Proton pencil beam scanning for mediastinal lymphoma: the impact of interplay between target motion and beam scanning.

The purpose of this study was to assess the feasibility of proton pencil beam scanning (PBS) for the treatment of mediastinal lymphoma. A group of 7 patients of varying tumor size (100-800 cc) were planned using a PBS anterior field. We investigated 17 fractions of 1.8 Gy(RBE) to deliver 30.6 Gy(RBE) to the internal target volume (ITV). Spots with σ ranging from 4 mm to 8 mm were used for all patients, while larger spots (σ = 6-16 mm) were employed for patients with motion perpendicular to the beam (⩾5 mm), based on initial 4-dimensional computed tomography (4D CT) motion evaluation. We considered volumetric repainting such that the same field would be delivered twice in each fraction. The ratio of extreme inhalation amplitude and regular tidal inhalation amplitude (free-breathing variability) was quantified as an indicator of potential irregular breathing during the scanning. Four-dimensional dose was calculated on the 4D CT scans based on the respiratory trace and beam delivery sequence, implemented by partitioning the spots into separate plans on each 4D CT phase. Four starting phases (end of inhalation, end of exhalation, middle of inhalation and middle of exhalation) were sampled for each painting and 4 energy switching times (0.5 s, 1 s, 3 s and 5 s) were tested, which resulted in 896 dose distributions for the analyzed cohort. Plan robustness was measured for the target and critical structures in terms of the percent difference between 'delivered' dose (4D-evaluated) and planned dose (calculated on average CT). It was found that none of the patients exhibited highly variable or chaotic breathing patterns. For all patients, the ITV D98% was degraded by <2% (standard deviations âˆ¼ 0.1%) when averaged over the whole treatment course. For six out of seven patients, the average degradation of ITV D98% per fraction was within 5% . For one patient with motion perpendicular to the beam (⩾5 mm), the degradation of ITV D98% per fraction was up to 15%, which was mitigated to 2% by employing larger spots and repainting. Deviation of mean lung dose was at most 0.2 Gy(RBE) (less than 1% of prescribed dose, 30.6 Gy(RBE)), while the deviation of heart maximum dose and cord maximum dose could exceed 5% of the prescribed dose. No significant difference in either target coverage or normal tissue dose was observed for different energy switching times compared via two-sided Wilcoxon signed-rank tests (p < 0.05). This feasibility study demonstrates that, for mediastinal lymphoma, the impact of the interplay effect on the PBS plan robustness is minimal when volumetric repainting and/or larger spots are employed.

Intrathoracic photodynamic therapy: a canine normal tissue tolerance study and early clinical experience.

Surgery with intraoperative photodynamic therapy (PDT) has the potential to improve the treatment of pleural malignancies. Before embarking on such treatment in humans, however, thoracic tissue tolerance to PDT was studied. For each of three (1 week, 1 month, and 6 month) study end-points, one control (no Photofrin II [PII]) and four treated animals underwent thoracotomy 72 hours after I.V. injection (6 mg/kg) PII. Red light (630 nm) was delivered (5-40 J/cm2) to the pleural surface (1 cm diameter) of selected thoracic organs. No clinical differences were observed between PDT and control dogs. The control showed no histological changes; however, in the treated animals focal areas of coagulation necrosis were found at 1 week which progressed to fibrosis at 1 month. The extent and depth of injury was proportional to light dose. The lung was the most sensitive; the chest wall was the most resistant. Myocardium had superficial damage, whereas coronary arteries appeared normal. The results provide the basis for proceeding to phase I human trials in the evaluation of PDT as an intraoperative adjuvant treatment in the management of pleural malignancies.

Long term tolerance of thoracic organs to intraoperative radiotherapy.

The tolerance of mediastinal structures to intraoperative radiotherapy (IORT) was investigated in 3 separate animals trials using 49 adult foxhounds and one limited Phase I trial in 4 patients with Stage II or III non-small cell lung cancer (NSCLC). The 1- to 2-year results of these trials have been previously reported with significant toxicity found at dose levels over 20 Gy. We now report the results of five dogs reserved for long term studies and one Stage II NSCLC patient alive at 5 years. Two dogs received 20 Gy IORT and one received 30 Gy IORT to the esophagus, all three to a single 6 cm field with 9 MeV electrons. One control dog underwent surgery without irradiation. One dog received 20 Gy IORT to a single 5 cm mediastinal field with 13 MeV electrons following left pneumonectomy. At 5 years, all five dogs reserved for a long term evaluation were alive and evaluable with minimal endoscopic and radiographic abnormalities. The one patient alive at 5 years for evaluation received 25 Gy IORT to two matched 6 cm fields with 13 MeV electrons. She has stable dyspnea on exertion and there is no evidence of cancer by endoscopy. We conclude, based on these limited data, that IORT in the mediastinum may be safe at dose levels that do not exceed 20 Gy, and further careful evaluation at these lower treatment doses is warranted to determine efficacy.

A light-diffusing device for intraoperative photodynamic therapy in the peritoneal or pleural cavity.

Light delivery to anatomic areas involved by tumor is critical for effective photodynamic therapy. The authors provide a detailed overview of a light-diffusing device which they have used for intraoperative illumination of the peritoneal and pleural cavities in patients with tumors involving the surfaces of these cavities. Their device represents an inexpensive modification of widely available endotracheal tubes. It has been used to deliver intraoperative photodynamic therapy in over 50 patients without episodes of device failure. When combined with a lipid-based, light-diffusing medium and on-line power/energy density monitoring, it allows homogeneous illumination of these complex surfaces.

Hepatic irradiation in the management of metastatic hormone-secreting tumors.

Three patients with extensive liver metastases from hormone-secreting tumors were treated with external beam radiation therapy to palliate signs and symptoms of tumor mass and/or hormone secretion. These patients experienced an objective response of 3, 14, and 24 months duration, respectively, as measured by plasma hormone levels and/or computed tomography (CT) scanning. Using conventional fractionation, a dose of 2400 to 3000 rad was delivered without significant acute or late toxicity. Although these tumors have a long natural history (many years), even after the development of liver metastases, radiation therapy can provide effective palliation and should be considered as a therapeutic option.