Optimal bladder filling during high-dose-rate intracavitary brachytherapy for cervical cancer: a dosimetric study.

PURPOSE: The aim of this study is to compare 3D dose volume histogram (DVH) parameters of bladder and other organs at risk with different bladder filling protocol during high-dose-rate intracavitary brachytherapy (HDR-ICBT) in cervical cancer, and to find optimized bladder volume. MATERIAL AND METHODS: This dosimetric study was completed with 21 patients who underwent HDR-ICBT with computed tomography/magnetic resonance compatible applicator as a routine treatment. Computed tomography planning was done for each patient with bladder emptied (series 1), after 50 ml (series 2), and 100 ml (series 3) bladder filling with a saline infusion through the bladder catheter. Contouring was done on the Eclipse Planning System. 7 Gy to point A was prescribed with the standard loading patterns. Various 3D DVH parameters including 0.1 cc, 1 cc, 2 cc doses and mean doses to the OAR's were noted. Paired t-test was performed. RESULTS: The mean (± SD) bladder volume was 64.5 (± 25) cc, 116.2 (± 28) cc, and 172.9 (± 29) cc, for series 1, 2, and 3, respectively. The 0.1 cm3,1 cm3, 2 cm3 mean bladder doses for series 1, series 2, and series 3 were 9.28 ± 2.27 Gy, 7.38 ± 1.72 Gy, 6.58 ± 1.58 Gy; 9.39 ± 2.28 Gy, 7.85 ± 1.85 Gy, 7.05 ± 1.59 Gy, and 10.09 ± 2.46 Gy, 8.33 ± 1.75 Gy, 7.6 ± 1.55 Gy, respectively. However, there was a trend towards higher bladder doses in series 3. Similarly, for small bowel dose 0.1 cm3, 1 cm3, and 2 cm3 in series 1, 2, and 3 were 5.44 ± 2.2 Gy, 4.41 ± 1.84 Gy, 4 ± 1.69 Gy; 4.57 ± 2.89 Gy, 3.78 ± 2.21 Gy, 3.35 ± 2.02 Gy, and 4.09 ± 2.38 Gy, 3.26 ± 1.8 Gy, 3.05 ± 1.58 Gy. Significant increase in small bowel dose in empty bladder (series 1) compared to full bladder (series 3) (p = 0.03) was noted. However, the rectal and sigmoid doses were not significantly affected with either series. CONCLUSIONS: Bladder filling protocol with 50 ml and 100 ml was well tolerated and achieved a reasonably reproducible bladder volume during cervical brachytherapy. In our analysis so far, there is no significant impact of bladder filling on DVH parameters, although larger bladders tend to have higher doses. Small bowel doses are lesser with higher bladder volumes. Further evaluation and validation are necessary.

Bioevaluation of (125) I Ocu-Prosta seeds for application in prostate cancer brachytherapy.

BACKGROUND & OBJECTIVES: In recent years, brachytherapy involving permanent radioactive seed implantation has emerged as an effective modality for the management of cancer of prostate. 125 I-Ocu-Prosta seeds were indigenously developed and studies were carried out to assess the safety of the indigenously developed 125 I-Ocu-Prosta seeds for treatment of prostate cancer. METHODS: Animal experiments were performed to assess the likelihood of in vivo release of 125 I from radioactive seeds and migration of seeds implanted in the prostate gland of the rabbit. In vivo release of 125 I activity was monitored by serial blood sampling from the auricular vein and subsequent measurement of 125 I activity. Serial computed tomography (CT) scans were done at regular intervals till 6 months post implant to assess the physical migration of the seeds. RESULTS: The laser welded seeds maintained their hermeticity and prevented the in vivo release of 125 I activity into the blood as no radioactivity was detected during follow up blood measurements. Our study showed that the miniature 125 I seeds were clearly resolved in CT images. Seeds remained within the prostate gland during the entire study period. Moreover, the seed displacement was minimal even within the prostate gland. INTERPRETATION & CONCLUSIONS: Our findings have demonstrated that indigenously developed 125 I-Ocu-Prosta seeds may be suitable for application in treatment of prostate cancer.

Predicting rectal and bladder overdose during the course of prostate radiotherapy using dose-volume data from initial treatment fractions.

PURPOSE: To evaluate whether information from the initial fractions can determine which patients are likely to consistently exceed their planning dose-volume constraints during the course of radiotherapy for prostate cancer. METHODS AND MATERIALS: Ten patients with high-risk prostate cancer were treated with helical tomotherapy to a dose of 60 Gy in 20 fractions. The prostate, rectum, and bladder were recontoured on their daily megavoltage computed tomography scans and the dose was recalculated. The bladder and rectal volumes (in mL) receiving ≥100% and ≥70% of the prescribed dose in each fraction and in the original plans were recorded. A fraction for which the difference between planned and delivered was more than 2 mL was considered a volume failure. Similarly if the difference in the planned and delivered maximum dose (D(max)) was ≥1% for the rectum and bladder, the fraction was considered a dose failure. Each patient's first 3 to 5 fractions were analyzed to determine if they correctly identified those patients who would consistently fail (i.e., ≥20% of fractions) during the course of their radiotherapy. RESULTS: Six parameters were studied; the rectal volume (RV) and bladder volumes (BV) (in mL) received ≥100% and ≥70% of the prescribed dose and maximum dose to 2 mL of the rectum and bladder. This was given by RV100, RV70, BV100, BV70, RD(max), and BD(max), respectively. When more than 1 of the first 3 fractions exceed the planning constraint as defined, it accurately predicts consistent failures through the course of the treatment. This method is able to correctly identify the consistent failures about 80% (RV70, BV100, and RV100), 90% (BV70), and 100% (RD(max) and BD(max)) of the times. CONCLUSIONS: This study demonstrates the feasibility of a method accurately identifying patients who are likely to consistently exceed the planning constraints during the course of their treatment, using information from the first 3 to 5 fractions.

Dose variation during hypofractionated image-guided radiotherapy for prostate cancer: planned versus delivered.

AIMS: To determine variation in the actual doses delivered to the organs at risk and the target in patients treated for localized carcinoma of the prostate using image-guided radiotherapy. MATERIALS AND METHODS: Ten patients treated with helical TomoTherapy underwent daily target localization with megavoltage CT, on which the prostate, rectum and bladder were recontoured. The planned adaptive module was used for dose recalculation. The study endpoints were to analyse the variations in certain dose-volume parameters of the rectum and bladder (BD 2cc , RD 2cc , BV 100% , BV 70% , RV 100% , RV 70% ), the maximum anteroposterior (AP) and lateral rectal diameters, the volume of the CTV receiving 100% of the prescription dose (CTV V 100% ) and the dose to 100% of the CTV (CTV D 100% ). RESULTS: The difference between the planned and delivered target doses (CTV V100% and CTV D100%) was small and clinically insignificant indicating adequate target coverage during treatment. There was a large variation in the AP and lateral rectal diameters, with no particular trend or correlation to dose parameters being noted during the course of treatment. The mean AP diameter during treatment was significantly less than the planned diameter (P < 0.05). The percentage of fractions where the delivered BV100%, BV70%, RV100%, and RV70% was more than the planned values were 42.8%, 17.1%, 45.4%, and 44.4%, respectively. The delivered BD2cc and RD2cc were similar to their planned values. CONCLUSIONS: This study demonstrates the usefulness of daily soft tissue image guidance in negating the effects of physiological variation of the rectum and bladder on the dose delivered to the prostate.

'Plan of the day' adaptive radiotherapy for bladder cancer using helical tomotherapy.

BACKGROUND AND PURPOSE: This study assessed the potential of tomotherapy based Image Guided Radiotherapy (IGRT) to increase the accuracy of bladder irradiation using a 'plan of the day' adaptive radiotherapy (ART) technique. MATERIALS AND METHODS: Ten patients with muscle invasive bladder cancer underwent bladder preservation with trimodality therapy in an ongoing trial. All patients received 64 Gy/32# to the whole bladder and seven of them received a boost of 68 Gy/32# to the tumour bed. The ART technique entailed the generation of six IMRT plans for each patient, using six isotropic PTVs of 5-30 mm applied to the bladder volume (CTV) to generate the PTVs. Megavoltage CT (MVCT) imaging was done to correct positioning errors and choose the 'plan of the day'. RESULTS: Post treatment MVCT scans (315 scans) were used to generate multiple anisotropic PTVs for three hypothetical scenarios. Overall, coverage of anterior and superior walls required larger margins than other walls. Maximum geographical miss, in spite of IGRT, was noted for the superior (13.8%) and anterior walls (10.3%). CONCLUSIONS: Plan of the day ART is a feasible and promising technique for optimal treatment and dose escalation in bladder cancer.