Strategies for effective physics plan and chart review in radiation therapy: Report of AAPM Task Group 275

BACKGROUND

While the review of radiotherapy treatment plans and charts by a medical physicist is a key component of safe, high-quality care, very few specific recommendations currently exist for this task.

AIMS

The goal of TG-275 is to provide practical, evidence-based recommendations on physics plan and chart review for radiation therapy. While this report is aimed mainly at medical physicists, others may benefit including dosimetrists, radiation therapists, physicians and other professionals interested in quality management.

METHODS

The scope of the report includes photon/electron external beam radiotherapy (EBRT), proton radiotherapy, as well as high-dose rate (HDR) brachytherapy for gynecological applications (currently the highest volume brachytherapy service in most practices). The following review time points are considered: initial review prior to treatment, weekly review, and end-of-treatment review. The Task Group takes a risk-informed approach to developing recommendations. A failure mode and effects analysis was performed to determine the highest-risk aspects of each process. In the case of photon/electron EBRT, a survey of all American Association of Physicists in Medicine (AAPM) members was also conducted to determine current practices. A draft of this report was provided to the full AAPM membership for comment through a 3-week open-comment period, and the report was revised in response to these comments.

RESULTS

The highest-risk failure modes included 112 failure modes in photon/electron EBRT initial review, 55 in weekly and end-of-treatment review, 24 for initial review specific to proton therapy, and 48 in HDR brachytherapy. A 103-question survey on current practices was released to all AAPM members who self-reported as working in the radiation oncology field. The response rate was 33%. The survey data and risk data were used to inform recommendations.

DISCUSSION

Tables of recommended checks are presented and recommendations for best practice are discussed. Suggestions to software vendors are also provided.

CONCLUSIONS

TG-275 provides specific recommendations for physics plan and chart review which should enhance the safety and quality of care for patients receiving radiation treatments.

Patterns of practice for safety-critical processes in radiation oncology in the United States from the AAPM safety profile assessment survey

PURPOSE

The purpose of this study is to report an overview of the patterns of practice for safety-critical processes in radiation oncology clinics in the United States.

METHODS AND MATERIALS

The Safety Profile Assessment (spa.aapm.org), developed by the American Association of Physicists in Medicine, was released in July 2013. It consists of 92 indicator questions designed to assess the safety and quality of radiation oncology operations. By December 2014, 114 surveys had been completed by clinics within the United States. This database was analyzed to identify those indicators of safety and quality performance with which there was the highest degree of compliance and those indicators with which there was the least. Additionally, we assessed the extent to which key clinical activities were supported by formal policies. Voluntary post assessment surveys were completed by 86 respondents (75%).

RESULTS

The mean number of patients treated per day on external beam radiation therapy devices was 64 (range, 8-600) in the clinics that responded to the survey. The average overall score for the 92 SPA indicator questions was 1.45 (range, 1.00-2.78) on a 5-point scale, with 1 being the most positive. Those indicators that were associated with the highest levels of compliance are dominated by activities that are either strongly recommended, regulated, or associated with revenue generation. Surprisingly, several of those indicators for which there was the least compliance relate to activities that are known to have contributed to serious radiation therapy misadministrations in the past. Formal policies, which are widely regarded as a backbone of a safe clinical system, were reported as lacking for some safety-critical procedures.

CONCLUSIONS

Although overall this analysis demonstrated reasonable performance across participating departments, several important areas for improvement were identified. The results may guide the allocation of resources both at the level of individual departments and at the professional society level.

Comparative dosimetry study of three UK centres implementing total skin electron treatment through external audit

OBJECTIVE

This article describes the external audit measurements conducted in two UK centres implementing total skin electron beam therapy (TSEBT) and the results obtained.

METHODS

Measurements of output, energy, beam flatness and symmetry at a standard distance (95 or 100 cm SSD) were performed using a parallel plate chamber in solid water. Similarly, output and energy measurements were also performed at the treatment plane for single and dual fields. Clinical simulations were carried out using thermoluminescent dosemeters (TLDs) and Gafchromic® film (International Specialty Products, Wayne, NJ) on an anthropomorphic phantom.

RESULTS

Extended distance measurements confirmed that local values for the beam dosimetry at Centres A and B were within 2% for outputs and 1-mm agreement of the expected depth at which the dose is 50% of the maximum for the depth-dose curve in water (R50,D) value. Clinical simulation using TLDs) showed an agreement of -1.6% and -6.7% compared with the expected mean trunk dose for each centre, respectively, and a variation within 10% (±1 standard deviation) across the trunk. The film results confirmed that the delivery of the treatment technique at each audited centre complies with the European Organisation for Research and Treatment of Cancer recommendations.

CONCLUSION

This audit methodology has proven to be a successful way to confirm the agreement of dosimetric parameters for TSEBT treatments at both audited centres and could serve as the basis for an audit template to be used by other audit groups.

ADVANCES IN KNOWLEDGE

TSEBT audits are not established in the UK owing to a limited number of centres carrying out the treatment technique. This article describes the audits performed at two UK centres prior to their clinical implementation.

Bone health in prostate cancer patients: A survivorship issue requiring intervention

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Background: In general, men are not routinely screened for bone health. Prostate cancer patients are at an increased risk because of treatment with androgen deprivation therapy (ADT). Unlike other patients diagnosed with a malignancy, they may survive a long time. Some risk factors include inadequate calcium, vitamin D deficiency, tobacco use and alcohol abuse. We implemented a pre-ADT program to mitigate the effects of ADT on bone health. This study evaluates the pre-existing risk factors and bone health by baseline DEXA scans pre-ADT initiation. Methods: We completed a chart review of 182 veterans referred to Radiation Oncology for curative treatment of prostate cancer from 2009 to 2013. Of those, 160 patients underwent baseline DEXA scans. Clinical variables analyzed were demographics, tobacco and alcohol use, vitamin D levels, incidence of AODM (adult onset diabetes mellitus), and calcium or vitamin D intervention. Descriptive statistics and bivariate analysis including Chi Square tests and odds ratios were carried out. Results: The mean age of the study participants was 66.6 years (range 47-82.8 years). Baseline DEXA scans were abnormal in 63% of patients, showing osteoporosis and/or osteopenia. Vitamin D levels were abnormal in 61% of patients- 26% of whom had normal DEXA scans. Twenty percent had a history of alcohol abuse, and 56% used tobacco; 33% had AODM. Smokers with an abnormal Vitamin D level were at increased risk of bone disease as compared to non smokers (OR 3.23, 95% CI 1.35-7.69 p<0.01). Variables significantly impacting bone health were age (OR 1.087, p=0.012, 95% CI 1.018-1.161) and Tobacco use (OR 0.424, p=0.045, 95% CI 0.183-0.980). Almost 90% of the patients in this study had intermediate risk prostate cancer with an expected cancer specific survival of 85 to 90% at 5 to 10 years. Conclusions: Pre-ADT screening confirms the risk of underlying bone disease in this veteran population with an expectation of long term survival. Guidelines for treatment and prevention of bone disease should be implemented in all patients over age of 50. Particular attention should be paid to patients who underwent ADT. This can affect the quality of life in this group of cancer survivors.

Using Schizosaccharomyces pombe as a host for expression and purification of eukaryotic proteins

We have established a eukaryotic protein expression and purification system by using the yeast Schizosaccharomyces pombe as the host and the glutathione S-transferase (GST) as a protein purification tag. This system provides opportunities for rapid, inexpensive, and high yield production of proteins in a eukaryotic organism. Unlike E. coli, S. pombe provides for post-translational modifications of the proteins, which are often critical for the structure and function of eukaryotic proteins. Two vectors have been constructed for protein expression in S. pombe, pESP-1 and pESP-2. Both vectors use the nmt1 promoter for constitutive or induced expression of the gene of interest. Expressed GST-tagged proteins are easily and rapidly purified using glutathione agarose beads. The GST tag can be removed from the fusion proteins by treatment with either the thrombin or enterokinase protease. Proteins expressed from the pESP-2 vector will yield native amino acid sequence when the GST tag is removed by treatment with enterokinase. Nine proteins have been purified by using the system with yields ranging from 1.0 mg/l to 12.5 mg/l of induced culture.

An efficient random mutagenesis technique using an E. coli mutator strain

Random mutagenesis of a cloned gene remains a central method to understand many aspects of the gene products function and structure. Having the ability to introduce a limited number of changes within a gene in a controlled fashion allows one to evaluate single changes and study the effect these variants have on the gene of interest. The in vivo random mutagenesis strategy described in this article, using an E. coli host, is a convenient method to introduce a limited number of mutations in a controlled manner.

A Clarkson's sector integration routine for personal computers

A Clarkson's sector integration scheme has been implemented on a personal computer to calculate mean scatter-air ratio (SAR) and mean tissue-air ratio (TAR) for external photon beams of irregular shape. To find where a given radial line from the point of interest intersects the edge of the radiation field, polygon clipping algorithms have been adapted from the field of image processing. The program has calculation run times of approximately 1 s on an 80387 with a math coprocessor for an integration of 36 sectors. The software was validated by comparison to program IRREG, where for various squares and clinical shapes, the agreement was typically 0.7%. The source code is available from the authors.

Identification of a novel promoter in the replication control region of plasmid R6K

A novel source of transcription has been detected in the replication region of plasmid R6K by using fusions involving the galK reporter gene. The -35 and -10 consensus RNA polymerase binding sites were identified in the region overlapping the binding sites for the R6K-encoded replication protein pi. Transcription from this promoter, designated P2, is repressed in vivo by pi-protein levels that are inhibitory for replication. Promoter-down mutations in P2 induced in vitro by bisulfite mutagenesis result in a reduced copy number of a beta-replicon but not of a gamma-replicon. Implications of the role of P2 in R6K replication are discussed.

Promoters of the broad host range plasmid RK2: analysis of transcription (initiation) in five species of gram-negative bacteria

A broad host range cloning vector was constructed, suitable for monitoring promoter activity in diverse Gram-negative bacteria. This vector, derived from plasmid RSF1010, utilized the firefly luciferase gene as the reporter, since the assay for its bioluminescent product is sensitive, and measurements can be made without background from the host. Twelve DNA fragments with promoter activity were obtained from broad host range plasmid RK2 and inserted into the RSF1010 derived vector. The relative luciferase activities were determined for these fragments in five species of Gram-negative bacteria. In addition, four promoters were analyzed by primer extension to locate transcriptional start sites in each host. The results show that several of the promoters vary substantially in relative strengths or utilize different transcriptional start sites in different bacteria. Other promoters exhibited similar activities and identical start sites in the five hosts examined.

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N-terminal truncated forms of the bifunctional pi initiation protein express negative activity on plasmid R6K replication

The replication initiation protein pi of the Escherichia coli plasmid R6K is a dual regulator in the control of plasmid copy number, functioning both as a specific initiator and inhibitor of replication. While the biochemical basis of these activities is not known, initiator activity requires binding of the protein to the seven 22 bp direct repeats within the gamma-origin region. By deleting C-terminal segments of the pi coding region, we have found that the N-terminal polypeptides of pi that are produced, corresponding to the first 117 and 164 amino acids, respectively, retain the negative activity of the bifunctional protein, i.e. these truncated pi proteins specifically inhibit R6K replication in vivo. These negatively acting polypeptides, however, are incapable of initiating replication in vivo and fail to bind to the gamma-origin of the R6K DNA in vitro. A correspondence between the observed negative activity of the N-terminal peptide and the negative regulatory activity of the intact pi protein is supported by the finding that point mutations introduced into the 164 amino acid N-terminal peptide that result in a decrease in its inhibitory activity also produce a plasmid high-copy phenotype when these mutations are incorporated into the full-length pi protein. These findings demonstrate that the negative domain of pi resides in the N-terminal segment of the protein. Furthermore, the data obtained suggest that inhibition of R6K replication by pi does not require direct binding to DNA.

Identification of human antibody fragment clones specific for tetanus toxoid in a bacteriophage lambda immunoexpression library

We have applied a molecular biology approach to the identification of human monoclonal antibodies. Human peripheral blood lymphocyte mRNA was converted to cDNA and a select subset was amplified by the polymerase chain reaction. These products, containing coding sequences for numerous immunoglobulin heavy- and kappa light-chain variable and constant region domains, were inserted into modified bacteriophage lambda expression vectors and introduced into Escherichia coli by infection to yield a combinatorial immunoexpression library. Clones with binding activity to tetanus toxoid were identified by filter hybridization with radiolabeled antigen and appeared at a frequency of 0.2% in the library. These human antigen binding fragments, consisting of a heavy-chain fragment covalently linked to a light chain, displayed high affinity of binding to tetanus toxoid with equilibrium constants in the nanomolar range but did not cross-react with other proteins tested. We estimate that this human immunoexpression library contains 20,000 clones with high affinity and specificity to our chosen antigen.

DNA and protein interactions in the regulation of plasmid replication

As for bacterial and animal viruses that employ different mechanisms for their duplication in a host cell, plasmids have evolved different strategies to assure their hereditary stability or maintenance at a specific copy number during cell growth and division. A characteristic feature of plasmid replication control, however, is an involvement of one or more negatively controlling elements. Furthermore, a majority of the bacterial plasmids examined to date contain direct nucleotide sequence repeats at their origin of replication and encode a replication protein that binds to these repeat sequences. The binding of the replication protein (pi protein) specified by the antibiotic resistance plasmid R6K to a set of 22 base pair direct nucleotide sequence repeats is required for the initiation of replication at each of three origins of replication (alpha, beta and gamma) within a 4 Kb segment of R6K. The pi initiation protein is multifunctional in that it has both positive and negative activities in both controlling the initiation of replication and autoregulating its own synthesis. Similarly, the direct repeats of plasmid R6K and several other plasmid systems play more than one role in plasmid replication. These repeats, termed iterons, are not only required for origin activity but also exert a negative effect on plasmid copy number possibly as a result of their 'titration' of a plasmid encoded replication protein. The properties of plasmid replication proteins and direct nucleotide sequence repeats that are important for their opposing positive and negative roles in the regulation of the initiation of replication are described with particular emphasis on plasmid R6K of Escherichia coli.

Autorepressor properties of the pi-initiation protein encoded by plasmid R6K

A DNA fusion containing the promoter of the pir gene of plasmid R6K that encodes for the pi-initiation protein and the beta-galactosidase gene of Escherichia coli (lacZ) is described. The synthesis of beta-galactosidase promoted by this pir-lac fusion was almost completely inhibited when an R6K sequence containing the pir gene was provided in trans in E. coli. Transcription in vitro from the pir promoter but not the trp promoter of E. coli, was inhibited by purified pi protein indicating that the pi protein alone is responsible for repression of its own gene and that the effect is promoter specific. The DNA-protein interaction sites in the pir regulatory region have been determined for the pi protein and E. coli RNA polymerase using the DNase I protection method. The binding sites for these two proteins overlap for three helical turns. Competition DNA binding experiments show that the pi protein will displace bound RNA polymerase. From these studies we conclude that repression of the pir gene is accomplished by binding of the pi protein and this association blocks access of RNA polymerase to the pir promoter region.

Identification of a novel genetic element in Escherichia coli K-12

Induction of the SOS repair processes of Escherichia coli K-12 caused a 14.4-kilobase species of circular deoxyribonucleic acid, called element e14, to be excised from the chromosome. To aid further characterization of this species, an 11.6-kilobase segment of e14 was inserted into the HindIII site of plasmid pBR313. To map e14 on the E. coli K-12 chromosome, the recombinant plasmid, pAG2, was used to transform a polA recipient, an event which required integration of pAG2 into the recipient chromosome. This recombinational event was dependent upon the region of homology between the incoming plasmid and the chromosome, as no transformants were scored when either a strain cured of the element was the recipient or pBR313 was the transforming deoxyribonucleic acid. Using these transformants, we have shown that e14 maps between the purB and pyrC loci near min 25. Several strains of E. coli K-12 were found to contain e14; however, one strain, Ymel trpA36, did not. In addition, e14 was found to be absent in both E. coli B/5 and E. coli C. The approach to mapping developed for this work could be used to map other fragments of E. coli deoxyribonucleic acid which have no known phenotype.

Effect of the petite mutation on maltose and alpha-methylgucoside fermentation inSaccharomyces cerevisiae

Several hundred petite mutants were isolated from yeast strains of different genotype to examine the effect of the petite mutation on maltose and alpha-methylglucoside fermentation. In most cases petite mutants isolated retain the ability to ferment maltose and alpha-methylglucoside, although at a slower rate. In one strain (1403-7A), however, the ability to ferment alpha-methylglucoside is completely lost in all petite mutants isolated from this strain. It is suggested that mitochondrial factors may be involved in the utilization of alpha-methylglucoside in strain 1403-7A.