ESTRO 2022 - Abstract Book

S1602

Abstract book

ESTRO 2022

Materials and Methods We retrospectively analyzed 33 patients with cervical cancer who treated with definitive radiotherapy including intracavitary brachytherapy, which was performed with VP in first one or two fractions and with rectal RR in subsequent fractions. We extracted two fractions for each patients: one fraction with VP and a next fraction with RR and compared dose volume parameters. 33 fractions each in VP group and RR group were analyzed. Treatment planning was prescribed 6 Gy to point A initially, and then manually optimized to reduce dose to organs at risk (OAR) and ensure coverage of the target. Dose to 90 % (D90) of high-risk CTV (CTV HR ), dose to point A and dose to 2.0 cc (D 2cc ) for OAR (bladder, rectum, sigmoid and small bowel) were collected from planning CT. The significance of differences of parameters were evaluated using paired t-tests. Results There were no significant difference between VP vs. RR in D90 of CTV HR (mean 750.2 cGy vs. 770.3 cGy p=0.2061). Dose to point A were significantly higher in VP (mean 622.1 cGy vs. 592.4 cGy, p=0.0310). D 2cc for the rectum (mean 392.8 cGy vs. 440.3 cGy, p=0.0149), D 2cc for the sigmoid (mean 415.7 cGy vs. 528.5 cGy, p<0.0001) and D 2cc for the bladder (mean 576.0 cGy vs. 827.6 cGy, p<0.0001) was significantly lower in VP. Significant differences were not found between VP vs. RR in D 2cc for the small bowel (mean 488.4 cGy vs. 486.4 cGy, p=0.9724). Conclusion Our results show that VP reduces the dose to rectum, sigmoid and bladder compared with RR without impairing dose to CTV or point A. N. Radhakrishna 1 , T. Pasha C R 2 , R.R. Bucchapudi 3 , H. R S 4 , S. Sunny Pullan 2 , E. Jerod 2 , S. Palled 5 , T. B 5 , N. Thimmaiah 5 , V. Patil 5 , L. Viswanath 5 1 Kidwai Memorial Institue of Oncology, Radiation Oncology, Bangalore, India; 2 Kidwai Memorial Institute of Oncology , Radiation Oncology, Bangalore, India; 3 Kidwai Memorial Institute of Oncology , Radiation Physics, Bangalore, India; 4 Sri Shankara Cancer Hospital & Research Centre, Radiation Oncology, Bangalore, India; 5 Kidwai Memorial Institute of Oncology, Radiation Oncology, Bangalore, India Purpose or Objective In Intracavitary Brachytherapy(ICBT) for cancer(Ca.) cervix, the largest sized ovoid that the vagina can accommodate is used to provide maximum lateral dose throw-off to the parametrium. However, we have observed that ovoids >2.5 cm can rarely be accommodated in our patients. Upper vaginal narrowing post External Beam Radiotherapy(EBRT) & racial difference in the pelvis size may be the causative factors. Patients having a partial response to EBRT with moderate volume residual disease are subjected to ICBT. Even with parametrial disease limited to less than medial half of its width at BT, ICBT may be suboptimal with undersized ovoids. Instead, they may require a combination of IC+interstitial brachytherapy(ISBT). We aim to determine the most commonly used size of ovoids in ICBT among South Indian patients and measure the maximum distance from the central uterine axis that can be covered with use of various sizes of ovoids. Materials and Methods Patients with Ca.cervix FIGO stage IB2 to IIIB who have completed EBRT and ICBT for residual disease limited to medial half of parametrium, were selected for this retrospective study. Those treated with ISBT/ low dose rate BT were excluded. High dose rate BT was delivered using GammaMed-plus Iridium 192 remote after-loading system with Fletcher Suit or Manchester applicator. A dose of 6-7 Gy/3-4 Fractions was prescribed to Point A. The target dose was optimized to cover the residual disease based on examination under anesthesia and CT simulation respecting the dose constraints to organs at risk (OARs). Distance covered by 100 % isodose curve at level of Point A, point A dose, Total Reference air kerma (TRAK), minimum dose received by the maximally irradiated 2 cc(D2cc) of rectum, bladder, and sigmoid colon were noted. One-way ANOVA was used for inter-group Comparison between different sizes of ovoids. ‘p’ value ≤ 0.05 was considered statistically significant* Results 219 ICBT applications were performed for 142 patients. 115(52%) applications with semi-small (20mm), 69(32%) with small(25mm) and 35 (16%) with medium(30mm) sized ovoids. The mean distance of 100% isodose curve obtained by semi- small, small and medium ovoids were 3.48 + 0.53cm, 3.57 + 0.45cm and 3.80 + 0.44cm respectively (*p = 0.005). This reflects that the maximum distance which can be covered on either side of central axis is 1.74cm, 1.78cm and 1.9 cm respectively. The difference in point A doses between the three ovoids was 5.40 + 0.71Gy, 5.59 + 0.75Gy and 5.79 + 0.70Gy respectively (*p=0.016). TRAK was 4137.35 + 509.35, 4433.60 + 554.80 and 4604.72 + 381.45 mGy m2 h-1for the respective ovoids (*p < 0.001). No significant impact was noted upon OAR doses. PO-1797 Impact of Ovoid size in Intra-cavitary Brachytherapy upon target dose in patients with Cancer Cervix