Analysis of Acute Rectal Toxicity, Interfraction Prostate and SV Shifts During kV-CBCT Image Guided IMRT for Prostate Cancer

Analysis of Acute Rectal Toxicity, Interfraction Prostate and SV Shifts During kV-CBCT Image Guided IMRT for Prostate Cancer

I. J. Radiation Oncology d Biology d Physics S186 1101 Volume 78, Number 3, Supplement, 2010 Analysis of Actual Delivered Dose and Volumetric Chan...

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I. J. Radiation Oncology d Biology d Physics

S186

1101

Volume 78, Number 3, Supplement, 2010

Analysis of Actual Delivered Dose and Volumetric Changes of Head and Neck Structures for Locally Advanced Oropharyngeal Carcinoma

D. Y. Lee, J. Liang, S. Li, Y. Chi, S. D. McGrath, I. S. Grills, P. Y. Chen, D. J. Krauss, A. A. Martinez, D. Yan William Beaumont Hospital, Royal Oak, MI Purpose/Objective(s): Comparison of planned to delivered radiotherapy dose and volume to normal structures in the management of locally advanced oropharyngeal carcinoma (OPC). Materials/Methods: Eighteen patients with Stage III-IV OPC were treated with IMRT to a dose of 70 Gy in 2 Gy fractions over 7 weeks with concurrent/induction chemotherapy. For each case, superior, middle, and inferior pharyngeal constrictors (SPC, MPC, IPC), glottic larynx (GL), supraglottic larynx (SGL), parotid glands (PG), submandibular glands (SMG), oral cavity (OC) and cochleas (C) were contoured in the planning helical CT. Daily cone-beam CT was obtained throughout treatment. Deformable image registration was carried out between daily CBCT and the planning helical CT. Daily dose distribution was reconstructed based on treatment patient anatomy and machine output. For each structure, its daily contour was autogenerated, and its volume and dose was evaluated. The cumulative D1 and equivalent uniform dose (EUD) of each structure were analyzed. Results: PGs showed most volume changes of -20.2% + 6.3 in average after the whole course of the treatment compared to the initial planning volume (t test, p \ 0.01). SMGs showed -8.4% + 4.8 volume changes (p \ 0.01). MPC and IPC volumes increased while SPC volume did not change (+5.7% + 6.4 (p \ 0.01), +4.1% + 7.1 (p = 0.03), -0.4% + 5.1 (p = 0.45)). GL volume decreased by -5.4% + 4.5 (p \ 0.01) while SGL volume did not show significant change (-1.6% + 7.4). OC and C also did not show significant volume changes. The actual EUD for PGs increased by 4.7% + 7.2 (p \ 0.01) on average compared to the planned EUDs. Similarly, as the volume decreased for SMGs, the actual EUDs increased by 1.5% + 3.6 (p = 0.04). EUD changes for SPC, MPC and IPCs were -0.3% + 1.2 (p = 0.27), +0.3% + 2.0 (p = 0.5) and +1.0% + 1.4 (p \ 0.01). EUD changes for GL was +1.6% + 1.1 (p \ 0.01). SGL did not show significant volume or EUD changes. OC EUDs increased by 1.4% + 3.0 (p = 0.03). Comparison of actual D1 vs. planned D1 showed minimal changes for the above structures. Large dose variations were found for cochleas. Cochlear D1 showed 8.8% + 26.8 increase compared to the initial planned D1(p = 0.53). Conclusions: Anatomic changes during the delivery of IMRT for locally advanced OPC are significant resulting in notable discrepancy between planned and delivered doses, especially for PG and SMG. MPC and IPC showed volume increase while SPC volume remained stable. The minimal EUD changes for SPC, MPC and IPCs were likely due to the close proximity/partial overlap to the target PTV. Adaptive planning could potentially reduce this overlap. These findings may have implications for incorporating dose constraints to above structures during the treatment planning and for adaptive planning strategies to minimize normal tissue toxicity. Author Disclosure: D.Y. Lee, None; J. Liang, None; S. Li, None; Y. Chi, None; S.D. McGrath, None; I.S. Grills, None; P.Y. Chen, None; D.J. Krauss, None; A.A. Martinez, None; D. Yan, None.

1102

Analysis of Acute Rectal Toxicity, Interfraction Prostate and SV Shifts During kV-CBCT Image Guided IMRT for Prostate Cancer

N. M. Reddy1, A. Ravi1, S. Coplowitz1, W. Yan1, S. Bolugoddu1, D. Sicurello1, C. Lagos1, H. Chang1, C. Lange2, D. Nori1 1

New York Hospital Queens, Flushing, NY, 2State University of NY, Brooklyn, NY

Purpose/Objective(s): To analyze the frequency and severity of diarrhea, its relationship to rectal dose, volumes of prostate + SV (CTV) and its influence on prostate and SV shifts during IMRT. Materials/Methods: Prostate, SV, rectum and bladder were contoured on planning CT. Margins were 5 mm posteriorly and superiorly and 10 mm in other dimensions. Prescription to CTV was 45 Gy and 36 Gy boost to prostate in 45 fractions (F). Rectal dose was estimated from DVH. Severity of rectal toxicity and diarrhea was scored as per RTOG criteria. Elekta Synergy Linac was used to deliver IMRT to 53 patients with daily kV-CBCT image guidance. Daily CBCT images were matched to planning CT images using bone (B), Grey Value (GV, matches voxel grayscale intensity values) and manual registrations to analyze composite and prostate and SV only shifts, off-line. Composite prostate and SV shifts were the sum of shifts due to patient setup variations and rectal volume changes (B + GV + manual registration). Prostate and SV only shifts were those due to rectal volume changes ((B + GV + manual) - (B + GV)). Magnitude and direction of composite, and prostate and SV only shifts in X (RT (+) / LT (-)), Y (S (+) / I (-)) and Z (anterior (+) / posterior (-)) directions, CTV and rectum volumes and rectal dose for patients with and without diarrhea were compared. Two-sample t test was used for statistical analysis. Results: RTOG grade 1 and 2 diarrhea occurred in six (11.3%) and one (1.9%) out of 53 patients, respectively. Mean volume of CTV in patients with (78.9 ± 26.8) and without (66.6 ± 22.9) diarrhea was the same (p.0.2). Mean volume of rectum in patients with diarrhea was larger (143.1 ± 26.4) than that in patients without (100.7 ± 32.3) diarrhea (p \ 0.01). Mean dose (Gy) to rectum for patients with (34.9 ± 3.9) and without (36.5 ± 2.1) diarrhea was the same (p . 0.2). Magnitude and direction of prostate and SV shifts due to patient setup deviation were random, detectable as bone misalignment and correctable with bone or GV registrations. Magnitude and frequency of prostate and SV only shifts due to diarrhea were larger in patients with distended rectum at panning CT and asymmetric: -5 to -14.8 vs. -8 to -20 mm, respectively. These shifts were not detected by GV registration: (B + GV) - B = \2 mm. Manual matching of prostate-to-prostate resulted in geometric miss of SV and vice versa because prostate and SV shifts were uneven and larger than 5 mm posterior margin (5-40 F). Conclusions: Diarrhea occurs during image guided IMRT for prostate cancer. Volumes of CTV and rectal dose were not correlated with the incidence of diarrhea, but rectal volume was. Where prostate and SV shifts are uneven and larger than margins, IGRT with bone, GV and manual matching is not a complete solution to minimize geometric miss of target; image guided online replanning is needed. Author Disclosure: N.M. Reddy, None; A. Ravi, None; S. Coplowitz, None; W. Yan, None; S. Bolugoddu, None; D. Sicurello, None; C. Lagos, None; H. Chang, None; C. Lange, None; D. Nori, None.