Hello, I can understand your concern. Radiation treatment for cancer is usually associated with the side effect of dry mouth where saliva secretion decreases and thus, bad odor is felt. This issue will solve itself as the saliva secretion will return to normal after few months of radiotherapy. Till then, you can rely on some symptomatic treatment. Drink lots of water in small sips so mouth does not feel dry. You can over the counter available salivary substitutes such as Pilocarpine. This will increase saliva secretion for 3-4 hours and then it can be repeated again. You can keep sucking on a sugarless candy. In addition, you should visit dentist every month so that any focus of infection in the mouth can be treated and mouth can be kept clean of debris, plaque and calculus with ultrasonic scaling. I hope this information helps you. Thank you for choosing HealthcareMagic. I wish you feel better soon. Best, Dr. Viraj Shah