Rectal Dose Research Articles

Dosimetric comparison of inverse optimisation methods versus forward optimisation in HDR brachytherapy of breast, cervical and prostate cancer

ObjectiveDosimetric comparison of HIPO (hybrid inverse planning optimisation) and IPSA (inverse planning simulated annealing) inverse and forward optimisation (FO) methods in brachytherapy (BT) of breast, cervical and prostate cancer.MethodsAt our institute 38 breast, 47 cervical and 50 prostate cancer patients treated with image-guided interstitial high-dose-rate BT were selected. Treatment plans were created using HIPO and IPSA inverse optimisation methods as well as FO. The dose–volume parameters of different treatment plans were compared with Friedman ANOVA and the LSD post-hoc test.ResultsIPSA creates less dose coverage to the target volume than HIPO or FO: V100 was 91.7%, 91% and 91.9% for HIPO, IPSA and FO plans (p = 0.1784) in breast BT; 90.4%, 89.2% and 91% (p = 0.0045) in cervical BT; and 97.1%, 96.2% and 97.7% (p = 0.0005) in prostate BT, respectively. HIPO results in more conformal plans: COIN was 0.72, 0.71 and 0.69 (p = 0.0306) in breast BT; 0.6, 0.47 and 0.58 (p < 0.001) in cervical BT; and 0.8, 0.7 and 0.7 (p < 0.001) in prostate BT, respectively. In breast BT, dose to the skin and lung was smaller with HIPO and FO than with IPSA. In cervical BT, dose to the rectum, sigmoid and bowel was larger using IPSA than with HIPO or FO. In prostate BT, dose to the urethra was higher and the rectal dose was smaller using FO than with inverse methods.ConclusionIn interstitial breast and prostate BT, HIPO results in comparable dose–volume parameters to FO, but HIPO plans are more conformal. In cervical BT, HIPO produces dosimetrically acceptable plans only when more needles are used. The dosimetric quality of IPSA plans is suboptimal and results in unnecessary larger active lengths.

Analysis of OAR Doses in DMPO-Based Prostate IMRT

Radiotherapy plays an eminent role in the treatment of the prostate cancers with rotational radiotherapy taking the leading edge in the recent years. The study aims to find the relevance of the Direct machine parameter optimization (DMPO) based static gantry IMRT treatment planning in the step and shoot environment for ca prostate case with involved nodes in the era of rotational radiotherapy. Also we aim to determine the relation between the femur dose and the rectum dose, and mean rectum dose and rest rectum volume if any. 32 ca prostate patients were selected retrospectively for this study with prescribed dose of 68Gy (EQD2 72.08Gy α/β 10) and 50Gy in 25 fractions to the prostate and nodes respectively treated with the simultaneous integrated boost technique. The plans were done on a treatment planning system with DMPO algorithm and delivered using step and shoot method in LINAC. For PTV, 95% volume covering 100% prescribed dose was achieved with posterior rectum wall receiving less than 34Gy and organs at risk (OARs) within the tolerance limit. Along with the percentage volume of the rest rectum (rectum minus PTV with 0.5cm margin), the mean doses of rectum, rest rectum, rest bladder (bladder minus PTV with 0.5cm margin) and femur were noted. The relation between rectum mean dose and femur mean dose were studied. Also comparison was done between mean rectum dose and percentage (%)rest rectum volume. The doses received by 5% of the femoral heads were also studied. Plot of mean rectum dose versus mean femur dose received by each patients shows the inverse relation with correlation coefficient of -0.401 (p<0.05). Also the mean rectum dose and %rest rectum volume are inversely related with correlation coefficient of -0.81 (p<0.001). The mean of the dose received by 5% volume of right and left femur is 40.39±4.7Gy and 40.2±3.8Gy respectively with p<0.001. The mean dose of rectum was 36.5±5.5Gy with median dose of 37.6Gy. For rest rectum the mean dose was 28.7±5.6Gy with median dose of 27.8Gy. The mean dose of the left and right femoral heads and rest bladder were 24.2±4.5Gy, 23.7±4.5Gy and 31.6±6.2Gy respectively with p value <0.001. For an optimal plan for ca prostate case achieved on a TPS with DMPO algorithm, we could predict the mean dose of rectum to be 36.5±5.5Gy with 95% Confidence interval for mean femoral head dose of 23.9±4.2Gy. We could also infer that the femur dose and mean rectum dose, and the %rest rectum volume and mean rectum dose were inversely correlated with correlation coefficient of -0.401 and -0.810 respectively. Ca Prostate being the fourth most commonly occurring cancers is widely treated using radiotherapy as an important mode of treatment with different treatment techniques all over the world. Although the rotational radiotherapy delivers the treatment in comparably lower beam on time, the DMPO based static gantry IMRT plans still holds the dosimetric relevance with comparable OAR doses.

Rectal Wall vs. Whole Rectum Dose: Which Volume Better Predicts Gastrointestinal Toxicity from Prostate External Beam Radiotherapy?

Radiation-induced gastrointestinal (GI) toxicity is an important complication of prostate cancer (PCa) radiotherapy (RT) that radiation oncologists seek to minimize by respecting dose constraints for the rectum. It remains unclear whether dose to the rectal wall or whole rectum better predicts GI toxicity. This study used prospectively collected toxicity data from a registered phase III randomized trial to address this question. Dose-volume histogram (DVH) data was extracted from patients enrolled in PCS V, a multi-institutional phase III trial that compared conventionally fractionated (76 Gy in 38 fractions) to hypofractionated RT (68 Gy in 25 fractions) in PCa patients. Acute and late GI toxicity was assessed at 0-6 months and 6-24 months, respectively, using the Common Terminology Criteria for Adverse Events (CTCAE v.4). Rectal wall and whole volumes were collected prospectively. Dosimetric values evaluated were the whole rectum and rectal wall V50, V60, V60, V65, V70, V75, Dmax, and Dmean. Spearman’s rho (ρ) was used to correlate each DVH point of both rectum contours to acute and late GI toxicity. A Fisher’s z-transformation was then performed to test the significance of the difference between the rectal wall and whole rectum ρ’s for individual DVH points. Wilcoxon signed rank test was used to determine whether paired differences of the GI toxicity grade associated with rectal wall vs. whole rectum were significant. In total, DVH data was obtained from 155 patients, with 83 patients having been treated conventionally and 72 with hypofractionation. Spearman’s ρ correlation test revealed a strong association between the whole rectum DVH points and acute GI toxicity, namely for V60 (p=0.04), V65 (p=0.01), V70 (p=0.01) and Dmax (p=0.04). When the same analysis was conducted for late toxicity, only the V50 and Dmean points yielded a marginally significant correlation (p=0.049 and 0.042, respectively). These findings were not observed in the hypofractionated arm. There was no significant association between the rectal wall’s DVH points with either acute nor late GI toxicity in both arms. While the Fisher’s z-transformation analysis did not reveal any significant differences between the correlations of individual DVH points obtained from the rectal wall and whole rectum with acute or late GI toxicity, the distribution of Spearman’s ρ was significantly higher for the whole rectum, compared to its wall for acute toxicity (p=0.047) in the conventional arm. Our data suggests that the whole rectum DVH profile better correlates with acute GI toxicity than that of the rectal wall. Furthermore, the whole rectum’s DVH distribution rather than individual DVH points correlated more reliably with acute GI toxicity. Set-up protocols aiming to minimize rectal wall inter- and intra-fractional movement to improve the accuracy of rectal wall dosimetric values to predict toxicity are thus worthy of future study.

MRI-Guided Brachytherapy PLAN Optimization with Three Versus FOUR Fraction Treatment for Locally Advanced Cervical Cancer

MRI-guided brachytherapy (MRgBT) has become the standard treatment for locally advanced cervical cancer. The ability to optimize target and organ-at-risk (OAR) doses with three-dimensional image-based planning has improved toxicity profiles and local control. MRgBT, however is considerably more resource-intensive than the classical 2D planning and most of the available data on MRgBT has been based on a four fraction protocol of 7 Gy per fraction (7x4). A potential alternative to minimize resource utilization is a three fraction regimen of 8 Gy per fraction (8x3). However, there is limited data on MRgBT using the 8x3 protocol. The ability of this higher dose per fraction treatment to meet EMBRACE II planning aims has not been extensively studied. This study aims to compare optimized 8x3 vs 7x4 plan dosimetry. Ten patients with locally advanced cervical cancer (FIGO IB2 – IVA) treated at a single institution between July 2018 and January 2019 were included in this planning study. Clinical plans that were optimized and treated using a prescription 7x4 and the EMBRACE II planning aims (CTVHR D90% 90-95 Gy, rectum D2cm3 < 65 Gy and bladder D2cm3 < 80 Gy) were retrieved. Plans were then scaled to 8x3 and adjusted using graphical optimization. Three scenarios were evaluated: (1) The CTVHR D90% EQD2 dose was adjusted to be equivalent to the 7x4 plans; while limiting doses to organs at risk. Bladder and rectum D2cm3 doses and GTV D98% doses were recorded. (2) The bladder D2cc EQD2 dose was adjusted to be equivalent to the 7x4 plans (3) The rectal D2cc EQD2 dose was adjusted to be equivalent to the 7x4 plans. An a/b of 10 was used for the tumor bioequivalent dose calculations and an a/b of 3 for the OAR calculations. Doses were compared using Mann-Whitney-Wilcoxon. The median GTVres and CTVHR volumes were 13.42 cc (1.02 – 92.2) and 32.5 cc (10.99 – 120.4). For the 7x4 plans optimized for clinical treatment, median CTVHR D90%, rectum and bladder D2cm3 EQD2 doses were 93.7 Gy (87.4 – 104.4), 58 Gy (51.3 – 83.7) and 77.7 Gy (72.2 – 89.1). For scenario 1, where CTVHR D90% was made equivalent , median rectum and bladder D2cm3 were 58.5 Gy (51.3 – 84.6 ) and 77.1 Gy (73.1 – 90.0), respectively, with no significant differences compared to the 7x4 plans (P=1.0, P=0.85). Median GTVres D98% for 8x3 plans vs 7x4 was 105.1 Gy (84.5 – 150) vs 110.2 Gy (86.4 - 144.4), P = 0.63. When bladder and rectum in 8x3 were set equal to 7x4 plans (scenarios 1 & 2), there was no significant difference in CTVHR D90% doses (P=0.63, P=0.91) or GTVres D98% (P=0.53, P=0.53) . In this study, planning optimization with the 8x3 fraction protocol yields similar EQD2 doses for CTVHR D90%, bladder and rectum D2cm3 when compared with the 7x4 fraction protocol. The EQD2 GTV D98% is marginally lower for 8x3 when compared to 7x4; however, remains clinically acceptable. Further evaluation in a large cohort of patients is underway.

Evaluation of Rectal Dose in Prostate Cancer Patients Having Hydrogel Spacer Insertion in LDR Brachytherapy and EBRT Radiotherapy

Evaluation of Rectal Dose in Prostate Cancer Patients Having Hydrogel Spacer Insertion in LDR Brachytherapy and EBRT Radiotherapy

Predictors of Intra-Fraction Prostate Motion during Stereotactic Body Radiation Therapy (SBRT)

The ultimate success and safety of prostate stereotactic body radiation therapy (SBRT) relies on adequate organ motion management. The hypothesis of this study is that there are patient clinical and anatomical variables that predict for prostate motion during treatment. Data were obtained on 52 prostate cancer patients treated with 5 or 6 fraction VMAT SBRT using simultaneous MV/kV imaging for intra-fraction fiducial marker monitoring. Patients were given strict instructions to have a full bladder and empty rectum for simulation and each treatment. 260 cone beam CTs (CBCTs) were used to measure pre-treatment bladder, rectal and gas volumes. Prostate motion end points included number of “beam-offs” and shifts from the position of the day. “Beam offs” occurred when therapists interrupted treatment due to fiducial makers tracking off by >1.5 mm from their reference for 12-15 seconds. Shifts in the lateral, ventral-dorsal and cranial-caudal directions, in addition to the three-dimensional vector from position of the day were measured at 35 MV/kV imaging control points during 2 minutes of treatment and averaged over each fraction. For each patient, urinary symptom score (IPSS), age and body mass index (BMI) were collected as well as the presence of rectal spacer and use of urinary dysfunction medications. Prostate motion data were evaluated per patient and per fraction. Statistical analysis included Spearman’s rank-order correlation, Wilcoxon Rank-Sum test and a Linear mixed model fit by restricted maximum likelihood. The average patient age, BMI and pre-treatment IPSS were 70 years old (range: 56-84), 30 kg/m2 (range:19-55), and 8 (range: 0-21), respectively. Most patients (48/52) had rectal spacers placed prior to SBRT. Data analysis for predictors of intrafraction prostate motion revealed that larger pre-treatment bladder and rectal volumes were associated with more beam offs per fraction (p = 0.018 and p = 0.014, respectively). In addition, there was a trend for larger bladder volumes to predict greater shifts in the ventral-dorsal direction (p= 0.052) and magnitude of the 3D vector (p = 0.051). Patients using urinary medications had fewer number of beam offs during their treatment course (p = 0.038). Patient age, BMI, baseline IPSS and pre-treatment gas volume did not correlate with prostate motion during treatment. Our results suggest that patient bladder and rectal volumes at the time of treatment can influence prostate motion during SBRT. We can conclude that rectal emptying prior to treatment is critical for rectal dose avoidance and prostate motion mitigation, however future studies will be needed to determine the optimal bladder volume during prostate SBRT.

Absolute Volume of Irradiated Rectum As a Predictor of Side Effects during Prostate Radiotherapy Using Proton Pencil Beam Scanning

Dose in relative rectal volume and mean rectal dose are widely used as main constraints for prostate irradiation. But these criteria are very sensitive to changes in rectal filling and also to used contouring standard (changes in length of contoured rectum). Using absolute volumes of irradiated rectum avoids these problems not only in proton beam radiotherapy. 300 patients with early-stage prostate cancer were treated with IMPT (intensity modulated proton therapy), extreme hypofractionated schedule (36.25 GyE in 5 fractions) between February 2013 and July 2016. And 300 patients with advanced prostate carcinoma were treated with IMPT, SIB (simultaneous integrated boost) (63 GyE in 21 fractions for prostate and 48.3 GyE in 21 fractions for lymph nodes). For all patients were recorded D5cm3 – D20cm3 for rectum. Acute toxicity, late toxicity and short-term results were evaluated and statistically analyzed. Analysis of toxicity data together with dosimetric data is ongoing. All patients finished radiotherapy without interruptions. The median of follow-up time in both groups was 39.5 months. Acute toxicity according to Common Terminology Criteria for Adverse Events (CTCAE) v 4.0 was: (gastrointestinal toxicity) GI (grade) G1-17% resp.34.5%, G2 3.5% resp. 21.2%, G3 0% resp. 0.4% (genitourinary toxicity) GU G1-40% resp. 61%, G2 19% resp.16.4%, no G3 toxicity was observed. Late toxicity was: GI G1 19% resp.11%, G2 5.5% resp. 15.6% G3 0% resp. 2%; GU G1 17% resp.18.2, G2 4% resp.2%, no G3 toxicity was observed. Ongoing statistical analysis shows rectal D8cm3 as a worth parameter for GIT toxicity prediction. Dosimetric parameters based on irradiated absolute rectal volume are feasible for GIT toxicity prediction not only in proton beam therapy. Main advantage of these parameters is their insensitivity to quality of rectal contouring and changes in rectal filling during treatment course.

A Phase II Study of Stereotactic Body Radiotherapy with Hydrogel Spacer for Prostate Cancer; Dosimetric Comparison, Acute Toxicity and Quality of Life

Volumetric modulated arc therapy (VMAT) stereotactic body radiotherapy (SBRT) with flattening filter-free (FFF) beam can achieve faster dose delivery and shorter treatment time for prostate cancer. A hydrogel spacer is used to reduce the rectal toxicity, but the clinical data of SBRT with hydrogel spacer are limited. The aim of this prospective single-center phase II study was to determine the efficacy and safety of FFF-VMAT SBRT combined with hydrogel spacer for localized prostate cancer. Men with localized prostate cancer were eligible for the study. A hydrogel spacer was inserted into the perirectal space between prostate and rectum before the initiation of SBRT. All patients underwent the planning CT scans before and after the spacer placement. Patients received 36.25 Gy to 95% of the PTV in 5 fractions every other day excluding weekends with 6MV single arc FFF-VMAT. The primary endpoint was acute toxicities during and within 3 months after the completion of SBRT. Toxicities were assessed using Common Terminology Criteria for Adverse Events v4.03. The secondary endpoints were International Prostate Symptom Score (IPSS) and quality of life (QOL) assessed by the Expanded Prostate Cancer Index Composite (EPIC) questionnaire. Target and normal tissue dosimetry were compared before and after the hydrogel spacer insertion. Between February 2017 and July 2018, forty patients with localized prostate cancer were enrolled. The median age was 70 years (55-79). Three, 25, 6, and 6 patients had low-, intermediate-, high-, and very high-risk prostate cancer according to the National Comprehensive Cancer Network (NCCN) risk classification. Twenty-three patients (58%) received concomitant androgen deprivation therapy. The hydrogel spacer placement was successful in 39 cases (98%). Seven (18%) and eighteen patients (45%) developed grade 2 acute gastrointestinal and genitourinary toxicities, respectively. No grade 3 acute toxicities were observed. Median IPSS temporarily increased at 2 weeks and 1 month after RT when compared to the pretreatment baseline (P < 0.05, 0.05, respectively), and returned to the baseline value in 3 months. EPIC urinary and bowel scores significantly declined at 2 weeks and 1 month after RT (P <0.05, 0.05, respectively), and no difference was observed at 3 months post-RT. Spacer use was associated with lower rectum dose for mean dose, maximum dose, and V100% to V50% (all P < 0.05). FFF-VMAT SBRT with a hydrogel spacer can be safely administered with acceptable acute toxicity. Hydrogel spacer insertion significantly reduced the dose to the rectum.

The Dosimetric Comparison of the Different Photon Energy of Radiotherapy Techniques Used in the Treatment of Cervical Cancer

Bu çalışma 2014-2017 yılları arasında Bursa Uludağ Üniversitesinde radyoterapi tedavisi almış, serviks kanseri tanılı 10 hastanın arşiv materyali kullanılarak retrospektif olarak yapılmıştır. Serviks kanseri radyoterapisinde kullanılan enerji seviyelerinin kullanılması amaçlanmıştır. Tedavi planlamasında kullanılan volumetrik ayarlı ark terapi (VMAT) ve yoğunluk ayarlı ark terapi(YART) 7 alan tekniği için 6 MV ve 15 MV enerjili foton enerjisi kullanılarak her hastaya özel 4 farklı planlama yapılmıştır. Planlanan hedef hacme 28 fraksiyondan 50.4 Gy doz verilmiş ve kritik organ olarak rektum, mesane, ince bağırsak, sağ ve sol femur başları konturlanarak dozimetrik karşılaştırma amaçlanmıştır. Ayrıca tedavi planı değerlendirme parametrelerinden Conformite İndeksi ve Homojenite İndeksi verileri de değerlendirilmiştir. Karşılaştırmalar sonucunda en uygun PTV doz homojenitesi, CI değerini VMAT 15 MV, en iyi HI değerini YART 15 MV sağlamıştır. Mesane ve Rectum Dort dozları açısından en iyi VMAT 6 MV tekniği, ince bağırsak Dmax değeri YART 15 MV tekniğinde elde edilmiştir. Tüm tekniklerde doz dağılımları kabul edilebilir sınır içerisinde olduğu gözlemlenmiştir Saçılan doz ve ikincil kanser riski düşünüldüğünde VMAT 6 MV tekniği diğer tekniklere oranla daha üstün bulundu. Bu yüzden yan etkiler ve çift oluşum meydana gelme ihtimali göz önüne alındığında tedavi tekniği olarak VMAT 6 MV tekniğinin uygun olduğunu desteklemekteyiz.

Development of a multicentre automated model to reduce planning variability in radiotherapy of prostate cancer.

Background and purposeInter-institutional studies highlighted correlation between consistent radiotherapy quality and improved overall patient survival. In treatment planning automation has the potential to address differences due to user-experience and training, promoting standardisation. The aim of this study was to evaluate implementation and clinical effect of a multicentre collaboratively-developed automated planning model for Intensity-Modulated Radiation Therapy/Volumetric-Modulated Arc Therapy of prostate. The model was built using a variety of public institutions’ clinical plans, incorporating different contouring and dose protocols, aiming at minimising their variation.Methods and materialsA model using 110 clinically approved and treated prostate plans provided by different radiotherapy centres was built with RapidPlan (RP), for use on intact and post-prostatectomy prostate cases. The model was validated, distributed and introduced into clinical practice in all institutions. To investigate its impact a total of 126 patients, originally manually inverse planned (OP), were replanned using RP without additional planner manual intervention. Target and organ-at-risk (OAR) metrics were statistically compared between original and automated plans.ResultsFor all centres combined and individually, RP provided plans comparable or superior to OP for all dose metrics. Statistically significant reductions with RP were found in bladder (V40Gy) and rectal (V50Gy) low doses (within 2.3% and 3.4% for combined and 4% and 10% individually). No clinically significant changes were seen for the PTV, independently of seminal vesicle inclusion.ConclusionThis project showed it is feasible to develop, share and implement RP models created with plans from different institutions treated with a variety of techniques and dose protocols, with the potential of improving treatment planning results and/or efficiency despite the original variability.

Quality of Life Changes >10 Years After Postoperative Radiation Therapy After Radical Prostatectomy for Prostate Cancer

To analyze long-term quality-of-life (QoL) changes related to postoperative radiation therapy (RT) after radical prostatectomy. Patients who received postoperative 3-dimensional conformal RT in the years 2003 to 2008 with 1.8 to 2.0 Gy fractions up to 66.0 to 66.6 Gy (n = 181) were surveyed using the Expanded Prostate Cancer Index Composite questionnaire before the beginning of RT (A); on the last day (B); and 2 months (C), 1 to 3 years (D), 6 to 9 years (E), and 10 to 13 years (F) after RT. Mean urinary bother, urinary incontinence bother, and bowel bother score changes (in relation to baseline at time A) of 13, 14, and 7 and 14, 15, and 7 were found at times E and F, respectively (P < .01 for all comparisons). Sexual function scores decreased 6 and 8 points on average (P < .01). Patient age at the time of RT had a considerable impact on urinary bother and urinary incontinence bother, with increasing differences over time when comparing patients aged <68 versus ≥68 years: 0 versus 7 and 0 versus 7 points at time D and 8 versus 23 and 6 versus 35 points at time F, respectively. Patients who did not respond to RT with a decreasing prostate-specific antigen level had greater urinary and urinary incontinence bother and bowel bother score changes >10 years after treatment (25 vs 12; P = .04, 36 vs 10; P = .03, and 20 vs 5; P = .07, respectively). A higher rectal dose was associated with greater acute and long-term bowel bother score decrease. No correlation was found between the dose to the bladder and QoL changes. In contrast to early evaluations in the first years, significantly decreasing QoL in the urinary, bowel, and sexual domains was found >5 years after RT. Aging is likely to be a major factor. Younger patients who responded to the treatment had the most favorable long-term QoL results. As 3-dimensional conformal RT was used in this study, intensity modulated concepts could result in improved outcomes.

Stereotactic prostate focal reirradiation therapy for local recurrence: preliminary results of Hartmann Oncology Radiotherapy Group.

Objective:Our objective was to report our experience and to evaluate the feasibility and toxicity of focal salvage stereotactic body radiation therapy (SBRT) in patients with post-radiation local recurrence of prostate cancer.Methods:We retrospectively reviewed medical records of patients treated with Cyberknife ® between October 2014 and April 2017 at our institution for a focal reirradiation delivered to the prostate/prostatic bed for local recurrence after radical or adjuvant radiotherapy. All patients underwent prostate biopsies at recurrence at the time of fiducial markers placement, had choline PET/CT and pelvic MRI. The treatment consisted in 36 Gy in six fractions delivered every other day. Post reirradiation toxicities were assessed according to the CTCAE v4 (Common Terminology Criteria for Adverse Events).Results:42 patients were treated with followed with a median follow-up of 21 months (range 3 – 31). 34 patients had biopsy proven recurrence. The initial treatment was radical prostatectomy and radiation therapy for 9 patients and radiation therapy alone for 33 patients. 23 patients from the group of prostate reirradiation had placement of rectal spacers. No Grade 4 or 5 toxicity were observed. 27 acute urinary events were recorded: 18 patients experienced Grade 1, 9 patients experienced Grade 2 toxicity and 1 patient experienced Grade 3 urinary toxicity, namely cystitis and/or dysuria. No Grade 2 or more digestive toxicity was observed. Rectal doses were significantly lower with rectal spacers.Conclusion:Salvage focal Cyberknife ® seems feasible and show promising results.Advances in knowledge:SBRT for local prostate cancer recurrence after initial radiotherapy is well tolerated with short follow-up.

Addition of Iodinated Contrast to Rectal Hydrogel Spacer to Facilitate MRI-Independent Target Delineation and Treatment Planning for Prostate Cancer

PurposeHydrogel spacers reduce rectal dose toxicity during prostate cancer radiation therapy. Current products require magnetic resonance imaging (MRI) for visualization during treatment planning, but MRI incompatibility and cost have prompted alternatives using computed tomography (CT). This case series evaluates the addition of iodinated contrast to hydrogel as such an alternative. Methods and materialsThree patients underwent rectal hydrogel spacer placement with iodinated contrast modification. CT was performed within 1 hour of injection and again 1 week later. MRI was obtained at the time of the second CT. Hydrogel delineation was compared between CT and MRI and between paired CT scans. ResultsSpacer enhancement was visible on CT immediately after hydrogel placement (mean Hounsfield units, 122; range, 52-193) but not at the second CT 1 week later (mean Hounsfield units, 8; range, −8 to 29). Delineated spacer volume did not significantly differ between immediate postprocedure CT and MRI ≥1 week later in 2 patients (patient 1: 16.6 vs 15.5 cm3; patient 2: 12.6 vs 14.7 cm3; paired t-test, P = .81). ConclusionsCT visualization of rectal hydrogel admixed with contrast is feasible and allows delineation of interface with rectum/prostate.

Comparison of bone alignment and fiducial marker alignment for online cone-beam computed tomography-guided radiation therapy for prostate cancer

Abstract Objective The aim of the study was to evaluate the coverage of the prostate when prostatic implanted fiducial markers are used to verify setup of the patients in comparison to the pelvic bones while using cone-beam computed tomography (CBCT). Methods Seventeen patients with prostate cancer were included. For each patient, daily online CBCT was done. CT planning was matched with CBCT with the help of fiducial markers (3-5 markers) and another matching with done the help of pelvic bony landmarks. Registration of clinical target volume (CTV) 1 including prostate plus seminal vesicles and CTV2 including prostate only was done and were used to confirm the target volume during the process of matching. Delineation of the rectum on every CBCT was done. Two automatic margin representing planning target volume (PTV) were created. PTV1 was generated by adding 1 cm in all directions (PTV1a) and 0.7 cm in the posterior direction (PTV1b). PTV2 was generated by adding 0.5 cm in all directions (PTV2a) and 0.3 cm in the posterior direction (PTV2b). PTV1a was prescribed to receive 46 Gy in conventional fractionation with a boost dose of 30 Gy to PTV1b. The same dose was prescribed to PTV2a and PTV2b. Calculation of the percentage of intersection between CTV1 and CTV2 created on CBCT with the original CTV scan was done. A comparison between the two CTVs (CTV1 and CTV2) mean dose and the original delineated CTV was done. Then a comparison to the mean dose of the original CTV of PTV1a, PTV2a (CTV1a and CTV2a), and for PTV1b and PTV2b (CTV1b and CTV2b). Calculation of the mean rectal dose and also V60, V70 and V74 was done on the delineated rectum on every CBCT, and then a comparison to the planned original rectal dose. Results The created CTV1 and CTV2 intersection percentage with the original CTV1 and CTV2 significantly increased by 85% (range, 65%-95%, P &lt; 0.05), when fiducial markers were used. The main difference of the received mean dose was significantly less in comparison to pelvic bone alignment (0.03% to 2% vs 0.03% to 11.6% for PTV1a, P &lt; 0.006; 0.01% to 1.8% vs 0.03% to 10.2% for PTV2a, P &lt; 0.014; 0.08 to 2.11 vs 0.04 to 11.29 for PTV1b, P &lt; 0.015 and 0.01 to 1.79 vs 0.01 to 9.69 for PTV2b, P &lt; 0.004). With the use of less PTV margins, significant decrease of the rectal mean dose, V60, V70 and V74 by P &lt; 0.004, P &lt; 0.004, P &lt; 0.0005 and P &lt; 0.009, respectively. Reduction of the CTV1a and CTV1b mean dose by 1.13% and 0.28% in comparison to the initial CTV1a and CTV2a. Conclusion A significant improvement of prostatic cancer patients alignment when fiducial markers are used, with more homogenous dose distribution, and with significant decrease in PTV margins. The delivered rectal dose is significantly less allowing prostate dose escalation.

High Dose 3D Conformal Radiotherapy of Prostate Cancer Using Spaceoar Gel

The aim of this study was to investigate the applicability of high dose radiation therapy following the administration of SpaceOar Hydrogel to decrease rectal toxicity in patients with prostate cancer who had received definitive three-dimensional conformal radiation therapy. Seven patients with a diagnosis of prostate cancer received, under general anesthesia, 10 ml of prostate SpaceOar hydrogel injections transperineally into the space between the prostate and the rectal front wall under the guidance of transrectal ultrasonography. Abdominal tomography and magnetic resonance images of the patients were taken before and after the application of hydrogel. Using both imaging sets and similar algorithms, 3D conformal radiotherapy plans were made that aided in making the calculations. The radiation dose to be applied was calculated from the dose-volume histograms of the target and at risk organs of the patients with tailor-made plans. In the treatment of prostate cancer patients with and without hydrogel plans, there was a statistically significant difference between the rectal V70 and V50 doses, which were 20% ± 14.9 vs 11% ± 2.2 ( p:0.002), and 34 ± 7.9 vs 28.2 ± 11 (p: 0.048), respectively. The D95 and D5 values were similar in all patients with and without hydrogel plans. Rectal toxicity decreased in patients with a distance of >15 mm (p=0.053). Consequently 3D conformal radiotherapy can be successfully and safely applied at high dose with low toxicity to prostate cancer patients after placing hydrogel between the rectum and prostate. Keywords : Prostate cancer, radiotherapy, spaceoar hydrogel, rectal toxicity DOI : 10.7176/JSTR/5-6-08

A simple algorithm to predict non-compliance with organ at risk dose-volume constraints when planning intensity modulated post-prostatectomy radiation treatment: 'Why we should put the CART before the horse'.

It is not always apparent when the optimal IMRT/VMAT plan for post-prostatectomy radiotherapy (PPRT) has been achieved. Individual variation in patient anatomy is a key contributor. This study aimed to create a model to determine the probability of rectum and/or bladder doses exceeding planning goals based on individual patient anatomy prior to planning. The IMRT/VMAT PPRT plans from 200 men were randomly and evenly allocated into the Training Cohort and the Validation Cohort. Univariate and multivariate analysis of the Training Cohort identified variables which impacted bladder and rectal doses. Significant variables were included in a Classification and Regression Tree (CART) analysis. The resultant algorithm was then applied to the Validation Cohort. On multivariate analysis, prescription dose; bladder and rectal volume; lymph node treatment; and percentage of bladder and rectal overlap with the PTV were significant variables. Following CART analysis, the overlap volume (OV) for both rectum (rectum overlap>20%) and bladder (bladder overlap>20%) were the key drivers of meeting planning goals. Treatment of pelvic lymph nodes was included as the secondary driving factor for bladder (but not rectal) dose. On application to the Validation Cohort, CART analysis predicted 95% and 87% of patients who would meet bladder and rectal planning goals respectively. A simple algorithm was developed to predict plan quality by using the OV of the bladder and rectum with the PTV. This algorithm may be used a priori to assess the planning process in the context of variable anatomy, and to optimise planning quality and efficiency.

The impact of simultaneous dose escalation VMAT to the focal lesion micro boost of localized prostate cancer.

e16592 Background: Dose Escalation to the prostate is showing promising results of increasing local control. The study aims to assess biochemical failure free survival (BFF) after dose escalation to the prostate 78Gy with simultaneous integrated boost (SIB) 87Gy to the focal lesion. Genito-urinary (GU) &amp; gastro-intestinal (GI) toxicity was assessed by comparing investigational toxicity score &amp; patient outcome reports. Methods: Thirty intermediate &amp; high risk localized prostate cancer patients were treated with dose escalated VMAT protocol of 78 Gy/35 fractions to prostate &amp; 87Gy boost to focal lesion detected by baseline multi-parametric MRI &amp; TRUS as well. Neo-adjuvant, Concurrent &amp; adjuvant hormonal therapy was applied. Risk structures dose statistics were matched to modified Quantec with EQD2 equation. For each patient, daily online fiducial markers image guided verification was done. Toxicity profile was assessed by RTOG for subjective assessment and FACIT quality of life protocol for objective assessment during the radiotherapy course &amp; follow up period. Results: About 80% of patients received the pre-determined protocol, however three patients received 76Gy to prostate &amp; 84Gy to the focal lesion to comply with the risk structure constrains. At median follow up period of 18 months-BFF was 93.3 %. By the end of radiotherapy, 80% developed G3 GU toxicity while 30% developed G2 GI toxicity. Correlation between bladder V40 (≥or≤ 40%) &amp; GU toxicity (≤ G3 vs G3) was of border line statistical significance (P = 0.05). After radiotherapy, GU toxicity dropped to 17.2% G2 &amp; 13% G3 at the 3rd month while 0 % G3 afterwards. Three patients developed G4 rectal toxicity (bleeding per rectum); one at 9th month of ending treatment &amp; two at 12th month; two of them needed cautery for angio-dysplasia as post radiation sequelae confirmed by colonoscopy. However, the correlation between V40 of the rectum ≥ 40% was significant with rectal toxicity (G0 vs G4) (P = 0.02). Comparing FACIT assessment during radiotherapy or in follow up showed no significant difference affecting the quality of life. Conclusions: Dose Escalation with SIB should be done using advanced technique like VMAT with image guidance. Re-validation of risk structure &amp; rectal dose constrains should be considered especially for dose escalation ≥ 72Gy. Clinical trial information: NCT03384199.

Prostate or Bone? – Comparing the Efficacy of Image Guidance Surrogates for Pelvis & Prostate Radiotherapy Using Accumulated Delivered Dose

Efficacy of an image guidance surrogate for pelvis and prostate radiotherapy has previously been reported based on geometric coverage only. Using the dose accumulation process, this study assessed the impact of dosimetry to both the target and normal tissue when either Bony Anatomy (BA) or Prostate (PRO) was used as surrogates for image guidance for pelvis and prostate radiotherapy. Thirty patients who received treatment to both the Pelvic Lymph Nodes (PLN) and prostate were included. A two-arc VMAT plan was generated to deliver 50-54Gy to the PTVs (PLN + 5mm; prostate + 10/7mm). Daily acquired CBCTs were rigidly registered to the CT using BA and PRO to simulate two different treatment positions. Daily dose was computed on all CBCTs and then accumulated on the planning CT using the output from the CT-CBCT deformable image registration. The Accumulated Delivered Dose (DAcc) of PLN, prostate, bladder and rectum for each surrogate were compared with the planned dose. Deviation from the planned dose (ΔDAcc-Plan) of >5% was considered significant. A total of 755 CBCTs was used to measure DAcc across 30 patients. Despite having the prostate displaced from bony anatomy by >5mm from planned position in 19% of fractions, mean DAcc of PLN and prostate were comparable between the two surrogates, with an absolute ΔDAcc-Plan of <2%. No significant deviation from planned dose was observed for bladder. In contrary, DAcc for rectum D50 was significantly greater than the planned dose when BA was used (Mean ΔDAcc-Plan = 6%, SD: 5%). The difference between the two surrogates also reached significance (6% vs 2%, p < 0.0006). When examining individual patient, there is a large variation in the magnitude of ΔDAcc-Plan for this endpoint. The range was 5 – 20% for 18 patients for BA, whereas the range for PRO was 5 – 8% for 8 patients, demonstrating the superiority of PRO in minimizing dose deviation for rectum. The use of either BA or PRO for image guidance could deliver dose to PLN and prostate with minimal deviation from the plan using existing PTV margins. However, deviation for rectum was significant when BA was used.

Rectal and Bladder Dose Measurements in the Intracavitary Applications of Cervical Cancer Treatment with HDR Afterloading System: Comparison of TPS Data with MOSFET Detector.

Background: Intracavitary brachytherapy plays a major role in management of cervical carcinoma. Assessment of dose received by OAR’s therefore becomes crucial for the estimation of radiation toxicities in HDR brachytherapy.Objective: Purpose of this study is to evaluate the role of in vivo dosimetry in HDR brachytherapy and to compare actual doses delivered to OAR’ s with those calculated during treatment planning.Material and Methods: In this retrospective study, 50 patients of cervical carcinoma were treated by Microselectron HDR. Out of 50 patients, 26 were treated with a dose of 7 Gy and 24 with a dose of 9 Gy, prescribed to point A. Brachytherapy planning and evaluation of dose to bladder and rectum was done on TPS & in vivo dosimetry was performed using portable MOSFET.Results: Calibration factors calculated for both dosimeters are almost equal and are 0.984 cGy/mV and 1.0895 cGy/mV. For bladder, dose deviation was found to be within ± 5% in 28 patients, ± 5-10% in 14 patients, ± 10-15% in 4 patients. Deviation between TPS-calculated dose and dose measured by MOSFET for rectum was within ± 5% in 31 patients, ± 5–10% in 8 patients, and ± 10–15% in 7 patients.Conclusion: TPS calculated doses were slightly higher than that measured by MOSFET. The use of small size MOSFET dosimeter is an efficient method for accurately measuring doses in high-dose gradient fields typically seen in brachytherapy. Therefore, to reduce the risk of large errors in dose delivery, in vivo dosimetry can be done in addition to TPS computations.

Evaluation of variation of interfraction doses to organs at risk during brachytherapy of cervical cancer

BackgroundTwo-dimensional treatment planning using radiographs or simulator films was the standard in planning brachytherapy for patients with cervical cancer. Three-dimensional (3D) treatment planning has improved treatment efficacy. This retrospective study compares conventional and 3D treatment planning of brachytherapy in patients with cervical cancer and interfraction dose variation to bladder and rectum (D2cc). MethodsThe mean doses to bladder and rectum (D2cc) were computed by computed tomography (CT)–based planning during 100 sessions of intracavitary brachytherapy for carcinoma cervix with the same source configuration as generated for conventional planning, and these estimates were compared with the doses at International Commission on Radiation Units and measurements (ICRU) rectal, bladder points and point A. Interfraction variation of doses to bladder and rectum during various sessions was also analysed. ResultThe mean ICRU bladder dose and D2cc of the bladder for all patients was 3.7 Gy and 7.4 Gy, respectively (p < 0.001). The mean ICRU rectal dose from conventional plan was 4.3Gy and with CT planning, 4.45 Gy (p = 0.04). Interfraction dose variations for D2cc of the bladder were min −5.3 Gy and max 4.8 Gy and those of the rectum were min −1.8 Gy and max 1.72Gy. ConclusionDosimetric evaluation of conventional and 3D CT-based treatment planning for the same brachytherapy sessions demonstrated underestimation of ICRU bladder dose points (p < 0.001) and the rectal ICRU point dose and D2cc (p=0.04). The doses to organs at risk did not show a statistically significant variation between the fractions. However, large variation was noted between the interfractional maximum and minimum doses to bladder and rectum.