In prostate permanent implants using 131Cs seeds, the prostatic edema developed during the implantation procedure, increases the separation between the seeds. This leads to a decrease in the prostate coverage and thus causes an edema induced dose reduction, which results in an increase in tumour cell surviving fraction (SF) with a corresponding decrease in tumour control probability (TCP). To investigate the impact of edema on the SF and the TCP, the expression of the SF of the linear quadratic (LQ) model was extended to account for the effects of edema using the exponential nature of edema resolution and the dose delivered to the edematous prostate. The SF and the TCP for edematous prostate implants were calculated for 31 patients who underwent real time 131Cs permanent seed implantation. The dose delivered to the edematous prostate was calculated to compute the SF and the TCP for these patients for edema half lives (EHL) ranging from 4 days to 34 days and for edemas of magnitudes (M0) varying from 5 to 60% of the actual prostate volume.

A reduction in the dose delivered to the edematous prostate was found with the increase of EHL and edema magnitude which results in an increase of the SF, and corresponding decrease in the TCP. The dose reductions in 131Cs implants varied from 1.1% (for EHL = 4 days and M0 = 5%) to 32.3% (for EHL = 34 days and M0 = 60%). These are higher than the dose reduction in 125I implants, which vary from 0.3% (for EHL = 4 days and M0 = 5%) to 17.5% (for EHL = 34 days and M0 = 60%). As edema half life increased from 4 days to 34 days and edema magnitude increased from 5 to 60% the SF increased by 4.57 log, and the TCP decreased by 0.80. Compensation of edema induced increase in the SF and decrease in the TCP in 131Cs seed implants should be carefully done by redefining seed positions with the guidance of post-needle plans. The presented model in this study can be used to estimate the SF or the TCP for pre plan or real time permanent prostate implants using day 0 post-implant CT images.

Purpose: High-dose-rate brachytherapy (HDR) boost is an effective method for dose escalation when treating prostate cancer. Optimal number and location of catheters play key role in radiation dose delivery. We studied the impact of catheters and associated trauma on the dose uncertainties and urethral toxicity.

Methods and Materials: Between July 2008 to August 2009, 50 patients with prostate cancer were treated with 46 Gy of external irradiation of whole pelvis (2 Gy per fraction) and two HDR brachytherapy fractions (each 14 Gy) at the end of 10 fractions of external beam. All brachytherapy implants were planned using real-time, ultrasound-based planning system. Variables were prostate and urethral volumes, number of catheters and their mean distance from base of bladder and dose volume histogram parameters. All data were collected during first implant only. The toxicities were graded according to Radiation Therapy Oncology Group Toxicity Criteria. Statistical analysis was done on SPSS version 17.0.

Results: The mean number of catheters implanted was 12.38 (8–19), and number of attempts per needle to achieve desired position was 1.6 (range = 0–5). Mean distance between the catheters tips to contrast filled bladder was 3.2 mm (1–8 mm) after the adjustment. Distances >5 mm showed lower doses to prostate and lower predicted tumour control probability (TCP) (p < 0.01). No correlation was found between numbers of catheters implanted, attempts per catheter and severity of acute genitourinary (GU) toxicity. Significant correlation was found between severity of acute GU toxicity and urethral V130, V150 (p < 0.001).

Conclusion: Dose decline and subsequently lower TCP were seen for the greater distances between the needles and bladder. Acute GU toxicity increased with higher urethral, but severity of acute GU toxicity does not increase with increase in prostate/urethral volumes, number of catheters needles and attempts.

Purpose: The aim of this study was to find out equivalency between two high-dose-rate (HDR) fractionation schemes, relevance to the International Commission on Radiation Units and Measurements report-38 (ICRU-38) reference volume with respect to point A dose and other ICRU reference points in two-dimensional (2D) planning.

Methods and Materials: Forty-nine patients having carcinoma of cervix of stages II–IIIB treated with external beam radiotherapy plus HDR brachytherapy (BT) were analysed. The external beam radiotherapy dose of 45 Gy/25 fractions delivered in 5 weeks followed by HDR BT delivered either in two fractions with 9.5 Gy per fraction (Group-1) or in three fractions with 7.5 Gy per fraction (Group-2) to point A. ICRU-38 recommendations were followed to determine reference volume with respect to Manchester dose point A, and biologically effective dose (BED) at different points.

Results: BED10 at bladder and rectum reference points were 17.11 ± 12.36 Gy and 13.92 ± 5.71 Gy in Group-1, and 15.69 ± 11.43 Gy and 16.24 ± 5.45 Gy in Group-2, respectively; and BED3 were 33.03 ± 29.67 Gy and 25.01 ± 12.35Gy in Group-1, and 27.00 ± 26.85 Gy and 27.44 ± 11.00 Gy in Group-2, respectively. The HDR BT reference volumes were 233.47 ± 27.30 cm3 and 227.83 ± 32.35 cm3 and corresponding CBED10 at point A with proliferation correction were 76.59 ± 2.31 Gy, and 76.41 ± 2.15 Gy for Group-1 and Group-2, respectively. The CBED10 and CBED3 at point B were 46.38 ± 2.26 Gy and 82.23 ± 0.72 Gy, respectively, for Group-1; and 45.03 ± 2.11 Gy and 82.89 ± 0.44 Gy, respectively, for Group-2.

Conclusion: No significant differences were found in the results of two HDR fractionation schemes. ICRU reference volume with respect to point A dose correlates with tumour control and is a good pre-treatment predictor in 2D planning. Neither ICRU bladder and rectum reference points nor trapezoid points showed correlation with complications. The trapezoid points did not also show any correlation with loco-regional control.