Monte Carlo skin dose simulation in intraoperative radiotherapy of breast cancer using spherical applicators.

The relatively new treatment modality electronic intraoperative radiotherapy (IORT) is gaining popularity, irradiation being obtained within a surgically produced cavity being delivered via a low-energy x-ray source and spherical applicators, primarily for early stage breast cancer. Due to the spatially dramatic dose-rate fall off with radial distance from the source and effects related to changes in the beam quality of the low keV photon spectra, dosimetric account of the Intrabeam system is rather complex. Skin dose monitoring in IORT is important due to the high dose prescription per treatment fraction. In this study, modeling of the x-ray source and related applicators were performed using the Monte Carlo N-Particle transport code. The dosimetric characteristics of the model were validated against measured data obtained using an ionization chamber and EBT3 film as dosimeters. By using a simulated breast phantom, absorbed doses to the skin for different combinations of applicator size (1.5-5 cm) and treatment depth (0.5-3 cm) were calculated. Simulation results showed overdosing of the skin (>30% of prescribed dose) at a treatment depth of 0.5 cm using applicator sizes larger than 1.5 cm. Skin doses were significantly increased with applicator size, insofar as delivering 12 Gy (60% of the prescribed dose) to skin for the largest sized applicator (5 cm diameter) and treatment depth of 0.5 cm. It is concluded that the recommended 0.5-1 cm distance between the skin and applicator surface does not guarantee skin safety and skin dose is generally more significant in cases with the larger applicators. HIGHLIGHTS: • Intrabeam x-ray source and spherical applicators were simulated and skin dose was calculated. • Skin dose for constant skin to applicator distance strongly depends on applicator size. • Use of larger applicators generally results in higher skin dose. • The recommended 0.5-1 cm skin to applicator distance does not guarantee skin safety.

Prognostic factors for elderly breast cancer patients in University Malaya Medical Centre, Malaysia.

BACKGROUND: Information about elderly breast cancer patients' outcome is limited. This study aimed to evaluate the treatment outcomes in women aged 70 and above with specific analysis on prognostic clinicopathological features and treatment modalities. MATERIALS AND METHODS: This retrospective study examined breast cancer patients between 1st January 1994 and 31st December 2004 in UMMC. Survival analysis was performed using the Kaplan-Meier method and comparisons between groups using the log-rank test. Univariate and multivariate analysis on prognostic factors were carried out using the Cox's proportionate hazard model for patient demographics, and tumour and treatment factors. RESULTS: One hundred and thirty six patients were identified, with a median age at diagnosis of 75 years. Most had at least one co-morbidity (61.8%). Only 75.0% had a good performance status (ECOG 0-1). Mean tumour size was 4.4 cm. Primary tumour stages (T stages) 3 and 4 were present in 8.1% and 30.1% of patients respectively, and 30.9% had stage III and 8.8% had stage IV disease based on overall AJCC staging. ER positivity was 58.1%. PR status was positive in 30.1%. Surgery was performed in 69.1% of the patients and mastectomy and axillary clearance were the commonest surgical procedures (50.7%). Some 79.4% of patients received hormonal therapy, 30.1% radiotherapy and only 3.6% chemotherapy. Non-standard treatment was given to 39.0% of patients due to a variety of reasons. The cumulative 5 years overall, relapse free and cause specific survivals were 51.9%, 79.7% and 73.3% respectively. Performance status, T3-4 tumour, presence of metastasis, tumour grade and ER status were independent prognostic factors for overall survival. For cause specific survival they were T4 tumour, presence of metastasis and ER status. CONCLUSION: The 5 years overall survival rate was 51.9% and 41.8% of deaths were non-breast cancer related deaths. Low survival rate was related to low life expectancy in this population. Locally advanced disease, metastatic disease and high ER negative rates play a major role in the survival of elderly breast cancer patients in Malaysia.