Evaluation of the surface dose for total body irradiation (TBI) technique with parallel-opposed anterior posterior geometry

Aim: Total body irradiation (TBI) is an external radiotherapy technique in which the whole body including the superficial regions is required to receive the therapeutic dose. The purpose of this study is to evaluate the received surface dose during TBI technique. Methods and materials: The anterior/posterior (AP/PA) TBI was implemented with 18-MV photon beam at 312-cm treatment distance for human-like phantom. The GAFCHROMIC-EBT3 films were used for superficial dose measurements. Results and discussion: The percentage of surface-absorbed dose relative to the prescription point for 8 points of measurements was between 102·78–121·48% and 104·51–127·43% at 5 and 10 mm depth, respectively. In the chest wall region due to the presence of lung blocks, the absorbed dose was below the acceptable level, so an electron boost was required to increase the chest wall absorbed dose. Conclusions: According to the results, the implemented technique was able to deliver sufficient dose to the shallow surface of phantom’s body.

Evaluation of tissue computed tomography number changes and dosimetric shifts after conventional whole-breast irradiation in patients undergoing breast-conserving surgery

The aim of this study was to assess tissue computed tomography (CT) number changes and corresponding dosimetric shifts in repeatedly performed simulation CT (re-sim CT) scans after conventionally fractionated irradiation in breast cancer patients. A total of 28 breast cancer patients who underwent breast-conserving surgery were enrolled in this study. All the patients had received 50.4 Gy of conventional whole-breast irradiation (WBI) and underwent re-sim CT scans for tumor bed boost. For evaluation of dosimetric shifts between initial and re-sim CT scans, electron boost plans in the same field size with the same monitor unit with source-to-skin distance of 100 cm were conducted. Dosimetric parameters (V105%, V103%, V100%, V98%, V95%, V90%: Vx% indicates volumes which receive X% of prescribed doses) between initial and re-sim CT scans were compared. The CT number data (CTmean, CTmax, CTmin) of the original and irradiated CT (re-sim CT) scans from each representative structure (lung, rib bone, soft tissue, muscle, etc.) were examined and recruited. CT numbers showed highly variable changes. Soft tissue CTmean and muscle CTmax/CTmin showed statistically and significantly increased values in the CT (re-sim CT) compared to the original CT scans. Rib bone CTmean/CTmin showed statistically and significantly decreased values in the re-sim CT compared to the original CT scans. Other CT number values showed no statistically significant changes. Among the dosimetric parameters, only V105% (p = 0.015, mean = 3.07 cc versus 1.63 cc) and V103% (p = 0.017, mean = 13.8 cc versus 11.9 cc) exhibited statistically increased values in the re-sim CT compared to the original CT scans. CT number changes after conventional WBI were different according to tissue component. For electron boost plans, the implementation of a re-sim CT might be helpfully considered because significant dosimetric factor changes were observed especially in the high-dose areas (hot spots: V105% and V103%).

Dosimetric comparison of simultaneous integrated boost versus concomitant electron boost in radiotherapy treatment of breast cancer

BackgroundThe aim of this study was to compare the dosimetric parameters and effects of simultaneous integrated boost (SIB) and traditional sequential electron boost, after helical tomotherapy, because of the lack of studies in this field in the current literature.MethodsComputed tomographic data of 14 patients who received SIB in 2012–2015 were collected from Hong Kong Sanatorium & Hospital. New tomotherapy with SIB plans and tomotherapy with sequential boost plans were generated for each patient, and results were compared.ResultsConformation number, mean dose, dose received by 95% volume (both sides), ipsilateral lung volume receiving 20 Gy (V20) and skin dose (right side) were found to be significantly better for SIB (p<0·05), however coverage index and gross target volume dose showed no significant difference, and heart dose was significantly higher for SIB on the right side.ConclusionTomotherapy with SIB may be able to offer less organ at risk dose (except for the heart), while maintaining the ability to deliver adequate dose coverage.