3-D Image-Based Radiotherapy Planning for Syed Interstitial HDR Brachytherapy in Patients with Parametrial Spread of Cervical Carcinoma

Objective: To investigate some practical issues involved in multi-fraction Syed interstitial HDR brachytherapy for patients with cervical carcinoma. Methods: Between 8/2009 and 10/2010, eight such patients were treated at our facility with this technique. The high risk CTV (HRCTV), intermediate risk CTV (IRCTV), and organs at risk (OAR: rectum, bladder, sigmoid, and small bowel) were contoured on the planning CT images. All patients received 7 fractions of 4.2Gy prescribed to HRCTV, administered over 4 days. Planning objectives included: doses to OARs were kept below 80% of prescription dose, D90 for HRCTV = 90% of prescription dose, and V150 and V200 = 50% and 20%, respectively. OAR doses were evaluated using the dose to 2mL (D2 mL). Results: An average of 2.4 treatment plans per patient was required to treat all fractions. The average dose to 2 mL (D2 mL) of the bladder was 63% ± 5% (1SD) of the prescription dose (29.4Gy). This value for the rectum was 64% ± 3.4%. The D2 mL values for sigmoid and small bowel were less than 40% of 29.4Gy. The D90 for HRCTV was on average 31.7Gy, whereas the D90 for IRCTV was on average 20Gy. V150 and V200 were on average 51% and 28%, respectively. Conclusion: The implanted needles tended to move during patient transfers to and from the inpatient room to the treatment suite so pre-treatment CT scans should be performed daily and a new treatment plan should be generated if needle movements are significant.