Radiobiological treatment planning evaluation of inverse planning simulated annealing for cervical cancer high-dose-rate brachytherapy.

AIM: To compare five inverse treatment plans with one conventional manually-optimized plan for cervical cancer brachytherapy (BT) using radiobiological parameters combined with dosimetric and volumetric parameters. MATERIALS AND METHODS: Five inverse treatment plans were calculated using an inverse planning simulated annealing (IPSA) algorithm for each of four fractions for 12 cervical cancer patients treated with high-dose-rate (HDR) brachytherapy. The inverse treatment plans were compared to a manually-optimized plan used for the actual treatment of the patients. The comparison of the plans was performed with respect to the probability of cure without complication (P+). RESULTS: Overall, the manually optimized plan scored the best results; however, the probability of cure without complication is within an acceptable clinical range for all the plans. CONCLUSION: Although there are still considerable uncertainties in the radiobiological parameters, the radiobiological plan evaluation method presents itself as a potential complement to physical dosimetric methods.

Adaptive brachytherapy of cervical cancer, comparison of conventional point A and CT based individual treatment planning.

BACKGROUND: Locally advanced cervical cancer is commonly treated with external radiation therapy combined with local brachytherapy. The brachytherapy is traditionally given based on standard dose planning with prescription of dose to point A. Dosimetric aspects when changing from former standard treatment to individualized treatment plans based on computed tomography (CT) images are here investigated. MATERIAL AND METHODS: Brachytherapy data from 19 patients with a total of 72 individual treatment fractions were retrospectively reviewed. Standard library plans were analyzed with respect to doses to organs at risk (OARs), and the result was compared to corresponding delivered individualized plans. The theoretical potential of further optimization based on prescription to target volumes was investigated. The treatments were performed with a Fletcher applicator. RESULTS: For standard treatment planning, the tolerance dose limits were exceeded in the bladder, rectum and sigmoid in 26%, 4% and 15% of the plans, respectively. This was observed most often for the smallest target volumes. The individualized planning of the delivered treatment gave the possibility of controlling the dose to critical organs to below certain limits. The dose was still prescribed to point A. An increase in target dose coverage was achieved when additional individual optimization was performed, while still keeping the dose to the OARs below predefined limits. Relatively low average target coverage, especially for the largest volumes was however seen. CONCLUSION: The individualized delivered treatment plans ensured that doses to OARs were within acceptable limits. This was not the case in 42% of the corresponding standard plans. Further optimized treatment plans were found to give an overall better dose coverage. In lack of MR capacity, it may be favorable to use CT for planning due to possible protection of OARs. The CT based target volumes were, however, not equivalent to the volumes described in magnetic resonance imaging (MRI) based recommendations. Prescription and assessment of dose, when introducing such target volumes, should be evaluated and preferably compared to well known treatment regimens.

Relative biological effectiveness of photon energies used in brachytherapy and intraoperative radiotherapy techniques for two breast cancer cell lines.

BACKGROUND: Partial breast irradiation (IORT or brachytherapy) differ from external radiation of whole breast in terms of irradiated volumes, fractionation, radiation energy and dose rate; all factors influencing the treatment outcome in a complex manner. Theoretically obtained RBE values comparing effects of radiation used in IORT and external therapy are published, but experimental studies are required to confirm these data. The aim of this study is to establish such RBE values for two breast cancer cell lines. MATERIALS AND METHODS: Colony formation of breast cancer cell lines (MCF-7 and T-47D) were studied after photon irradiation with qualities and dose rates used in IORT, brachytherapy and external radiation. RBE values from survival data were used to compare effects. RESULTS: Increasing the photon energy (dose rate 0.2 Gy/min) from 50 kV (Intrabeam) to 380 keV (¹9²Ir source) and 6 MV (linear accelerator) yielded an increase in the cell survival, whereas increasing the dose rate to 6 Gy/min had minor effect. Average RBE values for 50 kV with 6 MV as reference radiation varied from about 1.4 (for doses < 5 Gy) to > 1.9 (for doses < 0.02 Gy) for MCF-7 cells and from about 1.4 to > 3.1 for T-47D cells for the same dose levels. Corresponding RBE values for 380 keV radiation were about 1.4 for MCF-7 cells and 1.3-2.3 for T-47D cells. CONCLUSION: RBE data for breast cancer cells exposed to radiation used in IORT, brachytherapy or external radiation differ among the cell lines tested. The values are in agreement with published theoretical and experimental work.