Forward-planning breast IMRT: early clinical experience

Abstract

Purpose/Objective: Women with larger breasts who undergo post-lumpectomy radiotherapy (RT) have a higher incidence of acute skin toxicity due to large and/or varied tissue separations. Forward-planning IMRT, also known as field-in-field (FIF) RT, uses varying energies and multiple asymmetrically blocked treatment fields, in a conventional opposed tangent orientation. We hypothesized that FIF breast RT may result in improved dose distribution and reduced acute toxicity in these patients.Materials/Methods: Patients were considered for FIF breast RT if conventional planning yielded hot-spots greater than 107% of prescription dose. Twelve such patients were consecutively evaluated, with treatment plans optimized using both a conventional (uncompensated) wedged plan, and a FIF plan. For each plan, adequacy of coverage was assessed by the volume of breast tissue included in the 98% isodose line (V98). The degree of “hot spots” was assessed by the V105. Patients were treated according to the more homogeneous plan, and followed prospectively. Skin toxicity was assessed weekly using the RTOG scoring system. Incidence and duration of moist desquamation, and resulting treatment breaks were recorded. This was compared to the acute skin toxicity observed in a control group of 51 non-FIF breast RT patients matched for similar tissue separations.Results: Coverage of breast volume was similar for FIF and conventional wedged plans. The mean V98 for FIF plans was 82.5% (range 64 to 98%) versus 80.3% (range 67 to 91%) for wedged plans. The volume of “hot spots” was reduced with FIF compared to conventional planning, with a mean V105 of 3% versus 23%, respectively (p=0.007, t-test). FIF plans showed better coverage or reduced hot-spots in all twelve patients, thus all were treated using this technique. Moist desquamations occurred less frequently in FIF patients than in the matched control group (8.3% vs. 31%, repectively). The duration of moist desquamation was reduced in FIF patients (0.8 vs 2.9 days/patient). Duration of treatment breaks for skin toxicity was less in FIF patients (0.2 vs. 1.0 days, respectively). Due to the sample size, none of these differences reached statistical significance.Conclusions: In breast patients with large or varied tissue separations, forward-planning IMRT significantly reduces the volume of breast tissue exposed to high dose RT, without a compromise in coverage. Analysis of more patients will be necessary to confirm the trends for reduced acute skin toxicity observed with this technique. Purpose/Objective: Women with larger breasts who undergo post-lumpectomy radiotherapy (RT) have a higher incidence of acute skin toxicity due to large and/or varied tissue separations. Forward-planning IMRT, also known as field-in-field (FIF) RT, uses varying energies and multiple asymmetrically blocked treatment fields, in a conventional opposed tangent orientation. We hypothesized that FIF breast RT may result in improved dose distribution and reduced acute toxicity in these patients. Materials/Methods: Patients were considered for FIF breast RT if conventional planning yielded hot-spots greater than 107% of prescription dose. Twelve such patients were consecutively evaluated, with treatment plans optimized using both a conventional (uncompensated) wedged plan, and a FIF plan. For each plan, adequacy of coverage was assessed by the volume of breast tissue included in the 98% isodose line (V98). The degree of “hot spots” was assessed by the V105. Patients were treated according to the more homogeneous plan, and followed prospectively. Skin toxicity was assessed weekly using the RTOG scoring system. Incidence and duration of moist desquamation, and resulting treatment breaks were recorded. This was compared to the acute skin toxicity observed in a control group of 51 non-FIF breast RT patients matched for similar tissue separations. Results: Coverage of breast volume was similar for FIF and conventional wedged plans. The mean V98 for FIF plans was 82.5% (range 64 to 98%) versus 80.3% (range 67 to 91%) for wedged plans. The volume of “hot spots” was reduced with FIF compared to conventional planning, with a mean V105 of 3% versus 23%, respectively (p=0.007, t-test). FIF plans showed better coverage or reduced hot-spots in all twelve patients, thus all were treated using this technique. Moist desquamations occurred less frequently in FIF patients than in the matched control group (8.3% vs. 31%, repectively). The duration of moist desquamation was reduced in FIF patients (0.8 vs 2.9 days/patient). Duration of treatment breaks for skin toxicity was less in FIF patients (0.2 vs. 1.0 days, respectively). Due to the sample size, none of these differences reached statistical significance. Conclusions: In breast patients with large or varied tissue separations, forward-planning IMRT significantly reduces the volume of breast tissue exposed to high dose RT, without a compromise in coverage. Analysis of more patients will be necessary to confirm the trends for reduced acute skin toxicity observed with this technique.