1061 Sigmoid Dose Delivered by High-Dose-Rate Brachytherapy Versus Low-Dose-Rate Brachytherapy forCervical Cancer

C. L. Holloway, D. A. O’Farrell, R. A. Cormack, A. N. Viswanathan

Brigham and Women’s Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA

Purpose/Objective(s): To compare the dose to the sigmoid between high-dose-rate (HDR) and low-dose-rate (LDR) cervicalcancer brachytherapy with a central tandem in place.

Materials/Methods: Between 04/04 and 04/06, 26 patients were treated for cervical cancer with external-beam radiationtherapy followed by brachytherapy. A total of 79 HDR fractions were delivered to 16 patients; they received 24-27.5 Gy in 4-5fractions with an HDR tandem and ovoid (HT/O). A total of 16 LDR fractions were delivered to 10 patients; they received 39.7-50 Gy in 1-2 fractions (0.4-0.8 Gy/h) with either LDR tandem and ovoid (LT/O) (4 patients) or LDR tandem and interstitial(LT/INT) (5 patients) or a combination of both (1 patient). The 6 patients treated with LT/INT had stage IIIA-IVA disease. Apost-implant CT contour of the sigmoid was made. Dose-volume histograms (DVH) were used to generate the D0.1 cc, D1 cc,and D2 cc for the sigmoid. 3D optimization of the HDR plans kept the D2 cc dose to the sigmoid, bladder, and rectum to �80%of the prescribed dose. Equivalent doses for the sigmoid were calculated for both HDR and LDR plans using a BED formulawith an alpha-beta ratio of 3, and assuming a repair half-life of 1.5 hours. Calculations were then made to normalize the BEDto 2 Gy per fraction (EQ2�/�3). A two-tailed t-test compared the dose to the sigmoid: HT/O versus LT/O and LT/INT.

Results: Of the 79 HDR fractions, tandem lengths were either 5 cm (5 fractions) or 6 cm (74 fractions). The median HDRtandem length was 6 cm. To decrease the dose to the sigmoid, 17% (14/79) of the treated fractions were primarily optimizedby turning off the top dwell position(s). Of the 16 LDR fractions, tandem lengths were 5 cm (3 fractions), 5.5 cm (3), 6 cm(5), and 7 cm (5). The median LDR tandem length was 6 cm. The median sigmoid EQ2�/�3 D0.1 cc, D1 cc, and D2 cc for HDRand LDR treatments are reported in the table. Non-normalized values were also not statistically significant.

Conclusions: There is no significant difference in the sigmoid EQ2�/�3 D2 cc between standard HDR and LDR treatments forcervical cancer when the HDR plans are optimized to keep the dose to the sigmoid �80% of the prescribed dose. Long-termfollow-up is necessary to determine whether the D0.1 cc, D1 cc or the D2 cc predict sigmoid complication rates.

Author Disclosure: C.L. Holloway, None; D.A. O’Farrell, None; R.A. Cormack, None; A.N. Viswanathan, None.

1062 Image-Based 3-D Intracavitary Brachytherapy With Integrated Simultaneous IMRT Boost for Cancer ofthe Cervix: Novel Approach for Improving Tumor Dose Coverage

R. Y. Kim, S. El Assal, J. Duan

University of Alabama Medical Center, Birmingham, AL

Purpose/Objective(s): Patterns of Care Study demonstrated that the intracavitary brachytherapy (ICBT) is the cornerstone ofradiotherapy for cervical cancer. However, our previous image-based treatment planning (TP) study confirmed that thepear-shaped dose distribution of ICBT often fails to cover the entire gross tumor volume (GTV), especially in large volumetumor. Therefore, improvement of tumor dose coverage may improve local control for large cervical tumor. Dosimetric studyof cervical cancer demonstrates that intensity-modulated radiotherapy (IMRT) can improve GTV coverage. However, there isa concern that IMRT is unable to deliver significantly high doses in the center of GTV which is a typical dose distribution forICBT. This presentation is to evaluate our novel approach which maintains conventional ICBT but adding simultaneous IMRTboost to the area of under dose by ICBT.

Materials/Methods: Six patients with cancer of the uterine cervix (3 IB2, 3 IIB) received whole pelvic irradiation of 45 Gyand underwent five of conventional high-dose-rate (C-HDR) at 6 Gy/fraction. CT and MRI images of the pelvis were done withplastic HDR applicators in place. GTV and organs at risk (OARs) were outlined on the CT images. CTV was defined as GTVwith 3 mm margin plus the uterus. For the C-HDR/IMRT technique, the C-HDR plan was modified to reduce the bladder andrectum dose below 80% of the prescription dose and then IMRT boost plan was subsequently optimized based on the HDR doseto compliment the dose coverage of CTV. To preserve anatomy from deformation, the IMRT plans would be deliveredimmediately following HDR treatment with applicator in place. For comparision, optimized HDR (O-HDR) and IMRT aloneplans were also generated by optimizing the dwell weights to cover the GTV. The three treatment techniques (O-HDR, IMRT,C-HDR/IMRT) were compared for the six patients by analyzing the dose volume histograms. V95% was used to evaluate GTVcoverage, and the minimum doses in 2.0 cm3 volume receiving the highest dose (D2) was calculated to compare doses to OARs.

Results: C-HDR failed to provide adequate tumor coverage (53% average tumor coverage). The O-HDR, IMRT, andC-HDR/IMRT techniques yielded substantially improved tumor coverage: 98%, 95% and 100%, respectively. However, theO-HDR technique resulted in unacceptably high average D2 dose to bladder (220%), rectum (164%) and bowel (160%). TheIMRT and C-HDR/IMRT boost plans both provided sufficient sparing to the bladder and rectum with average D2 doses forIMRT (67.9% and 55.7%) moderately lower than C-HDR/IMRT (77.4% and 69.5%). However, the average D2 dose to thebowel for C-HDR/IMRT (98.4%) was lower than IMRT (111.2%). There was unnecessary dose spillage outside of OARs withIMRT plan. In addition, the C-HDR/IMRT technique provided significantly higher integral tumor dose than IMRT alone.

Table: Sigmoid EQ2�/�3

HT/O LT/O. T/INT

p-ValueMedian Range % Rx Median Range % Rx

D0.1 cc 84.4 55.6-119.5 97.1 79 57.5-101.4 80.2 0.12D1 cc 72.8 52.4-89.1 82.5 74 55.9-91.1 75.5 0.8D2 cc 68.7 51.2-81.7 78.1 72.3 54.9-87.4 73.6 0.8

S165Proceedings of the 48th Annual ASTRO Meeting