CNS depression potentiated with alcohol, other CNS depressants. Possible neurotoxicity with lithium: monitor, discontinue if occurs. Caution with drugs that prolong the QT interval (eg, ketoconazole, paroxetine). May be potentiated by CYP3A4 or CYP2D6 inhibitors/substrates (eg, itraconazole, nefazodone, buspirone, venlafaxine, alprazolam, fluvoxamine, quinidine, fluoxetine, sertraline, chlorpromazine, promethazine. May be antagonized by CYP3A4 inducers (eg, rifampin, carbamazepine); monitor and adjust doses. May increase intraocular pressure with anticholinergics, antiparkinson agents. Monitor anticoagulants.
Figure 4-1 Typical depth–dose curves for megavoltage photon and electron beams commonly used in the therapy of head and neck cancers. The upper panel shows curves for 10 cm × 10 cm fields for a 4-MV (80-cm SAD) linear accelerator (dashed line), a 6-MV (100-cm SAD) linear accelerator (solid line), and a 15-MV (100-cm SAD) linear accelerator (dotted line). The lower panel shows depth–dose curves for 10 cm × 10 cm fields for 6-MeV (dashed line), 12-MeV (solid line), and 20-MeV (dotted line) electron energies.
a higher dose of radiation to a deeper tumor. Higher energy photon beams can be used with even greater values of Dmax, but these have increased usefulness for the more deeply seated tumors of the thorax, abdomen, or pelvis.
Alternatively, the high-energy electron beam produced by the linear accelerator can be used directly in patient treatments. Typical depth–dose curves for various electron energies are shown in the lower panel of Figure 4–1 . Note that these beams typically penetrate a given distance and then fall off rapidly. There is a slight amount of skin sparing for the 6 MeV beam but not for the others. These beams are useful for treating skin cancers, tumors of the buccal mucosa, or even superficial tumors of the oral cavity, provided that appropriate applicator cones are used. Optimal treatment of a given lesion may require some combination of electron and photon beams, and this in turn requires the services of a comprehensive radiation treatment facility. Megavoltage electron beams have the same biologic properties as megavoltage photon beams for an equivalent dose of absorbed radiation.
An encephalopathic syndrome (characterized by weakness, lethargy , fever, tremulousness and confusion, extrapyramidal symptoms, leukocytosis , elevated serum enzymes, BUN , and fasting blood sugar) followed by irreversible brain damage has occurred in a few patients treated with lithium plus HALDOL. A causal relationship between these events and the concomitant administration of lithium and HALDOL has not been established; however, patients receiving such combined therapy should be monitored closely for early evidence of neurological toxicity and treatment discontinued promptly if such signs appear.