[Show abstract][Hide abstract] ABSTRACT: To examine the geometric relationship between local recurrence (LR) and external beam radiotherapy (RT) volumes for soft-tissue sarcoma (STS) patients treated with function-preserving surgery and RT.
Sixty of 768 (7.8%) STS patients treated with combined therapy within our institution from 1990 through 2006 developed an LR. Thirty-two received preoperative RT, 16 postoperative RT, and 12 preoperative RT plus a postoperative boost. Treatment records, RT simulation images, and diagnostic MRI/CT data sets of the original and LR disease were retrospectively compared. For LR location analysis, three RT target volumes were defined according to the International Commission on Radiation Units and Measurements 29 as follows: (1) the gross tumor or operative bed; (2) the treatment volume (TV) extending 5 cm longitudinally beyond the tumor or operative bed unless protected by intact barriers to spread and at least 1-2 cm axially (the TV was enclosed by the isodose curve representing the prescribed target absorbed dose [TAD] and accounted for target/patient setup uncertainty and beam characteristics), and (3) the irradiated volume (IRV) that received at least 50% of the TAD, including the TV. LRs were categorized as developing in field within the TV, marginal (on the edge of the IRV), and out of field (occurring outside of the IRV).
Forty-nine tumors relapsed in field (6.4% overall). Nine were out of field (1.1% overall), and 2 were marginal (0.3% overall).
The majority of STS tumors recur in field, indicating that the incidence of LR may be affected more by differences in biologic and molecular characteristics rather than aberrations in RT dose or target volume coverage. In contrast, only two patients relapsed at the IRV boundary, suggesting that the risk of a marginal relapse is low when the TV is appropriately defined. These data support the accurate delivery of optimal RT volumes in the most precise way using advanced technology and image guidance.
International journal of radiation oncology, biology, physics 06/2011; 82(4):1528-34. DOI:10.1016/j.ijrobp.2011.03.061 · 4.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To evaluate inter- and intrafractional motion and rotational error for lower extremity soft tissue sarcoma patients by using cone beam computed tomography (CBCT) and an optical localization system.
Thirty-one immobilized patients received CBCT image-guided intensity-modulated radiation therapy. Setup deviations of >3 mm from the planned isocenter were corrected. A second CBCT acquired before treatment delivery was registered to the planning CT to estimate interfractional setup error retrospectively. Interfractional error and rotational error were calculated in the left-right (LR), superoinferior (SI), and anteroposterior (AP) dimensions. Intrafractional motion was assessed by calculating the maximum relative displacement of optical localization system reflective markers placed on the patient's surface, combined with pre- and postfraction CBCT performed for 17 of the 31 patients once per week. The overall systematic error (SE) and random error (RE) were calculated for the interfractional and intrafractional motion for planning target volume margin calculation.
The standard deviation (SD) of the interfractional RE was 1.9 mm LR, 2.1 mm SI, and 1.8 mm AP, and the SE SD was 0.6 mm, 1.2 mm, and 0.7 mm in each dimension, respectively. The overall rotation (inter- and intrafractional) had an RE SD of 0.8° LR, 1.7° SI, and 0.7° AP and an SE SD of 1.1° LR, 1.3° SI, and 0.3° AP. The SD of the overall intrafractional RE was 1.6 mm LR, 1.6 mm SI, and 1.4 mm AP, and the SE SD was 0.7 mm AP, 0.6 mm SI, and 0.6 mm AP.
A uniform 5-mm planning target volume margin was quantified for lower extremity soft tissue sarcoma patients and has been implemented clinically for image-guided intensity-modulated radiation therapy.
International journal of radiation oncology, biology, physics 03/2010; 78(5):1437-44. DOI:10.1016/j.ijrobp.2009.09.054 · 4.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To examine the relationship between tumor location, bone dose, and irradiated bone length on the development of radiation-induced fractures for lower extremity soft tissue sarcoma (LE-STS) patients treated with limb-sparing surgery and radiotherapy (RT).
Of 691 LE-STS patients treated from 1989 to 2005, 31 patients developed radiation-induced fractures. Analysis was limited to 21 fracture patients (24 fractures) who were matched based on tumor size and location, age, beam arrangement, and mean total cumulative RT dose to a random sample of 53 nonfracture patients and compared for fracture risk factors. Mean dose to bone, RT field size (FS), maximum dose to a 2-cc volume of bone, and volume of bone irradiated to >or=40 Gy (V40) were compared. Fracture site dose was determined by comparing radiographic images and surgical reports to fracture location on the dose distribution.
For fracture patients, mean dose to bone was 45 +/- 8 Gy (mean dose at fracture site 59 +/- 7 Gy), mean FS was 37 +/- 8 cm, maximum dose was 64 +/- 7 Gy, and V40 was 76 +/- 17%, compared with 37 +/- 11 Gy, 32 +/- 9 cm, 59 +/- 8 Gy, and 64 +/- 22% for nonfracture patients. Differences in mean, maximum dose, and V40 were statistically significant (p = 0.01, p = 0.02, p = 0.01). Leg fractures were more common above the knee joint.
The risk of radiation-induced fracture appears to be reduced if V40 <64%. Fracture incidence was lower when the mean dose to bone was <37 Gy or maximum dose anywhere along the length of bone was <59 Gy. There was a trend toward lower mean FS for nonfracture patients.
International journal of radiation oncology, biology, physics 04/2009; 75(4):1119-24. DOI:10.1016/j.ijrobp.2008.12.006 · 4.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to determine the accuracy and efficiency of a custom-designed immobilization device for patients with extremity soft-tissue sarcoma. The custom device consisted of a thermoplastic shell, vacuum pillow, and adaptable baseplate. The study included patients treated from January 2005 to March 2007, with 92 patients immobilized with the custom device and 98 with an established standard. Setup times for these cohorts were analyzed retrospectively for conformal and intensity modulated radiotherapy techniques (IMRT). Thigh tumor setup times were analyzed independently. A subset of patients treated with IMRT was analyzed for setup error using the radiographically verified isocenter position measured daily with electronic portal imaging and cone-beam computed tomography. Mean setup time was reduced by 2.2 minutes when using the custom device for conformal treatment (p = 0.03) and by 5.8 min for IMRT of thigh tumors (p = 0.009). All other setup time comparisons were not significant. A significant systematic error reduction was seen in all directions using the custom device. Random error standard deviations favored the custom device. The custom device offers immobilization advantages. Patient setup time was reduced for conformal techniques and IMRT of thigh tumors. Positioning uncertainty was improved, permitting a reduction of the planning target volume margin by 2 to 4 mm.
Medical dosimetry: official journal of the American Association of Medical Dosimetrists 02/2009; 34(3):243-9. DOI:10.1016/j.meddos.2008.10.003 · 0.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Most IMRT techniques have been designed to treat targets smaller than the field size of conventional linac accelerators. In order to overcome the field size restrictions in applying IMRT, we developed a two isocenter IMRT technique to treat long volume targets. The technique exploits an extended dose gradient throughout a junction region of 4-6 cm to minimize the impact of field match errors on a junction dose and manipulates the inverse planning and IMRT segments to fill in the dose gradient and achieve dose uniformity. Techniques for abutting both conventional fields with IMRT ('Static + IMRT') and IMRT fields ('IMRT + IMRT') using two separate isocenters have been developed. Five long volume sarcoma cases have been planned in Pinnacle (Philips, Madison, USA) using Elekta Synergy and Varian 2100EX linacs; two of the cases were clinically treated with this technique. Advantages were demonstrated with well-controlled junction target uniformity and tolerance to setup uncertainties. The junction target dose heterogeneity was controlled at a level of +/-5%; for 3 mm setup errors at the field edges, the junction target dose changed less than 5% and the dose sparing to organs at risk (OARs) was maintained. Film measurements confirmed the treatment planning results.
Physics in Medicine and Biology 09/2007; 52(15):4541-52. DOI:10.1088/0031-9155/52/15/012 · 2.76 Impact Factor