AI model could help make cancer treatment less toxic

Medical professionals generally administer maximum safe drug doses to shrink the tumour as much as possible. But these strong pharmaceuticals still cause debilitating side effects in patients.

In a paper being presented at the 2018 Machine Learning for Healthcare conference at Stanford University, MIT Media Lab researchers detail a model that could make dosing regimens less toxic but still effective.

Powered by a 'self-learning' machine-learning technique, the model looks at treatment regimens currently in use, and iteratively adjusts the doses. Eventually, it finds an optimal treatment plan, with the lowest possible potency and frequency of doses that should still reduce tumour sizes to a degree comparable to that of traditional regimens.

In simulated trials of 50 patients, the machine-learning model designed treatment cycles that reduced the potency to a quarter or half of nearly all the doses while maintaining the same tumour-shrinking potential. Many times, it skipped doses altogether, scheduling administrations only twice a year instead of monthly.

“We kept the goal, where we have to help patients by reducing tumour sizes but, at the same time, we want to make sure the quality of life — the dosing toxicity — doesn’t lead to overwhelming sickness and harmful side effects,” said Pratik Shah, a principal investigator at the Media Lab who supervised this research.

The researchers’ model uses a technique called reinforced learning (RL), a method inspired by behavioral psychology, in which a model learns to favor certain behavior that leads to a desired outcome.

The technique comprises artificially intelligent 'agents' that complete 'actions' in an unpredictable, complex environment to reach a desired 'outcome.' Whenever it completes an action, the agent receives a 'reward' or 'penalty,' depending on whether the action works toward the outcome. Then, the agent adjusts its actions accordingly to achieve that outcome.

Rewards and penalties are basically positive and negative numbers, say +1 or -1. Their values vary by the action taken, calculated by probability of succeeding or failing at the outcome, among other factors. The agent is essentially trying to numerically optimise all actions, based on reward and penalty values, to get to a maximum outcome score for a given task.

The approach was used to train the computer program DeepMind that in 2016 made headlines for beating one of the world’s best human players in the game 'Go.' It’s also used to train driverless cars in maneuvers, such as merging into traffic or parking, where the vehicle will practice over and over, adjusting its course, until it gets it right.

The researchers adapted an RL model for glioblastoma treatments that use a combination of the drugs temozolomide (TMZ) and procarbazine, lomustine, and vincristine (PVC), administered over weeks or months.

The model’s agent combs through traditionally administered regimens. These regimens are based on protocols that have been used clinically for decades and are based on animal testing and various clinical trials. Oncologists use these established protocols to predict how much doses to give patients based on weight.

As the model explores the regimen, at each planned dosing interval — say, once a month — it decides on one of several actions. It can, first, either initiate or withhold a dose. If it does administer, it then decides if the entire dose, or only a portion, is necessary.

At each action, it pings another clinical model — often used to predict a tumour’s change in size in response to treatments — to see if the action shrinks the mean tumour diameter. If it does, the model receives a reward.

However, the researchers also had to make sure the model doesn’t just dish out a maximum number and potency of doses. Whenever the model chooses to administer all full doses, therefore, it gets penalised, so instead chooses fewer, smaller doses.

“If all we want to do is reduce the mean tumour diameter, and let it take whatever actions it wants, it will administer drugs irresponsibly,” Shah said. “Instead, we said, ‘We need to reduce the harmful actions it takes to get to that outcome.’”

This represents an “unorthodox RL model, described in the paper for the first time,” Shah said, that weighs potential negative consequences of actions (doses) against an outcome (tumour reduction). Traditional RL models work toward a single outcome, such as winning a game, and take any and all actions that maximise that outcome.

On the other hand, the researchers’ model, at each action, has flexibility to find a dose that doesn’t necessarily solely maximise tumour reduction, but that strikes a perfect balance between maximum tumour reduction and low toxicity.

This technique, he adds, has various medical and clinical trial applications, where actions for treating patients must be regulated to prevent harmful side effects.

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Image credit: MIT.