July 2002

Inverse Planning

By Michael J. Katin, MD

Intermittently events occur that bring to our attention that activities we do every day in our specialty, or that we should be doing every day in our specialty, have parallels in real life. Many things we do involve consultation, simulation, status checks, and followups, whether it be buying a car or dating. The equivalent of DVHs can even be imagined. Now we have finally achieved sophistication in treatment planning that catches up with techniques that have been in use elsewhere for many years.

Contractors would not have much success if houses were built by putting components together and deciding during the course of the project about what the endpoint should be, although this is probably done routinely in Massachusetts. Almost everything can come to a better conclusion is it is possible to work backward from the desired outcome. Now for the first time we can specify a dose to a tumor volume and have assurance that the fields and beam modifiers used are not selected strictly because the dosimetrist has too many plans to run that day. Now they can be selected because the persons who programmed the planning computer decided to use those parameters, since they had too many programming projects that day.

Of course, inverse planning is encountered throughout every day, from deciding where you can drive before you have to get gasoline, to deciding how many Twinkies you can eat before you have to go to the next size. The classic example is the typical tourist going to Las Vegas who has carefully budgeted his or her gambling money not to exceed a certain amount per day. The existence of the Bellagio is testimony to the fact that this plan usually is history after the first few hours.

But not in history or biology, but the best recent application of inverse planning is in megacorporations. We now know that Xerox, Worldcom, and Tyco, to name but a few, have been involved in creative bookkeeping in order to have the quarterly profit picture match the desired number. It's hard to believe that every year I agonize about whether my taxes will be pulled out for audit because of some technicality that would result in my being sent away to Oz . And the best part is that after some of these manipulations are exposed, the reaction of the corporations is to fire 17,000 employees. You have to admire that.

I suppose the logical extension of this would be to go ahead and prescribe the desired dose to the target volume, get the treatment plan generated, and then go ahead and make up the treatment dates and quality control measurements, and we could even save more time and money if we didn't check if the patients even showed up for the treatments. And if we got caught we could respond by giving ourselves bonuses and firing half the physics department. And somebody needs to call Martha Stewart and let her know about this.

Another possible interpretation . . .

Webmaster's note....Dr. Katin's column is being concluded at this time since he has already used the maximum number of ideas allocated for this month.

email: mkatin@radiotherapy.com