<prompt> Phase of the Cell cycle which is most sensitive to radiation:G2SG1,G2G2MG0, G1  <response>: Ans. c. G2M Ref: Harrison 19e 103e-4, 18e p691-692; Schwartz 9e p264-265Susceptibility of various phases of cell cycle to radiation: G2MQ G2M G1 Early S Late S PhaseQ.Radiation energy is absorbed by tissue causing ionization or excitationQ, which are responsible for various biological effects.Susceptibility of various phases of cell cycle to radiation: G2MQ G2M G1 Early S Late S PhaseQ.Phase of Cell CycleCommentG2MG2Most sensitiveQ to radiationEnd of S phaseMost resistantQ to radiationG1Radiation exposure leads to chromosomal aberrationG2Radiation exposure leads to chromatid aberrationRadiotherapyX-rays and gamma rays are the most common radiations used to treat cancersQ.X-rays are generated by linear acceleratorsQGamma rays are generated from decay of atomic nuclei in radio-isotopes like cobaltQ.RadiotherapyRadiosensitiserRadiation Protectors OxygenQ most effective Radiosensitiser MetronidazoleQ, misonidazole, tinidazole 5-FUQ non-hypoxic cell sensitizer HydroxyureaQ non-hypoxic cell sensitizer BUDR and IUDRQ non-hypoxic cell sensitizer CisplatinQ, paclitaxel, gemcitabine MitomycinQ, topotecan, vinorelbine Dactinomycin Actinomycin DQ Amifostine IL-1 GM-CSFIn RadiotherapyMost radiosensitive tissue of body: Bone marrowQLeast radiosensitive tissue of body: Nervous tissueBrainQMost radiosensitive blood cell: LymphocyteQ Thats why Lymphocytic predominant Hodgkins lymphoma has best prognosisLeast radiosensitive blood cell: PlateletQMost common organ to be affected by radiation: SkinQ Erythema earliest change, layer most commonly affected stratum basalisSebaceous gland function does not recover after radiotherapy.Pinna and axillae are common sites of radionecrosis i.e. for skin doses.Most radio resistant organ: VaginaMost common mucosa to be affected by radiation: Intestinal mucosaQ Earliest symptom is diarrheaMost sensitive abdominal organ: KidneyEffect of radiation on Testes and OvariesType B spermatogonia are exquisitely sensitive to the effects of radiationQ.Sertoli cells and Leydig cells are less radiosensitive than spermatogoniaQ.The single dose required for permanent sterilization on human males is 6-10 Gray GyQ.The radiation dose necessary to induce ovarian failure is age dependent.A single dose of 3-4 Gray 300-401 rads can induce amenorrhea in almost all women over 40 years of ageQ.In young women, oogenesis is much less sensitive to radiation than is spermatogenesis in men.Most radiosensitive ovarian tumor DysgerminomaQMost radiosensitive brain tumor MedulloblastomaQMost radiosensitive testicular tumor SeminomaQMost radiosensitive lung tumor Small cell CAQMost radiosensitive kidney tumor Wilms tumorQMost radiosensitive bone tumor Ewings sarcomaQ and Multiple myelomaQ 