34. Optimization in HDR gynecological brachytherapy

Analysis of Interfraction Prostate Motion Using Megavoltage Cone Beam Computed Tomography by Bylund et al. ( Int J Radiat Oncol Biol Phys 2008;72:949–956)

Variability in prostate gland positioning during RT for prostate tumors is a recognized challenge in both human and veterinary oncology. This retrospective study investigates the interfractional variability in prostate gland positioning in relation to rectal and bladder volumes in dogs undergoing radiation therapy (RT) for prostate tumors. The study tracked 10 dogs undergoing five RT sessions from February 2016 to November 2021, delivering a total of 25Gy each. Each dog underwent CT scans for treatment simulation, and cone-beam CT (CBCT) images were acquired before each RT. The focus was to analyze the positional shifts of the prostate gland concerning the volumes of the rectum and urinary bladder. The pelvic bones were used as the point of reference. The rectal and bladder volumes were measured before each RT, and shifts in the prostate gland position were calculated by comparing coordinates from planning CT and treatment session images. Findings revealed significant correlations between prostate positional shifts in the dorsal-ventral (repeated measures correlation coefficient of -0.58 [range 00.75-00.33]; P<.001) and cranial-caudal directions (repeated measures correlation coefficient [95%CI] 0.56 [range 0.31-0.74]; P<.001) and rectal volume, while no significant relationship was observed with bladder volume. Shifts in the lateral direction were not correlated with either organ's volume. This study highlights the importance of considering rectal volume in canine prostate tumor RT to minimize positional uncertainties. Maintaining consistent rectal volume may enhance the precision of prostate targeting, potentially influencing the safety of RT.

Cervical cancer is the most common gynecologic malignancy and a leading threat to women’s health. Intensity-modulated radiation therapy (IMRT) is a cornerstone treatment, but its success depends on precise patient positioning and consistent bladder distension to minimize setup errors and organ motion. This study evaluated the impact of bladder volume variation on setup errors during IMRT and the accuracy and clinical utility of a bladder volume scanner (BVS) for bladder volume management. We conducted a prospective, allocated comparative study of 62 cervical cancer patients treated with IMRT between April 2021 and August 2022. Patients were allocated to a BVS group (n = 31) that used a bladder scanner to maintain a target bladder volume of 250–350 mL (± 30 mL) or to a control group (n = 31) that relied on a strong urge to urinate for bladder filling. We compared bladder volume consistency, setup errors in left-right (X), anterior-posterior (Y), and superior-inferior (Z) directions, homogeneity and conformity indices, and the volumes of bladder, rectum, and small intestine receiving 45 Gy between groups. We also analyzed the correlation between bladder volume measured by BVS and by computed tomography (CT). The BVS group had significantly more consistent bladder volumes and significantly smaller setup errors in all directions than the control group. The median (interquartile range, IQR) setup errors in the BVS vs. control group were 1.0 (0.8–1.5) vs. 1.7 (1.2–2.5) mm in the X-axis, 0.4 (0.2–1.1) vs. 1.9 (1.5-3.0) mm in the Y-axis, and 1.1 (0.9–1.3) vs. 2.8 (2.0-3.5) mm in the Z-axis, respectively (all P < 0.01). The BVS group also showed improved dosimetry, with a better homogeneity index (1.01 vs. 1.11) and conformity index (0.98 vs. 0.94), and significantly lower bladder, rectum, and small intestine volumes receiving 45 Gy (24.6% vs. 29.1%, 19.7% vs. 25.3%, and 17.4% vs. 18.1%, respectively; all P < 0.01). Bladder volumes measured by the scanner were strongly correlated with CT-derived volumes (R = 0.977). Precise bladder volume control using a BVS leads to more reproducible patient positioning, as evidenced by significantly reduced bony anatomy-based setup errors, and resulted in significantly reduced radiation exposure to adjacent organs. The strong correlation between BVS and CT measurements confirms the device’s reliability. By ensuring a reproducible daily anatomical setup, BVS-guided bladder management improves the precision of IMRT delivery. This approach mitigates a key source of treatment uncertainty and establishes a foundation for potentially safer margin reduction or dose escalation strategies in the future. The bladder scanner was highly accurate and reproducible, improving target delineation and potentially allowing safer dose escalation.

Quantification of Organ Motion During Chemoradiotherapy of Rectal Cancer Using Cone-Beam Computed Tomography

The purpose of this study is to develop a model that quantifies in three dimensions changes in bladder shape due to changes in bladder and/or rectal volume. The new technique enables us to predict changes in bladder shape over a short period of time, based on known urinary inflow. Shortly prior to the treatment, the patient will be scanned using a cone beam CT scanner (x-ray volume imager) that is integrated with the linear accelerator. After (automated) delineation of the bladder, the model will be used to predict the short-term shape changes of the bladder for the time interval between image acquisition and dose delivery. The model was developed using multiple daily CT scans of the pelvic area of 19 patients. For each patient, the rigid bony structure in follow-up scans was matched to that of the planning CT scan, and the outer bladder and rectal wall were delineated. Each bladder wall was subdivided in 2500 domains. A fixed reference point inside the bladder was used to calculate for each bladder structure a "Mercator-like" 2D scalar map (similar to a height map of the globe), containing the distances from this reference point to each domain on the bladder wall. Subsequently, for all bladder shapes of a patient and for all domains on the wall individually, the distance to the reference point was fitted by a linear function of both bladder and rectal volume. The model uses an existing bladder structure to create a new structure via expansion (or contraction), until the expressed volume is reached. To evaluate the predictive power of the model, the jack-knife method was used. The errors in the fitting procedure depended on the part of the bladder and range from 0 to 0.5 cm (0.2 cm on average). It was found that a volume increase of 150 cc can lead to a displacement up to about 2.5 cm of the cranial part of the bladder. With the model, the uncertainty in the position of the bladder wall can be reduced down to a maximum value of about 0.5 cm in case the bladder volume increase is known. Furthermore, it was found that a change in rectal filling causes a shift of the bladder, while its shape is hardly influenced. In conclusion, we developed a model that describes the bladder shape and position as a function of the bladder volume and the rectal filling. The model accurately describes the complex shape of the bladder as it works on each domain of the bladder separately.

Introduction: Cervical cancer has a high incidence in developing countries including India. Brachytherapy (BT) is an important component in the curative management of carcinoma of the cervix, and significantly improves survival. In gynaecologic BT, correlation between the radiation dose and the normal tissue effects have been assessed using point doses. Since 1985, these points have been defined in the international commission of radiation units and measurements (ICRU-38) report. However GEC-ESTRO recommended volume based treatment planning in their respective series (I-IV). For cervical cancer BT, the correlation of ICRU point doses and volume based treatment planning is investigational till date. Analysis becomes feasible when cross sectional image-based treatment planning for BT using computerized tomography (CT) or magnetic resonance imaging (MRI) is utilised as per GEC-ESTRO recommendation. Methods: It is a retrospective pilot study includes patients (pts.) of carcinoma cervix treated with high dose rate (HDR) BT 9 Gy in 2 fractions 1 week apart. All volume based dosimeteric parameters regarding high risk clinical target volume (HRCTV), intermediate risk clinical target volume (IRCTV) like D90, D100 and for organ at risk (OAR) D 0.1 cc, D 1.0 cc and D 2.0 cc were delineated and dose coverage was analysed in point dose based planning. Results: We have analysed twenty pts. of squamous cell carcinoma (SCC) cervix. The median age was 52 yrs. (41-65 yrs), stage II B 10 pts. &amp; III B 10 pts. The mean value of D90 &amp; D100 in HRCTV during I and II session were 8.64, 6.75 and 5.76, 4.36 Gy respectively. Same values for IRCTV were 6.31, 4.91 and 3.68, 3.15 Gy respectively. Analysis of OARs demonstrated that mean dose received by 0.1, volume of bladder during I and II session received 10.68, 9.47, by 1 cc volume 8.39, 7.57 and by 2 cc volume 6.84, 6.21 Gy respectively. The mean dose received by 0.1 cc of rectum were 11.59, 10.12, by 1 cc volume 9.53, 8.19 and by 2 cc volume 7.76, 6.81 Gy respectively. In point based analysis mean dose delivered to bladder point during I and II session were 5.63, 6.02 and to rectum point were 5.98, 5.46 Gy respectively. Doses to 0.1 cc volume of bladder and rectum were higher in volume based BT as compared to point based BT in respective fractions. Conclusion: Both HRCTV and IRCTV had better dose coverage in 1st fraction as compared to 2nd fraction. Point doses to bladder and rectum is underestimated in point based (ICRU-38) BT. We need more number of pts in prospective randomized trial for more consistent result.

A study on prostate movement and dosimetric variation because of bladder and rectum volumes changes during the course of image-guided radiotherapy in prostate cancer.

Daily bladder variations make it difficult to utilize standard radiotherapy as a primary treatment option for muscle-invasive bladder cancer. Our purpose was to develop a model comparing dose distributions of image-guided and adaptive radiotherapy (ART) techniques for canine bladder cancer. Images were obtained retrospectively from cone-beam computed tomography (CBCT) scans used for daily positioning of four dogs undergoing fractionated image-guided radiotherapy (IGRT). Four different treatment plans were modeled for each dog, and dosimetric data were compared. Two plans were developed using planning target volumes based on planning computed tomography (CT) bladder volume. These plans then used bony anatomy or soft tissue anatomy for daily positioning and dosimetric modeling. The third plan type was a hybrid IGRT and ART technique utilizing a library of premade anisotropic planning target volumes using bladder wall motion data and selection of a "plan-of-the-day" determined from positioning CBCT bladder volumes. The fourth plan was an ART technique that constructed a new planning target volume each day based on daily bladder volume as determined by pretreatment CBCT. Dose volume histograms were generated for each plan type and dose distribution for the bladder and rectum were compared between plan types. Irradiated rectal volume decreased and irradiated bladder volume increased as plan conformality increased. ART provided the greatest rectal sparing, with lowest irradiated rectal volume (P < 0.001), and largest bladder volume receiving 95% of the prescription dose (P < 0.001). In our model, adaptive radiotherapy techniques for canine bladder cancer showed significant reduction in rectal volume irradiated when compared to nonadaptive techniques, while maintaining appropriate bladder coverage.

PurposeThe purpose of the present study was to quantify the inter-fractional motion of the rectum and the rectal and bladder volumes using CBCT scans taken during chemoradiation therapy (CRT) for rectal cancer. Also, assessment was made for a better margin for simultaneous integrated boost - intensity modulated radiation therapy (SIB-IMRT) for rectal cancer.Methods and materialsThere were 32 patients in this study undergoing preoperative CRT for rectal cancer. Each rectum and bladder was contoured on all planning CTs and CBCTs (day 1, 7, 13, 19, 25). The target volume was configured by adding margins (0, 3, 5, 7, 10, and 15 mm) to the rectum on planning CT. The respective percentage of rectal volume that exceeds the target volume was calculated for each of these margins. The percentage of bladder volume that exceeds the bladder volume in the planning CT and motion of the center of gravity of rectum were also analyzed.ResultsPlanning CTs and series of each 5 CBCTs for 32 patients were analyzed in this study. The rectal volume tended to shrink week after week. The mean values (± SD) in the 32 series per patient of the percentage of rectum on the CBCTs exceeding target volume in which the margins of 0, 3, 5, 7, 10, and 15 mm were added to the rectum on planning CT were 20.7 ± 12.5%, 7.2 ± 8.3%, 3.9 ± 5.9%, 2.1 ± 3.9%, 0.7 ± 1.8%, and 0.1 ± 0.3%, respectively. No association was seen between the percentage of changes of bladder volume and motion of rectal centroid.ConclusionsIn this study, we estimated the motion of the rectum using planning CT and CBCT. Ten to fifteen mm is a sufficient margin for the rectum during SIB-IMRT for rectal cancer in the supine position.

The purpose is to compare CT-based dosimetry with International Commission on Radiation Units and Measurements (ICRU 38) bladder and rectum reference points in patients of carcinoma of uterine cervix treated with intracavitary brachytherapy (ICA). Twenty-two consecutive patients were evaluated. Orthogonal radiographs and CT images were acquired and transferred to PLATO planning system. Bladder and rectal reference points were identified according to ICRU 38 recommendations. Dosimetry was carried out based on Manchester system. Patient treatment was done using 192Iridium high dose rate (HDR) remote after-loading machine based on the conventional radiograph-based dosimetry. ICRU rectal and bladder point doses from the radiograph plans were compared with D2, dose received by 2 cm3 of the organ receiving maximum dose from CT plan. V2, volume of organ receiving dose more than the ICRU reference point, was evaluated. The mean (±standard deviation) volume of rectum and bladder was 60 (±28) cm3 and 138 (±41) cm3 respectively. The mean reference volume in radiograph and CT plan was 105 (±7) cm3 and 107 (±7) cm3 respectively. It was found that 6 (±4) cm3 of rectum and 16 (±10) cm3 of bladder received dose more than the prescription dose. V2 of rectum and bladder was 7 (±1.7) cm3 and 20.8 (±6) cm3 respectively. Mean D2 of rectum and bladder was found to be 1.11 (±0.2) and 1.56 (±0.6) times the mean ICRU reference points respectively. This dosimteric study suggests that comparison of orthogonal X-ray-based and CT-based HDR ICA planning is feasible. ICRU rectal point dose correlates well with maximum rectal dose, while ICRU bladder point underestimates the maximum bladder dose.

Aim:Since anatomical and geometric variations occur with every fraction, planning, and dose optimization is necessary for every fraction of high-dose rate intracavitary brachytherapy of carcinoma cervix. In this study, we have tried to quantify the differences in doses to organs at risk (OAR) for each fraction of brachytherapy.Methods and Materials:One hundred and seventy computed tomography datasets of cervical cancer patients receiving intracavitary brachytherapy at our institution between January and April 2015 were analyzed. The volumes of the high-risk clinical target volume and OAR contoured were recorded for every insertion. Dose-volume histograms were generated and D90 and D100CTV and D0.1, D1, and D2cc were recorded for bladder, rectum, and sigmoid for each insertion.Results:Sixty-one percent had a decrease in bladder volume in the second fraction, 35% had an increase in bladder volume and 4% had no change in bladder volume. There was a strong positive correlation between increase in volume and dose (D2cc), which was statistically significant, rs = 0.441, P = 0.013. Nearly 49.4% of patients had an increase in rectal volume during the second fraction. 45.9% had decrease in rectal volume during the second fraction. There was a positive correlation between the increase in volume and dose (D2cc), which was statistically significant, rs = 0.393, P = 0.010. About 63.5% of the patients had a decrease in sigmoid volume during the second fraction, whereas 30.6% had an increase in volume and 5.9% had no change in volume.Conclusion:First, this study emphasizes the importance of imaging and planning for every fraction of brachytherapy to quantify the exact doses to the target and OAR s. Second, it is important to follow a uniform bladder protocol for every fraction, and adequate bowel preparation is needed for every fraction to minimize the interfraction variations. Finally, it also opens the realm of an adaptive planning strategy in cervical cancers which are known for rapid tumor regression during radiotherapy.

The purpose of this article was to determine the suitability of the prostate and seminal vesicle volumes as factors to consider patients for treatment with image-guided 3D-conformal radiation therapy (3D-CRT) or intensity-modulated radiation therapy (IMRT), using common dosimetry parameters as comparison tools. Dosimetry of 3D and IMRT plans for 48 patients was compared. Volumes of prostate, SV, rectum, and bladder, and prescriptions were the same for both plans. For both 3D and IMRT plans, expansion margins to prostate+SV (CTV) and prostate were 0.5 cm posterior and superior and 1 cm in other dimensions to create PTV and CDPTV, respectively. Six-field 3D plans were prepared retrospectively. For 3D plans, an additional 0.5 cm margin was added to PTV and CDPTV. Prescription for both 3D and IMRT plans was the same: 45 Gy to CTV followed by a 36 Gy boost to prostate. Dosimetry parameters common to 3D and IMRT plans were used for comparison: Mean doses to prostate, CDPTV, SV, rectum, bladder, and femurs; percent volume of rectum and bladder receiving 30 (V30), 50 (V50), and 70 Gy (V70), dose to 30% of rectum and bladder, minimum and maximum point dose to CDPTV, and prescription dose covering 95% of CDPTV (D95). When the data for all patients were combined, mean dose to prostate and CDPTV was higher with 3D than IMRT plans (P < 0.01). Mean D95 to CDPTV was the same for 3D and IMRT plans (P > 0.2). On average, among all cases, the minimum point dose was less for 3D-CRT plans and the maximum point dose was greater for 3D-CRT than for IMRT (P < 0.01). Mean dose to 30%, rectum with 3D and IMRT plans was comparable (P > 0.1). V30 was less (P < 0.01), V50 was the same (P > 0.2), and V70 was more (P < 0.01) for rectum with 3D than IMRT plans. Mean dose to bladder was less with 3D than IMRT plans (P < 0.01). V30 for bladder with 3D plans was less than that of IMRT plans (P < 0.01). V50 and V70 for 3D plans were the same for 3D and IMRT plans (P > 0.2). Mean dose to femurs was more with 3D than IMRT plans (P < 0.01). For a given patient, mean dose and dose to 30% rectum and bladder were less with 3D than IMRT plans for prostate or prostate+SV volumes <65 (38/48) and 85 cm3 (39/48), respectively (P < 0.01). The larger the dose to rectum or bladder with 3D plans, the larger also was the dose to these structures with IMRT (P < 0.001). For both 3D and IMRT plans, dose to rectum and bladder increased with the increase in the volumes of prostate and seminal vesicles (P < 0.02 to 0.001). Volumes of prostate and seminal vesicles provide a reproducible and consistent basis for considering patients for treatment with image-guided 3D or IMRT plans. Patients with prostate and prostate+SV volumes <65 and 85 cm3, respectively, would be suitable for 3D-CRT. Patients with prostate and prostate+SV volumes >65 and 85 cm3, respectively, might get benefit from IMRT.

Image Guided Radiation Therapy for Prostate IMRT: Rectum Volume Changes and Dosimetric Considerations

Prostate Bed Radiation Therapy: The Utility of Ultrasound Volumetric Imaging of the Bladder

Purpose: The purpose of this study was to evaluate prostate treatment planning utilizing three planning paradigms: volumetric modulated arc delivery using SmartArc and RapidArc and a hybrid technique consisting of a combination of dynamic conformai arcs and static IMRT beams. The impact of this study was to evaluate three arc systems for prostate treatment planning.Method and Materials: Ten randomly selected previously‐treated patients were used for this study. Each patient received 180cGy per fraction for 44 fractions for a total of 7920cGy to the prostate and proximal seminal vesicles. Pinnacle System v9.0 was used for SmartArc planning, Eclipse was used for RapidArc planning and iPlan was used for HybridArc planning. Each treatment plan was optimized following departmental guidelines. The ten patient plans were then analyzed for several dosimetric endpoints: %PTV coverage; maximum plan hotspot; conformality index; and volume of rectum and bladder receiving 75Gy, 70Gy, 50Gy and 20Gy. Results: All three planning systems were able to meet/exceed our standard departmental guidelines. When compared to SmartArc and RapidArc, HybridArc plans demonstrated a small, though statistically significant, increase in the volume of rectum receiving 75Gy, 70Gy and 50Gy. RapidArc plans demonstrated a statistically significant improvement in the volume of bladder receiving 75Gy, 70Gy, and 50Gy as well as an improvement in the conformality index when compared to SmartArc and HybridArc plans. RapidArc plans delivered more monitor units when compared to SmartArc and HybridArc plans. Conclusions: Our results demonstrate that all three arc treatment strategies can be utilized to achieve the same strict dosimetric criteria. While the differences between some of the dosimetric parameters for the planning systems were statistically significant, these differences were overall quite small and are likely to be of minimal clinical consequence. We are currently exploring methods of reducing monitor units in our RapidArc plans.