Comparing the monoisocentric and dual isocentric techniques in chest wall radiotherapy of mastectomy patients

Abstract

The monoisocentric (MIT) and dual isocentric (DIT) techniques are compared for the mastectomy patients undergoing chest wall radiotherapy, and a new practical method is suggested for determining the dose calculation reference point to be used in the MIT. Data of 18 mastectomy patients having chest wall radiotherapy were used. To find the appropriate dose calculation reference point for the MIT, the target tissue was divided into nine regions with 17 points as the appropriate candidates. After finding the best reference point for the MIT, dose calculations were made for each patient based on the MIT and DIT to determine the dose distributions of the target volume and organs at risk. The lateral component of the dose calculation reference point was found to be located at one‐third of the distance between the geometrical center and the lateral border of the chest wall in the lateral direction toward the outer border. The longitudinal component of this point was found to be located at the geometrical center of the chest wall with a depth located around 2–3 cm under the patients’ skin. There was no significant difference between the two radiotherapy planning techniques (MIT and DIT) regarding the dose distributions in the organs at risk and the 95% of the prescribed dose coverage of the target tissue. However, a significant difference for the 105% of the prescribed dose coverage, maximum dose delivered to the target tissue, and the level 2 lymph nodes dose was found, with the DIT showing higher values. Because of the good matching and no superposition observed between the treatment fields in the MIT, it was expected and confirmed that the hot and cold regions (with higher and lower doses than the prescribed dose) with the MIT are significantly fewer than that of the DIT. Therefore, to perform a better conformal radiotherapy for the patients having mastectomy, it could be recommended to use the MIT instead of the DIT and other conventional techniques.PACS numbers: 87.53.Bn, 87.53.Kn, 87.55.D‐, 87.55.ne

Dosimetric comparison of level II lymph nodes between mono-isocentric and dual-isocentric approaches in 3D-CRT and IMRT techniques in breast radiotherapy of mastectomy patients

“…A similar expectation existed regarding hot and cold points (points with higher and lower doses than the prescribed dose) in field junction regions of DIT, which was also confirmed by previous researches. 18,23 As expected, it was confirmed that D max in the field junction and overlap regions for DIT was significantly higher compared with MIT (59•59 versus 52•8 Gy in 3D-CRT and 56•48 versus 51•6 Gy in IMRT). Previous investigations have also reported similar findings in this regard.…”

“…Assaoui et al 18 and Banaei et al 23 reported the same results for dosimetric parameters regarding the chest wall, lung and heart resulting from MIT and DIT with 3D-CRT technique. In another study by Lefkopoulos et al, 32 a general optimisation procedure for stereotactic small-beam using multi-isocentric radiotherapy was investigated.…”

“…More details about MIT and DIT, such as isocentre point locations, have been described in a previous study. 23 According to Figure 1, no divergence or overlapping occurs in MIT. However, regions with higher/lower doses than the prescribed doses are observed at the junctions of treatment fields in DIT.…”

“…Several parameters were used for evaluating dose distributions. 1,23 D mean and V (xGy) represent average dose delivered to a structure and percentage of its volume receiving xGy or higher, respectively. D mean , D min (minimum dose) and D max (maximum dose), and a dose at 95% to the level II lymph node volume were assessed.…”

“…In some previous studies, 23,24 tangential and supraclavicular fields matching in MIT and DIT were evaluated for 3D-CRT. Level II lymph nodes are located in field junction area; however there are not any investigations comparing dose distribution of these nodes in the two methods (MIT and DIT) for mastectomy patients by IMRT.…”