The GEC ESTRO guideline has been widely adopted in cervical cancer treatment that combines external beam radiation therapy (EBRT) and CT-guided HDR brachytherapy (BT). In this guideline the minimum dose to 90% (D90) High Risk Clinical Target Volume (HRCTV), to 2cc of bladder (BD(2cc)) or rectum (RD(2cc)) are used for plan evaluation. The total dose in EQD2 is obtained by direct summation of EQD2 dose from EBRT and BT. However, in fractionated BT the high dose region varies due to variation of tumor volume, insertion configuration, and bladder/rectum shape. Direct dose summation thus introduces dosimetric uncertainties. With recent advances in image fusion software, we can also estimate these parameters from deformable composite dose. In this study, we use MiM Software (v6.04) to obtain deformable composite dose of all BT plans. D90, BD(2cc)/RD(2cc) are extracted from the final composite dose, and then compared with those estimated per GEC ESTRO. Total of 30 HDR BT plans for 6 patients with stage IB2-IIB cervical cancer were retrospectively reviewed. All 30 insertions were planned in Oncentra (v4.3). The prescribed dose was 5∼6 Gy/fraction x 5. The HRCTV, bladder/rectum were contoured, and D90, BD(2cc)/RD(2cc) were evaluated per GEC ESTRO in clinic. Each plan was then imported into MiM. RT dose was converted into EQD2 in MiM. Using the CT dataset for the 5th fraction as the primary image set, deformable image fusion and composite dose were performed sequentially with the other 4 fractions. The total dose was obtained for each patient. During image fusion, the tandem and smit sleeve were used as markers. The alignment of HRCTV was the primary fusion objective. D90, BD(2cc)/RD(2cc) were then extracted from the composited DVH. Our result shows that BD(2cc)/RD(2cc) per GEC ESTRO are generally higher than those extracted in MiM. On average, RD(2cc) is 5.3Gy higher (ranging 2.2∼12 Gy), and BD(2cc) is 1.1Gy higher (ranging -0.7∼3.3Gy). The difference for D90 between that reported per GEC ESTRO and that in MiM ranges -11∼13.1Gy. The D90 in 5 patents' treatments meet GEC ESTRO criteria (within 80∼90 Gy), and one is 78.9 Gy. However, the reported D90 in MiM is > 90Gy when HRCTV decreases linearly after each treatment. Otherwise it is < 80 Gy. The HRCTV in 2 out of 6 patients reduces continuously from the 1st to 5th treatment. Our retrospective study suggests that the GEC ESTRO criteria for BD(2cc)/RD(2cc) are relatively conservative. The actual maximum dose to rectum/bladder may be overestimated with GEC ESTRO. Current D90 reported per GEC ESTRO may present moderate uncertainty in overall dose delivered to target. A cross check using deformable composite dose may be beneficial. However the difference of D90 between that per GEC ESTRO and that from deformable composite dose needs further investigation.

Purpose: Bladder/rectum sparing is always the challenge in HDR 3D CT‐guided brachytherapy treatment planning for cervical cancer due to the tight separation between them and High Risk Clinical Target Volume (HRCTV). In this study, we analyzed the minimum CTV‐to‐Bladder distance (MCBD), the minimum CTV‐to‐Rectum distance (MCRD), dose to 2cc of bladder (BD(2cc)) and rectum (RD(2cc)) respectively. The potential application of MCBD and MCRD as plan optimization indicators was investigated. Methods: Total 49 consecutive HDR plans for 11 patients with stage I–IIB cervical cancer were retrospectively reviewed. The prescribed dose (PD) was either 6 Gy/fraction × 5 or 7 Gy/fraction × 4 fractions. For each plan, MCBD and MCRD were measured on relevant transverse CT slices. BD(2cc), RD(2cc), the minimum dose cover 90% HRCTV (D90) were recorded. All plans were optimized with dose constrains BD(2cc)<80%PD, RD(2cc)<70%PD, D90>90%PD. Results: For 49 insertions, MCRD was 14±7mm. MCBD was 2±1mm. D90 was 100±15%PD. RD(2cc) and BD(2cc) were 57±12%, 74±10% of PD respectively. The correlation coefficient of MCBD and BD(2cc) was 0.31(p=0.03), indicating that bladder dose was significantly impacted by MCBD.Among 49 insertions, 19 cases had MCBD<=1mm with BD(2cc)>75% PD and D90 96±13%PD. 13 cases had 1mm75% PD. 17 out of 49 insertions had MCBD>2mm with D90 105±15%PD. Only 2/17 cases had BD(2cc)>75% PD. For 46/49 insertions, MCRD was >=5mm, which caused RD(2cc) extremely low. Conclusion: Our study shows that bladder sparing is correlated with MCBD. 65% of 49 insertions had MCBD<=2mm. Among them, 72% cases had BD(2cc)>75%PD. We believe that MCBD and MCRD can be used as plan optimization indicators. When any of them is <2mm, the target coverage would be comprised in order to spare bladder or rectum. This allows physicians have a reasonable expectation before plan is completed and guide further insertions.

Image-Guided Radiation Therapy (IGRT) increases the precision and accuracy of external beam radiation therapy and provides a safer delivery of higher, more curative levels of radiation dose. However, when significant changes to internal anatomy occur, IGRT alone will not be able to compensate for the dose degradation that may occur from using the original IMRT plan. A real-time planning (RTP) or adaptive planning technique would enable the continued use of tight margins with the assurance of full target coverage and efficient normal tissue sparing. In its current stage, the adaptive planning technique requires a physician to manually redraw the involved structures before each treatment. These day-to-day contouring variations could potentially be significant and thus overestimate the superiority of the newly created adaptive IMRT plan. A total of 60 CT scans were used during the course of IMRT treatment of 6 prostate cancer patients. An in-room diagnostic CT-on-Rails was used for the purposes of performing daily IGRT in conjunction with an adaptive IMRT planning technique. While the data was analyzed for the standard purposes of IGRT, a brand new optimized IMRT plan was created based on a new set of structures drawn by the on-call physician. This resulting plan was then compared to the initial IMRT plan or "recalculated plan" which was copied onto the new data set and recalculated with the daily IGRT implemented shifts. The RTP plan consistently showed at least equal effectiveness in target coverage and normal-tissue sparing as the initial IMRT recalculated plan. In 25% of the cases, greater rectal sparing was seen in the RTP plan with the largest single case reducing V50 by 40% and V60 by 50%. The most frequent anomalies seen in this study, however, were target coverage of the prostate and PTV. While the RTP plan maintained minimum prescription dose coverage of 97% to the prostate, the recalculated IMRT plan's minimum dose routinely fell below 95%, and in 20% of the cases, it dropped below 90%. In terms of PTV minimum coverage, the recalculated IMRT plan showed consistent dose degradation with 90% of the cases falling below 90% of the prescribed dose. Daily changes of the internal anatomy warrant the need for RTP. To our knowledge, we are one of the first to implement this technique in our daily clinical practice on a consistent basis. RTP possesses the ability to treat other cancer sites besides the prostate and its full potential maybe realized once better and faster auto-segmentation programs are available to minimize manual contouring variability.