to skin. RBEs (FN) for the three tumors were lower at 1.5-2 Gy(FN)/fraction than at 5-6 Gy(FN)/fraction, i.e. the opposite to that reported for normal tissue (RBE increases with decreasing dose per fraction). A TGF (relative to skin reaction) > 1 for fast neutron therapy was found only for SCCVII when treated at large doses/fraction; this was true for air or O2 1 ATA conditions.