It is well known that a head and neck tumor often shrinks and thus ... A Combined Breath Hold and Free Breathing Protocol Is not ... larynx, pharyngeal constrictor muscles and cochleae according to pub- .... downloaded to the user computer.
S876
International Journal of Radiation Oncology Biology Physics
mean and median doses to the parotid grand compared to the SIB technique under the same HI. It is well known that a head and neck tumor often shrinks and thus the SIB may cause more late toxicity to the parotid grand without an indication in the calculated DVH. It is anticipated that the combination of the two-step adaptive technique and the 5-mm low transmission MLC may reduce complication to the parotid grand while maintaining the tumor control. Author Disclosure: A. Sakumi: None. K. Yamamoto: None. A. Haga: None. K. Okuma: None. H. Igaki: None. Y. Iwai: None. K. Yoda: None. K. Nakagawa: None.
Scientific Abstract 3692; Table BH-CT and FB-CT
3692 A Combined Breath Hold and Free Breathing Protocol Is not Feasible for Locoregional Radiation Therapy of Left-Sided Breast Cancer R.H. Tijssen,1,2 T.T. Nuver,2 T.K.H. Eiland,2 D. Martens,2 and A.W.H. Minken2; 1University Medical Center Utrecht, Utrecht, Netherlands, 2Radiotherapeutic Institute RISO, Deventer, Netherlands
RL (mm)
AP (mm)
CC (mm)
0.0 [-3.6,2.3] 0.0 [-2.6,2.2] -0.2 [-3.2,2.0]
10.6 [0.0,22.0] 6.2 [-1.3,15.2] 2.1 [-0.7,6.1]
9.0 [2.4,20.3] 7.0 [0.4,19.9] 2.0 [-6.8,13.6]
clavicular motion observed in this study suggests that geometric verification during breath hold is desirable when irradiating the supraclavicular LN with highly conformal IMRT. Author Disclosure: R.H. Tijssen: None. T.T. Nuver: None. T.K.H. Eiland: None. D. Martens: None. A.W.H. Minken: None.
3693
Purpose/Objective(s): Deep inspiration breath hold (BH) during irradiation with tangential fields of the left breast has been shown to reduce cardiac dose. For the supraclavicular lymph nodes (LN), however, irradiation during free breathing (FB) may be preferable as BH verification (e.g., by EPID imaging) is cumbersome and limits the use of more complex IMRT. In this study, we explore the possibility of combining BH tangential fields with FB supraclavicular fields. We quantify the amount of displacement of the supraclavicular structures between BH and FB. Materials/Methods: We retrospectively registered the free breathing CT to the breath hold CT of 13 patients, who were previously treated for (local) left-sided breast cancer in supine position on a breast board. For each patient three rigid body image registrations, translations only, were performed using the following landmarks: 1) EPID skin markers placed on the cranial side of the left breast, 2) the sternal edge of the clavicle denoting the caudal side of the supraclavicular LN, and 3) the acromial edge of the clavicle representative of the cranial border. In this approach landmarks 1 and 2 are indicative of the match line between the fields, while the difference in displacement between marker 2 and 3 represent the variation of motion within the supraclavicular field. Results: All landmarks showed a small displacement in the RL direction (Table 1). The breast marker (1) and sternal end of the clavicle (2) did show a considerable amount of motion in the AP and CC direction (mean displacement of 9 mm and 7 mm, respectively), which was also strongly correlated (R2 Z 0.94 and R2 Z 0.72 for AP and CC, respectively). The mean displacement of the acromial end of the clavicle (3) was found to be considerably smaller (CC Z 2 mm). Further, the difference between the sternal and acromial end of the clavicle was -4.0 mm in the AP direction (range Z -14.6 to 0.9 mm), and -4.9 mm (range Z -14.2 to 0 mm) in the CC direction. Finally, it is worth noting that the inter-patient variability (Table 1, range of displacements) was large for all landmarks. Conclusions: Due to the large displacement in the CC and AP direction around the match line, we conclude that it is not feasible to combine the irradiation of supraclavicular fields in FB and the tangent fields in BH in locoregional treatment of left-sided breast cancer. The large extent of
Scientific Abstract 3693; Table
1. Breast marker 2. Clavicle sternal end 3. Clavicle acromial end
Average displacement and range between
Automatic Segmentation to Define Organs at Risk (OARs) for Function Sparing Head and Neck IMRT D. Thomson, C. Boylan, T. Liptrot, A. Aitkenhead, L. Lee, B. Yap, A. Sykes, C. Rowbottom, and N. Slevin; The Christie NHS Foundation Trust, Manchester, United Kingdom Purpose/Objective(s): The introduction of function sparing and adaptive IMRT for head and neck cancer has increased the number and frequency of delineation of OARs. We investigated whether automatic segmentation with Smart Probabilistic Image Contouring Engine (SPICE) may reduce contouring time, decrease variability and maintain accuracy. Materials/Methods: Ten radiation therapy planning CT scans were selected where the OARs of interest were not distorted by tumor or artefact. Five clinicians (4 Attending Physicians and 1 Fellow) recorded for each scan the time to delineate the parotid and submandibular glands, larynx, pharyngeal constrictor muscles and cochleae according to published guidelines. SPICE was then used to define these structures. Each clinician determined by visual inspection the acceptability of SPICE defined volumes and the total time to modify contours for each patient. The Simultaneous Truth and Performance Level Estimation (STAPLE) algorithm created a reference standard from all clinician contours. Clinician and SPICE defined contours were compared to STAPLE by three matrices: conformity index (CI, ratio of volumes, target Z 1.0), Dice similarity coefficient (DSC, 2x intersection volume/sum of total volumes, target Z 1.0, acceptable>0.7) and distance to agreement (DTA), the per voxel shortest distance from the surface of one structure to another (maximum and mean DTA, target Z 0.0mm). Results: The proportions of SPICE defined contours deemed not to require alteration were: parotid glands (17%), submandibular glands (41%), larynx (8%), pharyngeal constrictor muscles (4%) and cochleae (28%). Comparisons between the clinicians’ contours and STAPLE (the reference standard) versus SPICE and STAPLE are shown in the Table. For the pharyngeal constrictor muscles and larynx, SPICE compared unfavorably for all matrices. For the parotid glands, only the DSC was significantly different and this remained acceptable for SPICE (median, 0.79). The DSC and DTA for SPICE defined submandibular glands were inferior. This was partly due to low inter-observer variability in clinician contours and the SPICE DSC was acceptable (median, 0.80). The SPICE defined cochleae had a low DSC (median, 0.30). The overall respective mean times to
Comparison between all clinicians and SPICE defined OARs and the reference standard (STAPLE) DSC (median, IQR)
OAR (N clinicians, N SPICE) Parotid glands (N Z 100, N Z 20) Submandibular glands (N Z 100, N Z 20) Larynx (N Z 50, N Z 10) Pharyngeal constrictor muscles (N Z 50, N Z 10) Cochleae (N Z 100, N Z 20)
Clinicians 0.90, 0.91, 0.85, 0.76, 0.63,
0.88-0.92 0.88-0.93 0.81-0.87 0.71-0.79 0.48-0.81
SPICE 0.79, 0.80, 0.57, 0.53, 0.30,
0.74-0.83*** 0.70-0.85*** 0.54-0.62*** 0.39-0.57*** 0.13-0.49***
Maximum DTA / mm (median, IQR) Clinicians 7.8, 3.8, 6.4, 6.0, 3.0,
5.2-11.1 2.9-5.1 5.5-7.8 5.1-7.5 1.3-3.3
Mean DTA / mm (median, IQR)
SPICE
Clinicians
SPICE
14.8, 11.6-19.1 5.7, 4.7-8.2*** 22.4, 15.8-25.4*** 12.9, 8.7-15.9*** 2.6, 1.8-5.0
0.86, 0.34-1.3 0.23, 0.11-0.50 0.45, 0.25-0.82 0.76, 0.53-0.92 1.1, 0.18-1.8
1.5, 0.93-2.0 0.61, 0.41-1.0*** 5.2, 2.4-6.3*** 1.2, 0.93-1.9* 0.89, 0.65-3.3
Abbreviations: OAR, organ at risk; N Z total number of OARs; CI, conformity index; DSC, Dice similarity coefficient; DTA, distance to agreement; IQR, interquartile range. Comparison: All clinicians versus STAPLE compared with SPICE versus STAPLE; *P
