The Importance of Quality Assurance in Radiation Oncology Clinical Trials

Clinical trials have been the center of progress in modern medicine. In oncology, we are fortunate to have a structure in place through the National Clinical Trials Network (NCTN). The NCTN provides the infrastructure and a forum for scientific discussion to develop clinical concepts for trial design. The NCTN also provides a network group structure to administer trials for successful trial management and outcome analyses. There are many important aspects to trial design and conduct. Modern trials need to ensure appropriate trial conduct and secure data management processes. Of equal importance is the quality assurance of a clinical trial. If progress is to be made in oncology clinical medicine, investigators and patient care providers of service need to feel secure that trial data is complete, accurate, and well-controlled in order to be confident in trial analysis and move trial outcome results into daily practice. As our technology has matured, so has our need to apply technology in a uniform manner for appropriate interpretation of trial outcomes. In this article, we review the importance of quality assurance in clinical trials involving radiation therapy. We will include important aspects of institution and investigator credentialing for participation as well as ongoing processes to ensure that each trial is being managed in a compliant manner. We will provide examples of the importance of complete datasets to ensure study interpretation. We will describe how successful strategies for quality assurance in the past will support new initiatives moving forward.

Retinopathy, Optic Neuropathy, and Cataract in Childhood Cancer Survivors Treated With Radiation Therapy: A PENTEC Comprehensive Review

PURPOSE

Few reports describe the risks of late ocular toxicities after radiation therapy (RT) for childhood cancers despite their effect on quality of life. The Pediatric Normal Tissue Effects in the Clinic (PENTEC) ocular task force aims to quantify the radiation dose dependence of select late ocular adverse effects. Here, we report results concerning retinopathy, optic neuropathy, and cataract in childhood cancer survivors who received cranial RT.

METHODS AND MATERIALS

A systematic literature search was performed using the PubMed, MEDLINE, and Cochrane Library databases for peer-reviewed studies published from 1980 to 2021 related to childhood cancer, RT, and ocular endpoints including dry eye, keratitis/corneal injury, conjunctival injury, cataract, retinopathy, and optic neuropathy. This initial search yielded abstracts for 2947 references, 269 of which were selected as potentially having useful outcomes and RT data. Data permitting, treatment and outcome data were used to generate normal tissue complication probability models.

RESULTS

We identified sufficient RT data to generate normal tissue complication probability models for 3 endpoints: retinopathy, optic neuropathy, and cataract formation. Based on limited data, the model for development of retinopathy suggests 5% and 50% risk of toxicity at 42 and 62 Gy, respectively. The model for development of optic neuropathy suggests 5% and 50% risk of toxicity at 57 and 64 Gy, respectively. More extensive data were available to evaluate the risk of cataract, separated into self-reported versus ophthalmologist-diagnosed cataract. The models suggest 5% and 50% risk of self-reported cataract at 12 and >40 Gy, respectively, and 50% risk of ophthalmologist-diagnosed cataract at 9 Gy (>5% long-term risk at 0 Gy in patients treated with chemotherapy only).

CONCLUSIONS

Radiation dose effects in the eye are inadequately studied in the pediatric population. Based on limited published data, this PENTEC comprehensive review establishes relationships between RT dose and subsequent risks of retinopathy, optic neuropathy, and cataract formation.

Quality improvements in radiation oncology clinical trials

Clinical trials have become the primary mechanism to validate process improvements in oncology clinical practice. Over the past two decades there have been considerable process improvements in the practice of radiation oncology within the structure of a modern department using advanced technology for patient care. Treatment planning is accomplished with volume definition including fusion of multiple series of diagnostic images into volumetric planning studies to optimize the definition of tumor and define the relationship of tumor to normal tissue. Daily treatment is validated by multiple tools of image guidance. Computer planning has been optimized and supported by the increasing use of artificial intelligence in treatment planning. Informatics technology has improved, and departments have become geographically transparent integrated through informatics bridges creating an economy of scale for the planning and execution of advanced technology radiation therapy. This serves to provide consistency in department habits and improve quality of patient care. Improvements in normal tissue sparing have further improved tolerance of treatment and allowed radiation oncologists to increase both daily and total dose to target. Radiation oncologists need to define a priori dose volume constraints to normal tissue as well as define how image guidance will be applied to each radiation treatment. These process improvements have enhanced the utility of radiation therapy in patient care and have made radiation therapy an attractive option for care in multiple primary disease settings. In this chapter we review how these changes have been applied to clinical practice and incorporated into clinical trials. We will discuss how the changes in clinical practice have improved the quality of clinical trials in radiation therapy. We will also identify what gaps remain and need to be addressed to offer further improvements in radiation oncology clinical trials and patient care.

Radiation Oncology: Future Vision for Quality Assurance and Data Management in Clinical Trials and Translational Science

The future of radiation oncology is exceptionally strong as we are increasingly involved in nearly all oncology disease sites due to extraordinary advances in radiation oncology treatment management platforms and improvements in treatment execution. Due to our technology and consistent accuracy, compressed radiation oncology treatment strategies are becoming more commonplace secondary to our ability to successfully treat tumor targets with increased normal tissue avoidance. In many disease sites including the central nervous system, pulmonary parenchyma, liver, and other areas, our service is redefining the standards of care. Targeting of disease has improved due to advances in tumor imaging and application of integrated imaging datasets into sophisticated planning systems which can optimize volume driven plans created by talented personnel. Treatment times have significantly decreased due to volume driven arc therapy and positioning is secured by real time imaging and optical tracking. Normal tissue exclusion has permitted compressed treatment schedules making treatment more convenient for the patient. These changes require additional study to further optimize care. Because data exchange worldwide have evolved through digital platforms and prisms, images and radiation datasets worldwide can be shared/reviewed on a same day basis using established de-identification and anonymization methods. Data storage post-trial completion can co-exist with digital pathomic and radiomic information in a single database coupled with patient specific outcome information and serve to move our translational science forward with nimble query elements and artificial intelligence to ask better questions of the data we collect and collate. This will be important moving forward to validate our process improvements at an enterprise level and support our science. We have to be thorough and complete in our data acquisition processes, however if we remain disciplined in our data management plan, our field can grow further and become more successful generating new standards of care from validated datasets.

Practice patterns of pediatric total body irradiation techniques: A Children's Oncology Group survey

PURPOSE

The aim of this study was to examine current practice patterns in pediatric total body irradiation (TBI) techniques among xxx member institutions.

METHODS AND MATERIALS

Between Nov 2019 and Feb 2020 a questionnaire, containing 52 questions related to the technical aspects of TBI was sent to medical physicists at 152 xxx institutions. The questions were designed to obtain technical information on commonly used TBI treatment techniques. Another set of 9 questions related to the clinical management of patients undergoing TBI was sent to 152 xxx member radiation oncologists at the same institutions.

RESULTS

Twelve institutions were excluded because TBI was not performed in their institutions. A total of 88 physicists from 88 institutions (63% response rate) and 96 radiation oncologists from 96 institutions responded (69% response rate). The AP/PA technique was the most common (49 institutions - 56%); 44 institutions (50%) used the lateral technique and 14 institutions (16%) used volumetric modulated arc therapy (VMAT)/Tomotherapy. Mid-plane dose rates of 6-15 cGy/min were most commonly used. The most common specification for lung dose was the mid lung dose for both AP/PA (71%) and lateral (63%) techniques. All physician responders agreed with the need to refine current TBI techniques and 79% supported the investigation of new TBI techniques to further lower the lung dose.

CONCLUSION

There is no consistency in the practice patterns, methods for dose measurement and reporting of TBI doses among xxx institutions. The lack of a standardization precludes meaningful correlation between TBI doses and clinical outcomes including disease control and normal tissue toxicity. The xxx radiation oncology discipline is currently undertaking several steps to standardize the practice and dose reporting of pediatric TBI using detailed questionnaires and phantom-based credentialing for all xxx centers.

Advances in radiotherapy technology for pediatric cancer patients and roles of medical physicists: COG and SIOP Europe perspectives

Over the last two decades, rapid technological advances have dramatically changed radiation delivery to children with cancer, enabling improved normal-tissue sparing. This article describes recent advances in photon and proton therapy technologies, image-guided patient positioning, motion management, and adaptive therapy that are relevant to pediatric cancer patients. For medical physicists who are at the forefront of realizing the promise of technology, challenges remain with respect to ensuring patient safety as new technologies are implemented with increasing treatment complexity. The contributions of medical physicists to meeting these challenges in daily practice, in the conduct of clinical trials, and in pediatric oncology cooperative groups are highlighted. Representing the perspective of the physics committees of the Children's Oncology Group (COG) and the European Society for Paediatric Oncology (SIOP Europe), this paper provides recommendations regarding the safe delivery of pediatric radiotherapy. Emerging innovations are highlighted to encourage pediatric applications with a view to maximizing the therapeutic ratio.

Quality assurance in radiation oncology

The Children's Oncology Group (COG) has a strong quality assurance (QA) program managed by the Imaging and Radiation Oncology Core (IROC). This program consists of credentialing centers and providing real-time management of each case for protocol compliant target definition and radiation delivery. In the International Society of Pediatric Oncology (SIOP), the lack of an available, reliable online data platform has been a challenge and the European Society for Paediatric Oncology (SIOPE) quality and excellence in radiotherapy and imaging for children and adolescents with cancer across Europe in clinical trials (QUARTET) program currently provides QA review for prospective clinical trials. The COG and SIOP are fully committed to a QA program that ensures uniform execution of protocol treatments and provides validity of the clinical data used for analysis.

Practice patterns and recommendations for pediatric image-guided radiotherapy: A Children's Oncology Group report

This report by the Radiation Oncology Discipline of Children's Oncology Group (COG) describes the practice patterns of pediatric image-guided radiotherapy (IGRT) based on a member survey and provides practice recommendations accordingly. The survey comprised of 11 vignettes asking clinicians about their recommended treatment modalities, IGRT preferences, and frequency of in-room verification. Technical questions asked physicists about imaging protocols, dose reduction, setup correction, and adaptive therapy. In this report, the COG Radiation Oncology Discipline provides an IGRT modality/frequency decision tree and the expert guidelines for the practice of ionizing image guidance in pediatric radiotherapy patients.

An in-silico quality assurance study of contouring target volumes in thoracic tumors within a cooperative group setting

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We aimed at quantifying inter-observer Pancoast tumors delineation variability.

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Experts’ delineations were used to define ground truth.

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Other observers’ delineations were compared against ground truth.

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High degree of variability was noted for most target volumes except GTV_P.

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This unveils potentials for protocol modification for future IMRT studies.

Introduction

Target delineation variability is a significant technical impediment in multi-institutional trials which employ intensity modulated radiotherapy (IMRT), as there is a real potential for clinically meaningful variances that can impact the outcomes in clinical trials. The goal of this study is to determine the variability of target delineation among participants from different institutions as part of Southwest Oncology Group (SWOG) Radiotherapy Committee’s multi-institutional in-silico quality assurance study in patients with Pancoast tumors as a “dry run” for trial implementation.

Methods

CT simulation scans were acquired from four patients with Pancoast tumor. Two patients had simulation 4D-CT and FDG-FDG PET-CT while two patients had 3D-CT and FDG-FDG PET-CT. Seventeen SWOG-affiliated physicians independently delineated target volumes defined as gross primary and nodal tumor volumes (GTV_P & GTV_N), clinical target volume (CTV), and planning target volume (PTV).

Six board-certified thoracic radiation oncologists were designated as the ‘Experts’ for this study. Their delineations were used to create a simultaneous truth and performance level estimation (STAPLE) contours using ADMIRE software (Elekta AB, Sweden 2017). Individual participants’ contours were then compared with Experts’ STAPLE contours.

Results

When compared to the Experts’ STAPLE, GTV_P had the best agreement among all participants, while GTV_N showed the lowest agreement among all participants. There were no statistically significant differences in all studied parameters for all TVs for cases with 4D-CT versus cases with 3D-CT simulation scans.

Conclusions

High degree of inter-observer variation was noted for all target volume except for GTV_P, unveiling potentials for protocol modification for subsequent clinically meaningful improvement in target definition. Various similarity indices exist that can be used to guide multi-institutional radiotherapy delineation QA credentialing.

The Children's Oncology Group Radiation Oncology Discipline: 15 Years of Contributions to the Treatment of Childhood Cancer

PURPOSE

Our aim was to review the advances in radiation therapy for the management of pediatric cancers made by the Children's Oncology Group (COG) radiation oncology discipline since its inception in 2000.

METHODS AND MATERIALS

The various radiation oncology disease site leaders reviewed the contributions and advances in pediatric oncology made through the work of the COG. They have presented outcomes of relevant studies and summarized current treatment policies developed by consensus from experts in the field.

RESULTS

The indications and techniques for pediatric radiation therapy have evolved considerably over the years for virtually all pediatric tumor types, resulting in improved cure rates together with the potential for decreased treatment-related morbidity and mortality.

CONCLUSIONS

The COG radiation oncology discipline has made significant contributions toward the treatment of childhood cancer. Our discipline is committed to continuing research to refine and modernize the use of radiation therapy in current and future protocols with the goal of further improving the cure rates and quality of life of children with cancer.

The impact of protocol assignment for older adolescents with hodgkin lymphoma

BACKGROUND AND PURPOSE

Hodgkin lymphoma (HL) treatment has evolved to reduce or avoid radiotherapy (RT) dose and volume and minimize the potential for late effects. Some older adolescents are treated on adult protocols. The purpose of this study is to examine the protocol assignment of older adolescents and its impact on radiation dose to relevant thoracic structures.

MATERIALS AND METHODS

Cooperative group data were reviewed and 12 adolescents were randomly selected from a pediatric HL protocol. Treatment plans were generated per one pediatric and two adult protocols. Dose volume histograms for heart, lung, and breast allowed comparison of radiation dose to these sites across these three protocols.

RESULTS

A total of 15.2% of adolescents were treated on adult HL protocols and received significantly higher radiation dosage to heart and lung compared to pediatric HL protocols. Adolescents treated on either pediatric or adult protocols received similar RT dose to breast.

CONCLUSION

Older adolescents treated on adult HL protocols received higher RT dose to thoracic structures except breast. Level of nodal involvement may impact overall RT dose to breast. The impact of varying field design and RT dose on survival, local, and late effects needs further study for this vulnerable age group. Adolescents, young adults, Hodgkin lymphoma, RT, clinical trials.

Future vision for the quality assurance of oncology clinical trials

The National Cancer Institute clinical cooperative groups have been instrumental over the past 50 years in developing clinical trials and evidence-based process improvements for clinical oncology patient care. The cooperative groups are undergoing a transformation process as we further integrate molecular biology into personalized patient care and move to incorporate international partners in clinical trials. To support this vision, data acquisition and data management informatics tools must become both nimble and robust to support transformational research at an enterprise level. Information, including imaging, pathology, molecular biology, radiation oncology, surgery, systemic therapy, and patient outcome data needs to be integrated into the clinical trial charter using adaptive clinical trial mechanisms for design of the trial. This information needs to be made available to investigators using digital processes for real-time data analysis. Future clinical trials will need to be designed and completed in a timely manner facilitated by nimble informatics processes for data management. This paper discusses both past experience and future vision for clinical trials as we move to develop data management and quality assurance processes to meet the needs of the modern trial.

Credentialing for participation in clinical trials

The National Cancer Institute (NCI) clinical cooperative groups have been instrumental over the past 50 years in developing clinical trials and evidence-based clinical trial processes for improvements in patient care. The cooperative groups are undergoing a transformation process to launch, conduct, and publish clinical trials more rapidly. Institutional participation in clinical trials can be made more efficient and include the expansion of relationships with international partners. This paper reviews the current processes that are in use in radiation therapy trials and the importance of maintaining effective credentialing strategies to assure the quality of the outcomes of clinical trials. The paper offers strategies to streamline and harmonize credentialing tools and processes moving forward as the NCI undergoes transformative change in the conduct of clinical trials.

Results of a multi-institutional benchmark test for cranial CT/MR image registration

PURPOSE

Variability in computed tomography/magnetic resonance imaging (CT/MR) cranial image registration was assessed using a benchmark case developed by the Quality Assurance Review Center to credential institutions for participation in Children's Oncology Group Protocol ACNS0221 for treatment of pediatric low-grade glioma.

METHODS AND MATERIALS

Two DICOM image sets, an MR and a CT of the same patient, were provided to each institution. A small target in the posterior occipital lobe was readily visible on two slices of the MR scan and not visible on the CT scan. Each institution registered the two scans using whatever software system and method it ordinarily uses for such a case. The target volume was then contoured on the two MR slices, and the coordinates of the center of the corresponding target in the CT coordinate system were reported. The average of all submissions was used to determine the true center of the target.

RESULTS

Results are reported from 51 submissions representing 45 institutions and 11 software systems. The average error in the position of the center of the target was 1.8 mm (1 standard deviation = 2.2 mm). The least variation in position was in the lateral direction. Manual registration gave significantly better results than did automatic registration (p = 0.02).

CONCLUSION

When MR and CT scans of the head are registered with currently available software, there is inherent uncertainty of approximately 2 mm (1 standard deviation), which should be considered when defining planning target volumes and PRVs for organs at risk on registered image sets.

Processes for quality improvements in radiation oncology clinical trials

Quality assurance in radiotherapy (RT) has been an integral aspect of cooperative group clinical trials since 1970. In early clinical trials, data acquisition was nonuniform and inconsistent and computational models for radiation dose calculation varied significantly. Process improvements developed for data acquisition, credentialing, and data management have provided the necessary infrastructure for uniform data. With continued improvement in the technology and delivery of RT, evaluation processes for target definition, RT planning, and execution undergo constant review. As we move to multimodality image-based definitions of target volumes for protocols, future clinical trials will require near real-time image analysis and feedback to field investigators. The ability of quality assurance centers to meet these real-time challenges with robust electronic interaction platforms for imaging acquisition, review, archiving, and quantitative review of volumetric RT plans will be the primary challenge for future successful clinical trials.

Preliminary results of a phase I/II study of HDR brachytherapy alone for T1/T2 breast cancer

PURPOSE

To investigate the feasibility, toxicity, cosmetic outcome, and local control of high-dose-rate (HDR) brachytherapy alone without whole breast external beam irradiation for early-stage breast carcinoma.

METHODS AND MATERIALS

Between June 1997 and August 1999, 32 women diagnosed with a total of 33 AJCC Stage I/II breast carcinomas underwent surgical breast excision and postoperative irradiation using HDR brachytherapy interstitial implantation as part of a multi-institutional clinical Phase I/II protocol. Eligible patients included those with T1, T2, N0, N1 (< or =3 nodes positive), and M0 tumors of nonlobular histologic features with negative surgical margins, no extracapsular lymph node extension, and a negative postexcision mammogram. Brachytherapy catheters were placed at the initial excision, reexcision, or either sentinel or full-axillary sampling. Direct visualization, surgical clips, and ultrasound and/or CT scan assisted in the delineation of the target volume, defined as the excision cavity plus a 2-cm margin. High-activity 192Ir (3-10 Ci) was used to deliver 340 cGy/fraction, 2 fractions/d, for 5 consecutive days, to a total dose of 34 Gy to the target volume. Source position and dwell times were calculated using standard volume optimization techniques.

RESULTS

The median follow-up of all patients was 33 months, and the mean patient age was 63 years. The mean tumor size was 1.3 cm, and 55% had an extensive intraductal component. Three patients had positive axillary nodes. Two patients experienced moderate perioperative pain that required narcotic analgesics. No peri- or postoperative infections occurred. No wound healing problems and no significant skin reactions related to the implant developed. The Radiation Therapy Oncology Group late radiation morbidity scoring scheme was applied to the entire 33-case cohort. In the assessment of the skin, 30 cases were Grade 0-1 and 3 cases were Grade 2. Subcutaneous toxicity was scored as 11 patients with Grade 0, 3 with Grade 1, 8 with Grade 2, 3 with Grade 3, and 8 with Grade 4. Clinically evident fat necrosis occurred in 8 patients at a median of 7.5 months after HDR brachytherapy completion. The only variables significantly associated with Grade 3-4 toxicity were the number of source dwell positions and the volume of tissue encompassed by the prescription isodose shell. The global cosmetic scores after a minimum of 18 months' follow-up were 0 cases with poor, 4 with fair, 5 with good, and 24 with excellent scores. One case of ipsilateral breast tumor recurrence was diagnosed 23 months after HDR brachytherapy, for a 4-year actuarial recurrence rate of 3%. This failure appeared to be a new primary tumor, because it was histologically distinct from the initial tumor and was located 9 cm from the initial tumor bed and 3 cm from the edge of the implant volume.

CONCLUSION

Radiotherapy of the tumor bed alone with HDR interstitial brachytherapy is associated with a 33% incidence of Grade 3-4 s.c. toxicity, but with generally favorable overall cosmetic results. The risk of toxicity appears to be primarily related to the implant volume. With limited follow-up, the incidence of ipsilateral breast tumor recurrence was low.

A method for checking high dose rate treatment times for vaginal applicators

A method is presented for checking the treatment time calculation for high dose rate (HDR) vaginal cylinder treatments. The method represents an independent check of the HDR planning system and can take into account nonuniform isodose line coverage around the cylinder. Only the air kerma strength of the source and information that is available from the written directive are required. The maximum discrepancy for a representative set of cylinder plans done on a Nucletron unit was 5%. A working HTML JavaScript program is included in the Appendix.

Clinically evident fat necrosis in women treated with high-dose-rate brachytherapy alone for early-stage breast cancer

PURPOSE

To investigate the incidence of and variables associated with clinically evident fat necrosis in women treated on a protocol of high-dose-rate (HDR) brachytherapy alone without external-beam whole-breast irradiation for early-stage breast carcinoma.

METHODS AND MATERIALS

From 6/1997 until 8/1999, 30 women diagnosed with Stage I or II breast carcinoma underwent surgical excision and postoperative irradiation via HDR brachytherapy implant as part of a multi-institutional clinical Phase I/II protocol. Patients eligible included those with T1, T2, N0, N1 (< or = 3 nodes positive), M0 tumors of nonlobular histology with negative surgical margins, no extracapsular lymph-node extension, and a negative postexcision mammogram. Brachytherapy catheters were placed at the initial excision, re-excision, or at the time of axillary sampling. Direct visualization, surgical clips, ultrasound, or CT scans assisted in delineating the target volume defined as the excision cavity plus 2-cm margin. High activity (192)Ir (3-10 Ci) was used to deliver 340 cGy per fraction, 2 fractions per day, for 5 consecutive days to a total dose of 34 Gy to the target volume. Source position and dwell times were calculated using standard volume optimization techniques. Dosimetric analyses were performed with three-dimensional postimplant dose and volume reconstructions. The median follow-up of all patients was 24 months (range, 12-36 months).

RESULTS

Eight patients (crude incidence of 27%) developed clinically evident fat necrosis postimplant in the treated breast. Fat necrosis was determined by clinical presentation including pain and swelling in the treated volume, computed tomography, and/or biopsy. All symptomatic patients (7 of 8 cases) were successfully treated with 3 to 12 months of conservative management. Continuous variables that were found to be associated significantly with fat necrosis included the number of source dwell positions (p = 0.04), and the volume of tissue which received fractional doses of 340 cGy, 510 cGy, and 680 cGy (p = 0.03, p = 0.01, and p = 0.01, respectively). Other continuous variables including patient age, total excised tissue volume, tumor size, number of catheters, number of days the catheters were in place, planar separation, dose homogeneity index (DHI), and uniformity index (UI) were not significant. Discrete variables including the presence/absence of DCIS, sentinel versus full axillary nodal assessment, receptor status, presence/absence of diabetes, and the use of chemotherapy or hormone therapy were not found to have a significant association with the risk of fat necrosis.

CONCLUSIONS

In this study of HDR brachytherapy of the breast tumor excision cavity plus margin, treatment was planned and delivered in accordance with the dosimetric parameters of the protocol resulting in a high degree of target volume dose homogeneity. Nonetheless, at a median follow-up of 24 months, a high rate of clinically definable fat necrosis occurred. The overall implant volume as reflected in the number of source dwell positions and the volume of breast tissue receiving fractional doses of 340, 510, and 680 cGy were significantly associated with fat necrosis. Future dosimetric optimization algorithms for HDR breast brachytherapy will need to include these factors to minimize the risk of fat necrosis.

Cosmetic outcome in patients receiving an interstitial implant as part of breast-conservation therapy

PURPOSE

To study factors related to breast cosmetic outcome in patients treated with an interstitial implant as part of breast-conservation therapy.

MATERIALS AND METHODS

One hundred fifty-six patients with stage I or II breast carcinoma who received 50 Gy of external-beam irradiation followed by a 20-Gy interstitial boost were examined. The dose homogeneity index (DHI) was calculated for each evaluable implant and was examined in light of other patient-, treatment-, and tumor-related variables previously demonstrated to affect cosmesis.

RESULTS

Of the variables examined, both the DHI (P = .021) and the total excision volume (P = .019) were significantly related to cosmetic outcome (excellent vs less than excellent) in a univariate model. In the multivariate analysis, only the total excision volume remained significant (P = .032). The mean total excision volume +/- SD in patients with excellent cosmetic outcome (81.8 cm3 +/- 84.0) was significantly less than that in patients with less than excellent cosmetic outcome (120 cm3 +/- 84). The probability of excellent cosmetic outcome linearly increased with an increase in DHI. The mean DHI was 0.74 +/- 0.12 for the cases with excellent cosmetic outcome and 0.68 +/- 0.10 for those with less than excellent cosmetic outcome.

CONCLUSION

To achieve optimal cosmesis, DHI should be maximized. The volume of tissue removed, however, remains the most significant determinant.

A technique for accurate planning of stereotactic brain implants prior to head ring fixation

PURPOSE

A two-step procedure is described for accurate planning of stereotactic brain implants prior to head-ring fixation.

METHODS AND MATERIALS

Approximately 2 weeks prior to implant a CT scan without the head ring is performed for treatment-planning purposes. An entry point and a reference point, both marked with barium and later tattooed, facilitate planning and permit correlation of the images with a later CT scan. A plan is generated using a conventional treatment-planning system to determine the number and activity of I-125 seeds required and the position of each catheter. I-125 seed anisotropy is taken into account by means of a modification to the treatment planning program. On the day of the implant a second CT scan is performed with the head ring affixed to the skull and with the same points marked as in the previous scan. The planned catheter coordinates are then mapped into the coordinate system of the second CT scan by means of a manual translational correction and a computer-calculated rotational correction derived from the reference point coordinates in the two scans.

RESULTS

The rotational correction algorithm was verified experimentally in a Rando phantom before it was used clinically. For analysis of the results with individual patients a third CT scan is performed 1 day following the implant and is used for calculating the final dosimetry.

CONCLUSION

The technique that is described has two important advantages: 1) the number and activity of seeds required can be accurately determined in advance; and 2) sufficient time is allowed to derive the best possible plan.

Factors determining outcome in patients treated with interstitial implantation as a radiation boost for breast conservation therapy

PURPOSE

To evaluate the relative utility of interstitial implant as a technique for tumor bed dose escalation and assess technical factors related to outcome.

METHODS AND MATERIALS

From 1982-1994, a prospectively applied institutional policy of margin-directed boost dose escalation to the tumor bed was followed whereby interstitial implantation was commonly employed for a final margin status (FMS) < or = 2 mm. There were 509 treated breasts, of which 127 received an implant boost. For purposes of comparison, cases were broadly classed as "implant" (all FMS < or = 2 mm) and "nonimplant" (FMS < or = 2 mm or FMS > 2 mm). The implant target volume was determined at completion of whole breast irradiation by clinical assessment. All implants were constructed in accordance with a preplanning algorithm designed to maximize dose homogeneity within a prescription isodose goal of 0.50 Gy/h for 40 h. Local control and cosmetic outcome were evaluated with respect to extent of tumor, histopathology, FMS, extent of surgery, and systemic adjuvant therapy. Implant quality was assessed using four calculated parameters: strand separation quotient (SSQ), planar separation quotient (PSQ), global separation quotient (GSQ), and dose homogeneity index (DHI). The mean implant volume was 48.3 +/- 20 cc, the mean prescribed dose rate was 0.46 +/- 0.08 Gy/h, and the mean total implant dose was 19.94 +/- 1.52 Gy.

RESULTS

Cosmetic outcome was good/excellent in 90% of implant and 83% of all nonimplant cases, which was not statistically different. Cosmesis was significantly superior with implant when compared to nonimplant cases receiving an external boost of 20 Gy. Logistic regression analyses of implant cases revealed that reexcision volume and decreased DHI were associated with adverse cosmesis. There were 10 local failures in the implanted patients (4 within the prescribed isodose volume, 5 at the periphery, and 1 elsewhere in the breast). The local failure rate at 5 and 7 years in the implanted group was 3.9 and 9.0%, respectively, compared to nonimplant cases with a margin < or = 2 mm of 3.2 and 3.2%, respectively. These differences were not significant. The crude local failure rate in patients with an associated DCIS component was 12% a compared to 3% in patients with pure invasive histology (p = 0.06). A proportional hazards survival model revealed a significant association of local failure with the performance of a reexcision and young age.

CONCLUSION

We conclude that interstitial implant boost for breast conserving irradiation is associated with cosmesis that is superior than the same nominal dose of external beam boost, although this is highly dependent upon the technical quality of the source position and the relative uniformity of dose deposition. Breast implantation results in a rate of local control no better than dose-matched external beam boost in patients with a final margin < or = 2 mm. Local control with implantation might be further enhanced by increasing implant volume and/or improved target localization.

Algorithms for the process management of sealed source brachytherapy

Incidents and misadministrations suggest that brachytherapy may benefit from clarification of the quality management program and other mandates of the U.S. Nuclear Regulatory Commission. To that end, flowcharts of step by step subprocesses were developed and formatted with dedicated software. The overall process was similarly organized in a complex flowchart termed a general process map. Procedural and structural indicators associated with each flowchart and map were critiqued and pre-existing documentation was revised. "Step-regulation tables" were created to refer steps and subprocesses to Nuclear Regulatory Commission rules and recommendations in their sequences of applicability. Brachytherapy algorithms were specified as programmable, recursive processes, including therapeutic dose determination and monitoring doses to the public. These algorithms are embodied in flowcharts and step-regulation tables. A general algorithm is suggested as a template from which other facilities may derive tools to facilitate process management of sealed source brachytherapy.

The use of scattering foil compensators in electron beam therapy

PURPOSE

This study was undertaken to show that scattering foils could be used as electron beam compensators.

METHODS AND MATERIALS

Two scattering foils were designed to improve the dose homogeneity when a curved surface is irradiated with electrons. One scattering foil, constructed of mylar, was designed for use with a single 6 MeV electron field. The second scattering foil, constructed of lead, was designed to homogenize the dose along the matchline of two abutting electron fields. Measurements with the second compensator were made at energies of 6, 9, and 12 MeV. The compensators were mounted over the topmost opening of the electron cone. A simple method for modeling the effect of the second compensator using a conventional treatment planning system was also evaluated.

RESULTS

When the mylar compensator was placed atop the 25 x 25 cm cone and a Rando phantom irradiated with 6 MeV electrons, the dose at the field edges was increased by about 10%. Use of the lead foil compensator for two abutting fields gave a highly uniform dose along the matchline, without perturbing the isodoses at depth or at the other field edges. Measured hot spots in the Rando phantom for 6 and 9 MeV electrons were 104 and 108%, respectively. The effect of the lead foil compensator was successfully modeled on a conventional treatment planning system by summing beams of different field sizes.

CONCLUSIONS

Both compensators were effective in improving the dose homogeneity within the target volume.

An isodose shift technique for obliquely incident electron beams

It is well known that when an electron beam is incident obliquely on the surface of a phantom, the depth dose curve measured normal to the surface is shifted toward the surface. Based on geometrical arguments alone, the depth of the nth isodose line for an electron beam incident at an angle theta should be equal to the product of cos theta and the depth of the nth isodose line at normal incidence. This method, however, ignores the effects of scatter and can lead to significant errors in isodose placement for beams at large angles of incidence. A semi-empirical functional relationship and a table of isodose shift factors have been developed with which one may easily calculate the depth of any isodose line for beams at incident angles of 0 degrees to 60 degrees. The isodose shift factors are tabulated in terms of beam energy (6-22 MeV) and isodose line (10%-90%) and are shown to be relatively independent of beam size and incident angle for angles less than 60 degrees. Extensive measurements have been made on a Varian Clinac 2500 linear accelerator with a parallel-plate chamber and polystyrene phantom. The dependence of the chamber response on beam angulation has been checked, and the scaling factor of the polystyrene phantom has been determined to be equal to 1.00.

A dose homogeneity index for evaluating 192Ir interstitial breast implants

To evaluate and optimize dose homogeneity of 192Ir interstitial breast implants, we define a quantity, the dose homogeneity index (DHI), as follows: DHI = [V(TDR)--V(HDR)]/V(TDR), where V(TDR) denotes the total treatment volume enclosed by the prescribed treatment dose rate (TDR) and V(HDR) denotes the volume enclosed by high-dose rate (HDR), which is 1.5 X TDR or greater. We have used the DHI to examine and compare 192Ir double-plane implants of various sizes planned by the Memorial system or the Tufts system. Criteria have been suggested for the number of planes required for implants in a given treatment volume. Anderson's volume-dose histogram with inverse square suppression is adopted for illustration.

Photon activation analysis as a new technique for body composition studies

A study was undertaken to demonstrate the usefulness of the recently developed photon activation analysis (PAA) technique for in vivo body composition studies. PAA can be used for direct measurement of total-body oxygen, nitrogen, and carbon. Sequential measurements were made on rats fed diets of 0%, 4.2%, or 20% protein for 6 1/2 wk, and significant changes in body composition were noted. In addition, rats of different ages, strains, nutritional states, and degrees of obesity were included in a comparison of PAA results in vivo with results from chemical analysis after sacrifice of the animals. High positive correlations were found between PAA measurements of carbon and chemical analysis measurements of fat and between PAA measurements of oxygen and chemical analysis measurements of total-body water. A low positive correlation was found between PAA measurements of nitrogen and chemical analysis measurements of protein.

Measurement of total-body oxygen, nitrogen, and carbon in vivo by photon activation analysis

A method has been developed to measure total-body oxygen, nitrogen, and carbon in vivo using the x-ray beam of a 45-MV betatron and a whole-body counter. Following x-ray irradiation of living tissue, the positron emitting activation products 15O, 11C, and 13N are produced. The decay of these radionuclides has been measured in both phantoms and animals, and a computer curve-fitting algorithm used to resolve the decay curve into separate contributions from 15O, 11C, and 13N. The decay curve was corrected for interfering activity from 30P, 38K, and 34mCl, and in the case of live animals, also corrected for a substantial fraction of 11C lost through exhalation. Activation uniformity profiles have been measured for phantoms up to 30 cm in thickness. With a radiation dose of 20 cGy, total-body O, N, and C were measured in dead rats with estimated accuracies of +/- 1.4%, +/- 4.5%, and +/- 1.5% [1 standard deviation (SD)], respectively. With a radiation dose of 40 cGy, total-body O, N, and C were measured in living rats with estimated accuracies of +/- 1.4%, +/- 6.9%, and +/- 1.5% (1 SD), respectively. It is anticipated that total-body O, N, and C similarly could be measured in human subjects with a radiation dose of 1-2 cGy and with accuracies comparable to those obtained in rats. Although most of the measurements were made using a beam energy of 45 MV, we have shown that useful results may be achievable with a beam energy as low as 25 MV. This accurate, convenient, and safe technique for total-body O, C, and N measurement should have applications in the study of nutritional status in health and disease, both in human subjects and in animals.