SulfonesPurinesPiperazinesPhosphodiesterase InhibitorsPhosphodiesterase 5 Inhibitors3',5'-Cyclic-GMP PhosphodiesterasesErectile DysfunctionCyclic Nucleotide Phosphodiesterases, Type 5Penile ErectionHomosexuality, MaleMethamphetamineVasodilator AgentsCyclic GMPGeorgiaUnsafe SexRisk-TakingSexual BehaviorRadiation DosageLethal Dose 50Drug Administration ScheduleAdministration, OralRadiometryTime FactorsDose-Response Relationship, RadiationDose FractionationRadiotherapy DosageDouble-Blind MethodTreatment OutcomeInjections, IntravenousArea Under CurveRadiotherapy Planning, Computer-AssistedHalf-LifeInfusions, Intravenous