Abstract
Stereotactic body radiation therapy (SBRT) employs precision target tracking and image‐guidance techniques to deliver ablative doses of radiation to localized malignancies; however, treatment with conventional photon beams requires lengthy treatment and immobilization times. The use of flattening filter‐free (FFF) beams operating at higher dose rates can shorten beam‐on time, and we hypothesize that it will shorten overall treatment delivery time. A total of 111 lung and liver SBRT cases treated at our institution from July 2008 to July 2011 were reviewed and 99 cases with complete data were identified. Treatment delivery times for cases treated with a FFF linac versus a conventional dose rate linac were compared. The frequency and type of intrafraction image guidance was also collected and compared between groups. Three hundred and ninety‐one individual SBRT fractions from 99 treatment plans were examined; 36 plans were treated with a FFF linac. In the FFF cohort, the mean (± standard deviation) treatment time (time elapsed from beam‐on until treatment end) and patient's immobilization time (time from first alignment image until treatment end) was 11.44 (± 6.3) and 21.08 (± 6.8) minutes compared to 32.94 (± 14.8) and 47.05 (± 17.6) minutes for the conventional cohort (p<0.01 for all values). Intrafraction‐computed tomography (CT) was used more often in the conventional cohort (84% vs. 25%; p<0.05), but use of orthogonal X‐ray imaging remained the same (16% vs. 19%). For lung and liver SBRT, a FFF linac reduces treatment and immobilization time by more than 50% compared to a conventional linac. In addition, treatment with a FFF linac is associated with less physician‐ordered image guidance, which contributes to further improvement in treatment delivery efficiency.PACS number: 87.55.‐x
Highlights
65 Prendergast et al.: Flattening filter-free Stereotactic body radiation therapy (SBRT) improves treatment efficiency weeks
Existing preclinical data using phantom delivery confirm that linacs generating flattening filterfree (FFF) photon beams can produce dosimetrically equivalent plans[8] while reducing beam-on time by more than 50%.(9-10) We hypothesized that clinical use of a FFF linac for SBRT would yield similar savings
The medical records of 111 lung and liver SBRT patients treated from July 2008 to July 2011 were reviewed and 99 cases with full treatment records were selected for further study
Summary
65 Prendergast et al.: Flattening filter-free SBRT improves treatment efficiency weeks. Prolonged treatment times are undesirable for patients who must remain immobilized in uncomfortable positions. Personal supervision of lengthy SBRT treatments is often an inefficient use of a practitioner’s clinical time. Several factors contribute to prolonged treatment times in SBRT, dose rate limitations of the linear accelerator (linac) are of paramount importance. Existing preclinical data using phantom delivery confirm that linacs generating flattening filterfree (FFF) photon beams can produce dosimetrically equivalent plans[8] while reducing beam-on time by more than 50%.(9-10) We hypothesized that clinical use of a FFF linac for SBRT would yield similar savings. We retrospectively compare beam-on time, treatment time, and patient immobilization times for patients treated with a conventional linac using flattened photons versus a FFF linac for SBRT of lung and liver malignancies
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