Current uses and applications of stereotactic body radiation therapy.

Stereotactic body radiation therapy (SBRT) is a modality that delivers high doses of radiation to a well-defined tumor target in a single or a few fractions and with high precision, which significantly reduces the dose received by surrounding normal tissues. SBRT is indicated for inoperable, early stage (T1 and T2) primary non-small cell lung cancer, lung metastases with a controlled primary tumor, prostate tumors and oligometastatic disease. Despite the lack of long-term or phase III studies, efficacy results in local control are higher than 90%, with similar toxicity to that reported with conventional fractionated radiotherapy. This article describes SBRT technology and technique, along with clinical applications, indications and limitations of this therapeutic modality.

La radioterapia corporal estereotáctica es una modalidad que con alta precisión administra dosis alta de radiación a un objetivo tumoral bien definido, en una o en pocas fracciones, y reduce significativamente la dosis que reciben los tejidos sanos circundantes. Está indicada en cáncer primario de pulmón de células no pequeñas en estadios tempranos (T1 y T2) no operable, metástasis pulmonares con un tumor primario controlado, tumores prostáticos y enfermedad oligometastásica. A pesar de la falta de estudios a largo plazo o fase III, los resultados de su eficacia en el control local es superior a 90 %, con toxicidad similar a la reportada con fraccionamientos convencionales de radioterapia. Este artículo describe la tecnología y la técnica de radioterapia corporal estereotáctica, con las aplicaciones clínicas, indicaciones y limitaciones de esta modalidad terapéutica.

Usos y aplicaciones actuales de la radioterapia corporal estereotáctica / Current uses and applications of stereotactic body radiation therapy

Resumen La radioterapia corporal estereotáctica es una modalidad que con alta precisión administra dosis alta de radiación a un objetivo tumoral bien definido, en una o en pocas fracciones, y reduce significativamente la dosis que reciben los tejidos sanos circundantes. Está indicada en cáncer primario de pulmón de células no pequeñas en estadios tempranos (T1 y T2) no operable, metástasis pulmonares con un tumor primario controlado, tumores prostáticos y enfermedad oligometastásica. A pesar de la falta de estudios a largo plazo o fase III, los resultados de su eficacia en el control local es superior a 90 %, con toxicidad similar a la reportada con fraccionamientos convencionales de radioterapia. Este artículo describe la tecnología y la técnica de radioterapia corporal estereotáctica, con las aplicaciones clínicas, indicaciones y limitaciones de esta modalidad terapéutica.

Abstract Stereotactic body radiation therapy (SBRT) is a modality that delivers high doses of radiation to a well-defined tumor target in a single or a few fractions and with high precision, which significantly reduces the dose received by surrounding normal tissues. SBRT is indicated for inoperable, early stage (T1 and T2) primary non-small cell lung cancer, lung metastases with a controlled primary tumor, prostate tumors and oligometastatic disease. Despite the lack of long-term or phase III studies, efficacy results in local control are higher than 90%, with similar toxicity to that reported with conventional fractionated radiotherapy. This article describes SBRT technology and technique, along with clinical applications, indications and limitations of this therapeutic modality.

Out-of-field mean photon energy and dose from 6 MV and 6 MV FFF beams measured with TLD-300 and TLD-100 dosimeters.

PURPOSE: To measure the out-of-field mean photon energy and dose imparted by the secondary radiation field generated by 6 MV and 6 MV FFF beams using TLD-300 and TLD-100 dosimeters and to use the technique to quantify the contributions from the different sources that generate out-of-field radiation. METHODS: The mean photon energy and the dose were measured using the TLD-300 glow curve properties and the TLD-100 response, respectively. The TLD-300 glow curve shape was energy-calibrated with gamma rays from 99m Tc, 18 F, 137 Cs, and 60 Co sources, and its energy dependence was quantified by a parameter obtained from the curve deconvolution. The TLD-100 signal was calibrated in absorbed dose-to-water inside the primary field. Dosimeters were placed on the linac head, and on the surface and at 4.5 cm depth in PMMA at 1-15 cm lateral distances from a 10 × 10 cm2 field edge at the isocenter plane. Three configurations of dosimeters around the linac were defined to identify and quantify the contributions from the different sources of out-of-field radiation. RESULTS: Typical energies of head leakage were about 500 keV for both beams. The mean energy of collimator-scattered radiation was equal to or larger than 1250 keV and, for phantom-scattered radiation, mean photon energies were 400 keV for the 6 MV and 300 keV for the 6 MV FFF beam. Relative uncertainties to determine mean photon energy were better than 15% for energies below 700 keV, and 40% above 1000 keV. The technique lost its sensitivity to the incident photon energy above 1250 keV. On the phantom surface and at 1-15 cm from the field edge, 80%-90% of out-of-field dose came from scattering in the secondary collimator. At 4.5 cm deep in the phantom and 1-5 cm from the field edge, 50%-60% of the out-of-field dose originated in the phantom. At the points of measurement, the head leakage imparted less than 0.1% of the dose at the isocenter. The 6 MV FFF beam imparted 8-36% less out-of-field dose than the 6 MV beam. These energy results are consistent with general Monte Carlo simulation predictions and show excellent agreement with simulations for a similar linac. The measured out-of-field doses showed good agreement with independent evaluations. CONCLUSIONS: The out-of-field mean photon energy and dose imparted by the secondary radiation field were quantified by the applied TLD-300/TLD-100 method. The main sources of out-of-field dose were identified and quantified using three configurations of dosimeters around the linac. This technique could be of value to validate Monte Carlo simulations where the linac head design, configuration, or material composition are unavailable.

Medical physics graduate education in Mexico and its relation to the advances in radiation oncology.

AIM: To evaluate the state of graduate education in medical physics and progress in radiation oncology (RO) equipment in Mexico since 2000, when conferring degrees from two master's-degree programs in Medical Physics began. BACKGROUND: Medical physics is a Health Profession and there are international recommendations for education, training, and certification. Both programs follow these education guidelines. The most common clinical occupation of graduates is in RO services. Techniques in Mexican RO include traditional and high-precision procedures. METHODS: Academic and occupational information about the programs and their graduates were obtained from official websites. Graduates were invited to respond to a survey that requested information about their present job. We obtained data on RO equipment and human resources from public databases and estimated staffing requirements of medical physicists (MPs). RESULTS: Medical physics programs have graduated a total of 225 MPs. Half of them work in a clinical environment and, of these, about 90 work in RO services. MPs with M.Sc. degrees constitute 36% of the current MP workforce in RO, estimated to be 250 individuals. Survey responses pointed out the main merits and limitations of the programs. The number of MPs in RO has increased fivefold and the number of linacs sixfold in 15 years. The present number of MPs is insufficient, according to published guidelines. CONCLUSION: All MPs in RO services with advanced modalities must be trained following international recommendations for graduate education and post-graduation clinical training. Education and health institutions must find incentives to create more graduate programs and clinical residencies.

Voluntary breath-hold reduces dose to organs at risk in radiotherapy of left-sided breast cancer.

AIM: To compare the dose to organs at risk with free breathing (FB) or voluntary breath-hold (VBH) during radiotherapy of patients with left sided breast cancer. BACKGROUND: Radiotherapy reduces the risk of breast-cancer-specific mortality but the effects on other organs increase non-cancer-specific mortality. Radiation exposure to the heart, in particular in patients with left sided breast cancer, can be reduced by breath hold methods that increase the distance between the heart and the radiation field. MATERIALS AND METHODS: Three-dimensional conformal radiotherapy (3D-CRT) dose plans for the left breast and organs at risk including the heart, left anterior descending coronary artery (LAD) and ipsilateral lung were compared with FB and VBH in ten patients with left sided breast cancer. RESULTS: The mean doses to the heart and LAD were reduced by 50.4 % (p < 0.001) and 58.8 % (p = 0.006), respectively, in VBH relative to FB. The mean dose to the ipsilateral lung was reduced by 13.8 % (p = 0.11) in VBH relative to FB. The planning target volume (PTV) coverage was at least 95 % in both FB and VBH (p = 0.78). CONCLUSION: The VBH technique significantly reduces the dose to organs at risk in 3D-CRT treatment plans of left sided breast cancer.

Implementation of intensity modulated radiotherapy for prostate cancer in a private radiotherapy service in Mexico.

Intensity modulated radiation therapy (IMRT) allows physicians to deliver higher conformal doses to the tumour, while avoiding adjacent structures. As a result the probability of tumour control is higher and toxicity may be reduced. However, implementation of IMRT is highly complex and requires a rigorous quality assurance (QA) program both before and during treatment. The present article describes the process of implementing IMRT for localized prostate cancer in a radiation therapy department. In our experience, IMRT implementation requires careful planning due to the need to simultaneously implement specialized software, multifaceted QA programs, and training of the multidisciplinary team. Establishing standardized protocols and ensuring close collaboration between a multidisciplinary team is challenging but essential.