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Comparison of Electron versus IMRT Treatment Planning for Extensive Squamous Cell Carcinoma (SCC) of the Scalp
I. J. Radiation Oncology d Biology d Physics
S908
3461
Volume 81, Number 2, Supplement, 2011
Retrospective Review of HDR Contura Breast Cases to Evaluate Plan Quality
1,2
I. Iftimia , E. T. Cirino1, R. Ladd1, M. Kazi1,2, H. W. Mower1,2, A. McKee1 1
Lahey Clinic, Burlington, MA, 2TUSM, Boston, MA
Purpose/Objective(s): Retrospective review of 10 HDR Contura Breast treatment plans to evaluate plan quality based on established DVH criteria. Materials/Methods: Recently we started an HDR - Contura breast implant program in our clinic. To increase our efficiency in planning and treating HDR breast patients we prepared in advance checklists for the day of simulation, second checking the plan, and treatment delivery. Also, we developed in-house software based on a point source approximation approach for second checking the plan. We generated a procedure for proficient contouring following the NSABP B-39 protocol guidelines, and a set of optimization constraints to meet the DVH criteria. Templates were created in our TPS for structures, isodose levels, optimization constraints, and plan report. We did preliminary tests for our DVH constraints using CT images provided by the vendor. This study is a review of our first 10 HDR Contura breast treatment plans completed by using the approach and forms described above. All 10 CT-based plans (slice thickness 2.5 mm) were generated on the Varian Brachyvision 8.6 TPS. For all cases the 4 - 5 cm Contura multi-lumen balloon was used (balloon volume ranged between 51 and 63 cc). The prescription dose was 3.4 Gy/Fx for 10 Fx. Before each treatment an AP image was acquired and the balloon diameter in SUP-INF direction was measured and compared with a baseline value (tol ± 15%). For each case we checked and recorded the balloon asymmetry, balloon to skin and ribs distances, and contoured air and seroma to evaluate patient eligibility. We did all the contours following the guidelines we formulated. Four planners were involved in this study. A checklist with the following criteria was used by the planner: a) PTV_Eval PV90% $ 90%; Goal PV95% $ 95%; b) Max skin dose (at 0.1 cc) # 125%Rx; Goal # 100%Rx; c) Max ribs dose (at 0.1 cc) # 145%Rx; Goal # 125%Rx; d) V150% # 50 cc; Goal # 30 cc; d) V200% # 10 cc; Goal # 8 cc; e) total dwell time (TDT) 300 ± 50 s. A calculation point was placed at about 5 cm from the implant plane. The second checker estimated the dose to the calculation point by using our in-house software. Results: The established DVH criteria were successfully met for all plans. For cases studied here: balloon-skin and balloon-ribs distances ranged between 9 - 43 mm and 3 - 20 mm, respectively; air-seroma volume/PTV_Eval volume # 3%; asymmetry # 1 mm; PV90% $ 97%; PV95% $ 94.8%; skin max dose # 98%Rx; ribs max dose # 137%Rx; V150% # 30 cc; V200% # 5 cc; TDT range 265 - 317 s; in-house software - Brachyvision discrepancy for the calculation point dose \ 3%. Conclusions: Based on our review of these cases the use of a checklist to document compliance to planning guidelines resulted in consistent results that were not dependant on the planner. They indicated good coverage for the target without sacrificing the critical structures. Author Disclosure: I. Iftimia: None. E.T. Cirino: None. R. Ladd: None. M. Kazi: None. H.W. Mower: None. A. McKee: None.
3462
Comparison of Electron versus IMRT Treatment Planning for Extensive Squamous Cell Carcinoma (SCC) of the Scalp
C. Della Biancia, N. Lee, J. G. Mechalakos Memorial Sloan-Kettering Cancer Center, New York, NY Purpose/Objective(s): To compare the relative merits and dosimetric benefits of four different radiation techniques in the treatment of extensive SCC of the scalp. Materials/Methods: Seven patients with extensive SCC of the scalp were retrospectively planned with competing techniques: matching photon-electron fields (E plan) and IMRT. Patients were divided into 3 categories based on extent of disease: (1) 1 patient had involvement of entire scalp, (2) 4 patients had involvement on one side of the scalp and neck metastases, and (3) 2 patients had involvement of entire scalp and neck metastases. The E plans for each category were designed as follows: (1) Parallel opposed lateral photon fields with matching electron fields. The outer rind of the scalp is treated with photons and the inner scalp is treated with matching electron fields to minimize brain dose; (2) Single en face electron field treating the unilateral scalp lesion and matching IMRT treating the parotid/neck nodes; (3) Two pairs of lateral electron and photon fields treating the whole scalp and matching IMRT treating the parotid/neck nodes. All 7 patients were planned with IMRT for comparison. For each patient, the E plan was compared to the IMRT for target coverage, brain mean dose, hot spots, and complexity. Results: For category 1, the hot spot (PTV Dmax) was comparable between both techniques. For 2 and 3, the hot spot was significantly reduced when using IMRT. The homogeneity (PTV D95) was improved when using IMRT, especially for categories 1 and 3. For category 1, the average increase in brain mean dose when using IMRT was 7.7 Gy; for category 2, 2.7 Gy (range: 1.1 6.5 Gy) and for category 3, 11.5 Gy (range: 1.8 - 21.2 Gy). Conclusions: This treatment planning comparison shows that IMRT offers a feasible alternative to matching electron techniques for treatment of extensive scalp lesions and neck metastases with less inhomogeneity. The PTV dose distribution with IMRT does not suffer from problems of matching static electron fields. The brain dose is higher with IMRT, but clinically acceptable. Regarding to practical implementations, the technique for category 1 is feasible, requires little planning time and provides significantly less brain dose. The technique for category 3 requires extensive planning and delivery time due to the complexity of matching fields. In terms of planning and delivery time, the IMRT plan is competitive with E plans and is a practical alternative for categories 2 and 3. Average PTV Dmax, PTV D95 and Brain mean dose (Brain Dmean) E plan
IMRT plan
Category
PTV Dmax (%)
PTV D95 (%)
Brain Dmean (Gy)
PTV Dmax (%)
PTV D95 (%)
Brain Dmean (Gy)
1 2 3
123.6 128.0 162.0
50.9 98.0 65.1
9.3 9.2 6.8
128.8 115.6 133.1
94.4 99.8 103.8
17.0 11.9 18.3
Author Disclosure: C. Della Biancia: None. N. Lee: None. J.G. Mechalakos: None.
S908
3461
Volume 81, Number 2, Supplement, 2011
Retrospective Review of HDR Contura Breast Cases to Evaluate Plan Quality
1,2
I. Iftimia , E. T. Cirino1, R. Ladd1, M. Kazi1,2, H. W. Mower1,2, A. McKee1 1
Lahey Clinic, Burlington, MA, 2TUSM, Boston, MA
Purpose/Objective(s): Retrospective review of 10 HDR Contura Breast treatment plans to evaluate plan quality based on established DVH criteria. Materials/Methods: Recently we started an HDR - Contura breast implant program in our clinic. To increase our efficiency in planning and treating HDR breast patients we prepared in advance checklists for the day of simulation, second checking the plan, and treatment delivery. Also, we developed in-house software based on a point source approximation approach for second checking the plan. We generated a procedure for proficient contouring following the NSABP B-39 protocol guidelines, and a set of optimization constraints to meet the DVH criteria. Templates were created in our TPS for structures, isodose levels, optimization constraints, and plan report. We did preliminary tests for our DVH constraints using CT images provided by the vendor. This study is a review of our first 10 HDR Contura breast treatment plans completed by using the approach and forms described above. All 10 CT-based plans (slice thickness 2.5 mm) were generated on the Varian Brachyvision 8.6 TPS. For all cases the 4 - 5 cm Contura multi-lumen balloon was used (balloon volume ranged between 51 and 63 cc). The prescription dose was 3.4 Gy/Fx for 10 Fx. Before each treatment an AP image was acquired and the balloon diameter in SUP-INF direction was measured and compared with a baseline value (tol ± 15%). For each case we checked and recorded the balloon asymmetry, balloon to skin and ribs distances, and contoured air and seroma to evaluate patient eligibility. We did all the contours following the guidelines we formulated. Four planners were involved in this study. A checklist with the following criteria was used by the planner: a) PTV_Eval PV90% $ 90%; Goal PV95% $ 95%; b) Max skin dose (at 0.1 cc) # 125%Rx; Goal # 100%Rx; c) Max ribs dose (at 0.1 cc) # 145%Rx; Goal # 125%Rx; d) V150% # 50 cc; Goal # 30 cc; d) V200% # 10 cc; Goal # 8 cc; e) total dwell time (TDT) 300 ± 50 s. A calculation point was placed at about 5 cm from the implant plane. The second checker estimated the dose to the calculation point by using our in-house software. Results: The established DVH criteria were successfully met for all plans. For cases studied here: balloon-skin and balloon-ribs distances ranged between 9 - 43 mm and 3 - 20 mm, respectively; air-seroma volume/PTV_Eval volume # 3%; asymmetry # 1 mm; PV90% $ 97%; PV95% $ 94.8%; skin max dose # 98%Rx; ribs max dose # 137%Rx; V150% # 30 cc; V200% # 5 cc; TDT range 265 - 317 s; in-house software - Brachyvision discrepancy for the calculation point dose \ 3%. Conclusions: Based on our review of these cases the use of a checklist to document compliance to planning guidelines resulted in consistent results that were not dependant on the planner. They indicated good coverage for the target without sacrificing the critical structures. Author Disclosure: I. Iftimia: None. E.T. Cirino: None. R. Ladd: None. M. Kazi: None. H.W. Mower: None. A. McKee: None.
3462
Comparison of Electron versus IMRT Treatment Planning for Extensive Squamous Cell Carcinoma (SCC) of the Scalp
C. Della Biancia, N. Lee, J. G. Mechalakos Memorial Sloan-Kettering Cancer Center, New York, NY Purpose/Objective(s): To compare the relative merits and dosimetric benefits of four different radiation techniques in the treatment of extensive SCC of the scalp. Materials/Methods: Seven patients with extensive SCC of the scalp were retrospectively planned with competing techniques: matching photon-electron fields (E plan) and IMRT. Patients were divided into 3 categories based on extent of disease: (1) 1 patient had involvement of entire scalp, (2) 4 patients had involvement on one side of the scalp and neck metastases, and (3) 2 patients had involvement of entire scalp and neck metastases. The E plans for each category were designed as follows: (1) Parallel opposed lateral photon fields with matching electron fields. The outer rind of the scalp is treated with photons and the inner scalp is treated with matching electron fields to minimize brain dose; (2) Single en face electron field treating the unilateral scalp lesion and matching IMRT treating the parotid/neck nodes; (3) Two pairs of lateral electron and photon fields treating the whole scalp and matching IMRT treating the parotid/neck nodes. All 7 patients were planned with IMRT for comparison. For each patient, the E plan was compared to the IMRT for target coverage, brain mean dose, hot spots, and complexity. Results: For category 1, the hot spot (PTV Dmax) was comparable between both techniques. For 2 and 3, the hot spot was significantly reduced when using IMRT. The homogeneity (PTV D95) was improved when using IMRT, especially for categories 1 and 3. For category 1, the average increase in brain mean dose when using IMRT was 7.7 Gy; for category 2, 2.7 Gy (range: 1.1 6.5 Gy) and for category 3, 11.5 Gy (range: 1.8 - 21.2 Gy). Conclusions: This treatment planning comparison shows that IMRT offers a feasible alternative to matching electron techniques for treatment of extensive scalp lesions and neck metastases with less inhomogeneity. The PTV dose distribution with IMRT does not suffer from problems of matching static electron fields. The brain dose is higher with IMRT, but clinically acceptable. Regarding to practical implementations, the technique for category 1 is feasible, requires little planning time and provides significantly less brain dose. The technique for category 3 requires extensive planning and delivery time due to the complexity of matching fields. In terms of planning and delivery time, the IMRT plan is competitive with E plans and is a practical alternative for categories 2 and 3. Average PTV Dmax, PTV D95 and Brain mean dose (Brain Dmean) E plan
IMRT plan
Category
PTV Dmax (%)
PTV D95 (%)
Brain Dmean (Gy)
PTV Dmax (%)
PTV D95 (%)
Brain Dmean (Gy)
1 2 3
123.6 128.0 162.0
50.9 98.0 65.1
9.3 9.2 6.8
128.8 115.6 133.1
94.4 99.8 103.8
17.0 11.9 18.3
Author Disclosure: C. Della Biancia: None. N. Lee: None. J.G. Mechalakos: None.