Clinical Outcomes Among Patients Treated With Stereotactic Body Radiation Therapy to Femur Metastases for Oligometastatic Disease Control or Reirradiation: Results From a Large Single-Institution Experience

Purpose

There are limited data regarding outcomes after stereotactic body radiation therapy (SBRT) for femur metastases, which was an exclusion criteria for the Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers (SABR-COMET) trial. We aimed to characterize clinical outcomes from a large single institution experience.

Methods and Materials

Forty-eight patients with 53 lesions were consecutively treated with femur SBRT from May 2017 to June 2022. The Kaplan-Meier method and Cox proportional hazard models were used to characterize time-to-event endpoints and associations between baseline factors and clinical outcomes, respectively. Local control and locoregional control were defined as the absence of tumor progression within the radiation treatment field or within the treated femur, respectively.

Results

Most patients had Eastern Cooperative Oncology Group performance status 0 to 1 (90%), prostate (52%) or breast/lung (17%) cancer, and 1 to 3 lesions (100%), including 29 proximal and 5 distal. Fifty-seven percent of the lesions were treated with concurrent systemic therapy. Median planning target volume was 49.1 cc (range, 6.6-387 cc). Planning target volume V100 (%) was 99% (range, 90-100). Fractionation included 18 to 20 Gy/1F, 27 to 30 Gy/3F, and 28.5-40 Gy/5F. Forty-two percent had Mirels score ≥7 and most (94%) did not have extraosseous extension. Acute toxicities included grade 1 fatigue (15%), pain flare (7.5%), nausea (3.8%), and decreased blood counts (1.9%). Late toxicities included fracture (1.9%) at 1.5 years and osteonecrosis (4%) from dose of 40 Gy in 5F and 30 Gy in 5F (after prior 30 Gy/10F). One patient (2%) required fixation postradiation for progressive pain. With median follow-up 19.4 months, 1- and 2-year rates of local control were 94% and 89%, locoregional control was 83% and 67%, progression-free survival were 56% and 25%, and overall survival were 91% and 73%. Fifty percent of local regional recurrence events occurred within 5 cm of gross tumor volume.

Conclusions

Femur SBRT for oligometastatic disease control in well-selected patients was associated with good outcomes with minimal rates of acute and late toxicity. Patterns of local regional recurrence warrant consideration of larger elective volume coverage. Additional prospective study is needed.

Prospective Evaluation of the Clinical Benefits of a Novel Tattoo-less Workflow for Nonspine Bone Stereotactic Body Radiation Therapy: Integrating Surface-Guidance With Triggered Imaging Reduces Treatment Time and Eliminates the Need for Tattoos

PURPOSE

Oligometastatic disease has expanded the indications for nonspine bone stereotactic body radiation therapy (NSB SBRT). We investigated whether optical surface monitoring systems (OSMS) could enable tattoo-less setup and substitute for 2-dimensional/3-dimensional or cone beam computed tomography (CBCT)-based mid-imaging in NSB SBRT.

METHODS AND MATERIALS

OSMS was incorporated in parallel with an existing workflow using pretreatment CBCT and 2-dimensional/3-dimensional kV/kV mid-imaging beginning November 2019. The ability of OSMS to detect out-of-tolerance (>2 mm/>2°) and commanded couch shifts was analyzed. A workflow incorporating OSMS reference captures, CBCT for pretreatment verification, and OSMS/triggered imaging (TI) for intrafraction monitoring was developed for rib/sternum SBRT beginning November 2021 and all NSB SBRT beginning February 2022. Treatment time and CBCT-related radiation dose between the OSMS and the non-OSMS intrafraction monitoring group was analyzed pre- and post-OSMS/TI workflow adoption. All fractions were analyzed through statistical process control with use of an XmR chart of treatment time per quarter from February 2019 to February 2023. Special cause rules were based on Institute for Healthcare Improvement criteria.

RESULTS

From February 2019 to February 2023, 1993 NSB SBRT fractions were delivered, including 234 rib, 109 sternum, 214 ilium, and 682 multisite. Over 20 commanded shifts, OSMS could detect 2-mm shifts to within 0.4 mm 67% of the time and 0.8 mm 95% of the time. All NSB SBRT sites showed significant reductions in treatment time, including the greatest improvement in rib total treatment (21.6-13.4 minutes; P = 1.16 × 10-17) and beam time (7.9-3.2 minutes; P = 7.32 × 10-27). Significant reductions in CBCT-related radiation were also observed for several NSB sites. These process improvements were associated with OSMS adoption.

CONCLUSIONS

Adoption of a novel NSB SBRT workflow incorporating OSMS/TI for bone intrafraction motion monitoring reduced treatment time and CBCT-related radiation exposure while also allowing for more continuous intrafraction motion monitoring for NSB SBRT. OSMS/TI enabled the transition to a tattoo-less workflow.

An Automated, Dynamic Radiation Oncology Prescription Checking System

PURPOSE

Despite serving as a critical communication tool, radiation oncology prescriptions are entered manually and prone to error. An automated prescription checking system was developed and implemented to help address this problem.

METHODS AND MATERIALS

Rules defining clinically appropriate prescriptions were generated, examining specific types of errors: (1) unapproved dose per fraction for a given disease site; (2) dose per fraction too large for nonstereotactic treatment technique; and (3) dose per fraction too low. With a goal of catching errors as upstream as possible to minimize their propagation, a report was created and ran every 30 minutes to check all newly written or approved prescriptions against the 3 rules. When a prescription violated these rules, an automated email was immediately sent to the prescriber alerting them of the potential error. System performance was continuously monitored and the criteria triggering an alert adjusted to balance error detection against false positives. Alerts leading to prescription amendment were considered true errors.

RESULTS

From June 2021 to November 2022, the system checked 24,047 prescriptions. A total of 241 email alerts were triggered, for an average alert rate of 1%. Of the 241 alerts, 198 (82.2%) were unapproved doses per fraction for the disease site, 14 (5.8%) were doses per fraction that were too low, and 29 (12%) were doses too large for nonstereotactic treatment technique. Thirty-one percent of alerts led to a change of prescription, suggesting they were true errors. The baseline rate of erroneous prescription entry was 0.3%. A regression model showed that trainee prescription entry and dose per fraction <150 cGy were significantly associated with true errors.

CONCLUSIONS

Given the significant consequences of erroneous prescription entry, which ranged from wasted resources and treatment delays to potentially serious misadministration, there is significant value in implementing automated prescription checking systems in radiation oncology clinics.

Prospective Evaluation of Implementation of a Tattoo-less Workflow for Non-Spine Bone SBRT

PURPOSE/OBJECTIVE(S)

Oligometastatic disease has expanded the clinical indications for non-spine bone (NSB) SBRT. Optical surface monitoring systems (OSMS) may reduce treatment time if it represents an effective surrogate for bone intrafraction motion monitoring. We aimed to identify whether OSMS could substitute for 2D-3D mid-imaging and enable a tattoo-less set up in NSB SBRT.

MATERIALS/METHODS

Beginning 11/2019, OSMS was incorporated in parallel with an existing workflow using CBCT and mid 2D-3D kV/kV imaging for pre- and mid-imaging for NSB SBRT. The ability of OSMS to detect both observed out-of-tolerance (>2mm/>2deg) shifts and manual couch shifts was analyzed. A workflow incorporating OSMS reference captures, CBCT for pre-treatment verification and OSMS/triggered imaging (TI) for intrafraction monitoring was developed and deployed for rib/sternum SBRT beginning 11/2021 and all NSB SBRT beginning 2/2022. All NSB SBRT treatment appointments were analyzed through statistical process control (SPC) with use of an XmR chart of average set up and total treatment time per quarter from 2/2019 to 2/2023. Special cause rules were based on IHI rules and conduced with spreadsheet software.

RESULTS

From 2/2019 to 2/2023, 1962 NSB SBRT fractions were delivered, including 337 rib, 150 sternum, 197 femur, 266 ilium, 222 multi-site. Over 104 femur and 87 ilium images, there were no over tolerance intra-fraction events detected with 2D-3D or OSMS. Over 20 manual shifts, OSMS could detect 2mm shifts to within 0.4mm 67% of the time and 0.8mm 95% of time. There was no difference in treatment set up time following adoption of an OSMS/TI workflow as a replacement for 2D-3D mid-imaging. A reduction in rib SBRT delivery and multi-site treatment set-up times was significantly associated with the adoption of OSMS/TI and OSMS, respectively, as assessed based on special cause variation with 8 consecutive points below the mean.

CONCLUSION

Integration of OSMS and triggered imaging has enabled the transition to a completely tattoo-less workflow, thus sparing patients the need for permanent tattoos whilst also allowing more continuous motion monitoring and reduced radiation exposure related to unnecessary 2D-3D or CBCT mid-imaging. Treatment times were significantly reduced for patients receiving rib SBRT or multi-site NSB SBRT with this workflow.

Outcomes of Stereotactic Body Radiation Therapy (SBRT) for Femur Oligometastases

PURPOSE/OBJECTIVE(S)

Stereotactic body radiation therapy (SBRT) is increasingly used for oligometastatic bone disease, but there is limited data regarding the clinical outcomes of utilizing SBRT in treatment for femur metastases, which was excluded from SABR-COMET. We aimed to identify patient or treatment factors associated with clinical outcomes among patients treated with SBRT to femur metastases for oligometastatic disease control or re-irradiation.

MATERIALS/METHODS

We identified 50 patients with 56 femur lesions consecutively treated with SBRT at a single institution May 2017-June 2022. The Kaplan-Meier method was used to characterize time-to-event endpoints and Cox proportional hazards models were performed to evaluate the associations between baseline factors and clinical outcomes. Local control was defined as the absence of regional tumor progression at treated area or need for surgical fixation post radiation.

RESULTS

Most patients had ECOG 0-1 (90%), prostate (50%) or breast/lung (16%) cancer, and 1-3 lesions (100%), including 30 proximal and 5 distal. 55% of lesions received concurrent systemic therapy, including ADT (n = 18) or immunotherapy (n = 6). Median PTV volume was 54.7cc (range, 6.6 to 387cc). PTV V100(%) was 99% (range 71.5-100). Fractionation included 18-20 Gy/1F, 27-30 Gy/3F, 25-40 Gy/5F, and 50 Gy/10F. 43% of lesions had Mirel's score ≥ 7 and 91% of lesions did not have extraosseous bone extension on diagnostic CT and/or MRI. Acute toxicities included grade 1 fatigue (14.3%), pain flare (7.1%), and decreased blood counts (1.8%). Late toxicities included fracture (1.8%) at 1.5 years and 2 patients with radiation-induced osteonecrosis (3.6%) from dose of 40 Gy in 5F and 30 Gy in 5F (after prior 30 Gy/10F). One patient (n = 2%) required fixation post-radiation due to progression of disease or symptoms. With median follow up 19.4 months, 1 and 2-year rates of local control were 84% and 69%, progression-free survival were 55% and 27%, and overall survival were 91% and 74%.

CONCLUSION

There was no significant association between patient or treatment characteristics and local control outcomes. Femur SBRT for oligometastatic disease control in well-selected patients was associated with good outcomes with minimal rates of acute and late toxicity. Further prospective study is warranted.

Radiation Treatment Preparation Safety Risk Prediction

PURPOSE/OBJECTIVE(S)

To determine the effect of delays in radiation treatment preparation task timeliness on reported safety events.

MATERIALS/METHODS

For 2022, all patients treated at four community-based radiation oncology clinics were included for analysis. Safety reports which occurred during treatment preparation tasks (i.e., between CT simulation and the first treatment) were included for this analysis. Patients with a reported safety event were the report cohort and those without were the control cohort. Treatment preparation tasks are completed sequentially and included contouring, treatment planning, Radiation Oncologist review, Medical Physicist review, Therapist quality check. At baseline, each task was scheduled a standard interval for completion based on treatment technique. The time taken to complete each task was captured using ARIA v16.0 Care Path module (Varian Medical Systems, Palo Alto, CA) and extracted through database query. For each task, two metrics were quantified: Task (1) Completion Timeliness: the time (hours) to complete each task, relative to the time allocated to each task. A negative value indicated more time taken than scheduled. (2) Overall Timeliness: specific task timeliness (hours) relative to overall timeliness for the whole Care Path. A negative value indicated the tasks were behind schedule. A student's t-test with an alpha of 0.05 was used to indicate significance.

RESULTS

Over the study period, 66 courses had a reported treatment preparation safety event (report) and 2690 did not (control). Techniques include 54% and 56% 3DCRT, 35% and 35% IMRT, 3% and 3% SRS, and 6% and 8% SBRT, for the report and control groups, respectively. Disease sites include breast, GU, GI, head and neck, CNS, thoracic, skin, secondary, gynecological, sarcoma, and heme. Table 1 displays the timeliness for each of the five tasks. Of the courses with safety events, overall timeliness was significantly behind the control group from the in contouring, treatment planning, Radiation Oncologist review, and Medical Physicist review. Courses with safety events took significantly more time than scheduled early in treatment preparation with a significant increase at treatment planning and significantly less time towards the end with the therapist quality check.

CONCLUSION

Patient courses with reported safety events had significantly longer treatment planning times, and as a result inadequate time to perform each downstream pre-treatment activity. The implication of this analysis is that a flag could be created to indicate risk of a safety event early in the treatment preparation process.

Association between radiation dose to organs at risk and acute patient reported outcome during radiation treatment for head and neck cancers

BACKGROUND

Associations between patient-reported outcomes and dose to organs at risk (OARs) may promote management and guide future investigations.

METHODS

We retrospectively evaluated PROs and OAR dose in head and neck (H&N) cancer.

RESULTS

In 169 patients, we identified weak associations between: "Difficulty swallowing/chewing" and increased mean RT dose to the oral cavity, larynx, pharyngeal constrictor muscles (PCM) and contralateral parotid; "choking/coughing" and larynx mean dose; "problems with mucus in mouth and throat" and oral cavity, contralateral parotid mean dose and parotid V30, contralateral submandibular gland and PCM mean dose; "difficulty with voice/speech" and oral cavity, contralateral parotid, contralateral submandibular gland and larynx mean dose; and "dry mouth" and ipsilateral submandibular gland, oral cavity and PCM mean dose.

CONCLUSION

We identified weak associations between PRO and dose to OARs-these data can guide on treatment management, patient counseling, and serve as a baseline for future investigations.

Coronary vasomotor dysfunction in cancer survivors treated with thoracic irradiation

BACKGROUND

We sought to test the hypothesis that thoracic radiation therapy (RT) is associated with impaired myocardial flow reserve (MFR), a measure of coronary vasomotor dysfunction.

METHODS

We retrospectively studied thirty-five consecutive patients (71% female, mean ± standard deviation (SD) age: 66 ± 11 years) referred clinically for positron emission tomography/computed tomography (PET/CT) myocardial perfusion imaging at a median (interquartile range, IQR) interval of 4.3 (2.1, 9.7) years following RT for a variety of malignancies. Radiation dose-volume histograms were generated for the heart and coronary arteries for each patient.

RESULTS

The median (IQR) of mean cardiac radiation doses was 12.0 (1.2, 24.2) Gray. There were significant inverse correlations between mean radiation dose and global MFR (MFRGlobal) and MFR in the left anterior descending artery territory (MFRLAD): Pearson's correlation coefficient = - .37 (P = .03) and - .38 (P = .03), respectively. For every one Gray increase in mean cardiac radiation dose, there was a mean ± standard error decrease of .02 ± .01 in MFRGlobal (P = .04) and MFRLAD (P = .03) after adjustment.

CONCLUSIONS

In patients with a history of RT clinically referred for cardiac stress PET, we found an inverse correlation between mean cardiac radiation dose and coronary vasomotor function.

Patient reported outcomes in patients with head and neck cancer treated with concurrent chemoradiation with weekly versus bolus cisplatin

BACKGROUND

Patient Reported Outcome (PRO) data comparing bolus (B-CP) with weekly (W-CP) cisplatin concurrent with radiation are lacking.

METHODS

We performed a retrospective study comparing PRO among 99 patients with head and neck radiation, 26% who received concurrent B-CP and 73% treated with W-CP.

RESULTS

W-CP patients had a higher Charlson comorbidity index (CCI) (P = .004). There were no differences in median cisplatin dose, PROs, percutaneous endoscopic gastrostomy (PEG) dependence or hospitalization between arms. Patients with a greater decline in their self-reported dysphagia score were more often PEG dependent at the end of radiation therapy (P = .03). There was also a trend toward PEG dependence with a higher maximum dysphagia score and greater change in aspiration score (P = .06). The maximum decline in white cell count and absolute neutrophil count were greater in the W-CP group (P = .04, P = .01).

CONCLUSION

Both B-CP and W-CP are well tolerated. PROs do not suggest a benefit to W-CP.

Pilot study of serial FLT and FDG-PET/CT imaging to monitor response to neoadjuvant chemoradiotherapy of esophageal adenocarcinoma: correlation with histopathologic response

OBJECTIVE

The aim of this prospective pilot study was to investigate the potential of serial FLT-PET/CT compared to FDG-PET/CT to provide an early indication of esophageal cancer response to concurrent neoadjuvant chemoradiation therapy.

METHODS

Five patients with biopsy-proven esophageal adenocarcinomas underwent neoadjuvant chemoradiation (Tx) prior to minimally invasive esophagectomy. The presence of residual tumor was classified histologically using the Mandard et al. criteria, categorizing patients as pathologic responders and non-responders. Participants underwent PET/CT imaging 1 h after intravenous administration of FDG and of FLT on two separate days within 48 h of each other. Each patient underwent a total of 3 scan "pairs": (1) pre-treatment, (2) during treatment, and (3) post-treatment. Image-based response to therapy was measured in terms of changes in SUVmax (ΔSUV) between pre- and post-therapeutic FLT- and FDG-PET scans. The PET imaging findings were correlated with the pathology results after surgery.

RESULTS

All tumors were FDG and FLT avid at baseline. Lesion FLT uptake was lower than with FDG. Neoadjuvant chemoradiation resulted in a reduction of tumor uptake of both radiotracers in pathological responders (n = 3) and non-responders (n = 2). While the difference in the reduction in mean tumor FLT uptake during Tx between responders (ΔSUV = - 55%) and non-responders (ΔSUV = - 29%) was significant (P = 0.007), for FDG it was not, [responders had a mean ΔSUV = - 39 vs. - 31% for non-responders (P = 0.74)]. The difference in the reduction in tumor FLT uptake at the end of treatment between responders (ΔSUV = - 62%) and non-responders (ΔSUV = - 57%) was not significant (P = 0.54), while for FDG there was a trend toward significance [ΔSUV of responders = - 74 vs. - 52% in non-responders (P = 0.06)].

CONCLUSION

The results of this prospective pilot study suggest that early changes in tumor FLT uptake may be better than FDG in predicting response of esophageal adenocarcinomas to neoadjuvant chemoradiation. These preliminary results support the need to corroborate the value of FLT-PET/CT in a larger cohort.

Radiation toxicity in patients with collagen vascular disease and intrathoracic malignancy treated with modern radiation techniques

BACKGROUND AND PURPOSE

There is concern that patients with collagen vascular disease (CVD) are at higher risk of developing radiation toxicity. We analyzed radiation toxicities in patients with intrathoracic malignancy and CVD treated using modern radiotherapy.

MATERIALS AND METHODS

This single-institution retrospective study included 31 patients with CVD and 825 patients without CVD treated from 1998 to 2014. Radiation esophagitis (RE) and radiation pneumonitis (RP) were scored by RTOG scales. RE was analyzed with logistic regression and RP with Cox regression.

RESULTS

CVD patients experienced similar grade ≥3 RE compared to control patients (23% vs. 19%, p = 0.64) but more grade ≥3 RP (26% vs. 10%, p = 0.01). There was no significant association between CVD subtype and toxicities. In multivariate analysis, CVD and lung V20 >30% were associated with grade ≥3 RP. We identified V20 ≤30%, V5 ≤50%, and MLD ≤18 Gy as dose thresholds in patients with CVD. CVD patients with mild severity disease and only 1 organ system involved were at low risk for RP.

CONCLUSIONS

Patients with CVD may be at higher risk of RP. However, CVD patients may be offered curative thoracic RT with particular attention to risk-reduction strategies and maintaining recommended dose constraints as described in this study.

Dose--volume effects on patient-reported acute gastrointestinal symptoms during chemoradiation therapy for rectal cancer

PURPOSE

Research on patient-reported outcomes (PROs) in rectal cancer is limited. We examined whether dose-volume parameters of the small bowel and large bowel were associated with patient-reported gastrointestinal (GI) symptoms during 5-fluorouracil (5-FU)-based chemoradiation treatment for rectal cancer.

METHODS AND MATERIALS

66 patients treated at the Brigham & Women's Hospital or Massachusetts General Hospital between 2006 and 2008 were included. Weekly during treatment, patients completed a questionnaire assessing severity of diarrhea, urgency, pain, cramping, mucus, and tenesmus. The association between dosimetric parameters and changes in overall GI symptoms from baseline through treatment was examined by using Spearman's correlation. Potential associations between these parameters and individual GI symptoms were also explored.

RESULTS

The amount of small bowel receiving at least 15 Gy (V15) was significantly associated with acute symptoms (p = 0.01), and other dosimetric parameters ranging from V5 to V45 also trended toward association. For the large bowel, correlations between dosimetric parameters and overall GI symptoms at the higher dose levels from V25 to V45 did not reach statistical significance (p = 0.1), and a significant association was seen with rectal pain from V15 to V45 (p < 0.01). Other individual symptoms did not correlate with small bowel or large bowel dosimetric parameters.

CONCLUSIONS

The results of this study using PROs are consistent with prior studies with physician-assessed acute toxicity, and they identify small bowel V15 as an important predictor of acute GI symptoms during 5-FU-based chemoradiation treatment. A better understanding of the relationship between radiation dosimetric parameters and PROs may allow physicians to improve radiation planning to optimize patient outcomes.

Evaluating FDG uptake changes between pre and post therapy respiratory gated PET scans

PURPOSE

Whole body (3D) and respiratory gated (4D) FDG-PET/CT scans performed pre-radiotherapy (pre-RT) and post-radiotherapy (post-RT) were analyzed to investigate the impact of 4D PET in evaluating 18F-fluorodeoxyglucose (FDG) uptake changes due to therapy, relative to traditional 3D PET.

METHODS AND MATERIALS

3D and 4D sequential FDG-PET/CT scans were acquired pre-RT and approximately one month post-RT for patients with non-small cell lung cancer (NSCLC). The lesions of high uptake targeted with radiotherapy were identified on the pre-RT scan of each patient. Each lesion on the 3D and each of the five phases of the 4D scan were analyzed using a region of interest (ROI). For each patient the ROIs of the pre-RT scans were used to locate the areas of initial FDG uptake on the post-RT scans following rigid registration. Post-RT ROIs were drawn and the FDG uptake was compared with that of the pre-RT scans.

RESULTS

Sixteen distinct lesions from 12 patients were identified and analyzed. Standardized uptake value (SUV) maxima were significantly higher (p-value <0.005) for the lesions as measured on the 4D compared to 3D PET. Comparison of serial pre and post-RT scans showed a mean 62% decrease in SUV with the 3D PET scan (range 36-89%), and a 67% decrease with the 4D PET scan (range 30-89%). The mean absolute difference in SUV change on 3D versus 4D scans was 4.9%, with a range 0-15% (p-value = 0.07).

CONCLUSIONS

Signal recovery with 4D PET results in higher SUVs when compared to standard 3D PET. Consequently, differences in the evaluation of SUV changes between pre and post-RT plans were observed. Such difference can have a significant impact in PET-based response assessment.

Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans

For PET/CT, fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D PET can reduce motion artifacts, though residual artifacts may persist depending on the CT dataset used for attenuation correction. We performed phantom studies to evaluate 4D PET images of targets near a density interface using three different methods for attenuation correction: a single 3D CT (3D CTAC), an averaged 4D CT (CINE CTAC), and a fully phase matched 4D CT (4D CTAC). A phantom was designed with two density regions corresponding to diaphragm and lung. An 8 mL sphere phantom loaded with 18F-FDG was used to represent a lung tumor and background FDG included at an 8:1 ratio. Motion patterns of sin(x) and sin4(x) were used for dynamic studies. Image data was acquired using a GE Discovery DVCT-PET/CT scanner. Attenuation correction methods were compared based on normalized recovery coefficient (NRC), as well as a novel quantity "fixed activity volume" (FAV) introduced in our report. Image metrics were compared to those determined from a 3D PET scan with no motion present (3D STATIC). Values of FAV and NRC showed significant variation over the motion cycle when corrected by 3D CTAC images. 4D CTAC- and CINE CTAC-corrected PET images reduced these motion artifacts. The amount of artifact reduction is greater when the target is surrounded by lower density material and when motion was based on sin4(x). 4D CTAC reduced artifacts more than CINE CTAC for most scenarios. For a target surrounded by water equivalent material, there was no advantage to 4D CTAC over CINE CTAC when using the sin(x) motion pattern. Attenuation correction using both 4D CTAC or CINE CTAC can reduce motion artifacts in regions that include a tissue interface such as the lung/diaphragm border. 4D CTAC is more effective than CINE CTAC at reducing artifacts in some, but not all, scenarios.

An independent dose calculation algorithm for MLC-based stereotactic radiotherapy

We have developed an algorithm to calculate dose in a homogeneous phantom for radiotherapy fields defined by multi-leaf collimator (MLC) for both static and dynamic MLC delivery. The algorithm was developed to supplement the dose algorithms of the commercial treatment planning systems (TPS). The motivation for this work is to provide an independent dose calculation primarily for quality assurance (QA) and secondarily for the development of static MLC field based inverse planning. The dose calculation utilizes a pencil-beam kernel. However, an explicit analytical integration results in a closed form for rectangular-shaped beamlets, defined by single leaf pairs. This approach reduces spatial integration to summation, and leads to a simple method of determination of model parameters. The total dose for any static or dynamic MLC field is obtained by summing over all individual rectangles from each segment which offers faster speed to calculate two-dimensional dose distributions at any depth in the phantom. Standard beam data used in the commissioning of the TPS was used as input data for the algorithm. The calculated results were compared with the TPS and measurements for static and dynamic MLC. The agreement was very good (<2.5%) for all tested cases except for very small static MLC sizes of 0.6 cm x 0.6 cm (<6%) and some ion chamber measurements in a high gradient region (<4.4%). This finding enables us to use the algorithm for routine QA as well as for research developments.

Variability Among Breast Radiation Oncologists in Delineation of the Postsurgical Lumpectomy Cavity

PURPOSE

Partial breast irradiation (PBI) is becoming more widely used. Accurate determination of the surgical lumpectomy cavity volume is more critical with PBI than with whole breast radiation therapy. We examined the interobserver variability in delineation of the lumpectomy cavity among four academic radiation oncologists who specialize in the treatment of breast cancer.

METHODS AND MATERIALS

Thirty-four lumpectomy cavities in 33 consecutive patients were evaluated. Each physician contoured the cavity and a 1.5-cm margin was added to define the planning target volume (PTV). A cavity visualization score (CVS) was assigned (1-5). To eliminate bias, the physician of record was eliminated from the analysis in all cases. Three measures of variability of the PTV were developed: average shift of the center of mass (COM), average percent overlap between the PTV of two physicians (PVO), and standard deviation of the PTV.

RESULTS

Of variables examined, pathologic resection volume was significantly correlated with CVS, with larger volumes more easily visualized. Shift of the COM decreased and PVO increased significantly as CVS increased. For CVS 4 and 5 cases, the average COM shift was 3 mm and 2 mm, respectively, and PVO was 77% and 87%, respectively. In multiple linear regression, pathologic diameter >4 cm and CVS > or =3 were significantly associated with smaller COM shift. When CVS was omitted from analysis, PVO was significantly larger with pathologic diameter > or =5 cm, days to planning <36, and older age.

CONCLUSIONS

Even among radiation oncologists who specialize in breast radiotherapy, there can be substantial differences in delineation of the postsurgical radiotherapy target volume. Large treatment margins may be prudent if the cavity is not clearly defined.

A dosimetric comparison of two multileaf collimator designs

We present the results of measurements designed to compare two different multileaf collimator (MLC) designs using a novel evaluation technique. The MLC designs evaluated were: a "single-focused" MLC (SF-MLC) mounted below the jaws, and a "double-focused" MLC, which is a complete replacement for the lower jaws. The ability of each MLC to conform isodose lines to a prescribed field edge (PFE) was evaluated using film dosimetry. Circular fields, centered on axis and off axis, were used because they produce a range of "angles of approach" between the MLC leaves and the PFE. They also have the advantage that for an ideal field shaping system the resulting isodoses are concentric perfect circles, a well-defined basis for evaluation. The amplitude of the oscillations of the 50% isodose line about the PFE and the penumbra width as determined by the 20%, 80%, and 90% isodose lines was examined. We observe that the 50% isodose line oscillates around the PFE with greater amplitude for SF-MLC. We attribute this, at least in part, to the rounded ends of the SF-MLC leaves. However, the SF-MLC has a noticeably sharper penumbra, which we attribute to its position further from the source. We conclude that these results are relevant for accurate dosimetric modeling of these devices.

A technique for optimization of digitally reconstructed radiographs of the chest in virtual simulation

INTRODUCTION

Virtual simulation (VS) of radiotherapy uses CT data. Digitally reconstructed radiographs (DRRs) are a critical element of this process, and the quality of these images is frequently suboptimal. We present techniques to improve DRR quality for clinical purposes. The results of two approaches to DRR optimization are presented.

METHODS AND MATERIALS

One approach to DRR optimization is to use traditional radiographs as a guide and to adjust the algorithm parameters based on image and objective contrast to produce images that more closely resemble traditional radiographs (Method 1). Another approach is to focus on the visibility of specific anatomic structures. Using this method, two DRR images are optimized manually by interactively adjusting reconstruction parameters, then they are combined into a single composite image (Method 2). DRRs for the chest region, generated using both methods, were evaluated by clinical staff based on usability for treatment verification and field definition.

RESULTS

Using Method 1, the resulting DRRs more closely resembled traditional radiographs. This technique allows DRR quality to be improved with little user interaction. These DRRs are generally adequate for clinical use, but not optimal for sites such as the chest. Images generated using Method 2 were considered clinically superior in terms of visibility of specific anatomic structures. These images also compare well with traditional radiographs, although they show an increased contrast level between bone and lower density structures.

CONCLUSION

Both Methods 1 and 2 can be used to improve DRR quality for clinical purposes. For the chest region, the additional effort required by Method 2 to achieve a more detailed image appears justified.

Beam shaping for conformal fractionated stereotactic radiotherapy: a modeling study

PURPOSE

The patient population treated with fractionated stereotactic radiotherapy (SRT) is significantly different than that treated with stereotactic radiosurgery (SRS). Generally, lesions treated with SRT are larger, less spherical, and located within critical regions of the central nervous system; hence, they offer new challenges to the treatment planner. Here a simple, cost effective, beam shaping system has been evaluated relative to both circular collimators and an ideal dynamically conforming system for effectiveness in providing conformal therapy for these lesions.

METHODS AND MATERIALS

We have modeled a simple system for conformal arc therapy using four independent jaws. The jaw positions and collimator angle are changed between arcs but held fixed for the duration of each arc. Eleven previously treated SRT cases have been replanned using this system. The rectangular jaw plans were then compared to the original treatment plans which used circular collimators. The plans were evaluated with respect to tissue sparing at 100%, 80%, 50%, and 20% of the prescription dose. A plan was also done for each tumor in which the beam aperture was continuously conformed to the beams eye view projection of the tumor. This was used as an ideal standard for conformal therapy in the absence of fluence modulation.

RESULTS

For tumors with a maximum extent of over 3.5 cm the rectangular jaw plans reduced the mean volume of healthy tissue involved at the prescription dose by 57% relative to the circular collimator plans. The ideal conformal plans offered no significant further improvement at the prescription dose. The relative advantage of the rectangular jaw plans decreased at lower isodoses so that at 20% of the prescription dose tissue involvement for the rectangular jaw plans was equivalent to that for the circular collimator plans. At these isodoses the ideal conformal plans gave substantially better tissue sparing.

CONCLUSION

A simple and economical field shaping device has been shown to provide all of the beam shaping advantage of a hypothetical ideal dynamically conforming system at the prescription level. This system may be immediately implemented in the clinic. It offers a substantial advantage over the currently used circular collimators in the high dose region with equivalent performance in the low dose region.

A numerical simulation of organ motion and daily setup uncertainties: implications for radiation therapy

PURPOSE

In radiotherapy planning, the clinical target volume (CTV) is typically enlarged to create a planning target volume (PTV) that accounts for uncertainties due to internal organ and patient motion as well as setup error. Margin size clearly determines the volume of normal tissue irradiated, yet in practice it is often given a set value in accordance with a clinical precedent from which variations are rare. The (CTV/PTV) formalism does not account for critical structure dose. We present a numerical simulation to assess (CTV) coverage and critical organ dose as a function of treatment margins in the presence of organ motion and physical setup errors. An application of the model to the treatment of prostate cancer is presented, but the method is applicable to any site where normal tissue tolerance is a dose-limiting factor.

METHODS AND MATERIALS

A Monte Carlo approach was used to simulate the cumulative effect of variation in overall tumor position, for individual treatment fractions, relative to a fixed distribution of dose. Distributions of potential dose-volume histograms (DVHs), for both tumor and normal tissues, are determined that fully quantify the stochastic nature of radiotherapy delivery. We introduce the concept of Probability of Prescription Dose (PoPD) isosurfaces as a tool for treatment plan optimization. Outcomes resulting from current treatment planning methods are compared with proposed techniques for treatment optimization. The standard planning technique of relatively large uniform margins applied to the CTV, in the beam's eye view (BEV), was compared with three other treatment strategies: (a) reduced uniform margins, (b) nonuniform margins adjusted to maximize normal tissue sparing, and (c) a reduced margin plan in which nonuniform fluence profiles were introduced to compensate for potential areas of reduced dose.

RESULTS

Results based on 100 simulated full course treatments indicate that a 10 mm CTV to PTV margin, combined with an additional 5 mm dosimetric margin, provides adequate CTV coverage in the presence of known treatment uncertainties. Nonuniform margins can be employed to reduce dose delivered to normal tissues while preserving CTV coverage. Nonuniform fluence profiles can also be used to further reduce dose delivered to normal tissues, though this strategy does result in higher dose levels delivered to a small volume of the CTV and normal tissues.

CONCLUSIONS

Monte Carlo-based treatment simulation is an effective means of assessing the impact of organ motion and daily setup error on dose delivery via external beam radiation therapy. Probability of Prescription Dose (PoPD) isosurfaces are a useful tool for the determination of nonuniform beam margins that reduce dose delivered to critical organs while preserving CTV dose coverage. Nonuniform fluence profiles can further alter critical organ dose with potential therapeutic benefits. Clinical consequences of this latter approach can only be assessed via clinical trials.