Clinical Target Volume Size Research Articles

EVALUATING THE RELATIONSHIP BETWEEN RADIOTHERAPY CLINICAL TARGET VOLUME AND GAIT ACTIVITY IN HIGH GRADE GLIOMA

Abstract AIMS Walking speed or peak cadence serves as a potential indicator of overall health, particularly in older individuals, with documented predictive value for various health-related outcomes. The emergence of wearable technology for gait analysis has facilitated early disease detection and monitoring in conditions like Parkinson’s disease. This study aimed to explore the association between gait metrics and radiotherapy Clinical Target Volume (CTV) in participants with High-Grade Glioma (HGG) enrolled in the BrainWear study, which captures longitudinal physical activity data through wearable devices. METHOD 21 HGG participants provided accelerometer data before and after a course of radiotherapy. Using Spearman rank correlation analysis, we examined the relationship between CTV and gait features while considering the total radiotherapy dose and tumour location. Participant data was cut at the same time point of 14-days either side of the start or end of radiotherapy to ensure the data was aligned. RESULTS The analysis revealed a moderately negative correlation between CTV and peak cadence at the onset of radiotherapy. At the end of radiotherapy and in the two weeks following completion, both peak cadence in 1 minute and 30 minutes showed a stronger inverse correlation with CTV (Spearman’s ρ = -0.52 and ρ = -0.44 respectively, p-value <0.05). This suggests that higher CTV may be associated with decreased peak cadence, particularly at the time of expected radiotherapy toxicity. Subgroup analysis focusing on patients with CTV covering the motor cortex further illustrated a more significant inverse correlation between CTV size and peak cadence (Spearman’s ρ = -0.77, p-value <0.05). CONCLUSION This study highlights the importance of understanding the interplay between tumour treatment volume, location and physical function. Further exploration of CTV volume in relation to anatomical areas such as the motor cortex could provide deeper insights into this relationship and provide opportunities for personalised monitoring in HGG.

Inter-subject cerebrovascular variability: a source of uncertainty for dose calculation to circulating blood cells for glioblastoma patients treated with modern radiotherapy techniques

Purpose. To assess how inter-subject variations in brain vasculature among glioblastoma (GBM) patients affects the calculated dose received by circulating blood cells (CBC) during radiotherapy and its subsequent impact on CBC depletion. Methods. Ten GBM patients treated with either intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) were selected. For each patient, 23 cerebrovascular models were developed based on 23 healthy subject MR-angiography data to simulate intra- and inter-subject blood vessel diversity. Based on the corresponding treatment plan of the patient, the dose to CBC was calculated for all the 230 scenarios. The impact of inter-subject variation on fraction of irradiated blood volume (VD >0 cGy) and lymphocyte kill rates as a function of the clinical target volume (CTV) size and treatment technique were analyzed. Results. The dose fluctuation to CBC was higher in IMRT plans compared to VMAT plans. The uncertainty in the VD >0 cGy was 18.3% for IMRT and 2.0% (CI95%) for VMAT and the dispersion of the D 2% index was 6 cGy for IMRT and 1 cGy for VMAT (CI95%) for one single treatment fraction of 200 cGy. The uncertainty in killed CBC due to inter-subject diversity in brain blood vessel increased with increasing CTV size and was σ = 11.2%. Conclusions. VMAT showed greater robustness against inter-subject variation in blood vessels compared to IMRT. We recommend considering the uncertainty in depleting CBC resulting from the use of less patient-specific and generic blood vessel phantoms to improve the radiation-induced lymphopenia assessments.

Rotational Set Up Uncertainly in Non-6D Couch and its Effects in Clinical Target Volume- Planning Target Volume Margin Calculation for Different Sites.

The purpose of this study was to estimate and incorporate rotational error to translational error for clinical target volume (CTV) to planning target volume (PTV) margin calculations for non-6D couch. The study involved cone-beam computed tomography (CBCT) images of the patients who already had treatment in Varian Trilogy Clinac. The different sites studied were brain (70 patients, 406 CBCT images), head and neck (72 patients, 356 CBCT images), pelvis (83 patients, 606 CBCT images), and breast (45 patients, 163 CBCT images). Rotational and translational patient shifts were measured with the help of Varian eclipse offline review. The rotational shift introduces translational shift as it resolved along craniocaudal and mediolateral directions. Both rotational and translational error follow normal distribution and their respective errors were used to calculate CTV-PTV margin using van Herk model. Rotational effect on CTV-PTV margin contribution increases with increase in size of CTV. It also increases with increase in distance between center of mass of CTV and isocenter. These margins were more pronounce in single isocenter supraclavicular fossa-Tangential Breast plans. There is always rotational error in all sites and it causes shift and rotation of the target. Rotational contribution to the CTV-PTV margin depends upon geometric center of CTV and isocenter distance and also on size of CTV. CTV-PTV margins should incorporate rotational error along with transitional error.

Performance evaluation of adaptive aperture's static and dynamic collimation in a compact pencil beam scanning proton therapy system: A dosimetric comparison study for multiple disease sites

A compact pencil beam scanning (PBS) proton therapy system, Mevion S250i with Hyperscan, is equipped with adaptive aperture (AA) to collimate the beam with 2 different techniques: Static aperture (SA) and dynamic aperture (DA). SA (single aperture) collimates the outermost contour of the target and DA (multi-layer aperture) collimates each energy layer of the proton beam. This study evaluates dosimetric performance of SA and DA for different disease sites. This study includes 5 disease sites (brain, head and neck (HN), partial breast, lung, and prostate), and 8 patients for each. A total of 80 patient treatment plans (5 sites × 8 patients per site × 2 collimation techniques) were created using 2 to 4 proton beams. Both SA and DA plans were made using the same plan and optimization parameters calculated by a Monte Carlo dose algorithm. Multi-field optimization (MFO) was used for HN treatment plans, whereas treatment plans for the other sites were made with single-field optimization (SFO). All plans were robustly optimized with 3 mm (brain and HN) or 5 mm (breast, lung, and prostate) position uncertainty along with 3.5% range uncertainty. Treatment plans were normalized such that 99% of the clinical target volume (CTV) received 100% of the prescribed dose. Dose volume histogram (DVH) parameters were evaluated for CTV and organs at risk (OARs). The CTV was also evaluated for dose homogeneity, dose conformity, and dose gradient. In general, the DA plan made CTV hotter, while it saved OARs better. DA produced better conformity with sharper dose falloff around CTV, while SA generated better homogenous target coverage. DA decreased Dmax to brainstem (1.2% = [(SA-DA)/DA × 100%]) for brain, Dmax to the spinal cord (137.3%) for HN, D1% of the ipsilateral lung (50.5%) for breast, and Dmax to the spinal cord (74.0%) for lung. The dose reduction in bladder and rectum for prostate plans with DA was less than 2.5%. The DA plans reduced the dose to OARs for all disease sites but escalated the target maximum dose for the same target coverage than the SA plans. The OAR saving and dose escalation depended on CTV size, proximity of the OARs to CTV, and the plan complexity.

Determining whether multiple needles are necessary in interstitial brachytherapy for thoracic tumors: A dosimetry analysis.

In interstitial brachytherapy, needles must be inserted in a regular, parallel arrangement to ensure a uniform target dose distribution and conformal distribution to the target. It is generally difficult to achieve this in thoracic tumors because of obstruction by the ribs. Furthermore, insertion of multiple needles may cause the patient considerable harm and could expose him/her to additional risks. Thus, we propose the single-dwell-position method, discuss its applicability, and compare it with the actual multiple-needle method using dosimetry. The aim of this study was to evaluate the necessity for multiple needles with irregular alignment in interstitial brachytherapy for thoracic tumors. Twelve patients' interstitial brachytherapy plans were reviewed. The single-dwell-position interstitial brachytherapy plans, wherein one needle was hypothetically inserted, were compared with the actual multiple-needle plans. Dose parameters, including clinical target volume (CTV) and volumes of the lung, spinal cord, heart, and ribs, were compared. We also evaluated the correlation between CTV size and dose difference in the lungs. The nonparametric Wilcoxon test was used. There were no statistically significant differences in the doses achieved with the single-dwell-position plans and actual multiple-needle plans. The correlation between the CTV size and dose difference in the lungs was weak. Irregularly arranged multiple-needle interstitial brachytherapy does not provide superior doses to the lung, heart, spinal cord, or ribs compared with single-dwell-position plans. If regular arrangement of multiple needles is difficult to achieve, the multiple-needle scheme is not the only viable option.

Patient and Dosimetric Predictors of Genitourinary and Bowel Quality of Life After Prostate SBRT: Secondary Analysis of a Multi-institutional Trial

Stereotactic body radiation therapy (SBRT) is an emerging option for localized prostate cancer. However, there are no standard dosimetric guidelines, and normal tissue tolerances for extreme hypofractionation are not well defined. We analyzed dosimetric correlations with patient-reported urinary and bowel quality of life (QOL) on a prospective trial. Patients with low- or intermediate-risk prostate cancer from 18 institutions were enrolled on a phase 2 trial from 2007 to 2012 and treated using robotic SBRT to 38Gy in 4 fractions on consecutive days. No androgen deprivation was used. Patients received simulation with Foley catheter for urethral delineation. The clinical target volume was prostate (low-risk patients) or prostate plus 1cm of proximal seminal vesicles (intermediate-risk patients). Multiple dosimetric measures for urethra, bladder, and rectum were prospectively recorded. QOL using the Expanded Prostate Cancer Index Composite was assessed before and after treatment at protocol-specific time points. Linear regression was used to assess factors associated with QOL at 1month and 2years. A total of 259 patients were enrolled. QOL data were available for 98%, 96%, and 84% at baseline, 1month, and 2years, respectively. Median age was 69years. Prior transurethral resection of the prostate and clinical target volume size were associated with 2-year urinary incontinence. There was a trend toward worse 2-year obstruction/irritation in older patients on multivariable analysis. Bladder and urethral doses were not associated with either 1-month or 2-year urinary QOL. In contrast, rectum maximum dose was associated with both 1-month and 2-year bowel QOL. At 2years, the proportion with moderate or big overall bowel problems (as defined by Expanded Prostate Cancer Index Composite-26) was significantly higher in patients with rectum maximum dose greater than versus less than the median 37.4Gy (11% vs 2%, Fisher's exact test P=.008). These results provide novel data that contribute to a better understanding of patient and dosimetric factors associated with adverse QOL effects from prostate SBRT.

The effects of the shape and size of the clinical target volume on the planning target volume margin.

PurposeTo investigate the impact of clinical target volume (CTV) shape and size on CTV to planning target volume (PTV) margin expansion.Methods and MaterialsUsing numerical integration methods, margins accounting for random errors and systematic errors were calculated for CTVs of different shapes and sizes. We use and to represent the coefficients, for random errors and systematic errors, respectively, that ensure that every point of the CTV receives ≥95% of the prescribed dose.ResultsThe part of the margin accounting for random errors depends on CTV shape and size; generally, a convex part of a CTV would have a larger margin than a concave part. However, the part of the margin accounting for systematic errors is independent of CTV shape and size.ConclusionsCTV shape and size should be considered when generating a PTV. For a complex CTV, the margins of the various parts of the CTV are different and related to local forms.

Proton reirradiation of locally recurrent pancreatic and ampullary adenocarcinomas.

317 Background: Local recurrences of pancreatic and ampullary cancer can be painful and cause significant morbidity. Their treatment after resection and chemoradiation is particularly challenging. A second course of radiotherapy (RT) in a previously radiated field carries the risk of RT-induced tissue injury. Proton therapy (PRT) may offer an advantage in the reirradiation setting due to the lack of exit dose and potential sparing of normal tissues. Methods: Between 2/2011 and 8/2012, 10 adult patients (pts) with locally recurrent pancreatic or ampullary malignancies in or near prior treatment fields began reirradiation. Toxicity was graded according to the CTC v4.0. Acute toxicity was defined within 90 days from start of PRT. Results: Median follow-up was 8.2 months (1.1-19.1) from the start of retreatment and 15 months (2.4-27.8) from the development of local recurrence. Mean age was 67 (54-75). Nine of the pts had pancreatic adenocarcinoma and 1 had ampullary adenocarcinoma. Median clinical target volume size was 86.4 cc (15-236). Nine received concurrent 5-fluorouracil or capecitabine-based chemotherapy. The median total dose was 59.4 Gy(RBE)(45-59.4); all pts were treated with PRT exclusively, except for one pt who was treated with 36% photon volumetric arc therapy. The median prior dose was 50.4 Gy (30-59.4). The median interval between RT courses was 34 months (17-461). Nine pts had Grade 2 and 1 had only Grade 1 non-hematologic acute toxicity. No Grade 2 or higher non-hematologic RT-related toxicities were observed after 90 days from the start of RT. Five pts developed metastatic disease at a median of 7.4 months (4.8-13.2) after starting RT, 1 of whom died at 5.3 months. One pt developed progressive regional (paraaortic) disease inferior to the fields while on treatment and was stopped early at 45 Gy. One pt developed a regional metastasis (porta hepatis) outside of the retreated volume. The other 8 pts were controlled locally within the retreated fields. Conclusions: Reirradiation of pancreatic/ampullary cancers with PRT and concurrent chemotherapy has minimal acute toxicity and encouraging short-term local control. Further follow-up on these pts is needed to assess the long-term morbidity and utility of PRT reirradiation. Clinical trial information: NCT01126476.

WE‐D‐204B‐06: Does the Shape and Size of Clinical Target Volume Affect the Planning Target Volume Margin?

Purpose: Recipes for margin design generally depend on clinical target geometric variation/motion characterization (the mean and the Standard Deviation). Tumor specific geometry was not considered. This study is to investigate the influence of the shape and size of a CTV on the design of non‐uniform margin. Method and Materials: Criterion of the target margin design is to ensure that at lest 95% probability of CTV occupancy is inside the PTV. The random error and the systematic error were considered separately in our margin calculation. Target margins are represented by kr−95σr and ks−95σs for compensation of the random error and the systematic error respectively, where kr−95 and ks−95 are coefficients, σr and σs are the SDs of the random error and the systematic error. We evaluated the value of kr−95 and kks−95 for CTVs with different shape and size. The shapes of CTV were chosen as point, sphere, cylinder and concave shapes. Results: For the random error, kr−95 is 2.79 for the point CTV. For the sphere CTVs, kr−95 is in the range of (1.65, 2.79). The upper and lower bounds correspond to the sphere size with zero and infinite large radius. The kr−95 for the cylinder CTV is in the range of (1.65, 2.45), the actual value for any surface point depends on its position and cylinder size. For points at the concave region, kr−95 depends on the local shape, and it could be less than 1.65. For systematic error, no matter what the shape and size the CTV is, the ks−95 is always 2.79. Conclusion: In addition to the random error of target position variation, the target margin also depends on a CTV's shape and size. However, for the systematic error of target motion, the shape and size of a CTV have no effect on the target margin design.

Endorectal MRI assessment of local relapse after surgery for prostate cancer: A model to define treatment field guidelines for adjuvant radiotherapy in patients at high risk for local failure

To assess the role of endorectal magnetic resonance imaging (MRI) in defining local relapse after radical prostatectomy for prostate cancer to help to reassess the clinical target volume (CTV) for adjuvant postprostatectomy radiotherapy. Sixty patients undergoing an endorectal MRI before salvage radiotherapy were selected. Spatial coordinates of the relapses were assessed using two reference points: the inferior border of the pubic symphysis (point 1) and the urethro-vesical anastomosis (point 2). Every lesion on MRI was delineated on the planning computed tomography and center of mass coordinates were plotted in two separate diagrams (along the x, y, and z axes) with the urethro-vesical anastomosis as the coordinate origin. An "ideal" CTV was constructed, centered at a point defined by the mathematical means of each of the three coordinates with dimensions defined as twice 2 standard deviations in each of the three axes. The dosimetric impact of the new CTV definition was evaluated in six adjuvantly treated patients. The ideal CTV center of mass was located at coordinates 0 (x), -5 (y), and -3 (z) mm with SDs of 6 (x), 6 (y), and 9 (z) mm, respectively. The CTV size was 24 (x) x 24 (y) x 36 (z) mm. Significant rectal sparing was observed with the new CTV. A CTV with an approximately cylindrical shape (approximately 4 x 3 cm) centered 5 mm posterior and 3 mm inferior to the urethro-vesical anastomosis was defined. Such CTV may reduce the irradiation of normal nontarget tissue in the pelvis potentially improving treatment tolerance.