Bladder Dose Research Articles

GSOR08 Presentation Time: 12:05 PM: Relationship between Late Bladder Toxicity & Dose to Bladder Sub-Volumes in Locally Advanced Cervical Cancer Treated with Interstitial Brachytherapy: A Prospective Study

GSOR08 Presentation Time: 12:05 PM: Relationship between Late Bladder Toxicity & Dose to Bladder Sub-Volumes in Locally Advanced Cervical Cancer Treated with Interstitial Brachytherapy: A Prospective Study

Co60 May be the Acceptable Alternative Radionuclides of Ir192 used in HDR Brachytherapy for the Treatment of Inoperable Carcinoma Cervix in the Treatment Modality of Concurrent Chemoradiation

Background: Cancer of the uterine cervix is the eighth most common cancer among women worldwide and third among all malignancies and the second most common cancers in female in Bangladesh. The treatment of cervical cancer requires multidisciplinary approaches Concurrent chemoradiation is the treatment of choice in locally advanced carcinoma cervix uteri. Radiotherapy is the primary local treatment for most patients having FIGO stage IIB to IVA diseases. The success of treatment depends on a careful balance between EBRT and Brachytherapy that optimizes the dose to tumor. Iridium192 is highly used radionuclide for modern remote after loading HDR brachytherapy till date. Recently Co60 source is available with miniature size and identical physical properties for remote after loaders. Methods: 60 patients with biopsy proven locally advanced carcinoma of the uterine cervix were enrolled in the study. Arm A was formed comprising 30 patients who were treated by Ir192 HDR brachytherapy and Arm B formed with equal number of 30 patients who received HDR brachytherapy treated with Co60 radionuclide. This prospective observational study was carried out to compare the treatment effect between two Arm. Results: 60 patients were enrolled in this study with age range from 35 to 63 years. Most of the patients presented with stage IIB disease, consisting of 39 patients (65.3%). Among them 48 patients had squamous cell carcinoma (80.60%), adenocarcinoma trailing with 9 patients (15.3%) and rest were adenoidsquamous carcinoma 2 and small cell carcinoma. In all three insertions, urinary bladder dose distribution was slightly smaller by HDR Co60 irradiation than HDR Ir192 exposure. These differences were statistically significant in first two insertions but not in third one Conclusion: In this study radiation dose distribution at OARs i.e. urinary bladder and rectum were compared between Arm A and Arm B. In all three insertions in urinary bladder the mean dose distribution was slightly smaller in HDR Co60 irradiation than HDR Iridium192 exposure. These differences were statistically significant in first two insertions but not in third one. In case of rectum point, the mean dose distribution was significantly lower in all three insertions of Co60 exposure than Ir192 exposure.

Long-term Results of Hypofractionated Radiotherapy With Intra-prostatic Boosts in Men With Intermediate- and High-risk Prostate Cancer: A Phase II Trial

AimsIn the conventionally fractionated phase III FLAME prostate trial, focal boosts improved local control and biochemical disease-free survival (bDFS). We explored the toxicity and effectiveness of a moderately hypofractionated schedule with focal boosts. Material and methodsBIOPROP20 is a phase II single-arm non-randomised trial for intermediate- to very high-risk localised prostate cancer patients with bulky tumour volumes. Multi-parametric magnetic resonance imaging (MRI) and 18F-choline positron emission tomography-computed tomography (PET-CT) scans were used for staging and boost volume definition. Patients were treated with 60Gy in 20 fractions with a boost dose up to 68Gy. Five patients with positive lymph nodes on the PET-CT scan received radiotherapy to pelvic lymph nodes (45Gy to elective nodes, boosted up to 50Gy to involved nodes). Primary outcomes were acute (≤18 weeks) and late urinary and gastrointestinal toxicity, prospectively recorded up to 5 years with Common Terminology Criteria for Adverse Events v4 (CTCAE). Secondary outcomes were biochemical or clinical progression, metastasis-free survival (MFS), and overall survival (OS). Results61 patients completed radiotherapy with hormone therapy (range: 6–36 months). Cumulative acute and late gastrointestinal toxicity was low at 6.6% and 5.0%, respectively. Cumulative acute and late urinary toxicity was 49.2% and 30.1%, respectively; the prevalence reduced to 5.9% at 5 years. At 5 years: 6 patients had biochemical progression (bDFS: 88.5%; 95% CI: 80.2–97.6%), the MFS was 82.4% (95% CI: 73.0–92.9%), 5 patients died (OS: 91.2%; 95% CI: 84.1–98.9%), one with prostate cancer. The prostate, boost, nodal planning volumes, and the organs at risk (rectum, bowel, urethra, and bladder) met the optimal protocol dose constraints. There was a trend to increased urinary toxicity with increasing urethral (RR: 1.95, 95% CI: 0.73–5.22, p = 0.18), but not bladder dose. ConclusionFocal boosts with a 20 fraction hypofractionated prostate radiotherapy schedule are associated with an acceptable risk of gastrointestinal and urinary toxicity and achieve good cancer control. ClinicalTrials.gov identifierNCT02125175.

Impact of contrast agents on organ dosimetry in pediatric diagnostic fluoroscopy: the voiding cystourethrogram.

ICRP Task Group 113 is developing reference values of organ and effective dose coefficients for radiography, fluoroscopy, and computed tomography imaging exams. In support of these efforts, our focus is on pediatric diagnostic fluoroscopy. Contrast agents used during clinical examinations are an important consideration of the work undertaken by the Task Group. This work demonstrates the importance of including organ contrast volume concentrations for the calculation of reference organ dose coefficients in the voiding cystourethrogram (VCUG). The ICRP newborn and 15-year female reference phantoms were utilized within the Particle and Heavy Ion Transport code System (PHITS) for the calculation of organ dose coefficients. A pediatric radiologist with over 30 years of clinical experience defined the imaging fields for a VCUG examination consistent with clinical practice. Of these, four imaging fields were selected for investigation. The transport simulations modeled an iodinated contrast solution similar to Bracco Group's 18% weight per volume, cystografin diatrizoate meglumine and typical bladder content was supplemented to make up the remainder volume. Iodinated contrast volumes of 0, 25, 50, 75, and 100 percent concentration by volume were modeled and associated dose coefficients for in-field organs were computed. Organ dose coefficients were calculated for the urinary bladder wall, colon wall, ovaries, and uterus for both female phantoms under irradiation geometries representative of a VCUG examination. Some organ dose coefficients increased with iodine volume in the bladder and other organ dose coefficients decreased as the iodine contrast volume completely filled the bladder (100%). The study results demonstrate for the newborn phantom percent differences in organ dose coefficients varied between 0-10% for the organs of interest, while they varied between 0-22% in the 15-year phantom suggesting the importance of including contrast media in Monte Carlo radiation transport simulations of the VCUG examination.&#xD.

Clinical implementation of real time motion management for prostate SBRT: A radiation therapist’s perspective

Background and purposeThe adoption of hypo-fractionated stereotactic body radiotherapy (SBRT) for treating prostate cancer has led to an increase in specialised techniques for monitoring prostate motion. The aim of this study was to comprehensively review a radiation therapist (RTT) led treatment process in which two such systems were utilised, and present initial findings on their use within a SBRT prostate clinical trial. Materials and Methods18 patients were investigated, nine were fitted with the Micropos RayPilotTM (RP) system (Micropos Medical, Gothenburg, SE) and nine were fitted with the Micropos Raypilot Hypocath TM (HC) system. 36.25 Gray (Gy) was delivered in 5 fractions over 7 days with daily pre- and post-treatment cone beam computed tomography (CBCT) images acquired. Acute toxicity was reported on completion of treatment at six- and 12-weeks post-treatment, using the Radiation Therapy Oncology Group (RTOG) grading system and vertical (Vrt), longitudinal (Lng) and lateral (Lat) transmitter displacements recorded. ResultsA significant difference was found in the Lat displacement between devices (P=0.003). A more consistent bladder volume was reported in the HC group (68.03 cc to 483.7 cc RP, 196.11 cc to 313.85 cc HC). No significant difference was observed in mean dose to the bladder, rectum and bladder dose maximum between the groups. Comparison of the rectal dose maximum between the groups reported a significant result (P=0.09). Comparing displacements with toxicity endpoints identified two significant correlations: Grade 2 Genitourinary (GU) at 6 weeks, P=0.029; and no toxicity, Gastrointestinal (GI) at 12 weeks P=0.013. ConclusionBoth the directly implanted RP device and the urinary catheter-based HC device are capable of real time motion monitoring. Here, the HC system was advantageous in the SBRT prostate workflow.

Dosimetric effect of collimator rotation on intensity modulated radiotherapy and volumetric modulated arc therapy for rectal cancer radiotherapy.

Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are the main radiotherapy techniques for treating and managing rectal cancer. Collimator rotation is one of the crucial parameters in radiotherapy planning, and its alteration can cause dosimetric variations. This study assessed the effect of collimator rotation on the dosimetric results of various IMRT and VMAT plans for rectal cancer. Computed tomography (CT) images of 20 male patients with rectal cancer were utilized for IMRT and VMAT treatment planning with various collimator angles. Nine different IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six different VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. The dosimetric results of various treatment techniques for target tissue (conformity index [CI] and homogeneity index [HI]) and organs at risk (OARs) sparing (parameters obtained from OARs dose-volume histograms [DVH]) as well as radiobiological findings were analyzed and compared. The 7-fields IMRT technique demonstrated lower bladder doses (V40Gy, V45Gy), unaffected by collimator rotation. The 9-fields IMRT and 2-arcs VMAT (excluding the 90-degree collimator) had the lowest V35Gy and V45Gy. A 90-degree collimator rotation in 2-arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90-degree rotation had adverse effects on small bowel NTCP (normal tissue complication probability). No superiority was found for a 45-degree collimator rotation over 0 or 30 degrees in VMAT techniques. Collimator rotation had minimal impact on dosimetric parameters in IMRT planning but is significant in VMAT techniques. A 90-degree rotation in VMAT, particularly in a 2-full arc technique, adversely affects PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes.

Evaluation of normal organ doses for extended kV- CBCT protocol in para-aortic region treatment using nanoDot dosimeter

Extended cone beam computed tomography (CBCT) imaging protocol was used to extend the longitudinal coverage by acquiring double CBCT which allows an overlapping of doubled doses from the two orbits. The aim of this study was to evaluate the absorbed doses of three normal organs; bladder, small bowel, and rectum in the overlapped region for extended CBCT imaging protocol with 125 kV and 592 mAs of Ethos™ machine in para-aortic lymph node treatment using nanoDot™ dosimeters placed on the Rando phantom. The nanoDot™ correction factor (CFOSLD) and an organ depth dose correction factor (CFDepth) were used to calculate the absorbed doses of each organ. The result showed that the absorbed dose for bladder, small bowel and rectum were 18.71 ± 0.99, 19.57 ± 0.05 and 20.93 ± 0.74 mGy, respectively, which are lower than the radiation tolerance doses. However, the overlapping dose from the extended CBCT protocol should be considered to estimate the imaging dose throughout the treatment course for managing the use of extended CBCT to verify patient positioning before treatment. Additionally, the results can be used to determine the radiation dose in treatment planning to keep the additional imaging dose to the patient as low as reasonably achievable.

Comparative analysis of simultaneous integrated boost and sequential boost radiotherapy in node-positive cervical cancer: dosimetric and radiobiological considerations.

For locally advanced cervical cancer, the standard therapeutic approach involves concomitant chemoradiation therapy, supplemented by a brachytherapy boost. Moreover, an external beam radiotherapy (RT) boost should be considered for treating gross lymph node (LN) volumes. Two boost approaches exist with Volumetric Intensity Modulated Arc Therapy (VMAT): Sequential (SEQ) and Simultaneous Integrated Boost (SIB). This study undertakes a comprehensive dosimetric and radiobiological comparison between these two boost strategies. The study encompassed ten patients who underwent RT for cervical cancer with node-positive disease. Two sets of treatment plans were generated for each patient: SIB-VMAT and SEQ-VMAT. Dosimetric as well as radiobiological parameters including tumour control probability (TCP) and normal tissue complication probability (NTCP) were compared. Both techniques were analyzed for two different levels of LN involvement - only pelvic LNs and pelvic with para-aortic LNs. Statistical analysis was performed using SPSS software version 25.0. SIB-VMAT exhibited superior target coverage, yielding improved doses to the planning target volume (PTV) and gross tumour volume (GTV). Notably, SIB-VMAT plans displayed markedly superior dose conformity. While SEQ-VMAT displayed favorable organ sparing for femoral heads, SIB-VMAT appeared as the more efficient approach for mitigating bladder and bowel doses. TCP was significantly higher with SIB-VMAT, suggesting a higher likelihood of successful tumour control. Conversely, no statistically significant difference in NTCP was observed between the two techniques. This study's findings underscore the advantages of SIB-VMAT over SEQ-VMAT in terms of improved target coverage, dose conformity, and tumour control probability. In particular, SIB-VMAT demonstrated potential benefits for cases involving para-aortic nodes. It is concluded that SIB-VMAT should be the preferred approach in all cases of locally advanced cervical cancer.

Comparative Analysis of External and Internal Radiotherapy- Dependent Plans in Patients with Gynecological Cancer.

Radiotherapy plays a key role in the treatment of gynecological cancer. Modern radiotherapy techniques with external beams (e-RT) are applied in a broad spectrum of gynecological cancer cases. However, high radiation doses, affecting normal tissue adjacent to cancer, represent the main disadvantage of e-RT regimens. For this reason, brachytherapy (BT), an internal beam-based technique (i-RT), is suggested following e-RT. Our purpose was to compare e-RT plans using volumetric-modulated arc therapy (VMAT) with those using 3D conformal techniques (3D-CRT) and compare BT plans guided by 3D or 2D imaging based on the potential corresponding toxicity levels. In this preliminary, non-randomized comparative retrospective study, 15 females suffering gynecological cancer were enrolled. Modern e-RT and i-RT (BT) techniques were applied. Concerning e-RT, D95/D99/rectum 2cc/bladder 2cc and small intestine 2cc were measured and compared; in i-RT, rectum 2cc/bladder 2cc were measured and compared. The median dose to the planning target volume in VMAT was 97.4 Gy compared with 92.9 Gy in 3D-CRT. Τhe rectum received almost 5 Gy less in VMAT compared to 3D-CRT (median of 43.5 Gy vs. 48.6 Gy; p=0.001). In the bladder, dose differences were minimal, while the small intestine received 47.6 Gy in VMAT (p=0.001). Regarding 3D-BT, the rectum received 63.1 Gy compared with 49.9 Gy (p=0.009) in 2D-BT. Concerning the bladder, mean 2D-BT and 3D-BT doses were 71.9 and 65 Gy, respectively, differing non-significantly. VMAT was found to be superior to 3D-CRT, especially in dose distribution, volume coverage and protection of critical organs. Similarly, 3D-BT should be preferred over 2D-BT due to critical advantages.

1674: Bladder and rectal dose accumulation for prostate radiotherapy agrees with planned dose goals

1674: Bladder and rectal dose accumulation for prostate radiotherapy agrees with planned dose goals

Late Urinary Toxicity and Quality of Life With Pelvic Radiation Therapy for High-Risk Prostate Cancer: Dose-Effect Relations in the POP-RT Randomized Phase 3 Trial

PurposeThe POP-RT phase III randomized trial showed improved biochemical failure-free survival and metastasis-free survival with whole pelvic radiotherapy (WPRT) versus prostate-only radiotherapy (PORT) for high/very high-risk prostate cancer, albeit with worse RTOG late urinary toxicity. We report updated late urinary adverse effects and bladder dose-effect relations within this trial. Materials/MethodsLate urinary toxicity, and cumulative severity of each symptom over the follow-up period was graded using CTCAE v5.0. Bladder dosimetry in 5-Gy increments (V5, V10, V15...V65Gy, V68Gy) in the approved radiotherapy plans was compared for urinary symptoms and overall grade 2+ toxicity. Potential factors influencing urinary toxicity were tested using multivariable logistic regression analysis. Updated urinary quality of life (QOL) scores were compared between the trial arms. ResultsComplete combined data for late urinary symptoms and dosimetry was available for 193/224 patients. At a median follow-up of 75 months, cumulative late urinary CTCAE grade 3 toxicity was low and similar for WPRT and PORT (5.2% vs 4.1%, p=0.49), while grade 2 toxicity was 31.3% vs 22.7% respectively (p=0.12). Cumulative rates of each urinary symptom were similar between both arms. Multivariable analysis with age at diagnosis, known diabetes, tumor stage, trial arm, prior TURP, grade 2+ acute urinary toxicity, low bladder dose (V10Gy) and moderate bladder dose (V40Gy) did not identify any significant association with late urinary toxicity. Urinary QOL scores was similar between both the arms for all the symptoms. ConclusionOver long term follow up, whole pelvic radiotherapy resulted in low (∼5%) and similar grade 3 cumulative urinary toxicity as prostate-only radiotherapy. The long term patient-reported QOL scores were similar. No causative factors affecting the late urinary toxicity were identified.

Evaluating outcomes and toxicities for a newly implemented MRI-based brachytherapy program for cervical cancer

ObjectiveWe report an updated analysis of the outcomes and toxicities of MRI-based brachytherapy for locally advanced cervical cancer from a U.S. academic center. MethodsA retrospective review was performed on patients treated with MRI-based brachytherapy for cervical cancer. EBRT was standardly 45 Gy in 25 fractions with weekly cisplatin. MRI was performed with the brachytherapy applicator in situ. Dose specification was most commonly 7 Gy for 4 fractions with optimization aim of D90 HR-CTV EQD2 of 85–95 Gyα/β=10 Gy in 2 implants each delivering 2 fractions. ResultsNinety-eight patients were included with median follow up of 24.5 months (IQR 11.9–39.8). Stage IIIA-IVB accounted for 31.6% of cases. Dosimetry results include median GTV D98 of 101.0 Gy (IQR 93.3–118.8) and HR-CTV D90 of 89 Gy (IQR 86.1–90.6). Median D2cc bladder, rectum, sigmoid, and bowel doses were 82.1 Gy (IQR 75.9–88.0), 65.9 Gy (IQR 59.6–71.2), 65.1 Gy (IQR 57.7–69.6), and 55 Gy (IQR 48.9–60.9). Chronic grade 3+ toxicities were seen in the bladder (8.2%), rectosigmoid (4.1%), and vagina (1.0%). Three-year LC, PFS, and OS were estimated to be 84%, 61.7%, and 76.1%, respectively. ConclusionMRI-based brachytherapy demonstrates excellent local control and acceptable rates of high-grade morbidity. These results are possible in our population with relatively large volume primary tumors and extensive local disease.

Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy.

Bragg peak FLASH radiotherapy (RT) uses a distal tracking method to eliminate exit doses and can achieve superior OAR sparing. This study explores the application of this novel method in stereotactic body radiotherapy prostate FLASH-RT. An in-house platform was developed to enable intensity-modulated proton therapy (IMPT) planning using a single-energy Bragg peak distal tracking method. The patients involved in the study were previously treated with proton stereotactic body radiotherapy (SBRT) using the pencil beam scanning (PBS) technique to 40 Gy in five fractions. FLASH plans were optimized using a four-beam arrangement to generate a dose distribution similar to the conventional opposing beams. All of the beams had a small angle of two degrees from the lateral direction to increase the dosimetry quality. Dose metrics were compared between the conventional PBS and the Bragg peak FLASH plans. The dose rate histogram (DRVH) and FLASH metrics of 40 Gy/s coverage (V40Gy/s) were investigated for the Bragg peak plans. There was no significant difference between the clinical and Bragg peak plans in rectum, bladder, femur heads, large bowel, and penile bulb dose metrics, except for Dmax. For the CTV, the FLASH plans resulted in a higher Dmax than the clinical plans (116.9% vs. 103.3%). For the rectum, the V40Gy/s reached 94% and 93% for 1 Gy dose thresholds in composite and single-field evaluations, respectively. Additionally, the FLASH ratio reached close to 100% after the application of the 5 Gy threshold in composite dose rate assessment. In conclusion, the Bragg peak distal tracking method can yield comparable plan quality in most OARs while preserving sufficient FLASH dose rate coverage, demonstrating that the ultra-high dose technique can be applied in prostate FLASH SBRT.

Dosimetric Comparison Study of Proton Therapy Using Line Scanning versus Passive Scattering and Volumetric Modulated Arc Therapy for Localized Prostate Cancer.

The proton irradiation modality has transitioned from passive scattering (PS) to pencil beam scanning. Nevertheless, the documented outcomes predominantly rely on PS. Thirty patients diagnosed with prostate cancer were selected to assess treatment planning across line scanning (LS), PS, and volumetric modulated arc therapy (VMAT). Dose constraints encompassed clinical target volume (CTV) D98 ≥ 73.0 Gy (RBE), rectal wall V65 < 17% and V40 < 35%, and bladder wall V65 < 25% and V40 < 50%. The CTV, rectal wall, and bladder wall dose volumes were calculated and evaluated using the Freidman test. The LS technique adhered to all dose limitations. For the rectal and bladder walls, 10 (33.3%) and 21 (70.0%) patients in the PS method and 5 (16.7%) and 1 (3.3%) patients in VMAT, respectively, failed to meet the stipulated requirements. The wide ranges of the rectal and bladder wall volumes (V10-70) were lower with LS than with PS and VMAT. LS outperformed VMAT across all dose-volume rectal and bladder wall indices. The LS method demonstrated a reduction in rectal and bladder doses relative to PS and VMAT, thereby suggesting the potential for mitigating toxicities.

High-dose-rate brachytherapy in uterine cervix carcinoma: a comparison of dosimetry and clinical outcomes among three fractionation schedules.

To assess the differences among three dose-fractionation schedules of image-guided adaptive brachytherapy (IGABT) in cervical squamous cell carcinoma (CSCC) by comparing the dosimetry and clinical outcomes. Forty-five patients with CSCC who underwent chemoradiotherapy and IGABT were retrospectively enrolled and divided into three groups based on their dose-fractionation schedules of brachytherapy as: Group-5.5 (5.5 Gy × 6 fractions), Group-6.0 (6.0 Gy × 5 fractions), and Group-7.0 (7.0 Gy × 4 fractions). The analyzed dose-volume histogram parameters included D90% and D98% of the high-risk clinical target volume (HR-CTV), D90% and D98% of intermediate-risk clinical target volume (IR-CTV), and D0.1cc and D2cc of the organs-at-risk (OARs, namely the bladder, rectum, sigmoid and small intestine). Furthermore, the therapeutic efficacy and late toxicities were also compared among the three groups. The doses of HR-CTV and IR-CTV in Group-5.5 were found to be the highest among the three groups, followed by those in Group-6.0. Significant differences were found for the doses of HR-CTV between Group-5.5 and the other groups. There were no significant differences in the bladder, sigmoid and small intestine dose among the three groups. However, Group-6.0 yielded the lowest rectum received doses, with a significant difference in D0.1cc being detected between Group-6.0 and Group-5.5. The median follow-up time was 30.08 months [range, 6.57-46.3]. The numbers of patients with complete response in Group-5.5, Group-6.0 and Group-7.0 were 13, 14 and 14, respectively (P > 0.05). In regard to the toxicitiy, the incidence of radiation cystitis and proctitis in Group-6.0 was lower than that in Group-5.5 and Group-7.0 (P > 0.05). The dose-fractionation schedule of 6.0 Gy × 5 fractions provided the most beneficial effects with relatively low OARs doses, suggesting that this dose-fractionation schedule should be prioritized in the clinical application of brachytherapy in cervical cancer.

Proton versus photon therapy for high-risk prostate cancer with dose escalation of dominant intraprostatic lesions: a preliminary planning study.

This study aimed to investigate the feasibility of safe-dose escalation to dominant intraprostatic lesions (DILs) and assess the clinical impact using dose-volume (DV) and biological metrics in photon and proton therapy. Biological parameters defined as late grade ≥ 2 gastrointestinal (GI) and genitourinary (GU) derived from planned (D P) and accumulated dose (D A) were utilized. In total, 10 patients with high-risk prostate cancer with multiparametric MRI-defined DILs were investigated. Each patient had two plans with a focal boost to the DILs using intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT). Plans were optimized to obtain DIL coverage while respecting the mandatory organ-at-risk constraints. For the planning evaluation, DV metrics, tumor control probability (TCP) for the DILs and whole prostate excluding the DILs (prostate-DILs), and normal tissue complication probability (NTCP) for the rectum and bladder were calculated. Wilcoxon signed-rank test was used for analyzing TCP and NTCP data. IMPT achieved a higher Dmean for the DILs compared to VMAT (IMPT: 68.1 GyRBE vs. VMAT: 66.6 Gy, p < 0.05). Intermediate-high rectal and bladder doses were lower for IMPT (p < 0.05), while the high-dose region (V60 Gy) remained comparable. IMPT-TCP for prostate-DIL were higher compared to VMAT (IMPT: 86%; α/β = 3, 94.3%; α/β = 1.5 vs. VMAT: 84.7%; α/β = 3, 93.9%; α/β = 1.5, p < 0.05). Likewise, IMPT obtained a moderately higher DIL TCP (IMPT: 97%; α/β = 3, 99.3%; α/β = 1.5 vs. VMAT: 95.9%; α/β = 3, 98.9%; α/β = 1.5, p < 0.05). Rectal D A-NTCP displayed the highest GI toxicity risk at 5.6%, and IMPT has a lower GI toxicity risk compared to VMAT-predicted Quantec-NTCP (p < 0.05). Bladder D P-NTCP projected a higher GU toxicity than D A-NTCP, with VMAT having the highest risk (p < 0.05). Dose escalation using IMPT is able to achieve a high TCP for the DILs, with the lowest rectal and bladder DV doses at the intermediate-high-dose range. The reduction in physical dose was translated into a lower NTCP (p < 0.05) for the bladder, although rectal toxicity remained equivalent.

CT-based online adaptive radiotherapy improves target coverage and organ at risk (OAR) avoidance in stereotactic body radiation therapy (SBRT) for prostate cancer

IntroductionStereotactic body radiation therapy (SBRT) is an emerging treatment modality for clinically localized prostate cancer (PCa). Online daily adaptive radiotherapy (ART) could potentially improve the therapeutic ratio of prostate SBRT by accounting for inter-fraction variation in target and OAR volumes. To our knowledge, no group has evaluated the clinical utility of a novel AI-augmented CT-based ART system for prostate SBRT. In this study we hypothesized that adaptive prostate SBRT plans would result in improved target coverage and lower dose to OARs in comparison to unadapted treatment plans. MethodsSeven patients with favorable intermediate to oligometastatic PCa treated with 5-fx prostate adaptive SBRT were retrospectively reviewed. Patients were treated with 3625 cGy to the prostate and seminal vesicles. 6 patients additionally received 2500 cGy to the pelvic nodes, 5 patients underwent a boost to 4000 cGy to the prostate. For each fraction, a CBCT was acquired and OARs (rectum, bladder, bowel, sigmoid, femurs) were segmented/deformed using AI. CTVs were rigidly registered. Volumes were adjusted manually and PTV expansions added. Adaptive treatment plans were developed based on the contoured targets and OARs and dose to these volumes for the adapted vs. initial plans were compared for each fraction. V100 and the D0.03 cc between scheduled and adapted treatment plans were compared using a Student’s t-test, with significance threshold of P < 0.05. ResultsSeven patients completed 35 Fx’s of adaptive RT. Daily adaptation resulted in a statistically significant mean improvement in PTV V100 for all targets: [21.4 % ± 4.3 % for PTV 4000 (p < 0.0001); 8.7 % ± 1.1 % for PTV 3625 (p < 0.0001); and 11.5 % ± 3.1 % for PTV 2500 (p = 0.0013)]. Mean rectal D0.03 was significantly reduced by 38.8 cGy ± 5.95 cGy (p < 0.0001) per fraction (194 cGy/5 fractions) compared to the initial plans. There was a modest increase in bladder dose of 10.9 cGy ± 4.93 cGy per fraction (p = 0.0424) for the adaptive plans. The adaptive plans met bladder constraints for every fraction. There were no statistically significant differences between sigmoid or bowel dose for adapted vs. initial plans. No patients experienced acute CTCAE grade ≥ 3 GI/GU adverse events (median F/U 9.5 months). All statistically significant differences were maintained in the presence and absence of rectal hydrogel spacer (p < 0.05). ConclusionsCT-based online adaptive SBRT resulted in statistically significant and clinically meaningful improvements in PTV coverage and D0.03 cc dose to the rectum. A trial evaluating CT adaptive whole-pelvis prostate SBRT is underway.

Does a patient-specific bladder-filling protocol affect bladder volume and dose in postprostatectomy radiotherapy?

Our aim is to develop a patient-specific bladder-filling protocol (PSP) using an ultrasound-based bladder scanner (BS) and compare the volumetric and dosimetric parameters with those of the standard filling protocol (SP) in postprostatectomy patients. Twenty postprostatectomy patients who received salvage radiotherapy (72Gy/36 fx) were included. For PSP, the patient was asked to drink 500mL of water after emptying his bladder. Bladder volume was measured using BS every 10min. Each patient's unique time to reach a 150-200cc volume was used for simulation and treatment. For the SP, the patient was asked about the feeling of having a full bladder. Organs at risk (OAR) were contoured on cone-beam computed tomography (CBCT) scans that were transferred to the treatment planning system (TPS). Treatment plans were applied to CBCTs. Changes in bladder volume and doses for planning computed tomography (PCT) and CBCT were determined. In the SP, there was no significant difference in mean bladder volume for PCT and CBCT (p = 0.139); however, there was a trend for significance in the mean bladder dose (p = 0.074). In PSP, there was no significant difference in the mean bladder volume or dose for PCT and CBCT (p = 0.139 and p = 0.799, respectively). There was a significant difference in terms of mean CBCT bladder volume between the two protocols (p = 0.007), whereas no significant difference was detected in terms of bladder dose (p = 0.130). With PSP, optimal bladder filling was obtained and maintained throughout the whole treatment course, and it was reproducible in every fraction.

IMRT as an Alternative Technique for Intracavitary Brachytherapy in Patients with Carcinoma of the Cervix: A Feasibility Study Using Unified Dosimetric Index.

Intracavitary brachytherapy (ICBT) plays an important role in the management of carcinoma of the cervix. This study attempts to find the feasibility of intensity-modulated radiation therapy (IMRT) as a boost for patients who are not suitable for ICBT in order to improve their disease-free and overall survival. Twenty patients with carcinoma of the cervix were included in this study. Nine fields of IMRT and ICBT plans were generated for PTVBoost. Various dosimetric indices like coverage, conformity, homogeneity, and gradient index were calculated, and the corresponding unified dosimetric index (UDI) values were generated. Plans were classified based on combined UDI, and the UDI values were compared with those of ICBT. In addition, rectum and bladder doses were compared. All the dosimetric indices were within acceptable limits except for the gradient index. The gradient index of the IMRT and ICBT plans were 8.77 ± 0.26 and 1.33 ± 0.06 respectively (p < 0.0001). The mean of combined UDI with standard deviation was 32.557 ± 8.940 and plan quality was calculated from these values. Rectum and bladder doses for ICBT were lesser than IMRT (p < 0.0001). ICBT is the gold standard for boost RT in carcinoma of the cervix patients. IMRT boost is feasible for patients who are unsuitable on medical grounds for brachytherapy.

Toxicity Analysis of a Modified Prostate Bed CTV Based on PSMA-PET Patterns of Failure.

After radical prostatectomy (RP), about 20-50% of prostate cancer patients experience biochemical failure, and many can be cured with salvage radiotherapy (sRT). Adding androgen deprivation and pelvic lymph node (PLN) RT to sRT decreases risk of disease progression at the cost of increased toxicity. PSMA PET patterns of local failure after RP show failures outside the RTOG prostate bed CTV (RTOG_CTV) occurring postero-laterally and inferiorly, while in much of the covered bladder local failures are not seen. A modified CTV (m_CTV) encompassing all sites of observed local failures and less of the bladder would potentially reduce dose to the bladder but increase dose to rectum. Herein, we compared sRT plans using RTOG_CTV vs. m_CTV and assessed predicted genitourinary (GU) and gastrointestinal adverse events (AEs). Volumes for RTOG_CTV, m_CTV, PLN CTV, and OARs were retrospectively contoured on planning CT scans of 28 post-RP patients. Plans were generated for each RTOG_CTV and m_CTV. Doses to prostate bed PTV (CTV + 8mm expansion, 6mm posteriorly) and PLN CTV were 68 Gy and 52.7 Gy, respectively, all in in 34 fractions. Dose-volume histogram (DVH) data for bladder, rectum, and bowel of each plan were extracted. Normal Tissue Complication Probability (NTCP) curves were generated using Lyman-Kutcher-Burman model to predict risk of late G≥3 GU AEs, early GU urgency, leakage, frequency, nocturia, late GI bleed, and late G≥3 GI AEs. Data were compared using 2 sample t-test and Wilcox signed rank test. Correlation of bladder volume and differences in DVH and NTCP data between plans was assessed using Pearson coefficient. The m_CTV and RTOG_CTV had a median volume of 70.56cc (IQR 59.72-82.17cc) and 132.14cc (IQR 109.33-155.84cc), respectively. Use of m_CTVs resulted in mean absolute decrease of 20.22% and 17.94% in bladder V65 Gy and V40 Gy, respectively (p<0.01 for both), without differences in rectum V65 Gy (p = 0.44), rectum V40 Gy (p = 0.11), or bowel V45 Gy (p = 0.29). Per NTCP curves, m_CTV plans had mean absolute decrease of 24.89% in predicted late G≥3 GU AEs (p<0.01). For predicted early GU AEs, there were mean absolute decreases ranging from 4.85 to 10.21% (p<0.01 for all). Predicted late GI bleed (p = 0.98) and late G≥3 GI AEs (p = 0.99) were not significantly different between plans. When assessed as a continuous variable, smaller bladder volumes had strong correlation with more benefit from m_CTV in bladder V65 Gy (r = -0.71, p<0.01) and moderate correlation with less early GU AEs (r -0.59 to -0.56, p<0.01 for all). There was no correlation with bladder V40 Gy (p = 0.27) or late G≥3 GU AEs (p = 0.14). The m_CTV plans had significantly less dose to the bladder, no increased dose to the rectum and significantly lower predicted rates of early and late GU toxicity. Using a m_CTV encompassing observed local failures from PSMA PET could improve the therapeutic ratio for patients undergoing sRT. Further clinical validation is warranted.