Optimizing dose prescription in stereotactic body radiotherapy for lung tumours using Monte Carlo dose calculation.

PURPOSE: To define a method of dose prescription employing Monte Carlo (MC) dose calculation in stereotactic body radiotherapy (SBRT) for lung tumours aiming at a dose as low as possible outside of the PTV. METHODS AND MATERIALS: Six typical T1 lung tumours - three small, three large - were constructed centrally, peripherally in the lung, and nearby the thoracic wall, respectively. For each of these, five treatment plans employing dynamic conformal arc technique were made in which the dose was prescribed to encompass the PTV with the prescription isodose level (PIL) set in a range between 50% and 80% of the isocenter dose. Three shells of respectively 10mm thickness around the PTV were constructed to assess the dose in the tissues directly adjacent to the PTV. RESULTS: The PTV was nicely covered (mean 98.8%+/-0.9%) with favourable conformity indices (mean 1.09+/-0.1). Mean doses around the PTVs were 73% (+/-1.3%), 76% (+/-3.5%), and 85% (+/-5.1%) of the prescribed dose in shell 1 for PIL50%, PIL65%, and PIL80%, respectively; 40% (+/-2.6%), 44% (+/-5.1%), 54% (+/-9.3%) in shell 2; and 24% (+/-1.9%), 26% (+/-3.6%), 33% (+/-6.8%) in shell 3. All normal tissue doses including the integral dose were also consistently worst for PIL80%. Monitor units were 30% higher for PIL65%, and 70% higher for PIL50%, compared with PIL80%. CONCLUSIONS: To improve normal tissue sparing the dose should be prescribed at an isodose lower than 80% of the isocenter dose in SBRT when using conformal arc technique with MC dose calculation.

Three-dimensional conformal simultaneously integrated boost technique for breast-conserving radiotherapy.

PURPOSE: To compare the target coverage and normal tissue dose with the simultaneously integrated boost (SIB) and the sequential boost technique in breast cancer, and to evaluate the incidence of acute skin toxicity in patients treated with the SIB technique. METHODS AND MATERIALS: Thirty patients with early-stage left-sided breast cancer underwent breast-conserving radiotherapy using the SIB technique. The breast and boost planning target volumes (PTVs) were treated simultaneously (i.e., for each fraction, the breast and boost PTVs received 1.81 Gy and 2.3 Gy, respectively). Three-dimensional conformal beams with wedges were shaped and weighted using forward planning. Dose-volume histograms of the PTVs and organs at risk with the SIB technique, 28 x (1.81 + 0.49 Gy), were compared with those for the sequential boost technique, 25 x 2 Gy + 8 x 2 Gy. Acute skin toxicity was evaluated for 90 patients treated with the SIB technique according to Common Terminology Criteria for Adverse Events, version 3.0. RESULTS: PTV coverage was adequate with both techniques. With SIB, more efficiently shaped boost beams resulted in smaller irradiated volumes. The mean volume receiving > or =107% of the breast dose was reduced by 20%, the mean volume outside the boost PTV receiving > or =95% of the boost dose was reduced by 54%, and the mean heart and lung dose were reduced by 10%. Of the evaluated patients, 32.2% had Grade 2 or worse toxicity. CONCLUSION: The SIB technique is proposed for standard use in breast-conserving radiotherapy because of its dose-limiting capabilities, easy implementation, reduced number of treatment fractions, and relatively low incidence of acute skin toxicity.

Radiation-induced sarcoma: a challenge for the surgeon.

BACKGROUND: Treatment of radiation-induced sarcoma (RIS) remains an unsolved problem. To provide more insight into the disease process, its characteristics, outcome, and potential outcome determinants were defined. METHODS: From 1978 to 2003, 27 patients--20 females (74%) and 7 males (26%) with a median age 44 years (range, 1-73 years) at the time of diagnosis of the primary tumor--developed an RIS after a median interval of 8 years (range, 3-41 years). The histology of the RIS was 10 (37%) undifferentiated high-grade pleomorphic sarcomas, 7 (26%) angiosarcomas, 6 (22%) fibrosarcomas, 2 (7%) osteosarcomas, 1 (4%) pleomorphic rhabdomyosarcoma, and 1 (4%) pleomorphic leiomyosarcoma. Surgical resection was performed in 21 patients: 13 (62%) R0 (microscopically radical), 4 (19%) R1 (microscopically irradical), 2 (9.5%) R2 (macroscopically irradical), and 2 (9.5%) RX (unknown radicality). Six (22%) patients underwent no resection. RESULTS: The 5-year disease-free and overall survival rates were 27% and 30%, respectively. The local failure rate after R0 resection was 54%. The distant failure rate for the entire group was 41%. Patients with an R0 resection had a significantly better survival rate (P < .05) than patients with an R1, R2, or no resection. CONCLUSIONS: RISs are aggressive malignancies with a high tendency for local recurrence and distant metastases. Previously applied treatment often hampers adequate resection. Therefore, radical surgical resection is the only chance to improve disease-free and overall survival, but it may also have a palliative role. Still, the overall prognosis remains poor.