Variation of Tumor Volume During Moderate Hypo-Fractionated Stereotactic Body Radiation Therapy for Lung Cancer

Aim To investigate the variation of tumor volume during moderate hypo-fractionated stereotactic body radiation therapy (SBRT). Patients and Methods Twenty patients, who received SBRT at our institution, were included in the analysis. A prescribed dose was 56 Gy at iso-center in seven fractions. Tumor volumes before and during SBRT were calculated. In order to investigate factors affecting the variation of tumor volume in RT 2 (after first irradiation) and RT 7 (after last irradiation), various parameters were verified by the Mann-Whitney U test. Results With regard to the low maximum standardized uptake values (SUVmax) group, transient increase of tumor volume was found in RT 2, and tumor volume reduction was hardly found in RT 7. With regard to the high SUVmax group, a transient increase was not found, and a definite reduction was found in the treatment course. Conclusion Accurate prediction of tumor volume variation is required for more accurate treatment, such as adaptive radiation therapy.