IMRT planning parameter optimization for spine stereotactic radiosurgery.

Spine stereotactic radiosurgery (SSRS) is a noninvasive treatment for metastatic spine lesions. MD Anderson Cancer Center reports a quality assurance (QA) failure rate approaching 15% for SSRS cases, which we hypothesized is due to difficulties in accurately calculating dose resulting from a large number of small-area segments. Clinical plans typically use 9 beams with an average of 10 segments per beam and minimum segment area of 2-3 cm2. The purpose of this study was to identify a set of intensity-modulated radiation therapy (IMRT) planning parameters that attempts to optimize the balance among QA passing rate, plan quality, dose calculation accuracy, and delivery time for SSRS plans. Using Pinnacle version 9.10, we evaluated the effects of 2 IMRT parameters: maximum number of segments and minimum segment area. Initial evaluation of the data revealed that 5 segments per beam along with minimum segment area of 4 cm2 and 4 monitor units (MU) per segment (5-4-4 plans) was the most promising. IMRT QA was performed using a PTW OCTAVIUS 4D phantom with a 2D detector array. Our data showed no significant plan quality change with decreased number of segments and increased minimum segment area. The average coverage of GTV and CTV was 82.5 ± 13% (clinical) vs 82.5 ± 13% (5-4-4) and 92.3 ± 8% (clinical) vs 91.5 ± 8% (5-4-4). Maximum point dose to cord was 11.4 ± 3.5 Gy (clinical) vs 11.0 ± 4.0 Gy (5-4-4). Total plan delivery time was decreased by an average of 11.3% for the 5-4-4 plans. For IMRT QA, the gamma index passing rate (distance to agreement: 2.5 mm, local dose difference: 4%) for the original plans vs the 5-4-4 plans averaged 90.3% and 91.9%, respectively. In conclusion, IMRT parameters of 5 segments per beam and 4 cm2 minimum segment areas provided a better balance of plan quality, delivery efficiency, and plan dose calculation accuracy for SSRS.

IMRT planning parameter optimization for spine stereotactic radiosurgery.

Spine stereotactic radiosurgery (SSRS) is a noninvasive treatment for metastatic spine lesions. MD Anderson Cancer Center reports a quality assurance (QA) failure rate approaching 15% for SSRS cases, which we hypothesized is due to difficulties in accurately calculating dose resulting from a large number of small-area segments. Clinical plans typically use 9 beams with an average of 10 segments per beam and minimum segment area of 2 to 3 cm2. The purpose of this study was to identify a set of intensity-modulated radiation therapy (IMRT) planning parameters that attempts to optimize the balance among QA passing rate, plan quality, dose calculation accuracy, and delivery time for SSRS plans. Using Pinnacle version 9.10, we evaluated the effects of 2 IMRT parameters: maximum number of segments and minimum segment area. Initial evaluation of the data revealed that 5 segments per beam along with minimum segment area of 4 cm2 and 4 minimum Monitor Units (MU) per segment (544 plans) was the most promising. IMRT QA was performed using an OCTAVIUS 4D phantom with a 2D detector array. Our data showed no significant plan quality change with decreased number of segments and increased minimum segment area. The average coverage of GTV and CTV was 82.5 ± 13% (clinical) vs 82.5 ± 13% (544) and 92.3 ± 8% (clinical) vs 91.5 ± 8% (544). Maximum point dose to cord was 11.4 ± 3.5 Gy (clinical) vs 11.0 ± 4.0 Gy (544). Total plan delivery time was decreased by an average of 11.3% for the 544 plans. In addition, the QA passing rate for the original plan vs the 544 plan averaged 90.3% and 91.9%, respectively. In conclusion, IMRT parameters of 5 segments per beam and 4 cm2 minimum segment area provided a better balance of plan quality, delivery efficiency, and plan dose calculation accuracy for SSRS.

Prospective Qualitative and Quantitative Analysis of Real-Time Peer Review Quality Assurance Rounds Incorporating Direct Physical Examination for Head and Neck Cancer Radiation Therapy.

PURPOSE: Our department has a long-established comprehensive quality assurance (QA) planning clinic for patients undergoing radiation therapy (RT) for head and neck cancer. Our aim is to assess the impact of a real-time peer review QA process on the quantitative and qualitative radiation therapy plan changes in the era of intensity modulated RT (IMRT). METHODS AND MATERIALS: Prospective data for 85 patients undergoing head and neck IMRT who presented at a biweekly QA clinic after simulation and contouring were collected. A standard data collection form was used to document alterations made during this process. The original pre-QA clinical target volumes (CTVs) approved by the treating-attending physicians were saved before QA and compared with post-QA consensus CTVs. Qualitative assessment was done according to predefined criteria. Dice similarity coefficients (DSC) and other volume overlap metrics were calculated for each CTV level and were used for quantitative comparison. Changes are categorized as major, minor, and trivial according to the degree of overlap. Patterns of failure were analyzed and correlated to plan changes. RESULTS: All 85 patients were examined by at least 1 head and neck subspecialist radiation oncologist who was not the treating-attending physician; 80 (94%) were examined by ≥3 faculty members. New clinical findings on physical examination were found in 12 patients (14%) leading to major plan changes. Quantitative DSC analysis revealed significantly better agreement in CTV1 (0.94 ± 0.10) contours than in CTV2 (0.82 ± 0.25) and CTV3 (0.86 ± 0.2) contours (P=.0002 and P=.03, respectively; matched-pair Wilcoxon test). The experience of the treating-attending radiation oncologist significantly affected DSC values when all CTV levels were considered (P=.012; matched-pair Wilcoxon text). After a median follow-up time of 38 months, only 10 patients (12%) had local recurrence, regional recurrence, or both, mostly in central high-dose areas. CONCLUSIONS: Comprehensive peer review planning clinic is an essential component of IMRT QA that led to major changes in one-third of the study population. This process ensured safety related to target definition and led to favorable disease control profiles, with no identifiable recurrences attributable to geometric misses or delineation errors.

Capsular contracture of subcutaneous breast implant following hypofractionated stereotactic body radiotherapy for early stage lung cancer.

BACKGROUND: Development of capsular contracture around subcutaneously implanted breast prostheses, producing poor cosmetic outcome and pain, has been reported following standard fractionated external beam radiotherapy to whole implants for breast cancer. We report capsular contracture following partial implant irradiation from hypofractionated stereotactic body radiotherapy (SBRT) for lung cancer in a 64 year-old female with augmentation mammaplasty. METHODS: The patient had biopsy-proven, T1 non-small cell lung carcinoma, adjacent to the implant. She received 50 Gy in 4 fractions to 91% of planning target volume using a 7-field, 3D-conformal plan with 6 MV photons and daily CT-guided target localization. The implant received 9.3 Gy mean dose, 51.7 Gy maximum point dose, with V10 41%, V20 15% and V30 4%. RESULTS: At seven months, the patient reported left breast pain requiring narcotic analgesics and demonstrated modified Baker/Palmer grade 4 capsular contracture. Breast retraction assessment measurement increased from baseline 10.4 mm to 19.8 mm. CONCLUSIONS: This represents the first reported case of capsular contracture from partial breast implant radiation following SBRT for lung cancer. Further investigation to elucidate maximum tolerated dose of radiation given to breast implants in this setting is needed.