THE TOP-IMPLART PROTON LINEAR ACCELERATOR: INTERIM CHARACTERISTICS OF THE 35 MEV BEAM.

In the framework of the Italian TOP-IMPLART project (Regione Lazio), ENEA-Frascati, ISS and IFO are developing and constructing the first proton linear accelerator based on an actively scanned beam for tumor radiotherapy with final energy of 150 MeV. An important feature of this accelerator is modularity: an exploitable beam can be delivered at any stage of its construction, which allows for immediate characterization and virtually continuous improvement of its performance. Currently, a sequence of 3 GHz accelerating modules combined with a commercial injector operating at 425 MHz delivers protons up to 35 MeV. Several dosimetry systems were used to obtain preliminary characteristics of the 35-MeV beam in terms of stability and homogeneity. Short-term stability and homogeneity better than 3% and 2.6%, respectively, were demonstrated; for stability an improvement with respect to the respective value obtained for the previous 27 MeV beam.

Procollagen type 1 C-terminal extension peptide serum levels following parathyroidectomy in hyperparathyroid patients.

Procollagen type 1 is mainly synthesized by osteoblasts and, after cleavage of the N- and C-terminal extension peptides, is utilized for collagen fibril deposition in the osteoid tissue. Serum levels of C-terminal extension peptide (Pcoll-1-C) of the procollagen molecule has been considered a useful marker for the evaluation of the rate of osteoblastic procollagen synthesis. To appraise whether in vivo parathyroid hormone (PTH) plays a suppressive role in the synthesis of procollagen type 1, a study has been carried out in 16 patients, 10 with severe secondary hyperparathyroidism of chronic renal failure and 6 with primary hyperparathyroidism. Following parathyroidectomy (PTX), in chronic renal failure patients a 94% fall in serum intact iPTH and a decline of serum calcium to hypocalcemic levels requiring calcitriol administration were observed. Serum Pcoll-1-C increased markedly with a peak after 7 days and a subsequent decline. Similar changes were observed for alkaline phosphatase and osteocalcin. In primary hyperparathyroidism, PTX was followed by an 88% drop in iPTH and mild hypocalcemia not requiring calcitriol administration. Also in this group serum Pcoll-1-C increased significantly with the same time course, unaccompanied by changes in alkaline phosphatase and osteocalcin. In 4 unsuccessfully neck-operated control patients no change in serum Pcoll-1-C levels was recorded during a period of 2 weeks postoperatively. In conclusion, acute withholding of parathyroid hypersecretion is accompanied by an abrupt and transitory increase of serum Pcoll-1-C, not dependent on calcitriol administration. Hypocalcemia following PTX may in part be due to uncoupling of bone formation and resorption.

Procollagen type I C-terminal extension peptide in predialysis chronic renal failure.

Collagen type 1 is the most abundant protein of bone. Serum levels of type 1 procollagen carboxy-terminal extension peptide (Procoll-1-C) may give a measure of the rate of synthesis of the collagen of bone and be therefore a marker of bone turnover. We have studied 38 patients with predialysis chronic renal failure; 14 of them were under long-term treatment with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] for prevention of secondary hyperparathyroidism. In all patients a transiliac bone biopsy for histomorphometry and determination of dynamic parameters was performed following double tetracycline labeling. In addition serum Procoll-1-C, intact and C-terminal parathyroid hormone (PTH), osteocalcin and alkaline phosphatase were determined. In the patients not receiving 1,25(OH)2D3, serum levels of Procoll-1-C were higher than normal. Procoll-1-C did not correlate with any of the humoral parameters, including serum creatinine, nor with static histomorphometric parameters. Contrarily to osteocalcin, the collagen type 1 marker correlated significantly with all dynamic parameters. Treatment with 1,25(OH)2D3 was accompanied by lower levels of osteocalcin, iPTH (n.s.), osteoblastic surface and by normal levels of Procoll-1-C (p < 0.001, compared to untreated patients), without substantial change in bone formation parameters (bone formation rate). In conclusion Procoll-1-C in predialysis chronic renal failure is a marker of bone turnover unparalleled by other markers. 1,25(OH)2D3 administration is associated with lower serum levels of the peptide unaccompanied by a decrement of bone formation parameters, therefore with an apparently better utilization of collagen type 1 in the mineralization process.(ABSTRACT TRUNCATED AT 250 WORDS)