Substantial Volume Changes and Plan Adaptations During Preoperative Radiation Therapy in Extremity Soft Tissue Sarcoma Patients.

Abstract

PURPOSE\nMany authors suggest that extremity soft tissue sarcomas (ESTS) do not change significantly in size during preoperative radiation therapy (RT). This cone beam computed tomography study investigates the justification to deliver the entire course with 1 initial RT plan by observing anatomic changes during RT.\n\n\nMETHODS AND MATERIALS\nBetween 2015 and 2017, 99 patients with ESTS were treated with either curative (n\xa0=\xa080) or palliative intent (n\xa0=\xa019) with a regimen of at least 6 fractions. The clinical target volume to planning target volume margin was 1\xa0cm. Action levels were assigned by radiation technicians. An extremity contour change of >1\xa0cm and/or tumor size change >0.5\xa0cm required a physician s action before the next fraction.\n\n\nRESULTS\nA total of 982 cone beam computed tomography logfiles were studied. In 41 of 99 patients, the dose coverage of the initial treatment plan was fully satisfactory throughout the RT course. However, action levels were observed in 58 patients (59%). In 41 of these 58 patients, a contour increase of 5 to 23\xa0mm was noted (29 tumor size increase only, 3 extremity contour increase, and 9 both). In 21 of 58 patients, a decrease of 5 to 33\xa0mm was observed (20 tumor size decrease only and 1 tumor size decrease and extremity contour decrease). In 4 cases, contours initially increased and subsequently decreased. In 33 of 41 patients with increasing contours, the dose distribution adequately covered gross tumor volume because of the 1\xa0cm planning target volume margin applied. For the remaining 8 patients (8%), the plan needed to be adapted.\n\n\nCONCLUSIONS\nESTS volumes may change substantially during RT in 59% of all patients, leading to plan adaptations resulting from increased volumes in 8%. Daily critical observation of these patients is mandatory to avoid geographic misses because of increases in size and overdosing of normal tissues when masses shrink.