Historically, anatomical CT and MR images were used to delineate the gross tumour volumes (GTVs) for radiotherapy treatment planning. The capabilities offered by modern radiation therapy units and the widespread availability of combined PET/CT scanners stimulated the development of biological PET imaging-guided radiation therapy treatment planning with the aim to produce highly conformal radiation dose distribution to the tumour. One of the most difficult issues facing PET-based treatment planning is the accurate delineation of target regions from typical blurred and noisy functional images. The major problems encountered are image segmentation and imperfect system response function. Image segmentation is defined as the process of classifying the voxels of an image into a set of distinct classes. The difficulty in PET image segmentation is compounded by the low spatial resolution and high noise characteristics of PET images. Despite the difficulties and known limitations, several image segmentation approaches have been proposed and used in the clinical setting including thresholding, edge detection, region growing, clustering, stochastic models, deformable models, classifiers and several other approaches. A detailed description of the various approaches proposed in the literature is reviewed. Moreover, we also briefly discuss some important considerations and limitations of the widely used techniques to guide practitioners in the field of radiation oncology. The strategies followed for validation and comparative assessment of various PET segmentation approaches are described. Future opportunities and the current challenges facing the adoption of PET-guided delineation of target volumes and its role in basic and clinical research are also addressed.

/pdf/pet-guided-delineation-of-radiation-therapy-treatment-3ypvotnulc.pdf

PET-guided delineation of radiation therapy treatment volumes: a survey of image segmentation techniques

Purpose This study aimed to evaluate the toxicity and clinical outcomes for cervical cancer patients treated definitively with intensity-modulated radiation therapy (IMRT) compared with non-IMRT treatment. Methods and Materials This prospective cohort study included 452 patients with newly diagnosed cervical cancer treated with curative intent (135 IMRT and 317 non-IMRT). Treatment involved external irradiation and brachytherapy, and 85% of patients received concurrent chemotherapy. All IMRT patients underwent an F-18 fluorodeoxyglucose positron emission tomography (FDG-PET/CT) simulation. A 3-month post-therapy PET was obtained to evaluate treatment response. Toxicity was scored by the Common Terminology Criteria for Adverse Events Version 3.0. Results The IMRT and non-IMRT groups had similar stage distribution and histology. For all patients, the post-therapy FDG-PET response correlated with overall recurrence risk ( p p p = 0.9774). The mean follow-up for all patients alive at the time of last follow-up was 52 months (72 months non-IMRT, 22 months IMRT). At last follow-up, 178 patients (39 IMRT, 139 non-IMRT) had developed a recurrence. The difference in recurrence-free survival between the two groups did not reach statistical significance ( p = 0.0738), although the IMRT group showed better overall and cause-specific survivals ( p p  = 0.0351). Conclusion Cervical cancer patients treated with FDG-PET/CT-guided IMRT have improved survival and less treatment-related toxicity compared with patients treated with non-IMRT radiotherapy.

Clinical outcomes of definitive intensity-modulated radiation therapy with fluorodeoxyglucose-positron emission tomography simulation in patients with locally advanced cervical cancer.

Renal toxicity associated with small-molecule radionuclide therapy has been shown to be dose-limiting for many clinical studies. Strategies for maximizing dose to the target tissues while sparing normal critical organs based on absorbed dose and biologic response parameters are commonly used in external-beam therapy. However, radiopharmaceuticals passing though the kidneys result in a differential dose rate to suborgan elements, presenting a significant challenge in assessing an accurate dose–response relationship that is predictive of toxicity in future patients. We have modeled the multiregional internal dosimetry of the kidneys combined with the biologic response parameters based on experience with brachytherapy and external-beam radiation therapy to provide an approach for predicting radiation toxicity to the kidneys. Methods: The multiregion kidney dosimetry model of MIRD pamphlet no. 19 has been used to calculate absorbed dose to regional structures based on preclinical and clinical data. Using the linear quadratic model for radiobiologic response, we computed regionally based surviving fractions for the kidney cortex and medulla in terms of their concentration ratios for several examples of radiopharmaceutical uptake and clearance. We used past experience to illustrate the relationship between absorbed dose and calculated biologically effective dose (BED) with radionuclide-induced nephrotoxicity. Results: Parametric analysis for the examples showed that high dose rates associated with regions of high activity concentration resulted in the greatest decrease in tissue survival. Higher dose rates from short-lived radionuclides or increased localization of radiopharmaceuticals in radiosensitive kidney subregions can potentially lead to greater whole-organ toxicity. This finding is consistent with reports of kidney toxicity associated with early peptide receptor radionuclide therapy and 166Ho-phosphonate clinical investigations. Conclusion: Radionuclide therapy dose–response data, when expressed in terms of biologically effective dose, have been found to be consistent with external-beam experience for predicting kidney toxicity. Model predictions using both the multiregion kidney and linear quadratic models may serve to guide the investigator in planning and optimizing future clinical trials of radionuclide therapy.

https://jnm.snmjournals.org/content/jnumed/49/11/1884.full.pdf

MIRD pamphlet no. 20: The effect of model assumptions on kidney dosimetry and response - Implications for radionuclide therapy

Purpose Reirradiation of painful bone metastases in nonresponders or patients with recurrent pain after initial response is performed in up to 42% of patients initially treated with radiotherapy. Literature on the effect of reirradiation for pain control in those patients is scarce. In this systematic review and meta-analysis, we quantify the effectiveness of reirradiation for achieving pain control in patients with painful bone metastases. Methods and Materials A free text search was performed to identify eligible studies using the MEDLINE, EMBASE, and the Cochrane Collaboration library electronic databases. After study selection and quality assessment, a pooled estimate was calculated for overall pain response for reirradiation of metastatic bone pain. Results Our literature search identified 707 titles, of which 10 articles were selected for systematic review and seven entered the meta-analysis. Overall study quality was mediocre. Of the 2,694 patients initially treated for metastatic bone pain, 527 (20%) patients underwent reirradiation. Overall, a pain response after reirradiation was achieved in 58% of patients (pooled overall response rate 0.58, 95% confidence interval=0.49–0.67). There was a substantial between-study heterogeneity ( I 2 = 63.3%, p = 0.01) because of clinical and methodological differences between studies. Conclusions Reirradiation of painful bone metastases is effective in terms of pain relief for a small majority of patients; approximately 40% of patients do not benefit from reirradiation. Although the validity of results is limited, this meta-analysis provides a comprehensive overview and the most quantitative estimate of reirradiation effectiveness to date.

Effectiveness of Reirradiation for Painful Bone Metastases: A Systematic Review and Meta-Analysis

This topical review provides an up-to-date overview of the theoretical and practical aspects of therapeutic kilovoltage x-ray beam dosimetry. Kilovoltage x-ray beams have the property that the maximum dose occurs very close to the surface and thus, they are predominantly used in the treatment of skin cancers but also have applications for the treatment of other cancers. In addition, kilovoltage x-ray beams are used in intra operative units, within animal irradiators and in on-board imagers on linear accelerators and kilovoltage dosimetry is important in these applications as well. This review covers both reference and relative dosimetry of kilovoltage x-ray beams and provides recommendations for clinical measurements based on the literature to date. In particular, practical aspects for the selection of dosimeter and phantom material are reviewed to provide suitable advice for medical physicists. An overview is also presented of dosimeters other than ionization chambers which can be used for both relative and in vivo dosimetry. Finally, issues related to the treatment planning and the use of Monte Carlo codes for solving radiation transport problems in kilovoltage x-ray beams are presented.

https://iopscience.iop.org/article/10.1088/0031-9155/59/6/R183/pdf

Advances in kilovoltage x-ray beam dosimetry

Principles and Practice of Radiation Oncology, 4th Edition

This study investigates alternative plastics for use in the construction of tissue equivalent gas-filled detectors. Four different alternative plastics (acrylic, nylon, polyethylene, and polystyrene) were tested in comparison with A-150 Five proportional counters were constructed possessing spherical ionization cavities each made of one of the five plastics with wall thickness of 3 mm and sensitive diameters of 4.48 cm. The detectors operated at 1400 V. They were exposed to three different energies of proton beams (87, 162, and 222 MeV) and five different heavy ion beams (143 MeV/amu He, 265 MeV/amu C, 440 MeV/amu Si, 430 MeV/amu Ar, and 421 MeV/amu Fe). The detectors were exposed to bare beams in air and no phantom was used. Lineal energy spectra derived from these measurements of energetic protons and heavy ion beams were used for comparison. Frequency averaged lineal energies and dose averaged lineal energies were calculated from each spectrum. Comparison of the experimental data indicates that the responses of the four alternative plastics tested are very similar to the response of A-150 tissue equivalent plastic.

Comparison of plastics used in proportional counters for proton and heavy ion measurements

Applications of Probability and Statistics in Health Physics

Has radiation protection become a health hazard

Book reviewMarine Radioactivity, H.D. Livingston (Ed.), Elsevier, Amsterdam, 2003, Hardbound (2004), p. 310p, Price GBP 93.50, EUR 140, USD 140, ISBN: 0-08-043714-1

Arthur C. Lucas

Papers

Principles and Practice of Radiation Oncology, 4th Edition

Comparison of plastics used in proportional counters for proton and heavy ion measurements

Applications of Probability and Statistics in Health Physics

Has radiation protection become a health hazard

Book reviewMarine Radioactivity, H.D. Livingston (Ed.), Elsevier, Amsterdam, 2003, Hardbound (2004), p. 310p, Price GBP 93.50, EUR 140, USD 140, ISBN: 0-08-043714-1