Study of Plan of the Day Adaptive Radiation Therapy Validity

Radiation therapy is the use of radiation sources or generators to treat patients. The most common usage is in the treatment of cancers. Adaptive radiation therapy (ART) is the use of either multiple radiation therapy plans or adjusting a radiation therapy plan for daily anatomical changes. Soft tissue in the lower abdomen and pelvis can be greatly displaced depending on a variety of factors, especially bladder and rectum fill. This paper focuses on the creation of multiple plans prior to treatment to have options each day. Depending on the alignment and anatomical changes, clinicians can choose which one is most appropriate to maximize target coverage while minimizing organ at risk (OAR) toxicity. This type of ART technique is referred to as plan-of-the-day (POTD). A total of 12 bladder, prostate and gynecologic cases were retrospectively considered for viability in this study. For most patients, the POTD approach did not prove beneficial due to unpredictable and non-reproducible anatomical changes that could not be accounted for with 2-3 plans. In 1 patient, the anatomical changes were predictable enough to be modeled with 2 POTD plans, represented by (1) an empty and (2) a full bladder. This patient was selected for a full dosimetric analysis. Contours were made for empty bladder plans on past patient computed tomography (CT) images and evaluated against daily cone beam CT (CBCT) for viability. Radiation dose was calculated on every CBCT to determine the delivered dose to target and OARs. The delivered dose, POTD possible dose, and the original planned dose were all compared. Planning target volume (PTV) coverage was comparable for both the ART and original plans with the possibility of reduced bowel dose when using the POTD style treatment, especially at higher dose levels. There was also a trend showing that dose metrics were almost identical if bladder volume was above 250cc. This proves viability of traditional non-ART treatment style with appropriate patient coaching. If ART-style treatments are desired, online adaptive platforms, which have more flexibility in accounting for daily anatomical changes, should be explored further for their viability and clinical benefits.