The more chemotherapy we give, the more cancer and normal cells are affected. To decrease the side effects, we have to decrease the dose of chemotherapy but, in turn, this weakens the effects against the cancer. Therefore, we want to give the highest dose of chemotherapy that is well tolerated, to maximize the effects against the cancer, yet avoiding side effects.
As simple as it sounds, there is no simple way to find that perfect dose. Each individual and each cancer will have variations. No tests can be done to predict the side effects or the effect against the cancer cells. I start with a standard dose of chemotherapy that is well tolerated by most patients. If side effects are seen, I decrease the dose of chemotherapy in the future. If multiple adjustments are needed and the dose is significantly decreased, I may recommend switching to a different protocol or stopping chemotherapy.
In special circumstances, when there is a strong suspicion that the patient may not tolerate the treatment well (very sick patient, very small patients, etc) I may choose to start with a lower than standard dose initially and increase it in the future if it is well tolerated.
Each chemotherapy drug has its own risk of side effects. Just because a patient had a problem with a drug, doesn’t mean he/she will have problems with other drugs and vice-versa. Occasionally there can be a cumulative effect of giving chemotherapy long term that increases the risk of side effects as we give more chemotherapy. We monitor the patients closely for side effects and recommend modifications as needed.